x \ \ \ \ \\ \ \ VVV> \ \ \ \ \ V \ % \ \ ' V ■> N \ \ \ \ \ A \ N \ N \ \ \ \ \ \ \ '\ \ \ • V \ V mtW " ■ \ \ \ v ' \ \ \ \A \ \ ■ \ "• , \ \ \ \ \ . \ \ \ ^ \ ' v V \ \ \ \ ' \ V \ ' \ S \ V ■ \ \ \ \ \ \ \ \ ' \ •. ■ X'"''' ■ ■ I \ \ \ \ \ \ \ \ x \ ,\ x x V \ \\ \ \ \ \ \ A , N \ \ . v ,\ N \ - .\V \ \ 'S y \ - \ \ s v, • '■ \ ’ X ' , \ \ \ \ S \ -. \ \ \ \- '\ \ \ \ ' X '■ vf.N \ \ ' , \ ' ■ \ N \ \ \,\ \ \ \ 1 7 / / / / / / / / / 7 / / / / / / ■' / / / /-/ / ' f / / ■ / /' / r, , " / /',/ , / / " / / / / / / / / / J /,/ / /A // / , ' /' / , / / / / / / r ' r / / / / / / / / fj ^ / /■ / / / / / / / / / ' / / / / / / / /// / f / / - / / f / / / / / '■ ^ J / / / / / / / / 7 / / / / / / / / / / / / / • / / ^ ' / ////// / / . • / / / / / / / / / / s tjt fx £(S IS ■> ENCYCLOPEDIA BRITANNICA. Cnwlopacfcta Bntaumta: OR, A DICTIONARY OF ARTS, SCIENCES, AND MISCELLANEOUS LITERATURE; ENLARGED AND IMPROVED. THE SIXTH EDITION. sllustratrti Until nearlp sir lumtntU fiEngraUmgs. VOL. III. INDOCTI DISCANT; AMENT MEMINISSE PERITI. EDINBURGH: PRINTED FOR ARCHIBALD CONSTABLE AND COMPANY: AND HURST, ROBINSON, AND COMPANY, 90, CHEAPSIDE, LONDON. 1823. 3 ;f, : APS ,5 ^ Encyclopaedia Britannica. ASS Aviacktbn. A SSOCIATION, the act of associating, or consti- ^ 1 \ toting a society, or partnership, in order to carry on some scheme or affair with more advantage. The word is Latin, associatio; and compounded of ad, to, and socio, to join. Association of Ideas, is where two or more ideas constantly and immediately follow or succeed one ano- ther in the mind, so that one shall almost infallibly pro¬ duce the other, whether there be any natural relation between them or not. See Metaphysics. Where there is a real affinity or connexion in ideas, it is the excellency of the mind, to be able to collect, compare, and range them in order, in its inquiries: but . where there is none, nor any cause to be assigned for their accompanying each other, but what is owing to mere accident or habit, this unnatural association be* comes a great imperfection, and is, generally speaking, a main cause of error, or wrong deductions in reasoning. Thus the idea of goblins and sprights, it has been observed, has really no more affinity with darkness than with light} and yet let a foolish maid inculcate these ideas often on the mind ol a child, and raise them there together, it is possible he shall never be able to separate them again so long as he lives, but darkness shall ever bring with it those frightful ideas. With regard to this instance, however, it must at the same time be ob- served, that the connection alluded to appears far from being either unnatural or absurd. See the article Ap¬ parition. Such wrong combinations of ideas, Mr Locke shows, are a great cause of the irreconcileable opposition be¬ tween the different sects of philosophy and religion : for we cannot imagine, that all who hold tenets different from, and sometimes even contradictory to, one ano¬ ther, should wilfully and knowingly impose upon them¬ selves, and refuse truth offered by plain reason : but some loose and independent ideas are, by education, custom, and the constant din of their party, so coupled in their minds, that they always appear there together : these they can no more separate in their thoughts, than if they were but one idea, and they operate as if they were so. This gives sense to jargon, demonstra¬ tion to absurdities, consistency to nonsense, and is the foundation of the greatest, and almost of all the errors hi the world. Association forms a principal part of Dr Hartley’s mechanical theory of the mind. He distinguishes it mto synchronous and successive j and ascribes our simple Vol. III. Part I. j ASS and complex ideas to the influence of this principle Association, or habit. Particular sensations result from previous 1 ' vibrations conveyed through the nerves to the medul¬ lary substance of the brain $ and these are so intimate¬ ly associated together, that any one of them, when im¬ pressed alone, shall he able to excite in the mind the ideas of all the rest. Thus wre derive the ideas of natural bodies from the association of the several sensible qua¬ lities with the names that express them, and with each other. I he sight of part of a large building suggests the idea of the rest instantaneously, by a synchronous association of the parts ; and the sound of the words, which begin a familiar sentence, brings to remembraime the remaining parts, in order, by successive association. Dr Hartley maintains, that simple ideas run into com¬ plex ones by association j and apprehends, that by pur¬ suing and perfecting this doctrine, we may some time or other be enabled to analyze those complex ideas, that are commonly called the ideas of reflection, or intel¬ lectual ideas, into their several component parts, i. e. into the simple ideas of sensation of which they consist} and that this doctrine may be of considerable use in the art of logic, and in explaining the various phenomena of the human mind. Association of Parliament. In the reign of King William HI. the parliament entered into a solemn as¬ sociation to defend his Majesty’s person and government against all plots and conspiracies} and all persons bear¬ ing offices civil or military, were enjoined to subscribe the association to stand by King William, on pain of forfeitures and penalties, &c. by stat. 7 and 8 W. III. c. 27. Association, African. This is an institution which was formed in the year 1788, for the purpose of pro¬ moting discoveries in the interior parts of Africa. Out of the number of the members, of which this society consists, five are elected for the management of its funds and correspondence, and for the appointment of persons to whom tiie missions are assigned. Mr Ledyard was the first who was sent out, for accomplishing the object of the society. He undertook the adventurous task, of traversing from east to west, the widest part of the African continent, in the latitude which was ascribed t:o the Niger} and with this view he arrived at Cairo in August 1788. But before his projected journey commenced, he died, and the hopes that were enter¬ tained of this enterprising and persevering traveller were disappointed. Mr Lucas was next chosen by the A committee. ASS [ 2 committee. In October 17885 he embarked for Tri¬ poli ; and he was instructed to proceed over the desert of Zaara to Fez//.an, to collect all the information that could he obtained, respecting the interior of the Afri¬ can continent, and to transmit it byway of Inpoj. He was then to return by way of Gambia, or the coast ot Guinea. But his peregrinations terminated at Mesurata. The difficulties arid dangers which presented themselves deterred him from proceeding farther. He transmitted to the society only the result of his conferences with the traders to Fezzan, with whom he was travelling; and soon after returned to England. > The society still persevered in its object,, and m the year 1790, appointed Major Houghton, with instiuc- tions to sail for the mouth of the Gambia, and to tra¬ verse the country from west to east. He. arrived on the coast in November the same year, immediately commenced his journey, ascended the river Gambia to Medina, 900 miles distant from his mouth, and thence proceeded to Bambouk, and to the adjoining kingdom of Kasson, where, in September the year following, he unfortunately terminated his travels with his hie, near to the town of Jarra. Mr Park was engaged by the society in the same service in 1795, and pursuing- the route of Major Houghton, more successfully explored the banks of the Niger, to Sego and to Silla, the first 01 that great line of populous cities which divide the southern from the northern deserts of Africa. The information which Mr Park collected, during his adventurous journey, was communicated to the society in 1798. In a second journey, commenced in 1805, this enterprising traveller perished, after having reached the Niger ; but the cir¬ cumstances of his death have not been ascertained with perfect certainty. Mr Horneman, who had offered himself to tne committee in 1796, departed from London in July 1797, and proceeding by Cairo, commenced his journey westward with the caravan, in September 1798. In November following, he arrived at Mourzouk in tez- zan, from which- his last despatches to the society were transmitted by way of Tripoli, but no accounts ot his death ever reached the society. r t> . • John L. Burckhardt, the son of a citizen of Basle in Switzerland, was engaged by the society in 1808. After some preparatory steps, he set out in March 1809. He remained two years and a had at Aleppo; thence he went to Egypt.' Unfortunately no caravan set out for the interior ol Africa for a series of yeais. He was thus disappointed in his leading object; but he made two journeys up the Nile, and visited Mecca, Medina, and Mount Sinai. Diseases brought on by fatigue and the climate, at length put a period to his life in September 1817. See Africa, Supplement. ASSOILZIE, in Law, to absolve or free. ASSONANCE, in Rhetoric and Poetry, a term used where the words of a phrase or a verse have the same sound, or termination, and yet make no proper rhyme. These are usually accounted vicious m English; though the Romans sometimes used them with.elegan¬ cy ; as, Militem comparavit, exercitum ordinuvit, acieni lustravit. . ASSONANT RHYMES, is a term particularly ap¬ plied to a kind of verses common among the Spaniards, where a resemblance of sound serves instead of a natu¬ ral rhyme. Thus ligera, cubierta, Uerra, mesa, may ] ASS answer each other in a kind of assoTtant rhyme, ha- As^oan, ving each an e in the penult syllable, and an a in the Assumpsit. last. ASSUAN See Syene. ASSUMPSIT, In the Law of England, a voluntary or verbal promise, whereby a person assumes, 01 takes upon him to perform or pay any thing to another. A promise is in the nature of a verbal convenant, and wants nothing hut the solemnity of writing und sealing to make it absolutely the same. If therefore it be to do any explicit act, it is an express contract, as much as anv covenant; and the breach of it is an equal in¬ jury. The remedy indeed is not exactly the same : since, instead of an action of covenant, there only lies an action upon the case, for what is called an assitmp- sit or undertaking of the defendant .; the failure of pei- forming which is the wrong or injury done to the plaintiff, the damages whereof a jury are to estimate and settle. As, if a builder promises, undertakes, or assumes to Caius, that lie will build and cover his house within a time limited, and fails to do it; Caius has an action on the case against the builder lor this breach of his express promise, undertaking, or as¬ sumpsit ; and shall recover a pecuniary satisfaction for the injury sustained by such delay, bo also in the case of a debt by simple contract, if the debtor pro¬ mises to pay it and docs not, this breach of promise entitles the creditor to his action on the case, instead of being driven to an action of debt. Ibus likewise a promissory note, or note ot hand not under seal, to pay money at a day certain, is an express assumpsit; and the payee at common law, or by custom and act of parliament the indorsee, may recover the value ot the note in damage, if it remains unpaid. Some agreements indeed, though never so expressly made, are deemed of so important a nature, that they ought not to rest in verbal promise only, which cannot be proved but by the memory (which sometimes will induce the perjury of witnesses. To prevent which, the statute of frauds and perjuries, 29 Car. II. c. 3. enacts, that in the five following cases no verbal promise shall be sufficient to ground an action upon, hut at the least some note or memorandum ot it shall he made in writing, and signed by the party to he charged there¬ with : 1. Where an executor or administrator promises to answer damages out of his own estate. 2. Where a man undertakes to answer for the debt, default, or miscarriage, of another. 3. Where any agreement is made upon consideration of marriage. 4. Where any contract or sale is made of lands, tenements, or heredi¬ taments, or any interest therein. 5. And lastly, where there is any agreement that is not to be performed witi in a year from the making hereof. In all these cases a mere verbal assumpsit E void. From these express contracts the. transition is easy to those that are only implied by law. Which are such as reason and justice dictate, and which therefore the law presumes that every man has contracted to perform, and, upon this presumption, makes him answerable to such persons as suffer by his non-performance. Thus, 1. If I employ a person to transact any busi¬ ness for me, or perform any work, the law implies that 1 undertook, or assumed, to pay him so much as his labour deserved ; and if I neglect to make him amends, he has a remedy for his injury by bringing lus action on the case upon this implied assumpsit: wherein he is ASS Assumpsit, at liberty to suggest that I promised to pay him so '-—'v "* "•J much as he reasonably deserved, and then to aver that his trouble was really worth such a particular sum, which the defendant has omitted to pay. But this valuation of his trouble is submitted to the determina¬ tion of a jury j who will assess such a sum in damages as they think he really merited. This is called an oc- sumpsit on a quantum meruit. 2. There is also an implied assumpsit on a quantum valebat, which is very similar to the former j being only where one takes up goods or wares of a tradesman, without expressly agreeing for the price. There the law concludes, that both parties did intentionally agree that the real value of the goods .should be paid 5 and an action on the case may be brought accordingly, if the vendee refuses to pay that value. 3. A third species of implied assumpsit is when one has had and received money belonging to another with¬ out any valuable consideration given on the receiver’s part *, for the law construes this to be money had and received for the use of the owner only $ and implies that the person so receiving, promised and undertook to account for it to the true proprietor. And, if he un¬ justly detains it, an action on the case lies against him for the breach of such implied promise and undertakings and he will be made to repair the owner in damages, equivalent to what he has detained in such violation of his promise. This is a very extensive and beneficial remedy, applicable to almost every case where the de¬ fendant has received money which ex cequo et bono he ought to refund. It lies for money paid by mistake, or on a consideration which happens to fail, or through imposition, extortion, or oppression, or where undue ad¬ vantage is taken of the plaintiff’s situation. 4. Where a person has laid out and expended his own money for the use of another at his request, the law implies a promise of repayment, and an action will lie on this assumpsit. 5. Likewise, fifthly, upon a stated account between two merchants, or other persons, the law implies that he against whom the balance appears has engaged to pay to the other ; though there be not any actual promise. And from this implication it is frequent for actions on the case to be brought, declaring that the plaintiff and defendant had settled their accounts toge¬ ther, insitnul computassent (which gives name to this species of assumpsit) ; and that the defendant engaged to pay the plaintiff the balance, but has since neglect¬ ed to do it. But if no account has been made up, then the legal remedy is by bringing a writ of account, ik computo ; commanding the defendant to render a just account to the plaintiff, or show the court good cause to the contrary. In this action, if the plaintiff' suc¬ ceeds, there are two judgments 5 the first is, that the defendant do account {quod computet) before auditors appointed by the court ; and when such account is finished, then the second judgment is, that he do pav the plaintiff so much as he is found in arrear. 6. The last cla ss of contracts, implied by reason and construction of law, arises upon this supposition, that every one who undertakes any office, employment, trust, or duty, contracts with those who employ or in¬ trust him, to perform it with integrity, diligence, and skill: and if by his want of either of those qualities any injury accrues to individuals, they have therefore their ASS remedy in damages by a special action on the case. A Assumpsit few instances will fully illustrate this matter. If an ii officer of the public is guilty of neglect of duty, or a palpable breach of it,of non-feasance,or of mis-feasance; , iiVt‘’ , as, if the sheriff does not execute a writ sent to him, or if he wilfully makes a false return thereof j in both these cases the party aggrieved shall have on action on the case for damages to be assessed by a jury. If a sheriff or gaoler suffers a prisoner who is taken upon mesne process (that is, during the pendency of a suit) to escape, he is liable to an action on the case. But if, after judgment, a gaoler or sheriff permits a debtor to escape, who is charged in execution for a certain sum $ the debt immediately becomes his own, and he is compellable by action of debt, being for a sum li¬ quidated and ascertained, to satisfy the creditor in his whole demand. An advocate or attorney that betray the cause of their client, or, being retained, neglect to appear at the trial, by which the cause miscarries, are liable to an action on the case, for a reparation to their injured client. There is also in law always an implied contract with a common innkeeper, to secure his guest’s goods in his inn ; with a common carrier or barge-master, to be answerable for the goods he car¬ ries ; with a common farrier, that he shoes a horse well, without laming him j with a common taylor, or other workman, that he performs his business in a workman¬ like manner : in which if they fail, an action on the case lies to recover damages for such breach of their general undertaking. Also, if an innkeeper, or other victualler, hangs out a sign and opens his house for tra¬ vellers, it is an implied engagement to entertain all persons who travel that way ; and upon this universal assumpsit an action on the case will lie against him for damages, if he without good reason refuses to admit a traveller. In contracts likewise for sales, if the seller doth upon the sale warrant it to be good, the law an¬ nexes a tacit contract to this warranty, that if it be not so, he shall make compensation to the buyer ; else it is an injury to good faith, for which an action on the case will lie to recover damages. ASSUMPITON, a festival in the Romish church, in honour of the miraculous ascent of the Virgin Mary into heaven : the Greek church, who also observe this festival, celebrate it on the 15th of August with great ceremony. Assumption, in Logic, is the minor or second pro¬ position, in a categorical syllogism. Assumption is also used for a consequence drawn from the proposition whereof an argument is composed. Assumption, an island in North America, in the gull of St Lawrence, at the mouth of the great river of the same name. It is covered with trees. W. Long. 60. 40. N. Lat. 49. 30. Assumption, a large and handsome town of Proper Paraguay, on the river of the same name in South Ame¬ rica. It is a bishop’s see, is well peopled, and seated in a country fruitful in corn and fruits, whose trees are al¬ ways green. There is likewise a quantity of pasture, and the air is temperate and salutary. W. Long. c8. 40. S. Lat. 24. 50. ASSUMPTIVE arms, in Heraldry, are such as a person has a right to assume, with the approbation of his sovereign, and of the heralds: thus, if a person who has no right by blood, and has no coat of arms, A 2 shall [ 3 1 ASS [ 4 ] ASS Assurance shall captivate in any lawful war any gentleman, no¬ bleman, or prince, be and his heirs are, in that case, entitled to bear the shield of that prisoner for ever. ASSURANCE, or Insurance, in Commerce. See Insurance. See also Assurance in the Supple¬ ment. ASSUROR, a merchant, or other person, who makes out a policy of assurance, and thereby insures a ship, house, or the like. ASSUS, or Assos, in Ancient Geography, a town ot Troas (though by others supposed to be of Mysia), and the same-with Apolloma (Uliny) j but different from the ApolIonia on the river Rhyndacus. Ptolemy places it on the sea-coast, but Strabo more inland ; if he does not mean the head of an inland bay, as appears from Diodorus Siculus. It was the country of Cleanthes the Stoic philosopher, who succeeded Zeno. St Luke and others of St Paul’s companians, in his voyage (Acts xx. 13. 14 )) went by sea from Troas to Assos : but St Paul went by land thither, and meeting them at Assos, they all went together to Mytelene. It is now called Bairani. E. Long. 26. 20. N. Lat. 39. 10. ASSYRIA, an ancient kingdom of Asia, concern¬ ing the extent, commencement, and duration of which, historians differ greatly in their accounts. Several an¬ cient writers, in particular Ctesias and Diodorus Sicu¬ lus, have affirmed, that the Assyrian monarchy, un¬ der Ninus and Semiramis, comprehended the greater part of the known world. Had this been the case, it is not likely that Homer and Herodotus would have omitted a fact so remarkable. The sacred records in¬ timate, that none of the ancient states or kingdoms were of considerable extent; for neither Chedorlaomer, nor any of the neighbouring princes, were tributary or subject to Assyria j and we find nothing of the greatness or power of this kingdom in the history of the judges and succeeding kings of Israel, though the latter king¬ dom was oppressed and enslaved by many different powers in that period. It is highly probable, therefore, that Assyria was originally of small extent. Accoidiug to Ptolemy, it was bounded on the north by Armenia Major ; on the west by the Tigris; on the south by Susiana } and on the east by Media. It is probable, that the origin and revolutions of the Assyrian monarchy were as follows.-—The founder of it was Ashur, the second son of Shem, who went out of Shinar, either by the appointment of Nimrod, or to elude the fury of a tyrant; conducted a large body of adventurers into Assyria ; and laid the foundation ot Piaufair't Nineveh (Gen. x. n.). These events happened not Chronolo- long after Nimrod had established the Chaldtean mo¬ narchy, and fixed his residence at Babylon. The Per¬ sian historians suppose that the kings of Persia of the first dynasty were the same with the kings of Assyria, of whom Zohah, or Nimrod, was the founder of Babel. (Herbelot Orient. Bibl. v. Bagdad). _ It does not, how¬ ever appear, that Nimrod reigned in Assyria. I lie kingdoms of Babylon and Assyria were originally di¬ stinct and separate (Micah, v. 6.) ; and in this state they remained until Ninus conquered Babylon and made it tributary to the Assyrian empire. . Ninus the successor of Asher (Gen. x. II. Diod. Sic. lib. i.)» seized on Chaldaea, after the death of Nimrod, and united the kingdoms of Assyria and Babylon. Ibis great prince is said to have subdued Asia, Persia, Media, try Egypt, &c. If lie did so, the effects of his conquests Absyria. were of no duration j for in the days ot Abraham, we do not find that any of the neighbouring kingdoms were subject to Assyria. He was succeeded by Se¬ miramis } a princess ot an heroic mind j bold, enter¬ prising, fortunate ; but of whom many fabulous tilings have been recorded. It appear, however, that there were two princesses of the same name, who flourished at very different periods. One of them was the consort of Ninus } and the other lived five generations before Ni- tocris queen of Nebuchadnezzar (Euseb. Chron. p. 58- Herod. lib. i. c. 184.). This fact has not been attend¬ ed to by many writers. Whether there was an uninterrupted series of kings from Ninus to Sardanapalus, or not, is still a question. Some suspicion has arisen, that the list which Gtesias has given of the Assyrian kings is not genuine ; for many names in it are ot Persian, Egyptian, and Grecian ex¬ traction. Nothing memorable has been recorded concerning the successors of Ninus and Semiramis. Of that effemi¬ nate race of princes it is barely said, that they ascend¬ ed the throne, lived in indolence, and died in their pa¬ lace at Nineveh. Diodorus (lib. ii.) relates, that, in the reign of Teutames, the Assyrians, solicited by Pi 1am their vassal, sent to the Trojans a supply of 20,000 foot and 200 chariots, under the command of Memnon, son of Tithonus president of Persia : But the truth of his relation is rendered doubtful by the accounts of other writers. # . Sardanapalus was the last of the ancient Assyrian kings. Contemning his indolent and voluptuous coursu of life, Arbaces, governor of Media, withdrew bis al¬ legiance, and rose up in rebellion against him. He was encouraged in this revolt by the advice and assistance of Belesis, a Chaldean priest, who engaged the Baby¬ lonians to follow the example of the Medes. These powerful provinces, aided by the I eisians anc otnex al¬ lies, who despised the effeminacy, or dreaded the ty¬ ranny of their Assyrian lords, attacked the empue on all sides. Their most vigorous efforts were, in the be¬ ginning, unsuccessful. Tirm and determined, however, in their opposition, they at length prevailed, defeated the Assyrian army, besieged Sardanapalus in his capital, which they demolished, and became masters of the em¬ pire, B. C. 821. After the death of Sardanapalus, the Assyrian empire was divided into three kingdoms, viz. the Median, As¬ syrian, and Babylonian. Arbaces retained the supreme power and authority, and fixed his residence at Ecba- tana in Media. He nominated governors in Assyria and Babylon, who were honoured with, the title of kino;.?, while they remained subject and tributary to tbe Median monarchs. Belesis received the government of Babylon as tbe reward of his services j and Phul was intrusted with that ot Assyria. Hie Assyrian.go¬ vernor gradually enlarged the boundaries ot his king¬ dom, and was succeeded by Tiglath-pileser, Salmana- sar, and Sennacherib, who asserted and maintained their independency. After the death of Assar-haddon, the brother and successor of Sennacherib, the kingdom of Assvria was split, and annexed to the kingdoms of Media' and Babylon. Several tributary princes after¬ wards reigned in Nineveh j hut no particular account? of them is found in the annals of ancient nations. W* hear AST [ 5 ] AST Attyii* hear no more of the kings of Assyria, but of those of 9 ^ Babylon. Cyaxares king of Media assisted Nebu- 'c ' . cbadnezzar king of Babylon, in the siege of Nineveh, which they took and destroyed, B. C. 606. The Chaldean or Babylonish kingdom was transferred to the Medes, after the reign of Nabonadius, son of Evil- merodach, and grandson of Nebuchadnezzar. He is styled Belshazzar in the sacred records, and was con¬ quered by Cyrus, B. C. 538. ASSYTHMENT. See Assithment. ASTA, an inland town of Liguria, a colony (Pto¬ lemy) on the river Tanarus : now Asti. E. Long. 8. 15. N. Lat. 44. 40. Asta Regia, a town of Baetica, (Pliny) ■, situated at the mouth of the Bsetis which was choked up with mud, to the north of Cadiz : 16 miles distant from the port of Cadiz, (Antonine). Its ruins show its former greatness. Its name is Phoenician, denoting a frith or arm of the sea, on which it stood. It is said to be the same with Xera ; which see. ASTABAT, a town of Armenia, in Asia, situated near the river Aras, 12 miles south of Nakshivan. The land about it is excellent, and produces very good wine. There is a root peculiar to this country, called ronas; which runs in the ground like liquorice, and serves for dyeing red. It is very much used all over the Indies, and in it they have a great trade. E. Long. 46. 30. N. Lat. 39. o. ASIAN DA, in antiquity, a royal courier or mes¬ senger, the same with angarus.—King Darius of Persia is said by Plutarch, in his book on the fortune of Alexander, to have formerly been an astanda. AST A ROTH, or Ashtaroth, in antiquity, a goddess of the Sidonians.—The word is Syriac, and signifies sheep, especially when their udders are turgid with milk. From the fecundity of these animals, which in Syria continue to breed a long time, they formed the notion of a deity, whom they called Astaroth, or Astarte. See Astarte. Astaroth, in Ancient Geography, the royal resi¬ dence of Og king of Bashan ; whether the same with Astaroth Carnaim, is matter of doubt: if one and the same, it follows from Eusebius’s account, that it lay ia Bashan, and to the east of Jordan, because in the con¬ fines of Arabia. ASTARTE, in Pagan mythology, (the singular of Astaroth), a Phoenician goddess, called in scripture the queen of heaven, and the goddess of the Sidonians. —Solomon, in compliment to one of his queens, erect¬ ed an altar to her. In the reign of Ahab, Jezebel cau¬ sed her worship to be performed with much pomp and ceremony 5 she had 400 priests *, the women were em¬ ployed in weaving hangings or tabernacles for her; and Jeremiah observes, that “ the children gathered the wood, the fathers kindled the fire, and the women kneaded the dough, to make cakes for the queen of heaven.” AstaK^e, in Ancient Geography, a city on the other side Jordan ; one of the names of Rabbath Ammon, in Arabia Petrsea, (Stephanus). ASTEISM, in Rhetoric, a genteel irony, or hand¬ some way of deriding another. Such, e. gr. is that of Virgil : Bavium non odit, amet tua carmina, Mcevi, fc.. Diomed places the characteristic of this figure, or spe- Asteisw, cies of irony, in that it is not gross and rustic, but in* Asteil. genious and polite. * '" " 1 ASTELL, Mary, an English lady who was an eminent writer, was born at Newcastle-upon-Tyne in the year 1668. Her father, who was a merchant, committed the education of his daughter to her uncle, who was a clergyman. Convinced of the general in¬ jury done to young ladies at that period by the defi¬ ciency of their education, he taught her the Latin and French languages, and instructed her in the principles of logic, mathematics, and natural philosophy. Ha¬ ving spent 20 years of her life in Nervcastle, she re¬ tired to London, where she continued the pursuit of her studies ; and, deeply affected with the general ig¬ norance of her sex, she employed the first fruits of her pen to rouse them to a proper emulation, in a work, “ A serious Proposal to the Ladies, wherein a Method is offered for the Improvement of their Minds,” print¬ ed in i2mo, at London 1697* The chief object of that book was to ex’ect a seminary for female educa- / tion. A certain lady, supposed to be the queen, form¬ ed the design of devoting io,oool. to this honourable purpose; but Bishop Burnet having suggested, that it would have too much the appearance of a nunnery, the design did not take effect. Disappointed in the article of marriage with an emi¬ nent clergyman, she next wrote a book entitled “ Re¬ flections on Marriage,” which was published in 1700. This lady was a zealous advocate for the religious system commonly called orthodox ; and in politics, de¬ fended the doctrine of nonresistance. About this time she published some controversial pieces, among which are the following : “ Moderation truly stated ;” “ A Fair Way with the Dissenters “ An Impartial En¬ quiry into the causes of the Rebellion ;” and “ A Vin¬ dication of the Royal Martyrs ;” all printed in 4U) in 1704. Her most finished performance was, “ The Christian religion as professed by a Daughter of the Church of England,” published in 1705, in a large octavo volume. Dr Waterland speaks of this book in very favourable terms; and such was the intrepidity of this lady, that she has attacked both Locke and Tillot- son in the controversial part. In the evening of her life Mrs Astell was attacked with the severe disease of a cancer in her breast; the amputation of which she bore with singular fortitude. At the advanced age of 63 she died in the year 1731. Mrs Astell appears to have been a woman, of uncom¬ mon talents as a writer and scholar ; rigid in her prin¬ ciples, and austere in her manners. Since a nerv era of female education has commenced, such an author as Mrs Astell would have attracted little notice ; but at a period of society when few women could read, and scarcely any could write, it was highly honourable for a female to suggest hints, however imperfect, for tire improvement of female education. It may farther be remarked, that it deserves to be mentioned, that about a century ago a lady informed the public by her pen, that “ women, who ought to be retired, are for this reason designed for speculation,” and that “ great im¬ provements might be made in the sciences, were not women enviously excluded from this their proper busi¬ ness.” Deeming her time more valuable than-to bir wasted by trifling visitors, and abhorring the practice of Asteii AHcria. AST [ ( of teaching servants to lie, she would humorously ac¬ cost such visitors by saying, “ Mrs Astell is not at home.” (Gen. Biog.'). ASTER, Starwort. See Botany Index. Aster, or Stella Marina, in Zoology. See Aste- rias, Helminthology Index. ASTERABAD, a small province in the north-east part of Persia, sometimes included in that of Mazan- deran. It is bounded by the Caspian sea on the west, by lofty mountains on the south, on the north by the river Abhor, and extends to the 58th degree of longitude on the east. It nearly coincides with the ancient Hyr- cania, and is the native province of the present king of Persia. It is a mountainous country, in some parts fruitful, in others sandy and barren. Asterabad is the chief town. E. Long. 54. N. Lat. 36. 50. ASTERIA, in 7joology, a name by which some au¬ thors have called the falco palumbarius, or goshawk. See Falco, Ornithology Index. Asteria is also the name of a gem, usually called the cat's eye, or oculus cati. It is a very singular and very beautiful stone, and somewhat approaches to the nature of the opal, in having a bright included colour, which seems to be lodged deep in the body of the stone, and shifts about, as it is moved, in various directions j but it differs from the opal in all other particulars, especially in its want of the great variety of colours seen in that gem, and in its superior hardness. It is usually found between the size of a pea and the breadth of a sixpence } is almost always of a semicircular form, broad and flat at the bottom, and rounded and convex at the top ; and it is naturally smooth and polished. It has only two colours, a pale brown and a white 5 the brown seeming the ground, and the white playing about in it, as the fire colour in the opal. It is considerably hard, and will take a fine polish, but is usually worn with its native shape and smoothness. It is found in the East and West Indies, and in Europe. The island of Borneo affords some very fine ones, but they are usually small $ they are very common in the sands of rivers in New Spain : and in Bohemia they are not un- frequently found immersed in the same masses of jasper with the opal. Asteria is also the name of an extraneous fossil, called in English the star-stone. The fossils are small, short, angular, or sulcated columns, between one and two inches long, and seldom above a third of an inch in diameter: composed of several regular joints 5 when separated, each resembles a radiated star. They are, not without reason, supposed to be a part of some sea- fish petrified, probably the asterias or sea-star. The aste¬ ria is also called astriies, astroites, and astenscvs. They may be reduced to two kinds : those whose whole bo¬ dies make the form of a star ; and those which in the whole are irregular, but are adorned as it were with constellations in the parts. Hr Lister, for distinction’s sake, onlv gives the name asteria to the former sort, distinguishing the latter by the appellation of astroi¬ tes; other naturalists generally use the two indiscrimi¬ nately. The asteria spoken of by the ancients, appears to be of this latter kind. The quality of moving in vinegar, as if animated, is scarce perceivable in the astroites, but is signal in the asteria. The former must be broken in small pieces before it will move ; but the latter will move, not only in a whole joint, but in two i ] AST or three knit together. The curious frequently meet Astena with these stones in many parts of England : at Cley- 11 don in Oxfordshire they are found rather larger than ^attacaii. common, but of a softer substance ; for, on being left a small space of time in a strong acid, they may easily be separated at the joints in small plates. ASTERIAS, Star-fish, or Sea-star. See Hel¬ minthology Index. Asterias, the ancient name of the bittern. See Ardea, Ornithology Index. ASTERISK, a mark in form of a star (*), placed over a word or sentence, to refer the reader to the mar¬ gin, or elsewhere, for a quotation, explanation, or the like. ASTERIUS, or Asturius, a Roman consul, in 449. W e have under his name, “ A Conference on the Old and New Testament,” in Latin verse : in which each strophe contains, in the first verse, an historical fact in the Old Testament 5 and in the second, an application of that fact to some point in the New. ASTERN, a sea phrase, used to signify any thing at some distance behind the ship 5 being the opposite of Ahead, wdiich signifies the space before her. See Ahead. ASTEROPODIUM, a kind of extraneous fossil, of the same substance with the asterise or star-stones, to which they serve as a base. See Asteria and Star- STONE. ASTHMA. See Medicine Index. ASTI, a city of Montferrat in Italy, seated on the Tanara, and capital of the county of the same name. It is a bishop’s see, and well fortified with strong walls and deep ditches ) and is divided into the city, borough, citadel, and castle, which contain altogether 22,000 in¬ habitants. There are a great many churches and con¬ vents, as well as other handsome buildings ; and its ter¬ ritory is well watered, beautiful, and fruitful. It was repeatedly taken and retaken by the French and Au¬ strians during the late wars. E. Long. 8. 15. N. Lat. 44. 58- . . ASTIGI, in Ancient Geography, a colony, and con- ventus juridicus, of Bsetica, surnamed Augusta Firma, situated on the Singulus, which falls into the Baetis j called also Colonia Astigitana (Pliny) : Now Ecya, midway between Seville and Cordova. W. Long. 50. N. Lat. 37. 20. ASTOMI, in anthropology, a people feigned with¬ out mouths. Pliny speaks of a nation of Astomi in India, who lived only by the smell or effluvia of bodies taken in bv the nose. ASTORGA, a very ancient city of Spain, in the kingdom of Leon, with a bishop’s see, is seated on the river Tuerta, and well fortified both by art and nature. It stands in a most agreeable plain, about 150 miles north-west of Madrid. There are excellent trouts in the river. W. Long. 6. 20. N. Lat. 42. 20. ASTRACAN, a province of Russia, and the most easterly part of Europe ; bounded on the north by Bul¬ garia and Baskiria ; on the south hy the Caspian sea ; on the west, by the Volga, which divides it from the Nagayan Tartars and Don Cossacks j and on the east, by the great ridge of mountains which part it from Great Tartary. The province extends from the 46th to the 52d degree of latitude. The summer is long, and intensely hot : the winter continues about three months AST [ A*tracan. months so severe, that the Volga Is frozen hard enough l-—-v —to hear loaded sledges. The soil is rich and fertile ; but the Tartars who inhabit it are strangers to agricul¬ ture. On the western and southern sides of the "Volga, are heaths of a prodigious extent, sandy, desert, and uncultivated •, these, however produce vast quantities of fine transparent salt in pits, where the sun bakes and incrustates it to the thickness of an inch on the surface of the water. There are pits in the neighbourhood of Astracan which yield this excellent salt in such abun¬ dance, that any person may carry it off, paying at the rate of one farthing a poost, which is equal to forty pounds. The metropolis, Astracan, is situated with¬ in the boundaries of Asia, on an island called Dolgoi, about 60 English miles above the place where the Vol. ga disembogues itself into the Caspian sea. The city derives its name from Hadgee Tarkan, a Tartar, by whom it was founded. It was conquered by Iwan Ba- silowitz, recovered by the Tartars in the year 1668, and retaken by the czar, who employed for this pur¬ pose a great number of flat-bottomed vessels, in which he transported his forces down the Volga from Casan. The city of Astracan is about two miles and a half in circumference, surrounded by a brick wall, which is now in a ruinous condition: but, if we comprehend the suburbs, the circuit will lie near five miles. The number of inhabitants amounts to 70,000, including Armenians and Tartars, as well as a few Persians and Indians. The garrison consists of six regiments of the best Russian troops, who, when this place was alarm¬ ed from the side of Persia, had in the adjacent plain erected a great number of small batteries, to scour the fields, and obstruct the approach of the enemy. The houses of Astracan are built of wood, and generally mean and inconvenient. The higher parts of the.city command a prospect of the Volga, which is here about three miles in breadth, and exhibits a noble appear¬ ance. The marshy lands on the banks of it render the place very sickly in the summer : the earth, being im¬ pregnated with salt, is extremely fertile, and produces abundance of fruit, the immoderate use of which is at¬ tended with epidemical distempers. Sickness is like¬ wise the consequence of those annual changes in the atmosphere produced by the floods in spring and au¬ tumn. All round the city of Astracan, at the distance of two miles, are seen a great number of gardens, or¬ chards, and vineyards, producing all sorts of herbs and roots. The grapes are counted so delicious, that they are preserved, in sand, and transported to court bv land-carriage at a prodigious expence: yet the wine of Astracan is very indifferent. The summer being ge¬ nerally dry, the inhabitants water their gardens by means of large wheels worked by wind or horses, which raise the water to the highest part of the gai*- den, from whence it runs in trenches to refresh the roots of every single tree and plant. The neighbour¬ ing country produces hares and partridges, plenty of quails in summer, with wild and water-fowl ©f all sorts in abundance. About ten miles below Astracan is a small island called Bostnaise, on which are built large storehouses for the salt, which is made about twelve miles to the eastward, and, being brought thither in boats, is conveyed up the Volga, in order to supply the coun¬ try as far as Moscow, and Twere. The quantity of 7 ] AST salt annually dug for these purposes amounts to some Astrac millions of pounds, the exclusive property of which is ’ r claimed by the crown, and yields a considerable reve¬ nue 5 for the soldiers and bulk of the people live almost entirely on bread and salt. I he neighbourhood of these salt-works is of great advantage to the fisheries, which extend from hence to the Caspian sea, and reach to the south-east as far as Yack, and even ico miles above Zaritzen. The principal fish here caught are sturgeon and belluga. These, being salted, are put on board of vessels, and sent away in the spring, for the use of the whole empire, even as far as Petersburg: but as fish may be kept fresh as long as it is frozen, the winter is no sooner set in, than they transport great quantities of it by land through ail the provinces of Russia. Of the roes ot the fish called belluga, which are white, transparent, and of an agieeable flavour, the fishers here prepare the caviare, which is in so much esteem all over Europe. These fisheries were first esta¬ blished by one Tikon Demedoff, a carrier, who settled in this place about 60 years ago, his whole wealth con¬ sisting of two horses. By dint of skill and industry, he soon grew the richest merchant in this country : but his success became so alluring to the crown, that of late years it hath engrossed some of the fisheries as well as the salt works. From the latter end of July to the beginning of Oc¬ tober, the country about Astracan is frequently infest¬ ed with myriads of locusts, which darken the air in then- progression from the north to the southward; and, wherever they fall, consume the whole verdure of the earth. These insects can even live for some time un¬ der water: for when the wind blows across the Volga, vast numbers of them fall in clusters, and are rolled ashore ; and their wings are no sooner dry, than they rise and take flight again. Heretofore the inhabitants of Astracan traded to Khuva and Bokhara ; but at present these branches are lost, and their commerce is limited to Persia and the dominions of Russia. Even the trade to Persia is much diminished by the troubles of that country; neverthe¬ less, the commerce of Astracan is still considerable. Some years ago, the city maintained about 40 vessels, from 100 to 200 tons burden, for the Caspian traffic. Some of these belong to the government, and are com¬ manded by a commodore, under the direction of the admiralty. This office is generally well stocked with naval stores, which are sold occasionally to the mer¬ chants. The trading ships convey provisions to the frontier towns of Terkie and Kislar, situated on the Caspian sea; and transport merchandise to several parts of Persia. The merchants of Astracan export to Persia, chiefly on account of the Armenians, red leather, linens, woollen cloths, and other European ma¬ nufactures. fn return, they import the commodities of Persia, particularly those manufactured at Casan ; such as silk sashes intermixed with gold, for the use of the Poles ; wrought silks and stuffs mixed with cot¬ ton ; rice, cotton, rhubarb, and a small quantity of other drugs ; hut the chief commodity is raw silk. The government has engrossed the article of rhubarb, the greater part of which is brought into Russia by the Tartars of Yakutski, bordering on the eastern Tartars belonging to China. They travel through Siberia to Samura, thence to Casan, and lastly to Moscow. The revemu, * AST [8 AcHaeatt revenue of Astracan is computed at 150,000 rubles, [} or 33,000!. arising chiefly from salt and fish. The Astroguo- cjty js ruled by a governor, under the check ol a , **• , chancery. He is nevertheless arbitrary enough, and exercises oppression rvith impunity. The officers of the admiralty and custom-house having very small sa¬ laries, are open to corruption, and extremely rapaci- o’js. At christening feasts, which are attended with great intemperance, the guests drink a kind of cherry- brandy out of large goblets; and every person invited throws a present of money into the bed of the mother, who sits up with great formality to be saluted by the company. The Indians have a Pagan temple at Astracan, in which they pay their adoration, and make offerings of fruit to a very ugly deformed idol. The priests of this pagod use incense, beads, cups, and prostrations. The Tartars, on the contrary, hold idol-worship in the ut¬ most abomination. ASTRiEA, in Astronomy, a name which some give to the sign Virgo, by others called Erigone, and some¬ times Isis. The poets feign that Justice quitted heaven t-o reside on earth, in the golden age ; but, growing weary of the iniquities of mankind, she left the earth, and returned to heaven, where she commenced a con¬ stellation of stars, and from her orb still looks down on the ways of men. ASTRAGAL, in Architecture, a little round mould¬ ing, which in the orders surrounds the top of the shaft or body of the column. It is also called the talon and tondino ; it is used at the bottoms as well as tops of co¬ lumns, and on other occasions : it properly represents a ring, on whatever part of a column it is placed ; and the original idea of it was that of a circle of iron put round the trunk of a tree, used to support an edifice, to prevent its splitting. The astragal is often cut into beads and berries, and is used in the ornamented en¬ tablatures to separate the several faces of the archi¬ trave. Astragal, in Gunnery, a round moulding encom¬ passing a cannon, about half a foot from its mouth. ASTRAGALOMANCY, a species of divination performed by throwing small pieces, with marks cor¬ responding to the letters of the alphabet; the accidental disposition of which formed the answer required. This kind of divination was practised in a temple of Hercules, in Achaia. The word is derived from and pciVTUct, divination. ASTRAGALUS, Milk-vetch, or Liquorice- vetch. See Botany Index. Astragalus. See Anatomy index. ASTRANTIA, Masterwort. See Botany In- ^ ASTRICTION, in Law. See Thirlage. Astriction, among physicians, denotes the opera¬ tion of astringent medicines. ASTRINGENTS, in the Materia Medico, sub¬ stances distinguished by a rough austere taste, and chan¬ ging solutions of iron, especially those made in the vi¬ triolic acid, into a dark purple or black colour ; such are galls, tormentil root, bistort root, balaustines, ter¬ ra japonica, acacia, &c. See Materia Medica In¬ dex. ASTROGNOSIA, the science of the fixed stars, ] AST or the knowledge of their names, constellations, magnl- Astregaa- tudes, &c. s** ASTROITES, or Star-stone, in Natural History. . ^ See Asteria and STAR-STONE. t ASTROLABE, the name for a stereographic pro¬ jection of the sphere, either upon the plane of the equa¬ tor, the eye being supposed to be in the pole of the world ; or upon the plane of the meridian, when tba eye is supposed in the point of the intersection of the equinoctial and horizon. Astrolabe is also the name of an instrument for¬ merly used for taking the altitude of the sun or stars at sea. Astrolabe, among the ancients, was the same as our armillary sphere. ASTROLOGY, a conjectural science, which teach¬ es to judge of the effects and influences of the stars, and to foretel future events by the situation and different as¬ pects of the heavenly bodies. This science has been divided into two branches, na¬ tural a\\A judiciary. To the former belongs the pre¬ dicting of natural effects ; as, the changes of weather, winds, storms, hurricanes, thunder, floods, earthquakes, &c. This art properly belongs to natural philosophy; and is only to be deduced, a posteriori, from phenomena and observations. Judiciary or judicial astrology, is that which pretends to foretel moral events; i. e. such as have a dependency on the free will and agency of man ; as if they were directed by the stars. This art, which owed its origin to the practices of knavery on credulity, is now universally exploded by the intelligent part of mankind. The professors of this kind of astrology maintain, “ That the heavens are one great volume or book, wherein God has written the history of the world; and in which every man may read his own fortune, and the transactions of his time. The art, say they, had its rise from the same hands as astronomy itself: while the ancient Assyrians, whose serene unclouded sky favour¬ ed their celestial observations, were intent on tracing the paths and periods of the heavenly bodies, they dis¬ covered a constant settled relation or analogy between them and things below ; and hence were led to con¬ clude these to be the Parcte, the Destinies, so much talked of, which preside at our births, and dispose of our future fate. “ The laws, therefore, of this relation being ascer¬ tained by a series of observations, and the share each planet has therein; by knowing the precise time of any person’s nativity, they were enabled, from their know¬ ledge in astronomy, to erect a scheme or horoscope of the situation of the planets at this point oi time ; and, hence, by considering their degrees of power and in¬ fluence, and how each was either strengthened or tem¬ pered by some other, to compute what must be the re¬ sult thereof.” Thus the astrologers.—But the chief province now remaining to the modern professors, is the making of calendars or almanacks. Judicial astrology is commonly said to have been invented in Chaldea, and thence transmitted to the Egyptians, Greeks, and Romans; though some will have it of Egyptian origin, and ascribe the invention to Cham. But it is to the Arabs that we owe it. At Rome the A S ' T [ Astrology, the people were so infatuated with it, that the astrolo- u-—-_v gers, or, as they were then called, the mathematicians, maintained their ground in spite of all the edicts of the emperors to expel them out of the city. See Ge- NETHLIACI. Add, that the Bramins, who introduced and practi¬ sed this art among the Indians, have thereby made them¬ selves the arbiters of good and evil hours, which gives them great authority : they are consulted as oracles, and they have taken care never to sell their answers but at good rates. The same superstition has prevailed in more modern ages and nations. The French historians remark, that in the time of Queen Catherine de Medicis, astrology was so much in vogue, that the most inconsiderable thing was not to be done without consulting the stars. And in the reigns of King Henry III. and IV. of France, the predictions of astrologers were the com- 9 ] ^ AST mon theme-of the court conversation. This predomi- Astrology nant humour in that court was well rallied by Barclay, U in his Argems, lib. ii. on occasion of an astrologer, who Astroncmi- had undertaken to instruct King Henry in the event 0fCi- • ,,i- a war then threatened by the faction of the Guises. ASTRONIUM. See Botany Index. ASTRONOMICAL, something relating to A- STRONOMY. Astronomical Calendar, an instrument engraven on copperplates, printed on paper, and pasted on a board, with a brass slider carrying a hair: it shows by inspec¬ tion the sun’s meridian altitude, right ascension, decli¬ nation, rising, setting, amplitude, &c. to a greater de¬ gree of exactness than the common globes. Astronomical Sector, a very useful mathematical instrument, made, by the late ingenious Mr Graham 5 a description of which is given in the course of the following article. ASTRONOMY. A STRONOMY is that science which treats of the motions of the heavenly bodies, and explains the laws by which these motions are regulated. It is the most sublime and the most perfect of all the sciences. No subject has been longer studied, or has made greater progress. There is a vast interval be¬ tween the rude observations of the earlier astronomers, and the precision and general views which direct our present observers. To ascertain the apparent motions of the heavenly bodies was a difficult task, and requi¬ red the united observations of ages. To unravel these intricate mazes, and detect and demonstrate the real motions, demanded the most patient perseverance, judgment, and dexterity. To ascertain the laws of these motions, and to resolve the whole of them in¬ to one general fact, required the exertions of a sagaci¬ ty scarcely to be expected in human nature. Yet all this has been accomplished; and even the most minute movement of the heavenly bodies has been shewn to depend upon the same general law with all the rest, and even to be a consequence of that law. Astrono¬ my, therefore, is highly interesting, were it only be¬ cause it exhibits the finest instance of the length that the reasoning faculties can go. It is the triumph of philosophy and of human nature. But this is not all. It has conferred upon mankind the greatest benefits, and may truly be considered as the grand improver and conductor of navigation. The following treatise will be divided into four parts. In the first part, we shall give a sketch of the history of astronomy j in the second, w'e shall treat of the appa¬ rent motions of the heavenly bodies ; in the third, of their real motions ; and in the fourth, of gravitation, or of that general fact to which all their motions may be referred, and from which they proceed. PART I. HISTORY OF ASTRONOMY. , Ibstory. THE antiquity of this science may be gathered from v~” "* what was spoken by the Deity at the time of creating the celestial luminaries, “ Let them be for signs and seasons,” &c. whence it is thought probable that the human race never existed without some knowledge of astronomy among them. Indeed, besides the motives of mere curiosity, which of themselves maybe supposed to have excited people to a contemplation of the glori¬ ous celestial canopy, as far as that was possible, it is easily to be seen that some parts of the science answer such essential purposes to mankind, that they could not t possibly be dispensed with. Astronomy By some of the Jewish rabbins, Adam, in his state supposed to of innocence, is supposed to have been endowed with a KtT jcnow!edSe °!’ the nature, influence, and uses of the Idam and bodies 5 and Josephus ascribes to Seth and his be Antedi- posterity an extensive knowledge of astronomy. But umns. whatever may be in this, the long lives of theAntedi- Vol. HI. Part I. ± luvians certainly afforded such an excellent opportunity H;sto for observing the celestial bodies, that we cannot but ■ suppose the science of astronomy to have been consider¬ ably advanced before the flood. Josephus says, that longevity was bestowed upon them for the very purpose of improving the sciences of geometry and astronomy. The latter could not be learned in less than 600 years: “for that period (says he) is the grand year. ” By which it is supposed he meant the period wherein the. sun and moon came again into the same situation as they were in the beginning thereof, with regard to the nodes, apogee of the moon, &c. “ This period (says Cassini), whereof we find no intimation in any monu¬ ment of any other nation, is the finest period that ever was invented : for it brings out the solar year more exactly than that of Hipparchus and Ptolemy ; and the lunar month within about one second of what is determined by modern astronomers. If the Antedilu- B vians ASTRONOMY. Part I. vians had such a period of 6oo years, they must have known the motion of the sun and moon more exactly than their descendants knew them some ages after the 2 flood.” Asironomi- On the building of the tower of Babel, Noah is sup- cal know- p0se(l to have retired with his children born after the ledge ofthefl00(j^ to t|ie north-easteru part of Asia, where his de- Chmese. scen(jants peopled the vast empire of China. “ This (says Dr Long) may perhaps account for the Chinese having so early cultivated the study of astronomy ; their being so well settled in an admirable police, and continuing so many hundred years as they did in the worship of the true God.” The vanity of that people indeed has prompted them to pretend a knowledge of astronomy almost as early as the flood itself. Some oi the Jesuit missionaries have found traditional accounts among the Chinese, of their having been taught this science by their first emperor Fo-hi, supposed to be Noah; andKempfer informs us, that this personage discovered the motions of the heavens, divided time into years and months, and invented the twelve signs into which they divide the zodiac, which they distinguish by the following names. I. The mouse. 2. The ox or cow. 3. The tiger. 4. The hare. 5. The dragon. 6. The 7. The horse. 8; The sheep. 9. The monkey. 10. The cock or hen. 11. The dog-, and, 12. The bear. They divide the heavens into 28 constellations, four of which are assigned to each of the seven planets-, so that the year always begins with the same planet; and their constellations answer to the 28 mansions of the moon used by the Arabian astronomers. These constellations, in the Chinese books of astronomy, are not marked by the figures of animals, as was in use among the Greeks, and from them derived to the other European nations, but by connecting the stars by straight lines ; and Dr Long informs us, that in a Chinese book in thin 4to, shown him by Lord Pem¬ broke, the stars were represented by small circles joined by lines; so that the Great Bear would be marked thus, .3 Their names for the signs of g nt> the zodiac. rnp. To the emperor Hong-ti, the grandson of Noah, they attribute the discovery of the pole-star, the inven¬ tion of the mariner’s compass, of a period of 60 years, and some kind of sphere. rlhis extraordinary antiqui¬ ty, however, is with good reason suspected, a,s is like¬ wise their knowledge in the calculation of eclipses ; of which Du Halde assures us, that 36 are recorded by Confucius himself, who lived 551 years before Christ ; and P. Trigault, who went to China in 1619, and read more than 100 volumes of their annals, says, “ It is certain that the Chinese began to make astronomical observations soon after the flood ; that they have ob¬ served a great number of eclipses, in which they have noted down the hour, day, month, and year, when they happened, but neither the duration nor the quantity ; and that these eclipses have been made use of for re¬ gulating their chronology.” “ But out of this abundance (says Dr Long), it is much to be regretted, that so very few of their obser¬ vations have been particularized ; for beside what has been mentioned above, we meet with no very ancient observations of the Chinese, except a winter solstice in 3: the year mi, and a summer solstice in the year 882, History before Christ. Martini indeed speaks of a summer sol- 'V— slice 2342 years before that period. But M. Cassini, who calculated it, found that there must have been an error in the Chinese computation of 500 years at least. An error of equal magnitude appears to have been committed in the conjunction of the five planets, which it is pretended they observed between the years 2513 and 2435 before Christ. In short, some have suppo¬ sed, that none of these are real observations, but the result of bungling calculations ; and it has been hinted, but surely on too slight a foundation, that even those good fathers themselves were greatly to be suspected. But let us come to things which are not contested. “ P. Gaubil informs us, that at least 120 years before Christ, the Chinese had determined by observation the number and extent of their constellations as they now stand ; the situation of the fixed stars with respect to the equinoctial and solstitial points ; and the ob¬ liquity of the ecliptic. He farther says, he cannot tell by what means it is that they foretel eclipses : but this is certain, that the theory by which they do predict them was settled about the same time; and that they were acquainted with the true length of the solar year, the method of observing meridian altitudes of the sun by the shadow of a gnomon, and of learning from thence his declination and the height of the pole, long before. We learn, moreover, from the same missiona¬ ry, that there are yet remaining among them some treatises of astronomy, which were written about 200 years before Christ, from which it appears, that the Chinese bad known the daily motion of the sun and moon, and the times of the revolutions of the planets, many years before that period. “ We are informed by Du Halde, that, in the pro¬ vince of Honan, and city Jeng-foang, which is nearly^ in the middle of China, there is a tower, on the top of which it is said that Tchcou-cong, the most skilful astro¬ nomer that ever China produced, made his observations. He lived 1200 years before Ptolemy, or more than 1000 years before Christ, and passed whole nights in observing the celestial bodies and arranging them into constellations. He used a very large brass table placed perfectly horizontal, on which was fixed a long upright plate of the same metal, both of which were divided into degrees, &c. By these he marked the meridian al¬ titudes ; and from thence derived the times of the sol¬ stices, which were their principal epoefia.” Dr Long represents the state of astronomy in China as at present very low ; occasioned, he says, prin¬ cipally by the barbarous decree of one of their em- perors*, to have all the. books in the empire burnt,' SeeC*j|T' excepting such as related to agriculture and medicine. We are informed, however, by the Abbe Grosier, in his description of China, that astronomy is cultivated in Pekin in the same manner as in most of the capital cities of Europe. A particular tribunal is established there, the jurisdiction of which extends to every thing relating to the observation of celestial phenomena. Its members are, an inspector; two presidents, one of them a Tartar and the other a Chinese ; and a certain number of mandarins who perform the duty of asses¬ sors ; but for near a century and a half the place of the Chinese president has been filled by an European. Since that time particular attention has been paid to the ASTRONOMY, I. Part 1. History, the instruction of the astronomical pupils $ and the pre- «. y———• sidents have always considered it as their duty to make them acquainted with the system and method of cal¬ culations made use of in Europe. Thus two-thirds of the astronomical pupils, maintained at the emperor’s expence, in all about 200, have a tolerable notion of the state of the heavens, and understand calculation so well as to be able to compose ephemerides of sufficient exactness. The missionaries have never been the au¬ thors of any of these ephemerides : their employment is to revise the labours of the Chinese mathematicians, verify their calculations, and correct any errors into which they have fallen. The Portuguese mission still continues to furnish astronomers for the academy, as it did at the first. The astronomical tribunal is subordinate to that of ceremonies. When an eclipse is to be observed, in¬ formation must be given to the emperor of the day and hour, the part of the heavens where it will be, &c. and this intelligence must be communicated some months before it happens j the eclipse must also be calculated for the longitude and latitude of the capital city of every province of the empire. These observations, as well as the diagram which represents the eclipse, are preserved by the tribunal of ceremonies, and another called the calao, by whom it is transmitted to the dif¬ ferent provinces and cities of the empire. Some days before the eclipse, the tribunal of ceremonies causes to be fixed upon a public place, in large characters, the hour and minute when the eclipse will commence, the quarter of the heavens in which it will be visible, with the other particulars relating to it. The mandarins are summoned to appear in state at the tribunal of astrono¬ my, and to wait there for the moment in which the phenomenon will take place. Each of them carries in his hand a sheet of paper, containing a figure of the eclipse and every circumstance attending in. As soon as the observation begins to take place, they throw themselves on their kness, and knock their heads against the earth, and a horrid noise of drums and cymbals im¬ mediately commences throughout the whole city : a ceremony proceeding from an ancient superstitious no¬ tion, that by such a noise they prevented the luminary from being devoured by the celestial dragon $ and though this notion is now exploded in China, as well as everywhere else, such is the attachment of the people to ancient customs, that the ceremonial is still observed. W hile the mandarins thus remain prostrated in the court, others, stationed on the observatory, examine, with all the attention possible, the beginning, middle, and end of the eclipse, comparing what they observe ^1 with the figure and calculations given. They then write down their observations, affix their seal to them, and transmit them to the emperor •, who, on his part, has been no less assiduous to observe the eclipse with accu¬ racy. A ceremonial of this kind is observed through the whole empire. The Japanese, Siamese, and inhabitants of the Mo¬ gul’s empire, have also, from time immemorial, been ac¬ quainted with astronomy ; and the celebrated observa¬ tory at Benares, is a monument both of the ingenuity of the people and of their skill in the science. Indian Bailty has been at great pains to investigate the astronomy, progress ot the Indians in astronomical knowledge, and gives a splendid account of their proficiency in the science, as well as of the antiquity of their observa- History, tions. He has examined and compared four different lv‘—v— astronomical tables of the Indian philosophers, i. Of the Siamese, explained by M. Cassini in 1689. 2. Those brought from India by M. le Gentil of the Academy of Sciences. 3. and 4. Two other manuscript tables found among the papers of the late M. de Lisle. All of these tables have different epochs, and differ in form, being also constructed in different ways \ yet they all evidently belong to the same astronomical sy¬ stem : the motions attributed to the sun and the moon are the same, and the different epochs are so well con¬ nected by the mean motions, as to demonstrate that they had only one, whence the others were derived by calculation. The meridians are all referred to that of Benares above mentioned. The fundamental epoch of the Indian astronomy is a conjunction of the sun and moon, which took place at no less a distance of time that 3102 years before the Christian era. Mr Bailly informs us, that, according to our most accurate astro¬ nomical tables, a conjunction of the sun and moon ac¬ tually did happen at that time. But though the bra- mins pretend to have ascertained the places of the two luminaries at that time, it is impossible for us at this time to judge of the truth of their assertions, by rea¬ son of the unequal motion of the moon ; which, as shall afterwards be more particularly taken notice of, now performs its revolution in a shorter time than for¬ merly. Our author informs us, that the Indians at present cal¬ culate eclipses by the mean motions of the sun and moon observed 5000 years ago j and with regard to the solar motion, their accuracy far exceeds that of the best Gre¬ cian astronomers. The lunar motions they bad also settled, by computing the spaces through which that lu¬ minary bad passed in 1,600,984 days, or somewhat more than 4383 years. They also make use of the cycle of 19 years attributed by the Greeks to Metonj and their theory of the planets is much better than that of Ptolemy, as they do not suppose the earth to be the centre of the celestial motions, and they believe that Mercury and Venus turn round the sun. Mr Bailly also informs us, that their astronomy agrees with the most modern discoveries of the decrease of the obliquity of the ecliptic, the acceleration of the motion of the e- quinoctial points, with many other particulars too tedi¬ ous to enumerate in this place. ^ It appears also, that even the Americans were not Astronomy unacquainted with astronomy, though they made useoftlieA_ only of the solar, and not of the lunar motions, in their raer*cails' division of time. The Mexicans have had a strange predilection for the number 13. Their shortest pe¬ riods consisted of 13 days ; their cycle of 13 months, each containing 20 days ; and their century of four periods of 13 years each. This excessive veneration for the number 13, according to Siguenza, arose from its being supposed the number of their greater gods. What is very surprising, though asserted as a fact by Abbe Clavigero, is that having discovered the excess of a few hours in the solar above the civil year, they made use of intercalary days, to bring them to an equa¬ lity : but with this difference in regard to the method established by Julius Caesar in the Roman calendar, that they did not interpose a dav every four years, but 13 days (making use even here of this favourite nuni- B 2 her) i2 ASTRO History, ber) every 52 years, which produces the same regula- ' v—-- tion of time. Among those nations who first began to make any Chaldeans figure in oncient liistory, we find the Chaldeans and and Egyp- Egyptians most remarkable for their astronomical tiaiiii. knowledge. Both of them pretended to an extravagant antiquity, and disputed the honour of having been the first cultivators of the science. The Chaldeans boast¬ ed of their temple of Belus •, and of Zoroaster, whom they placed 5000 years before the destruction of Troy : the Egyptians boasted of their colleges of priests, where astronomy was taught j and of the monument of Osy- niandyas, in which we are told was a golden circle 365 cubits in circumference and one cubit thick. The ujr- per face was divided into 365 equal parts, answering to the days of the year ; and on every division were written the name of the day, and the heliacal rising of the several stars for that day, with the prognostications from their rising, principally, as Long conjectures, for the weather. The Chaldeans certainly began to make observa¬ tions very soon after the confusion of languages j for when Alexander the Great took Babylon, Calisthenes, by his order, inquired after the astronomical observa¬ tions recorded in that city, and obtained them for 1903 years back. Nothing, however, now remains of the Chaldean astronomy, excepting some periods of years which they had formed for the more ready com¬ putation of the heavenly bodies. But though they must have laboured under great disadvantages for want of proper instruments, in those early ages, Ge- mina, as quoted by Petarius in his Uranologion, in¬ forms us, that they had determined, with tolerable exactness, the length both of a synodical and periodi¬ cal month. They had also discovered that the mo¬ tion of the moon was not uniform, and even attempt¬ ed to assign those parts of her orbit in which it was quicker or slower. Ptolemy also assures us, that they were not unacquainted with the motion of the moon’s nodes and that of her apogee, supposing that the for¬ mer made a complete revolution in 6585^ days, or 18 years 15 days and 8 hours j which period, con¬ taining 223 complete lunations, is called the Chal¬ dean Sciros. The same author also gives us, from Hipparchus, several observations of lunar eclipses which had been made at Babylon about 720 years be¬ fore Christ; but though he might very probably meet with many of a more ancient date, it was impossible to mention them particularly, on account of the im¬ perfect state of the Chaldean chronology, which com¬ menced only with the era of Nabonassar, 747 years be¬ fore Christ. Aristotle likewise informs us, that they had many observations of the occultations of fixed stars and planets by the moon ; and from hence, by a very natural and easy inference, they were led to con¬ clude that the eclipses of the sun were occasioned also by the moon, especially as they constantly happened when the latter was in the same part of the heavens with the sun. They had also a considerable share in arranging the stars into constellations. Nor had the comets, by which astronomers in all ages have been so much perplexed, escaped their observation : for both Diodorus Siculus and Appollinus Myndius, in Seneca, inform us, that many of the Chaldeans held these to be lasting bodies, which have stated revolutions as N O M Y. Part I. well as the planets, but in orbits vastly more extensive ; History, on which account they are only seen by us while near —y—» the earth, but disappear again when they go into the higher regions. Others of them were of opinion, that the comets were only meteors raised very high in the air, which blaze for a while, and disappear when the matter of which they consist is consumed or dispersed. Dialling was also known among them long before the Greeks were acquainted with any such thing. It is evident, indeed, that the countries both of Chaldea and Egypt were exceedingly proper for astro¬ nomical observations, on account of the general puri¬ ty and serenity of the air. The tower or temple of Belus, which was of an extraordinary height, with stairs winding round it up to the top, is supposed to have been an astronomical observatory; and the lofty pyramids of Egypt, whatever they were ori¬ ginally designed for, might possibly answer the same purpose. Indeed these very ancient monuments show the skill of this people in practical astronomy, as they are all situated with their four fronts exactly facing the cardinal points. Herodotus ascribes the Egyptian knowledge in astronomy to Sesostris, whom Sir Isaac Newton makes contemporary with Solo¬ mon ; but if this was the case, he could not be tit© instructor of the Egyptians in astronomical mat¬ ters, since we find that Moses, who lived 500 years before Solomon, was skilled in all the wisdom of the Egyptians, in which we are undoubtedly to include astronomy. From the testimony of some ancient authors, we learn that they believed the earth to be spherical, that they knew the moon was eclipsed by falling into its shadow, and that they made their observations with the greatest exactness. They even pretended to foretel the appear¬ ance of comets, as well as earthquakes and inundationsy which extraordinary knowledge is likewise ascribed to the Chaldeans. They attempted to measure the mag¬ nitude of the earth and sun ; but the methods they took to find out the latter were very erroneous. It does not indeed appear with certainty that they had any know¬ ledge of the true system of the universe ; and by the time of the emperor Augustus, their astronomical knowledge was entirely lost. ^ From Chaldea the science of astronomy most probably Of the Ph< passed into Phenicia ; though some are of opinion that iiician*. the Phenicians derived their knowledge of this science from the Egyptians. They seem, however, to have been the first who applied astronomy to the purposes of navi¬ gation ; by which they became masters of the sea, and of almost all the commerce in the world. They became adventurous in their voyages, steering their ships by one of the stars of the Little Bear ; which being near the immoveable point of the heavens called the Pole, is the most proper guide in navigation. Other nations made their observations by the Great Bear : which being too distant from the pole could not guide them in long voy¬ ages ; and for this reason they never durst venture far from the coasts. 8 The first origin of astronomical knowledge amongAsironos* the Greeks is unknown. Sir Isaac Newton supposes^^ that most of the constellations were invented about the time of the Argonautic expedition : but Dr Long is of opinion that many of them must have been of a much older date; and that the shepherds, who were certainly Part I. ASTRONOMY. History, certainly tlie first observers, gave names to them ac- -y—' cording to their fancy ; from whence the poets invent¬ ed many of their fables. Several of the constellations are mentioned by Hesiod and Homer, the two most ancient writers among the Greeks, who lived about 870 years before Christ: Hesiod desiring the farmer to regulate the time of sowing and harvest by tbe ri¬ sing and setting of the Pleiades ; and Homer inform¬ ing ns, that observations from tbe Pleiades, Orion, and Arcturus, rvere used in navigation. Their astronomi¬ cal knowledge, however, was greatly improved by Improved ^ia^es the Milesian, who travelled into Egypt, and by Thales, brought from thence the first principles of the science. He is said to have determined the height of the pyra¬ mids by measuring their shadows at the time the sun was 45 degrees high, and when of consequence the lengths of the shadows of objects are equal to their perpendicular heights. But his reputation was raised to the highest pitch among his countrymen, by the prediction of an eclipse, which happened just at the time that the armies of Alyattes king of Lydia, and Cyaxares the Mede, were about to engage } and being regarded as an evil omen by both parties, inclined them to peace. To him Callimachus attributes the form¬ ing of the constellation of the Little Bear j the know¬ ledge of which he certainly introduced into Greece. He also taught the true length of the year 5 determined the cosmical setting of the Pleiades in his time to have been 25 days after the autumnal equinox j divided the earth into five zones by means of the polar circles and tropics ; taught the obliquity of the ecliptic ; and show¬ ed that the equinoctial is cut by the meridians at right angles, all of which intersect each other at the poles. He is also said to have observed the exact time of the solstices, and from thence to have deduced the true length of the solar year ; to have observed eclipses of the sun and moon 5 and to have taught that the moon had no light but what she borrowed from the sun. According to Stanley, he also determined the diameter of the sun to be one-720th part of his annual orbit. “ But (says Dr Long) these things should be received with caution. There are some reasons which might be assigned for supposing that the knowledge of Thales in these matters was much more circumscribed: and indeed it is not unreasonable to suppose, that that veneration for the ancients which leads authors to write professedly on the history of ancient times, may have induced them to ascribe full as much knowledge to those who lived in them as was really their due.” ro 1 he successors of Thales, Anaximander, Anaxime- manderU neS’ aru^ Anaxagoras, contributed considerably to the &c. ' advancement of astronomy. The first is said to have invented or introduced the gnomon into Greece $ to have observed the obliquity of the ecliptic j and taught that the earth was spherical, and the centre of the universe, and that the sun was not less than it. He is also said to have made the first globe, and to have set up a sun-dial at Lacedemon, which is the first we hear of among the Greeks 5 though some are of opini¬ on that these pieces of knowledge were brought from Babylon by Pherycides, a contemporary of Anaximan¬ der. Anaxagoras also predicted an eclipse which hap¬ pened in the filth year of the Peloponnesian war ; and taught that the moon was habitable, consisting of hills, valleys, and waters, like the earth. His contemporary^ Pythagoras, however, greatly improved not only astro- History, nomy and mathematics, but every other branch of phi- 1——v—— losophy. He taught that the universe was composed 1 r. of four elements, and that it had the sun in the centre} that the earth was round, and had antipodes; and thatg0rag) the moon reflected the rays of the sun ; that the stars" were worlds, containing earth, air, and ether ; that the moon was inhabited like the earth ; and that the comets were a kind of wandering stars, disappearing in the superior parts of their orbits, and becoming visible on¬ ly in the lower parts of them. The white colour of the milky-way he ascribed to the brightness of a great number of small stars ; and he supposed th& distances -of the moon and planets from the earth to be in certain harmonic proportions to one another. He is said also to have exhibited the oblique course of the sun in the eclip¬ tic and the tropical circles, by means of an artificial sphere; and he first taught that the planet Venus is both the evening and morning star. This philosopher is said to have been taken prisoner by Cambyses, and thus to have become acquainted with all the mysteries of tire Persian magi ; after which he settled at Crotona in Ita¬ ly, and founded the Italian sect. About 440 years before the Christian era, Philolaus, a celebrated Pythagorean, asserted the annual motion of the earth round the sun ; and soon after Hicetas, a Syracusan, taught its diurnal motion on its own axil. About this time also flourished Melon and Euctemon at Athens, who took an exact observation of the sum¬ mer solstice 432 years before Christ; which is the oldest observation of the kind we have, excepting what is delivered by the Chinese. Melon is said to have com¬ posed a cycle of 19 years, which still bears his name ; and he marked the risings and settings of the stars, and what seasons they pointed out ; in all which he was as¬ sisted by his companion Euctemon. The science, how¬ ever, was obscured by Plato and Aristotle, who em¬ braced the system afterwards called the Ptolemaicy which places the earth in the centre of the universe. Eudoxus the Cnidian was a contemporary with A- ristotle, though considerably older, and is greatly ce¬ lebrated on account of his skill in astronomy. Pie was the first who introduced geometry into the science, and he is supposed to be the inventor of many propositions attributed to Euclid. Having travelled into Egypt in the earlier part of his life, and obtained a recom¬ mendation from Agesilaus to Nectanebus king of Egypt, he, by his means, got access to the priests, who had the knowledge of astronomy entirely among them, after which he taught in Asia and Italy. Seneca tells us that he brought the knowledge of the planetary mo¬ tions from Egypt into Greece ; and Archimedes, that he believed the diameter of the sun to be nine times that of the moon. He was also well acquainted with the method of drawing a sun-dial upon a plane; from whence it may be inferred that he understood the doc¬ trine of the projection of the sphere : yet, notwithstand¬ ing what has been said concerning the observations of Eudoxus, it is not certain that his sphere was not taken from one much more ancient, ascribed to Chiron the Centaur. The reason given for this supposition is, that had the places of the stars been taken from his own observations, the constellations must have been half a sign farther advanced than they are said to be in his writings. S00& f 14 ASTRONOMY. Part t History. Soon after Eudoxus, Calippus flourished, whose sy- -y—. stem of the celestial sphere is mentioned by Aristotle $ but he is better known from a period ot 76 years, con¬ taining four cori’ected metonic periods, and winch had its beginning at the summer solstice in the year 330 before Christ. But about this time, or rather earlier, the Greeks having begun to plant colonies in Italy, Gaul, and Egypt, these became acquainted with the Pythagorean system, and the notions ol the ancient Druids concerning astronomy. Julius Caesar informs us, that the latter wex-e skilled in this science ; and that the Gauls in general were able sailors, which at that time ‘they could not be without a competent knowledge of astronomy : and it is related of Pythoas, who lived at Marseilles in the time of Alexander the Great, that he observed the altitude of the sun at the summer solstice by means of a gnomon. He is also said to have travelled as far as Thule to settle the cli- 12 mates. State of as- After the death of Alexander the Great, science Ervpt'after flourished in Egypt more than in any other part of the the death of world 5 and a famous school was set up at Alexandria Alexander, under the auspices of Ptolemy Philadelphus, a prince instructed in all kinds of learning, and the patron of all those who cultivated them ; and this school conti¬ nued to be the seminary of all kinds of literature, till the invasion of the Saracens in 650. Timocharis and Arystillus, who first cultivated the astronomical science in this school, began to put it on a new footings being much more careful in their observations, and exact in noting down the times when they were made, than their predecessors. Ptolemy assures us, that Hippar¬ chus made use of their observations, by means of which he discovered that the stars had a motion in longitude of about one degree in an hundred years 5 and he cites many of their observations, the oldest ot which is before the erection of this school, in the yfear 295, when the moon just touched the northern star in the forehead of the Scorpion j and the last of them was in the 13th year of Philadelphus, when Venus hid the former star of the four in the left wing of Virgo. From this time the science of astronomy continued greatly to advance. Aristarchus, who lived about 270 years before Christ, strenuously asserted the Pythago¬ rean system, and gave a method of determining the di¬ stance of the sun by the moon’s dichotomy. Eratos¬ thenes, born at Cyrene in 271 B. C. determined the measure of a great circle of the earth by means of a gnomon. His reputation was so great, that he was invited from Athens to Alexandria by Ptolemy Euer- getes, and made by him keeper of the royal library at that place. At his instigation the same prince set up those armillas or spheres, which Hipparchus and Pto¬ lemy the astronomer afterwards employed so successful¬ ly in observing the heavens. He also found the distance between the "tropics to be eleven such parts as the whole meridian contains eighty-three. About the same time Berosus a native of Chaldea, flourished at A- thens. He is by some said to have brought many ob¬ servations from Babylon, which are ascribed to the 13 Greeks j while others contend, that the latter owe Discoveries JJjtle or nothing of their astronomical knowledge to of Archi- Babylonians. The celebrated Archimedes, who meaes. to Sir j£aac ]sjewton holds the first place among mathematicians, was nothing inferior as an astronomer History, to what he was as a geometrician. He determined-y— the distance of the moon from the earth, of Mercury from the moon, of Venus from Mercury, of the sun from Venus, of Mars from the sun, of Jupiter from Mars, and of Saturn from Jupiter j as likewise the di¬ stance of the fixed stars from the orbit of Saturn. That he made astronomical observations, is not to be doubt¬ ed j and it appears from an epigram of the poet Clau- dian, that he invented a kind of planetarium, or orrery, to represent the phenomena and motions of the heavenly bodies. 14 Hipparchus was the first who applied himself to the Of Hippar- study of every part of astronomy, his predecessors ha-c^us* ving chiefly considered the motions and magnitudes of the sun and moon. Ptolemy also informs us, that he first discovered the orbits of the planets to be eccen¬ tric, and on this hypothesis wrote a book against Eu¬ doxus and Calippus. He gives many of his observa¬ tions : and says, that by comparing one of his with another made by Aristarchus 145 years before, he was enabled to determine the length of the year with great precision. Hipparchus also first found out the anticipation of the moon’s nodes, the eccentricity of her orbit, and that she moved slower in her apogee than in her perigee. He collected the accounts of such ancient eclipses as had been observed by the Chal¬ deans and Egyptians. He formed hypotheses con¬ cerning the celestial motions, and constructed tables of those of the sun and moon, and would have done the same with those of the other planets if he could have found ancient observations sufficient for the purpose $ but, these being wanting, he was obliged to content himself with collecting fit observations for that purpose, and endeavouring to form theories of the five planets. By comparing his own observations on the Spica Vir- ginis with those of Timochares at Alexandria made 100 years before, he discovered that the fixed stars changed their places, and had a slow motion of their own from west to east. He corrected the Calippic period, and pointed out some errors in the method laid down by Eratosthenes for measuring the circumference of the earth. By means of geometry, which was now great¬ ly improved, he was enabled to attempt the calculation of the sun’s distance in a more correct manner than any of his predecessors ; but unhappily it required so much accuracy in observation as was found impracti- 15 cable. His greatest work, however, was his catalogue Makes the of the fixed stars, which he was induced to attempt by the appearance of a new star. The catalogue is pre-e(i starSt served by Ptolemy, and contains the longitudes and la¬ titudes of 1022 stars, with their apparent magnitudes. He wrote also concerning the intervals between eclipses both solar and lunar, and is said to have calculated all that were to happen for no less than 600 years from his time. 16 Little progress was made in astronomy from the timesystem of Hipparchus to that of Ptolemy, who flourished the first century. The principles on which his system is built are indeed erroneous : but his work will al¬ ways be valuable on account of the number of ancient observations it contains. It was first translated out of the Greek into Arabic in the year 827, and into La¬ tin from the Arabic in 1230. The Greek original was unknown in Europe till the beginning of the 15th century, Part I. Hi*ioiy. century, when it was brought from Constantinople, then ' ’ taken by the Turks, by George a monk ofTrapezond, who translated it into Latin. Various editions were af¬ terwards published : but little or no improvement was 17 made by the Greeks in this science. ^fthe'lra Durin& the long period from the year 800 to the bians? ^ beginning of the 14th century, the western parts of Europe were immersed in deep ignorance and barbarity. However, several learned men arose among the Arabians. The caliph A1 Mansur was the first who introduced a taste for the sciences in his empire. His grandson A1 Mamun, who ascended the throne in 814, was a great encourager of the sciences, and devoted much of his own time to the study of them. He made many astronomi¬ cal observations himself, and determined the obliquity of the ecliptic to be 230 35'. He employed many able mechanics in constructing proper instruments, which he made use of for his observations ; and under his auspices a degree of the earth was measured a second time in the plain of Singar, on the border of the Red sea. From this time astronomy was studiously cultivated by the Arabians j and Elements of Astronomy were written by Alferganus, who was partly cotemporary with the caliph A1 Mamun. Rut the most celebrated of all their astronomers is Alhategnius, who lived about the year of Christ 880. He greatly reformed astronomy, by comparing his own observations with those of Ptole¬ my. Thus he calculated the motion of the sun’s apo¬ gee from Ptolemy’s time to his own •, determined the precession of the equinoxes to be one degree in 70 years; and fixed the sun’s greatest declination at 23.35'. Find¬ ing that the tables ot Ptolemy required much correc¬ tion, he composed new ones of his own fitted to the meridian of Aracta, which were long held in estimation by the Arabians. After his time, though several emi¬ nent astronomers appeared among the Saracens, none made any very valuable observations for several centu¬ ries, excepting Ebn Younis astronomer to the caliph of Egypt; who observed three eclipses with such care, that by means of them we are enabled to determine the quan¬ tity of the moon’s acceleration since that time. Other eminent Saracen astronomers were, Arzachel a Moor of Spain, who observed the obliquity of the ecliptic, and constructed tables of sines, or half chords of double arcs, dividing the diameter into 300 parts ; and Alhazen, his cotemporary, who first showed the im¬ portance of the theory ot refractions in astronomy ; writing also upon the twilight, the height of the clouds, and the phenomenon of the horizontal moon. Ulug Beg, a grandson of the famous Tartar prince Timur Beg, or Tamerlane, was a great proficient in practical astronomy. He is said to have had very large instruments for making his observations ; particularly a quadrant as high as the church of Sancta Sophia at Con¬ stantinople, which is 180 Roman feet. He composed astronomical tables from his own observations for the meridian of Samarcand his capital, so exact as to differ very little from those afterwards constructed by Tycho Brahe ; but his principal work is his catalogue of the fixed stars, made from his own observations in the year of Christ 1437. I he accuracy of his observations may be gathered from his determining the height of the pole at Samarcand to be 390 37' 23". Besides these improvements, we are indebted to the 15 Arabians for the present form of trigonometry. Me- History. nelaus, indeed, an eminent Greek astronomer who—v ' flourished about the year 90, had published three books of Spherics, in which he treated of the geometry ne¬ cessary to astronomy, and which show great skill in the sciences ; but his methods were very laborious, even after they had been improved and rendered more sim¬ ple by Ptolemy : but Geber the Arabian, instead of the ancient method, proposed three or four theorems, which are the foundation of our modern trigonome¬ try. The Arabians also made the practice still more simple, by using sines instead of the chords of double arcs. The arithmetical characters they had from the Indians. lS During the greatest part of this time, almost all Eu-Revival of rope continued ignorant not only of astronomy but 0f^str®nomy every other science. The emperor Frederick II. first1U ■Eur°l>e‘ began to encourage learning in 1230 ; restoring some universities, and founding a new one in Vienna. He also caused the works of Aristotle, and the Almagest or Astronomical Treatise of Ptolemy, to be translated into Latin ; and from the translation of this book we may date the revival of astronomy in Europe. Two years after its publication, John de Sacro Bosco, or of Halifax, an Englishman, wrote his four books JDe Sph&ra, which he compiled from Ptolemy Albateg- nius, Alferganus, and* other Arabian astronomers : this work was so much celebrated, that for 300 years it was preferred in the schools to every other; and has been thought worthy of several commentaries, particu¬ larly by Clavius in 1531. In 1240, Alphonso king of Castile caused the tables of Ptolemy to be correct¬ ed : for which purpose he assembled many persons skilled in astronomy, Christians, Jews, and Moors ; by whom the tables called Alphonsine were composed, at the expence of 40,000, or according to others 400,000 ducats. About the same time Roger Bacon, an English monk, published many things relative to astronomy ; par¬ ticularly of the places of the fixed stars, solar rays, and lunar aspects. Vitellio, a Polander, wrote a treatise on Optics about 1270, in which he showed the use of re¬ fractions in astronomy. From this time to that of Purbach, who was born Improve- in 1423, few or no improvements were made in astro-meats of nomy. He wrote a commentary on Ptolemy’s Al- Purbach. rnagest, some treatises on Arithmetic and Dialling, with tables for various climates. He not only used spheres and globes, but constructed them himself; and formed new tables of the fixed stars, reduced to the middle of that age. He composed also new tables of sines for every ten minutes, which Regiomontanus af¬ terwards extended to every single minute, making the whole sine 60, with 6 ciphers annexed. He likewise corrected the tables of the planets, making new equa¬ tions to them, because the Alphonsine tables were very faulty in this respect. In his solar tables he placed the sun’s apogee in the beginning of Cancer ; but retained the obliquity of the ecliptic 230 33^', to which it had been reduced by the latest observations. He made new tables for computing eclipses, of which he observed some, and had just published a theory of the planets, when he died in 1461. 2a John Muller of Monteregio (Koningsberg), a town, Of Regio- of Franconia, from whence he was called montan us. nus} ASTRONOMY. 16 ASTRO Ilistw'', nus, was the scholar and successor of Purbach. He <—-y—l™ completed the epitome of Ptolemy’s Almagest which Purbach had begunand after the death of the latter, went to Ptome, where he made many astronomical ob¬ servations. Having returned to Nuremberg in 1471, he was entertained by a wealthy citizen named Ber¬ nard Walt her, who having a great love for astronomy, caused several instruments to be made under the direc¬ tion of Regiomontanus, for observing the altitude of the sun and stars, and other celestial phenomena. A- mong these was an armillary astrolabe, like that which had been used by Hipparchus and Ptolemy at Alexan¬ dria, and with which many observations were made. He also made ephemerides for 30 years to come, show¬ ing the lunations, eclipses, &c. He wrote the Theory of the Planets and Comets, and a Treatise of Triangles yet in repute for several extraordinary cases. He is said to have been the first who introduced the use of tangents into trigonometry j and to have published in print (the art of printing having been lately invented) the works of many of the most celebrated ancient astronomers. After his death, which happened at Rome, Walther made a diligent search for all his instruments and papers which could be found : and continued his observations with the instruments he had till his death. The obser¬ vations of both were collected by order of the senate of Nuremberg, and published there by John Schoner in 1 944 ; afterwards by Snellius at the end of the Obser¬ vations made by the landgrave of Hesse in 1618 ; and lastly, in 1666, with those of Tycho Brahe. Walther, however, as we are told by Snellius, found fault with his armiila, not being able to give any observation with certainty to less than ten minutes. He made use of a good clock, which also was a late invention in those tt days. Of Werner. John Werner, a clergyman, succeeded Walther as astronomer at Nuremberg-, having applied himself with great assiduity to the study of that science from his in¬ fancy. He observed the motion of the comet in 1500 > and published several tracts, in which he handled ma¬ ny capital points of geometry, astronomy, and geo¬ graphy, in a masterly manner. He published a trans¬ lation of Ptolemy’s Geography, with a commentary, which is still extant. In this he first proposed the me¬ thod of finding the longitude at sea by observing the moon’s distance from the fixed stars which is now so successfully put in practice. He also published many other treatises on mathematics and geography 5 but the most remarkable of all his treatises, are those concern¬ ing the motion of the eighth sphere or of the fixed stars, and a short theory of the same. In this he show¬ ed, by comparing his own observations of the stars Re- gulus, Spica Virginis, and the bright star in the south¬ ern scale of the Balance, made in 1514, with the pla¬ ces assigned to the same stars by Ptolemy, Alphonsus, and others, that the motion of the fixed stars, now called the precession of the equinoctial points, is one de¬ gree ten minutes in 100 years, and not one degree on¬ ly, as former astronomers had made it. He made the obliquity of the ecliptic 230 28', and the first star of Aries 26° distant from the equinoctial point. He also constructed a planetarium representing the celestial mo¬ tions according to the Ptolemaic hypothesis, and made a great number of meteorological observations with a ^iew towards the prediction of the weather. The ob- N O M Y. Part I- liquity of the ecliptic was settled by Dominic Maria History, the friend of Copernicus, at 230 29', which is still held 1—-v——J to be just. 2j The celebrated Nicholas Copernicus next makes his Pytbago- appearance, and is undoubtedly the great reformer °frean sysu-iu the astronomical science. He was originally bred to Copernicus, the practice of medicine, and had obtained the degree of doctor in that faculty : but having conceived a great regard for the mathematical sciences, especially astro¬ nomy, he travelled into Italy, where he for some time was taught by Dominic Maria, or rather assisted him in his astronomical operations. On his return to his own country, being made one of the canons of the church, he applied himself with the utmost assidui¬ ty to the contemplation of the heavens, and to the stu¬ dy of the celestial motions. He soon perceived the de¬ ficiency of all the hypotheses by which it had been at¬ tempted to account for these motions ; and for this rea¬ son he set himself to study the works of the ancients, with all of whom he also was dissatisfied excepting Py¬ thagoras ; who, as has been already related, placed the sun in the centre, and supposed all the planets, with the earth itself, to revolve round him. He in¬ forms us, that he began to entertain these notions about the vear 1507 ; but not being satisfied with stating the general nature of his hypothesis, he became desirous of determining the several periodical revolutions of the planets, and thence of constructing tables of their mo¬ tions which might be more agreeable to truth than those of Ptolemy and Alphonsus. The observations he was enabled to make, however, must have been ex¬ tremely inaccurate : as he tells us, that if with the in¬ struments he made use of he should be able to come within ten .minutes of the truth, he would rejoice no less than Pythagoras did when he discovered the pro¬ portion of the hypothenuse to the other two sides of a right-angled triangle. His work was completed in the year 1530; but he could not be prevailed upon to publish it till towards the end of his life, partly through diffidence, and partly through fear of the offence which might be taken at the singularity of the doc¬ trines set forth in it. At last, overcome by the im¬ portunities of his friends, he suffered it to be published at their expence, and under the inspection of Schoner and Osiander, with a dedication to Pope Paul III. and a preface, in which it was attempted to palliate as much as possible the extraordinary innovations it con¬ tained. During the time of its publication the au¬ thor himself was attacked with a bloody flux, succeeded by a palsy •, so that he received a copy only a few hours before his death, which happened on the 23d of May 1543. After the death of Copernicus, the astronomical science was greatly improved by Schoner, Nonius, Ap- pian, and Gemma Frisius. Schoner survived Coper¬ nicus only four years j however, he greatly improved the methods of making celestial observations, reformed and explained the calendar, and published a treatise of cosmography. Nonius had applied himself very early to the study of astronomy and navigation •, but finding the instruments at that time in use excessively inaccu¬ rate, he applied himself to the invention of others which should be less liable to inconvenience. Thus he invented the astronomical quadrant, in which he divid¬ ed the degrees into minutes by a number of concentric circles. Part I. ASTBONOMY. Hiitow. circles. Tlie first of these was divided into 90 equal ——v—-—' parts, the second into 89, the third into 88, and so on, as low as 46 ; and thus, as the index of the qua¬ drant would always fall upon one or other of the divi¬ sions, or very near it, the minutes might he known by computation. lie published many treatises on ma¬ thematical subjects, particularly one which detected the errors of Orontius, who had imagined that he could square the circle, double the cube, &c. by find¬ ing two mean pronortionals betwixt two right lines. Appian’s chief work was entitled The Ceesarean Astro¬ nomy; and was published at Xngolstadt in 1540, de¬ dicated to the emperor Charles V. and his brother Ferdinand. In this he showed how to resolve astrono¬ mical problems by means of instruments, without either calculations or tables j to observe the places of the stars and planets by the astrolabe ; and to foretel eclipses and describe the figures of them : the whole illustrated by proper diagrams. In his second book he describes the method of dividing an astronomical quadrant, and of using it properly. His treatise con¬ cludes with the observation of five comets. Gemma Frisius wrote a commentary on a work of Appian en¬ titled his Cosmography, with many observations of eclip¬ ses. He invented also the astronomical ring, and se¬ veral other instruments, which, though they could not boast of much exactness superior to others, were yet of considerable utility in taking observations at sea ; and he is also memorable for being the first who proposed a time-keeper for determining the longitude at sea.— George Joachim Rheticus was a scholar of Copernicus, to attend whose lectures he gave up his professorship of mathematics at Wittemberg. For the improvement of astronomical calculations, he began to construct a table of sines, tangents, and secants, for every minute and ten seconds of the quadrant. In this work he first showed the use of secants in trigonometry, and greatly enlarged the use of tangents, first invented by Regio¬ montanus j but he assigned for the radius a much larger number of places than had been done before, for the greater exactness of calculation. This great work he did not live to accomplish j but it was completed by his disciple Valentine Otho, and published at Heidelberg s in 1594- Several il- During this century, the list of astronomers was dig- ustrious nified by some very illustrious names. About the year persons ap- 1561, William IV. landgrave of Hesse Cassel, applied tud^of1 a k'mse^ ^ie study °f astronomy. With the assistance tronomy." °f Rothman and Burgius, the former an astronomer, the latter an excellent mathematical instrument-maker, he erected an observatory on the top of his palace at Cassel, and furnished it with such instruments as were then in use, made in the best manner the artists of that age could execute. With these he made a great number of observations, which were by Hevelius preferred to those of Tycho Brahe, and which were published by Snellius in 1618. From these observations he deter¬ mined the longitudes and latitudes of 400 stars, which he inserted in a catalogue where their places are recti- fied to the beginning of the year 1593. )bserva- Tycho Brahe began his observations about the same ioni of time with the landgrave of Hesse, already mentioned, •rahe 0^served the great conjunction of Saturn and Ju¬ piter in 1563 ; and finding the instruments he could procure very inaccurate, he made a quadrant capable Vol. III. Part I. -f of showing single minutes, and likewise a sextant four History, cubits radius. In 1571, he discovered a new star in'——v——^ the chair of Cassiopeia ; which induced him, like Hip¬ parchus, to make a catalogue of the stars. This contain¬ ed the places of 777 stars, rectified to the year 1600 j but instead of the moon, which was used by the ancients to connect the places of the sun and stars, Tycho sub¬ stituted Venus, as having little or no parallax, and yet being like the moon visible both day and night. By the recommendation of the landgrave of Hesse, he obtained from the king of Denmark the island of Hu- enna, opposite to Copenhagen, where an observatory was built. The first stone of this building, afterwards 25 called Uranihurg, was laid in the year 1576. It wasAccountof of a square form, one side of it being about 60 feet in Uraniburg, length 5 and on the east and west sides were two roundlns obser* towers of 32 feet diameter each. The instruments™101*’ were larger and more solid than had ever been seen be¬ fore by any astronomer. They consisted of quadrants, sextants, circles, semicircles, armillae both equatorial and zodiacal, parallactic rulers, rings, astrolabes, globes, clocks, and sun-dials. These instruments were so di¬ vided as to show single minutes ; and in some the arch might be read off to 10 seconds. Most of the divisions were diagonal : but he had one quadrant divided ac¬ cording to the method invented by Nonius ; that is, by 47 concentric circles. The whole expence is said to have amounted to 200,000 crowns. The method of dividing by diagonals, which Tycho greatly admired, was the invention of Mr Richard Chanceler, an Eng¬ lishman : Tycho, however, shows, that it is not accu¬ rately true when straight lines are employed, and the circles at equal distances from each other ; but that it may be corrected by making circular diagonals, which if continued would pass through the centre. Tycho employed his time at Uraniburg to the best advantage j but falling into discredit on the death of the king, he was obliged to remove to Holstein, and at last found means to get himself introduced to the em¬ peror, with whom he continued to his death. He is well known to have been the inventor of a system of astronomy, which bears his name; and which he vainly endeavoured to establish on the ruins of that of Copernicus : but the simplicity and evident conso- nancy to the phenomena of nature, displayed in all parts of the Copernican system, soon got the better of the unnatural and complicated system of Tycho. His works, however, which are very numerous, discover him te have been a man of vast abilities. After his death the castle of Uraniburg quickly fell to decay, and in¬ deed seems to have been purposely pulled down 3 for, in 1652, when Mr Huet went to Sweden, it was almost level with the ground, and few traces of the walls could he discerned. None of the neighbouring inhabitants had ever heard of the name of Tycho or Uraniburg, excepting one old man, whom Mr Huet found out with great difficulty, and who had been a servant in the family ! All the discoveries of Purback, Regiomon¬ tanus, and Tycho, were collected and published in the year 1621, by Longomontanus, who had been Tycho’s favourite scholar. While Tycho resided at Prague with the emperor, HiS(,,j^ene he invited thither John Kepler, afterwards so famous for his discoveries. Under the tuition of so great an astronomer, the latter quickly made an amazing C progress. 18 ASTRONOMY. Part I. i History. *7 Invention of tele¬ scopes, and consequent discoveries. progress. He found that his predecessors had erred in supposing the orbits of the planets to be circular, and their motions uniform : on the contrary, he per¬ ceived, from his own observations, that they were el¬ liptical, and their motions unequal, having the sun in one of the foci of their orbits ; but that, however they varied in absolute velocity, a line drawn from the cen¬ tre of the sun to the planet, and revolving with it, would always describe equal areas in equal times. He discovered, in the year 1618, that the squares of the periodical times are as the cubes of the distances of the planets; two laws which have been of the greatest im¬ portance to the advancement of astronomy. He seems to have had some notion of the extensive power of the principle of gravity: for he tells us, that gravity is a mutual power betwixt two bodies j that the moon and earth tend towards each other, and would meet in a point nearer the earth than the moon in the proportion of the superior magnitude of the former, were they not hindered by their projectile motions. He adds also, that the tides arise from the gravitation of the waters towards the moon : however, he did not adhere steadily to these principles, hut afterwards substituted others as the causes of the planetary motions. Cotemporary with Kepler were Mr Edward Wright, and Napier baron of Merchiston. To the former we owe several very good meridional observations of the sun’s altitude, made with a quadrant of six feet radius, In the years 1594, I595> and 1596 j from which he greatly improved the theory of the sun’s motion, and computed more exact tables of his declination than had been done by any person before. He published also, in 1599, an excellent treatise, entitled, “ Cer¬ tain Errors in Navigation discovered and detected.” To the latter we are indebted for the knowledge of logarithms j a discovery, as was justly observed by Dr Halley, one of the most useful ever made in the art of numbering. John Bayer, a German, who lived about the same time, will ever be memorable for his work, entitled, Uranometria, which is a very complete ce¬ lestial atlas, or a collection of all the constellations vi¬ sible in Europe. To this he added a nomenclature, in which the stars in each constellation are marked with the letters of the Greek alphabet ; and thus every star in the heavens may be referred to with the utmost pre¬ cision and exactness. About the same time also, astro¬ nomy was cultivated by many other persons ; abroad, by Magmus, Mercator, Maurolycus, Homelins, Schul- tet, Stevin, &c.; and by Thomas and Leonard Digges, John Dee, and Robert Flood, in England : hut none of them made any considerable improvement. The beginning of the 17th century was distinguish¬ ed not only by the discovei'y of logarithms, but by that of telescopes ; a sort of instruments by which astronomy was brought to a degree of perfection utter¬ ly inconceivable by those who knew nothing of them. The question concerning the inventor is discussed under the article Optics ; but whoever was entitled to this merit, it is certain that Galileo was the first who brought them to such perfection as to make any con¬ siderable discoveries in the celestial regions. With in¬ struments of his own making, Galileo discovered the inequalities in the moon’s surface, the satellites of Ju¬ piter, and the ring of Saturn ; though this last was unknown to him after he had seen it, and the view he 3 got made him conclude that the planet had a threefold History, body, or that it was of an oblong shape like an olive. v»" 1 v— He discovered spots on the sun, by means of which he found out the revolution of that luminary on his axis ; and he discovered also that the milky way and nebulae were full of small stars. It was not, however, till some time after these discoveries were made, that Ga¬ lileo and others thought of applying the observations on Jupiter’s satellites to the purpose of finding the lon¬ gitude of places on the surface of the earth ", and even after this was thought of, astronomers found it so dif¬ ficult to construct tables of their motions, that it was not till after many observations had been made in distant places of the world, that Cassini was able to determine what positions of the satellites were most proper for finding out the longitude. At last he per¬ ceived that the entrance of the first satellite into the shadow of Jupiter, and the exit of it from the same, were the most proper for this purpose : that next to these the conjunctions of the satellites with Jupiter, or with one another, may be made use of; especially when any two of them, moving in contrary directions, meet with each other: and lastly, that observations on the shadows of the satellites, which may he seen on the disk of Jupiter, are useful, as also the spots which are seen upon his face, and are carried along it with greater velocity than has hitherto been discovered in any of the other heavenly bodies. While astronomers were thus busy in making new Lo"-arith- discoveries, the mathematicians in different countries mic tables were no less earnestly employed in constructing loga-composed, rithmic tables to facilitate their calculations. Benja¬ min Ursinus, an excellent mathematician of Branden¬ burg, calculated much larger tables of logarithms than had been done by their noble inventor, and published them in 1625. They were improved by Henry Briggs, Savilian professor of Oxford ; who by making unity the logarithm often, thus rendered them much more con¬ venient for the purposes of calculation. Logarithmic tables of sines and tangents were also composed by Mr Briggs and Adrian Vlacq at Goude, so that the busi¬ ness of calculation was now rendered nearly as easy as possible. ^ In 1733, Mr Horrox, a young astronomer of very Transit of extraordinary talents, discovered that Venus would pass Venus firs over the disk of the sun on the 24th of Novemberol)serve^b 1639. This event he announced only to one friend, * om> a Mr Crabtree 5 and these two were the only persons in the world who observed this transit the first time it had ever been viewed by human eyes. Mr Horrox made many useful observations at the time ; and had even formed a new theory of the moon, so ingenious as to attract the notice of Sir Isaac Newton : but the hopes of astronomers from the abilities of this excellent young man were blasted by his death in the beginning of Ja¬ nuary 1640. About the year 1638 many learned men began to p0Unjali0 assemble at Paris in order to hold conferences on dif-0f tjje ^Cj ferent scientific subjects, which was the first foundation demy of of the Royal Academy of Sciences in that capital. ^°ie.nces 1 This practice was introduced in France by Mersennus, and soon after at London by Oldenburg 5 which laidcjetyat the foundation of the Royal Society there. About London, this time also the celebrated astronomer Hevelius flou¬ rished at Dantz.ic, building an observatory in his own house, h mi Part I. A S T R 31 unprove- uents in tlescope History, house, and furnishing it with excellent instruments of —v——' his own construction 5 particularly octants and sextants of brass of three and four feet radius, as well as te¬ lescopes, with which he constantly observed the spots and phases of the moon, and from which observations he afterwards compiled his excellent and beautiful work entitled Selenographia. This noble building, together with all the books and instruments it contained, was consumed by fire on the 26th of September 1679 ; but the memory, as well as the form and construction of the instruments, is preserved in a curious work of the ingenious inventor, entitled Machina Ccelestis; though almost the whole impression of this book was in¬ volved in the same fate with the instruments it describes. The damage sustained on this occasion was estimated at 30,000 crowns. The celebrated English mechanic Dr Hooke, who was cotemporary with Hevelius, had in the mean time invented instruments with telescopic sights, which he preferred to those used by Hevelius so much* that a dispute commenced, which procured Hevelius a visit from Dr Halley. The latter had at that time taken a voyage to St Helena, at the desire of the Royal So¬ ciety, in order to observe and form a catalogue of the stars in the southern hemisphere. The result of his observations with Hevelius’s instruments was, that three several observations on the Spica Virginis and Regulus differed only a few seconds from each other. They were the invention of Tycho Brahe, and are described under the article Optics. At this visit Hal¬ ley and Hevelius observed an occultation of Jupiter by the moon, and determined the diameter of the latter * to be 30', 33". In 1671 the royal observatory in Paris was finished, and the use of it assigned to Mr Cassini, after it had been furnished with instruments at a very great expence : and the observatory at Greenwich being likewise built five years after, Mr Flamstead was appointed astronomer- royal. The observations in both these places, however, have been so numerous, that it is in vain to attempt any account of them. Before the middle of the 17th century the construc¬ tion of telescopes had been greatly improved, particular¬ ly by Fontana and Huygens. The latter constructed one of 123 feet, which is still preserved in the museum of the Royal Society at London. With this he observed the moon and planets for a long time, and discovered that Saturn was encompassed with a ring. The French, however, still outdid the English artists; and by means of telescopes of 200 and 300 feet focus, Mr Cassini was enabled to see all the five satellites of Saturn, his belts, and the shadows of Jupiter’s satellites passing over his body. In 1666 Mr Azout applied a micrometer to te¬ lescopes, for the purpose of measuring the diameters of the planets, and small distances in the heavens; how¬ ever, an instrument of this kind had been before invent¬ ed by Mr Gascoigne, though it was but little known abroad. Notwithstanding all these discoveries by means of telescopes, it was evident that they still continued in a very imperfect state, and their imperfections at the time appeared to be without remedy. One defect was the enoimous length requisite to admit of any very considerable magnifying power; and another was the mcori ectness of the image arising from the aberration of O N O M Y. I9 the rays, as was then supposed, by the spherical figure History. of the glass. To obviate these inconveniences, Mer- sennus is said to have first proposed, in a letter to Descartes, the use of reflectors instead of lenses in the construction of telescopes ; but this he did in such an obscure manner, that the latter laboured to persuade him of the falsehood of the principle on which his scheme was founded. In 1663, however, James Gre¬ gory of Aberdeen showed how such a telescope might be constructed. He showed also, that, in order to form a perfect image of an object in this manner, the figure of the speculum ought to be parabolic ; but Sir Isaac Newton, who applied himself to the framing of telescopes of the reflecting kind, found it impracticable to grind them of the desired figure. Laying aside the idea of reflecting telescopes, therefore, he applied him¬ self to the execution of a scheme formed by Descartes, viz. that of grinding lenses of the figure of one of the conic sections. In prosecuting this plan, he discovered, that the greatest errors to which telescopes were subject arose from the different refrangibility of the rays of light, for which he could not then find any remedy. He there¬ fore returned to the scheme he had just abandoned ; and, in the year 1672, presented to the Royal Society two reflectors which were Constructed with spherical spe- culums, as he could not procure any other. The in¬ conveniences arising from the different refrangibility of the rays of light, have since been in the fullest manner corrected by Mr Dollond, the excellency of whose achromatic telescopes is too well known to need any en¬ comium. About the beginning of the 18th century, the practical part of astronomy seemed to languish for want of proper instruments. Roemer, indeed, had invented some new ones, and Dr Hooke had turned bis atten¬ tion towards this subject in a very particular manner; but either through want of skill in the artists, or some other unfortunate circumstance, it happened that no¬ thing effectual was done. But at the very time when this was the case with practical astronomy, the specu¬ lative part was carried in a manner to its utmost pitch by the labours of the immortal Newton, whose Principia gave an entire new face to the science. It was not, however, for many years relished by the foreign philosophers, though almost immediately adopt¬ ed at home, and has continued ever since to spread its reputation farther and farther, so that now it is in a manner established all over the world. “But Csay* Dr Long) that, after Newton’s system had for so long a time been neglected, it should all at once be uni¬ versally received and approved of, is not to be attri¬ buted to chance, or the caprice of fashion, as some who are ignorant of it are apt to think, and from thence to expect that some other system will hereafter take its place, and bury it in oblivion. The system of New¬ ton, like that of Copernicus, is so agreeable to the phe¬ nomena of nature, and so well put together, that it must last as long as truth and reason endure, although some may perhaps bring the word attraction into disuse ; and though it may no longer be thought inherent in mat¬ ter, yet the laws of gravitation, as they are now called, and on which this system is founded, will never be for¬ gotten.” It was also in Britain that the first improvements i/i astronomical instruments took place. The celebrated C 2 mechanic 20 History. 32 Astronomi¬ cal instru- rnents first improved in England. ASTRONOMY. Part I. 33 Improve¬ ment* within this last cen¬ tury. mechanic and watchmaker, Graham, carried the accu¬ racy of his instruments to a degree which surprised every one. He also greatly improved the principles of watch- work, and made clocks to go with much greater regu¬ larity than before. The old eight-feet mural arch at Greenwich was also constructed by him; as was a small equatorial sector for making observations out of the meridian ; but he is chiefly remarkable for con¬ triving the zenith sector of 24 feet radius, and after¬ wards one of 12I feet, by which Dr Bradley discover¬ ed the aberration of the fixed stars. The reflecting telescope, which had been invented by Gregory, and executed by Newton, was greatly improved by Mr Had¬ ley, and a very complete and powerful instrument of that kind was presented to the Koyal Society in 1719. The same gentleman has also immortalized his memory by the invention of the reflecting quadrant, which be presented to the Society in 1731, which is now in uni¬ versal use at sea 5 and without which all improvements of the lunar theory would have been useless for deter¬ mining the longitude, through the want of an instru¬ ment proper to make the observations with. It howr- ever appears, that an instrument, exactly similar to this in its principles, had been invented by Sir Isaac New¬ ton, and a description of it, together with a drawing, given by tbe inventor to Dr Halley, when he was pre¬ paring for his voyage to discover tbe variation of the needle in 1701. About the middle of this century, the constructing and dividing of large astronomical in¬ struments was carried to a great degree of perfection by Mr John Bird reflecting telescopes were equally improved by Mr Short, who first executed the divided object-glass micrometer. This had indeed been thought of by M. Louville, and several other persons long be¬ fore j and a description of one nearly agreeing with that of Mr Short had been published in the Philoso¬ phical Transactions for 1753 : but had it not been for the great skill of Mr Short in figuring and centering glasses of this kind, it is very probable the scheme might never have been executed. About this time also Mr Dollond brought refracting telescopes to such perfection, that they became superior to reflectors of equal length ; though all of them are now excelled by those of Mr Herschel, whose telescopic discoveries have been far more numerous and surprising than those of any other astronomer. We shall close this history with a short account of the labours of the principal astronomers since thebuilding tbe royal observatories at Paris and Greenwich, and tbe ap¬ pointment of Mr Flamstead to the office of astronomer royal. This gentleman not only made observations on tbe sun, moon, planets, and comets which appeared in his time, but on the fixed stars also, of which l>e gave a cata¬ logue of 3000 *, many of them so small that they cannot be d iscerned without the help of a telescope : he also published new solar tables, and a theory of tbe moon ac¬ cording to Horrox. He published a very curious tract on the doctrine of the sphere, in which be shewed bow to construct eclipses of the sun and moon, as well as occultations of the fixed stars by the moon, geometri¬ cally ; and it was upon his observations that Halley’s tables and Newton’s theory of the moon were con¬ structed. Mr Cassini also distinguished himself very considerably. Pie erected the gnomon, and drew tbe famous meridian line in the church of Petronia at Bolog¬ na. He enjoyed his office more than 40 years, making History. many observations on the sun, moon, planets, and co- * > mets, and greatly amended the elements of their mo¬ tions *, though the result of his labours was much in¬ ferior to Mr PJamstead’s. Tbe office was continued in his family, and his grandson still enjoys it. Boemer, a celebrated Danish astronomer, first discovered the pro¬ gressive motion of light by observing tbe eclipses of Ju¬ piter, and read a dissertation upon it before the lloyal Academy of Sciences at Paris in the year 1675. He was also the first who made use of a meridional tele¬ scope. Mr Flamstead was succeeded in 1719 by Dr Halley, “ the greatest astronomer (says M. de la Lande) without contradiction in England j” and, adds Dr Long, “ I believe he might have said in the whole world,” He had been sent, at the age of 21, by King Charles II. to the island of St Helena, in order to make a catalogue of the southern stars, which was published in 1679. I7°5» ^ie published his Synop¬ sis Astronomice Cometicce, in which, after immense cal¬ culation, he ventured to predict tbe return of one in 1758 or 1759. He also published many learned dis¬ sertations in the Philosophical Transactions concerning the use that might be made of the next transit of Ve¬ nus in determining the distance of the sun from the earth. He was tbe first who discovered the accelera¬ tion of the moon, and gave a very ingenious method of finding her parallax by three observed phases of a solar eclipse. He composed tables of the sun, moon,, and all the planets j and, in the nine years in which he was at Greenwich, made near 1500 observations of the moon 5 all which he compared with the tables, and noted the differences ; and these, he thought, would return in about 18 years. He recommended the method of determining the longitude by means of the moon’s distance from the sun and certain fixed stars. He was convinced of its superior excellence 5 and it has since been adopted by all tbe most emi¬ nent astronomers in Europe. It is at present the only sure guide to the mariner; and the great perfection to which it is now brought is much owing to the in¬ dustry and exertions of Dr Maskelyne, the present astronomer-royal, to whom we are indebted for the pub¬ lication of the Nautical Almanack, the Bequisite Ta¬ bles, and other works of the utmost service to practical astronomy. ^ In the mean time an attempt was made in France to True figure measure a degree of the earth, which occasioned a very the eartf warm dispute concerning tbe figure of it. Cassini, ^*SCOTere<^ from Picart’s measure, concluded that the earth was an oblong spheroid ; but Newton, from a considera¬ tion of the laws of gravity and the diurnal motion of the earth, had determined the figure of it to be an ob¬ late spheroid, and flatted at the poles. To determine this point, Louis XV. resolved to have two degrees of the meridian measured ; one under, or very near the equator ; and the other as near the pole as possible. For this purpose the Boyal Academy of Sciences sent M. Maupertuis, Clairault, Camus, and Le Monier, to Lapland. They were accompanied by the abbe Ou¬ tlier, a correspondent of tbe same academy. They were joined by M. Celsius professor of anatomy at Up- sal ; and having set out from France in the spring of the year 1736, returned to it in 1737, after having fully at I, Part I. ASTRONOMY. 2 l lory. History. ered 35 Improve- M ments by the French astrono¬ mers. fully accomplislietl tlieir errand. On the southern ex¬ pedition were despatched M. Godin, Condamine, and Bouguer, to whom the king of Spain joined Don George Juan and Don Anthony de Ulloa, two very ingenious gentlemen and officers of the marine. They left Europe in 1735 j and after enduring innumerable hardships and difficulties in the execution of their com¬ mission, returned to Europe at different times, and by different ways, in the years 1744, 1745, and 1746. The result of this arduous task was a confirmation of Newton’s investigation. Picart’s measure was revised by Cassini and De la Caille 5 and, after his errors were corrected, it was found to agree very well with the other two. On this occasion too it was discovered, that the attraction of the great mountains of Peru had an effect on the plumb-line of one of their largest instru¬ ments, drawing it seven or eight seconds from the true perpendicular. Dr Halley, dying in 1742, was succeeded hy Dr Bradley, who, though inferior as a mathematician, greatly exceeded him as a practical astronomer. He was the first who made observations with an accuracy sufficient to detect the lesser inequalities in the motions of the planets and fixed stars. Thus he discovered the aberration of light, the nutation of the earth’s axis, and, was able to make the lunar tables much more perfect than they had ever been. He also observed the places, and computed the elements of the comets which ap¬ peared in the years 1723, 1736, 1743, and 1757. He made new and most accurate tables of the motions of Jupiter’s satellites, from his own observations and those of Dr Pound ; and from a multitude of observations of the sun, moon, and stars, was enabled to give the most accurate table of mean refractions yet extant, as well as tbe best methods of computing the variations of those refractions arising from the different states of the air as indicated by the thermometer and barometer. In 1750, having procured a very large transit instrument made hy Mr Bird, and a new mural quadrant of brass eight feet radius, he began to make observations with re¬ doubled industry ; so that betwixt this time and his death, which happened in 1762, he made observations for settling the places of all the stars in the British ca¬ talogue, together with near 1500 places of the moon, much the greater part of which he compared with the tables of Mr Mayer. In the mean time the French astronomers were assi¬ duous in their endeavours to promote the science of astronomy. The theory of the moon, which had been given in a general way by Sir Isaac Newton, began to he particularly considered by Messrs Clairault, D’Alem¬ bert, Euler, Mayer, Simpson, and Walmsly j though Clairault, Euler, and Mayer, distinguished themselves beyond any of the rest, and Mr Euler has been particu¬ larly happy in the arrangement of his tables for the ease and expedition of computation. He was excelled in exactness, however, by Mayer, who published his ta¬ bles in the Gottingen Acts for 1753. In these the errors in longitude never exceeded two minutes 5 and having yet farther improved them, he sent a copy to the lords of the British admiralty in 1755; and it W'as this copy which Dr Bradley compared with his ob¬ servations, as already mentioned. His last corrections of them were afterwards Sent over by his widow j for which she and her children received a reward of 3000I. Accurate tables for Jupiter’s satellites were also com- History. posed by Mr Wargentin, a most excellent Swedish ■—v astronomer, and published in the Upsal Acts in 1741 } which have since been corrected by the author in such a manner as to render them greatly superior to any ever published before. ^5 Amongst the many French astronomers who contri- Of M. de buted to the advancement of the science, we are parti-la Caille. cularly indebted to M. de la Caille, for a most excel¬ lent set of solar tables, in which he has made allowances for the attractions of Jupiter, Venus, and the moon. In 1750 he went to the Cape of Good Hope, in order to make observations in concert with the most celebrated astronomers in Europe, for determining the parallax of the moon, as well as of the planet Mars, and from thence that of the sun j from whence it appeared that the parallax of the sun could not greatly exceed 10 se¬ conds. Here he re-examined and adjusted the places of the southern stars with great accuracy, and mea¬ sured a degree of the meridian at that place. In Italy the science was cultivated with the greatest assiduity by Signior Bianchini, Father Boscovich, Frisi, Manfredi, Zanotti, and many others $ in Sweden by Wargentin already mentioned, Blingenstern, Mallet, and Plan- man j and in Germany, by Euler elder and younger, Mayer, Lambert, Grischow, &c. In the year 1760 all the learned societies in Europe began to prepare for observing the transit of Venus over the sun, foretold by Dr Halley upwards of 80 years before it happened, showing, at the same time, the important use which might be made of it. Unfortunately, however, for the cause of science, many of the astronomers sent out to obsei've this phenomenon were prevented by unavoid¬ able accidents from reaching the places of their desti¬ nation, and others were disappointed by the badness of the weather. It happened also, that the circumstances of the phenomenon were much less favourable for the purpose of determining the sun’s parallax than had been expected by Dr Halley, owing to the faults of the tables he had made use of: so that, notwithstanding all the labours of astronomers at that time, they were not able to determine the matter : and even after their observations in 1769, when the circumstances of the transit were more favourable, the parallax of the sun remained still uncertain. Dr Bradley was succeeded in his office of astrono¬ mer-royal by Mr Bliss, Savilian professor of astronomy at Oxford ; who, being in a very declining state of health at the time of his accession to the office, did not enjoy it long. He was succeeded by the learned Nevil Maskelyne, D. D. the pi’esent astronomer-royal, whose name will be rendered immortal by his assiduity and success in bringing the lunar method of determining the longitude at sea into general practice. Such was the general state of astronomy', when Dr Herschel’s great discovery of augmenting the power of telescopes, beyond the most sanguine hopes of astrono¬ mers, opened at once a scene altogether unlocked for.. By this indefatigable observer we are made acquainted with a new primary planet attended by six seconda¬ ries belonging to our solar system j so that the latter now appears to have double the bounds formerly assign¬ ed to it; this new planet being at least twice the di¬ stance of Saturn from the sun. In the still farther di¬ stant celestial regions, among the fixed stars, his obser¬ vations , 22 ASTRONOMY. Part II Histo’>\ vations are equally surprising; of which we shall only v—~ say with Dr Priestley*, “ Mr Herschel’s late disco- * Exper. veries in and beyond the bounds of the solar system, the great yiews that he has given of the arrangement PrefVi °f t*16 stars> their revolutions, and those ot the im¬ mense systems into which they are formed, are pecu¬ liarly calculated to inspire an ardent desire of seeing so great a scene a little more unfolded. Such discoveries as these give us a higher idea of the value of our be- ing, by raising our ideas of the system of which we are a part j and with this an earnest wish for the continu¬ ance of it.” History. PART II. OF THE APPARENT MOTIONS OF THE HEAVENLY BODIES. WHEN we cast our eyes up towards the heavens, we perceive a vast hollow hemisphere at an unknown di¬ stance, of which our eyes seem to constitute the centre. The earth stretches at our feet like an immense plain, and at a certain distance appears to meet and to bound the heavenly hemisphere. Now the circle all around, where the earth and the heavens seem to meet and touch each other, is called the horizon. We can scarcely avoid supposing, that besides the hemisphere which we per¬ ceive, there is another, exactly similar, concealed from our view by the earth, and that the earth, therefore, is somehow or other suspended in the middle of this heavenly sphere, with all its inhabitants. A little ob¬ servation turns this suspicion into certainty. For in a clear evening the heavenly hemisphere is seen studded with stars, and its appearance is changing every instant. New stars are continually rising in the east, while others in the mean time are setting in the west. Those stars, that, towards the beginning of the evening, were just seen above the eastern horizon, late at night are seen in the middle of the starry hemisphere, and may be traced moving gradually westward, till at last they sink altogether under the horizon. If we look to the north, we soon perceive that many stars in that quarter never set at all, but move round and round, describing a com¬ plete circle in 24 hours. These stars describe their circles round a fixed point in the heavens ; and the circles are the smaller, the nearer the star is to the fix¬ ed point. This fixed point is called the north pole. There must be a similar fixed point in the southern he¬ misphere, called the south pole. Thus the heavenly sphere appears to turn round two fixed points, called the poles, once every 24 hours. The imaginary line ^ which joins the points is called the axis of the world. Appear- In order to have precise notions of the motions of aace of the the heavenly bodies, it is necessary to be able to assign heavens, precisely the place in which they are. This is done by means of several imaginary lines, or rather circles, supposed described upon the surface of the sphere 5 and these circles, as is usual with mathematicians, are di¬ vided into 360 equal parts called degrees. Every degree is divided into 60 minutes: every minute into 60 seconds, and so on. That great circle of the sphere, which is perpendicular to the axis of the world, and of course 90° distant from either pole, is called the equator. The smaller circles, which the stars describe in consequence of their diurnal motions, are called parallels, because they are obviously parallel to the e- quator. The equator divides the heavenly sphere into two equal parts, the north and the south ■, but to be able to assign the position of the stars, it is necessary to have another circle, passing through the poles, and cutting the equator perpendicularly. This circle is called a meridian. It is supposed, not only to pass through the poles, but to pass also through the point directly over the head of the observer, and the point of the sphere exactly opposite to that. The first of these points is called the zenith, the second is called the nadir. The meridian divides the circles described by the stars into two equal parts 5 and when they reach it they are either at their greatest height above the horizon, or they are at their least height. The situation of tho pole is easily determined 5 for it is precisely half way between the greatest and least height of those stars which never set. When we advance towards the north we perceive that the north pole does not remain sta¬ tionary, but rises towards the zenith, nearly in propor¬ tion to the space we pass over. On the other hand it sinks just as much when we travel towards the south. Hence we learn that the surface of the earth is not plane, as one would at first suppose, but curved. All the heavenly bodies appear to describe a com¬ plete circle round the earth in 24 hours. But be¬ sides these motions which are common to them all, there are several of them which possess motions pecu¬ liar to themselves. The sun, the most brilliant of alt the heavenly bodies, is obviously much farther to the south during winter than during summer. He does not, therefore, keep the same station in the heavens, nor describe the same circle every day. The moon not only changes her form, diminishes, and increases 5 but if we observe the stars, near which she is situated one evening, the next evening we shall find her consider¬ ably to the eastward of them ; and every day she re¬ moves to a still greater distance, till in a month she makes a complete tour of the heavens, and approaches them from the west. There are eight other stars, be¬ sides, which are continually changing their place ; some¬ times we observe them moving to the westward, some¬ times to the eastward, and sometimes they appear sta¬ tionary for a considerable time. These stars are called planets. There are other bodies which appear only occasionally, move for some time with immense celerity, and afterwards vanish. These bodies are called comets. But the greater number of the heavenly bodies always retain nearly the same relative distance from each 0- ther, and are therefore called fixed stars. It will be necessary for us to consider the nature and apparent motions of all these bodies. We shall, therefore, di¬ vide this first part of our treatise, into the following 2s r Arrange- I . y-k . Let the points at A, .B, C, D, E, F, &c. quite round from to again Found equal portions of the ecliptic, gone through in equal times by the real sun } and those at a, b, c, d, e, f &c. equal portions of the equator de¬ scribed in equal times by the fictitious sun ; and let Zqpss he the meridian. As the real sun moves obliquely in the ecliptic, and the fictitious sun directly in the equator, with respect to the meridian ; a degree, or any number of degrees, between 'Y’ and F on the ecliptic, must be nearer the meridian Z*Y’«, than a degree, or any corresponding number of degrees, on the equator from to f; and the more so, as they are the more oblique : and there¬ fore the true sun comes sooner to the meridian every day whilst he is in the quadrant solar spots; the difference is chiefly in superficial ex-account 0 tent of length and breadth; their depth or thickness them, is very small; some have been so large, as by compu¬ tation to be capable of covering the continents of Asia and Africa ; nay, the whole surface of the earth, or even five times its surface. The diameter of a spot, when near the middle of the disk, is measured by com¬ paring the time it takes in passing over a cross hair in a telescope, with the time wherein the whole disk of the sun passes over the same hair; it may also be mea¬ sured by the micrometer ; and by either of these me¬ thods we may judge how many times the diameter of the spot is contained in the diameter of the sun. Spots are subject to increase and diminution of magnitude, and seldom continue long in the same state. They are of various shapes ; most of them having a deep black nucleus surrounded by a dusky cloud, whereof the in¬ ner parts near the black are a little brighter than the outskirts. They change their shapes, something in the manner that our clouds do ; though not often so sud¬ denly ; thus, what is of a certain figure to-day, shall to-morrow, or perhaps in a few hours, be of a different one ; what is now but one spot, shall in a little time he broken into two or three ; and sometimes two or three spots shall coalesce, and be united into one. Dr Long, many years since, while he was viewing the image of the sun through a telescope cast upon white paper, saw one roundish spot, by estimation not much less than the diameter of our earth, break into two, which receded from one another with prodigious velo¬ city. This observation was singular at the time ; for though several writers had taken notice of this after it was done, none of them had been making any observa¬ tion at the time it was actually doing. |k lOtl r } The tl rr'^l; ’art II. A S T R apparent num^ei‘ of spots on the sun is very uncertain j Motions sometimes there are a great many, sometimes very few j of the and sometimes none at all. Schemer made observa- ieavenly tions on the sun from 1611 to 16295 and says he ne- IBodies. vef f0Linf] ]ts qL1Jte free 0f spots, excepting a few days in December 1624. At other times he frequent¬ ly saw 20, 30, ami in the year 1625 he was aide to count 50 spots on the sun at a time. In an interval af¬ terwards of 20 years, from 1650 to 1670, scarce any spots were to be seen, and since that time some years have furnished a great number of spots, and others none at all 5 but since the beginning of the last century, not a year passed wherein some were not seen j and at present, says Mr Cassini, in his Elemens cVAstronomic published in 1740, they are so frequent, that the sun is seldom without spots, and often shows a good number of them at a time. From these phenomena, it is evident, that the spots are not endowed with any permanency ; nor are they at all regular in their shape, magnitude, number, or in the time of their appearance or continuance. He- velius observed one that arose and vanished in 16 or 17 hours j nor has any been observed to continue longer than 70 days, which was the duration of one in the year 1676. Those spots that are formed gradually, are gradually dissolved ; while those that arise sudden¬ ly, are for the most part suddenly dissolved. When a spot disappears, that part where it was generally be¬ comes brighter than the rest of the sun, and continues so for several days : on the other hand, those bright parts (called faculce, as the others are called macnlcc) some¬ times turn to spots. The solar spots appear to have a motion which >ts move carr‘es them across the sun’s disk. Every spot, if it m west continues long enough without being dissolved, appears east. to enter the sun’s disk on the east side, to go from thence with the velocity continually increasing till it has gone half its way 5 and then to move slower and slower, till it goes off at the west side ; after which it disap¬ pears for about the same space of time that it spent in crossing the disk, and then enters upon the east side again, nearly in the same place, and crosses it in the same track, and with the same unequal motion as before. This apparent inequality in the motion of the spots is purely optical, and is in such proportion as demonstrates them to be carried round equably or in a circle, the plane of which continued passes through or near the eye of a spectator upon the earth. Besides the real changes of the spots already men¬ tioned, there is another which is purely optical, and is owing to their being seen on a globe differently turned towards us. If we imagine the globe of the sun to have a number of circles drawn upon its surface, all passing through the poles, and cutting his equator at equal distances, these circles which we may call meri¬ dians, if they were visible, would appear to us at un¬ equal distances, as in fig. 2. Now, suppose a spot were round, and so large as to reach from one meri¬ dian to another, it would appear round only at g-, when it was in the middle of that half of the globe which is towards our earth 5 for then we view the full extent of it in length and breadth : in every other place it turns away from us, and appears narrower, though of the same length, the farther it is from the middle j and on 67 e solar O N O M Y. its coming on at 0, and going off at », it appears as Apparent small as a thread, the thin edge being then all that we Motions see. of tfie These spots have made us acquainted with a very important phenomenon, namely the rotation of the sun . ^ . upon its axis. Amidst the changes which these spots are continually undergoing, regular motions may be detected, agreeing exactly with the motion of the sur¬ face of the sun, on the supposition that this luminary revolves round an axis almost perpendicular to the ecliptic in the same direction with its motion in its or¬ bit round the earth. By a careful examination of the motion of these spots, it has been ascertained that the sun turns round its axis in about 25 days and a half, and that its equator is inclined to the ecliptic about 70;5; The spots on the sun’s disk are almost always con¬ fined to a zone, extending about 30°.5 on each side of the equator. Sometimes, however, they have been observed at the distance of 39°.5 from the equator of the sun. Bouguer demonstrated, by a number of curious ex¬ periments on the sun’s light, that the intensity of the light is much greater toward the centre of the sun’s disk than towards its circumference. Now, when a portion of the sun’s surface is transported by the rota¬ tion of that luminary from the centre to the circumfe¬ rence of his disk, as it is seen under a smaller angle, the intensity of its light, instead of diminishing, ought to increase. Hence it follows, that part of the light which issues from the sun towards the circumference of his disk, must be somehow or other prevented from making its way to the earth. This cannot be account¬ ed for, without supposing that the sun is surrounded by a dense atmosphere, which, being traversed obliquely by the rays from the circumference, intercepts more ol them than of those from the centre which pass it per¬ pendicularly. 6g The phenomena of the solar spots, as delivered by Account of Scheiner and Hevelius, may be summed up in thetliephe- following particulars. 1. Every spot which hath a nymena by nucleus, or considerably dark part, hath also an umbra, ^^^ers, or fainter shade, surrounding it. 2. The boundary between the nucleus and umbra is always distinct and well defined. 3. The increase of a spot is gradual, the breadth of the nucleus and umbra dilating at the same time. 4. In like manner, the decrease of a spot is gra¬ dual, the breadth of the nucleus and umbra contracting at the same time. 5. The exterior boundary of the umbra never consists of sharp angles 5 but is always curvilinear, how irregular soever the outline of the nu¬ cleus may be. 6. The nucleus of a spot, whilst on the decrease, often changes its figure by the umbra encroaching irregularly upon it, insomuch that in a small space of time new encroachments are discernible, wiiereby the boundary between the nucleus and um¬ bra is perpetually varying. 7. It often happens, by these encroachments, that the nucleus of a spot is di¬ vided into two or more nuclei. 8. The nuclei of the spots vanish sooner than the umbra. 9. Small umbrae are often seen without nuclei. 10. An umbra of any considerable size is seldom seen without a nucleus in the middle of it. 11. When a spot which consisted of a nucleus and umbra is about to disappear, if it is not sue- of the Heavenly Bodies. 32 ASTRO Apparent ceeded by a facula, or spot brighter than the rest of Motions the disk, the place where it was is soon after not di¬ stinguishable from the rest. In the Philosophical Transactions, vol. Ixiv. Dr Wilson, professor of astronomy at Glasgow, hath given a dissertation on the nature of the solar spots, and men¬ tions the following appearances. 1. When the spot is about to disappear on the western edge of the sun’s limb, the eastern part of the umbra first contracts, then va¬ nishes, the nucleus and western part of the umbra re¬ maining ; then the nucleus gradually contracts and va¬ nishes, while the western part of the umbra remains. At last this disappears also} and if the spot remains long enough to become again visible, the eastern part of the umbra first becomes visible, then the nucleus 5 and when the spot approaches the middle of the disk, the nucleus appears environed by the umbra on all sides, as already mentioned. 2. When two spots lie very near to one another, the umbra is deficient on that side which lies next to the other spot: and this will he the case, though a large spot should be contiguous to one much smaller j the umbra of the large spot will be totally wanting on that side next the small one. If there are little spots on each side of the large one, the umbra does not totally vanish 5 but appears flattened or pressed in towards the nucleus on each side. When the little spots disappear, the umbra of the large one extends it¬ self as usual. This circumstance, he observes, may sometimes prevent the disappeai’ance of the umbra in the manner above mentioned j so that the western umbra may disappear before the nucleus, if a small spot happens to break out on that side. In the same volume, p. 337. Mr Wollaston observes, that the appearances mentioned by Dr Wilson are not constant. He positively affirms, that the faculae or bright spots on the sun are often converted into dark ones. “ I have many times (says he) observed, near the eastern limb, a bright facula just come on, which has the next day shown itself as a spot, though I do not recollect to have seen such a facula near the western one after a spot’s disappearance. Yet, I believe, both these circumstances have been observed by others; and perhaps not only near the limbs. The circumstance of the faculse being converted into spots, I think I may be sure of. That there is generally (perhaps always) a mottled appearance over the face of the sun, when carefully attended to, I think I may be as certain. It is most visible towards the limbs, but I have undoubt¬ edly seen it in the centre; yet I do not recollect to have observed this appearance, or indeed any spots, to¬ wards the poles. Once I saw, with a twelve inch re¬ flector, a spot burst to pieces while I was looking at it. I could not expect such an event, and therefore cannot be certain of the exact particulars ; but the appearance, as it struck me at the time, was like that of a piece of ice when dashed on a frozen pond, which breaks to pieces and slides in various directions.” He also ac¬ quaints us, that the nuclei of the spots are not always in the middle of the umbrae ; and gives the figure of one seen in November 13th I773> which is a remarkable in- Mr Dunns stance t0 t]le contrary. Mr Dunn, however, in his new Atlas or the Mundane bystem, gives some particulars very different from the above. “ The face of the sun (says he) has frequently many large black spots, of various forms and dimensions, which move from east to N O M Y. Part I 69 west, and round the sun, according to some observa- Apparen Ap Motions of the 70 pci tions in 25 days, according to others in 26, and accord¬ ing to some in 27 days. The black or central part of each spot is in the middle of a great number of very *3 small ones, which permit the light to pass between them. The small spots are scarce ever in contact with the central ones: but, what is most remarkable, when the whole spot is near the limb of the sun, the sur¬ rounding small ones form nearly a straight line, and the central part projects a little over it, like Saturn in his ring.” Dr Herschel, with a view of ascertaining more ac-Herschel curately the nature of the sun, made frequent observa-°.bserva' tions upon it from the year 1779 to the year 1794.tlons’ He imagines that the dark spots on the sun are moun¬ tains on its surface, which, considering the great at¬ traction exerted by the sun upon bodies placed at its surface, and the slow revolution it has upon its axis, he thinks may be more than 300 miles high, and yet stand very firmly. He says, that in August 1792, he examined the sun with several powers from 90 to 500; and it evidently appeared that the dark spots are the opaque ground or body of the sun; and that the lu¬ minous part is an atmosphere, which, being interrupted or broken, gives us a view of the sun itself. Hence he concludes, that the sun has a very extensive atmosphere, which consists of elastic fluids that are more or less lucid and transparent; and of which the lucid ones fur¬ nish us with light. This atmosphere, he thinks, is not less than 1843, nor more than 2765 miles in height; and, he supposes, that the density of the luminous solar clouds need not be much more than that of our aurora borealis, in order to produce the effects with which we are acquainted. The sun then, if this hypothesis be ad¬ mitted, is similar to the other globes of the solar system, with regard to its solidity—its atmosphere—its surface diversified with mountains and valleys—its rotation on its axis—and the fall of heavy bodies on its surface ; it therefore appears to be a very eminent, large, and lu¬ cid planet, the primary one in our system, dissemina¬ ting its light and heat to all the bodies with which it is connected. Dr Herschel has lately given up the use of the old terms such as spots, nuclei, penumbrce, &c. and has in¬ troduced a number of new terms, which he considers as more precise. It will be necessary, before W7e proceed farther, to insert his explanation of these terms. “ The expressions,” says he, u which I have usedExplana- are openings, shallows, ridges, nodules, corrugations, tion of hit indentations, and pores. “ Openings are those places where, by the accidental removal of the luminous clouds of the sun, its own solid body may be seen ; and this not being lucid, the open¬ ings through which we see it may, by a common tele¬ scope, be mistaken for mere black spots, or their nuclei. “ Shallows are extensive and level depressions of the luminous solar clouds, generally surrounding the open¬ ings to a considerable distance. As they are less lumi¬ nous than the rest of the sun, they seem to have some distant, though very imperfect resemblance to penum- brse; which might occasion their having been called so formerly. “ Ridges are bright elevations of luminous matter, extended in rows of an irregular arrangement. “ Nodules are also bright elevations of luminous mat¬ ter, terms. 'od«j tt otl')a< Motions ofthe . .-r ii )dies, 7° j chel'ii rva- 1 Ilfart II. ate,1iApparent ter, tut confined to a small space. 1* (penings. ridges, on account of their being brighter than the ge- ?enl oft*ie neral surface of the sun, and also differing a little from "W in colour, have been called faculse, and luculi. “ Corrugations, I call that very particular and re¬ markable unevenness, ruggedness, or asperity, which is peculiar to the luminous solar clouds, and extends all over the surface of the globe of the sun. As the de¬ pressed parts of the corrugations are less luminous than the elevated ones, the disk of the sun has an appearance which may be called mottled. Indentations are the depressed or low parts of the corrugations ; they also extend over the whole surface of the luminous solar clouds. Pores are very small holes or openings, about the middle of the indentations. From the numerous observations of this philosopher he has drawn the following conclusions :— i. Openings are places where the luminous clouds of the sun are removed : large openings have generally shallows about them ; but small openings are generally without shallows. They have generally ridges and nodules about them, and they have a tendency to run into each other. New openings often break out near other openings. Hence he supposes that the openings are occasioned by an elastic but not luminous gas, which comes up through the pores and incipient openings, and spreads itself on the luminous clouds, forcing them out of its way, and widening its passage. Openings sometimes difi’er in colour; they divide when decayed ; sometimes they increase again ; but when divided they usually decrease and vanish ; sometimes they become large indentations, and sometimes they turn into 73 P°res- Billows. 2. Shallows are depressed below the general surface of the sun, and are places from which the luminous so¬ lar clouds of the upper regions are removed. Their thickness is visible ; sometimes they exist without open¬ ings in them. Incipient shallows come from the open¬ ings, or branch out from shallows already formed, and go forward. He supjjoses that the shallows are occa¬ sioned by something coming out of the openings, which, by its propelling motion, drives away the luminous clouds from the place where it meets with the least re¬ sistance ; or which, by its nature, dissolves them as it comes up to them. If it be an elastic gas, its .levity must be such as to make it ascend through the inferior region of the solar clouds, and diffuse itself among the superior luminous matter. 3. Ridges are elevations above the general surface of the luminous clouds of the sun. One of them, which he measured, extended over an angular space of 2' 45,/.9, which is nearly 75,000 miles. Ridges generally accompany openings: but they often also exist in places where there are no openings. They usually disperse very soon. He supposes, that the openings permit a transparent elastic fluid to come out, which disturbs the luminous matter on the top, so as to occasion ridges and nodules; or, more precise¬ ly, that some elastic gas, acting below the luminous clouds, lifts them up, or increases them ; and at last forces itself a passage through them, bv throwing them ASTRONOMY. These nodules, and He thinks that they may be ridges fore-short- 33 71 v aua. ,fM 74 iges. IS Stales. aside. Nodules are small, but highly elevated luminous Vol. III. Part L f Apparent Motions of the places, ened. 5. Corrugations consist of elevations and depressions They extend all over the surface of the sun ; they change ^odies'^ their shape and situation ; they increase, diminish, di- > ■ vide, and vanish quickly. Dispersed ridges and no¬ dules form corrugations. ^ 6. The dark places of corrugations are indentations. p0res. Indentations are usually without openings, though in some places they contain small ones. They change to openings, and are of the same nature as shallows. They are low places, which often contain very small open¬ ings. They are of different sizes, and are extended all over the sun. With low magnifying powers they appear like points. The low places of indentations are 'pores. Pores increase sometimes, and become openings : they vanish quickly. “ It must be sufficiently evident,” says Dr Hers- chel, “from what we have shown of the nature of openings, shallows, ridges, nodules, corrugations, in¬ dentations, and pores, that these phenomena could not appear, if the shining matter of the sun were a liquid ; since, by the laws of hydrostatics, the openings, shal¬ lows, indentations, and pores, would instantly be fill¬ ed up ; nor could ridges and nodules preserve their elevation for a single moment. Whereas, many open¬ ings have been known to last for a whole revolution of the sun ; and extensive elevations have remained supported for several days. Much less can it be an elastic fluid of an atmospheric nature : this would be still more ready to fill up the low places, and to ex¬ pand itself to a level at the top. It remains, therefore, only for us to admit this shining matter to exist in the manner of empyreal, luminous, or phosphoric clouds, residing in the higher regions of the solar atmo¬ sphere.” From his observations, Dr Herschel concludes, that xSvo re- there are two different regions of solar clouds ; that the gions of so- inferior clouds are opaque, and probably not unlike lar clouds, those of our planet; while the superior are luminous, and emit a vast quantity of light: that the opaque inferior clouds probably suffer but little of the light of the self-luminous superior clouds to come to the body of the sun. “ The shallows about large openings,” he observes, “ are generally of such a size, as hardly to permit any direct illumination from the superior clouds to pass over them into the openings ; and the great height and closeness of the sides of small ones, though not often guarded by shallows, must also have nearly the same effect. By this it appears, that the planetary clouds are indeed a most effectual curtain, to keep the brightness of the superior regions from the body of the sun. “ Another advantage arising from the planetary clouds of the sun, is of no less importance to the whole solar system. Corrugations are everywhere dispersed over the sun ; and their indentations may be called shallows in miniature. From this we may conclude, that the immense curtain of the planetary solar clouds is everywhere closely drawn ; and, as our photometri- cal experiments have proved that these clouds reflect no less than 469 rays out of 1000, it is evident that they must add a most capital support to the splendour of the sun, by throwing back so great a share of the E brightness 34 Apparent Motions of the Heavenly Bodies. , 7S Theory of the solar phenome- ASTRO brightness coming to them from the illumination of the ■whole superior regions.” These observations are sufficient to prove, that the sun has an atmosphere of great density, and extending to a great height. Like our atmosphere, it is obvi¬ ously subject to agitations, similar to our winds j and it is also transparent. The following is Dr Her- schel’s theoretical explanation of the solar pheno¬ mena. “ We have admitted,” says he, “ that a transparent elastic gas comes up through the openings, by forcing itself a passage through the planetary clouds. Our observations seemed naturally to lead to this supposi¬ tion, or rather to prove it; for* in tracing the shal¬ lows to their origin, it has been shown, that they al¬ ways begin from the openings, and go forwards. We have also seen, that in one case, a particular bias gi¬ ven to incipient shallows, lengthened a number of them out in one certain direction, which evidently de¬ noted a propelling force acting the same way in them all. I am, however, well prepared to distinguish be¬ tween facts observed, and the consequences that in rea¬ soning upon them we may draw from them j and it will be easy to separate them, if that should hereafter be required. If, however, it be now allowed, that the cause we have assigned may be the true one, it will then appear, that the operations which are carried on in the atmosphere of the sun are very simple and uni¬ form. “ By the nature and construction of the sun, an ela¬ stic gas, which may be called empyreal, is constantly formed. This ascends everywhere, by a specific gra¬ vity less than that of the general solar atmospheric gas contained in the lower regions. When it goes up in moderate quantities, it makes itself small passages among the lower regions of clouds: these we have frequently observed, and have called them pores. We have shewn that they are liable to continual and quick changes, which must be a natural consequence of their fleeting generation. “ When this empyreal gas has reached the higher regions of the sun’s atmosphere, it mixes with other gases, which, from their specific gravity, have their residence there, and occasions decompositions which produce the appearance of corrugations. It has been shown, that the elevated parts of the corrugations are small self-luminous nodules, or broken ridges j and I have used the name of self-luminous clouds, as a gene¬ ral expression for all phenomena of the sun, in what shape soever they may appear, that shine by their own light. These terms do not exactly convey the idea af¬ fixed to them } but those of meteors, coruscations, in¬ flammations, luminous wisps, or others, which I might have selected, would have been liable to still greater objections. It is true, that when speaking of clouds, we generally conceive something too gross, and even too permanent, to permit us to apply that expression properly to luminous decompositions, which cannot float or swim in air, as we are used to see our plane¬ tary clouds do. But it should be remembered, that, on account of the great compression arising from the force of the gravity, all the elastic solar gases must be much condensed j and that, consequently, phenomena in the sun’s atmosphere, which in ours would be mere transi- 2 N O M Y. Part Ifa tory coruscations, such as those of the aurora borealis, will be so compressed as to become much more effica¬ cious and permanent. # “ The great light occasioned by the brilliant supe¬ rior regions, must scatter itself on the tops of the infe¬ rior planetary clouds, and, on account of their great density, bring on a very vivid reflection. Between the interstices of the elevated parts of the corrugations, or self-luminous clouds, which, according to the ob¬ servations that have been given, are not closely con¬ nected, the light reflected from the lower clouds will be plainly visible, and, being considerably less intense than the direct illumination from the upper regions, will occasion that taint appearance which we have call¬ ed indentations. “ This mixture of the light reflected from the inden¬ tations, and that which is emitted directly from the higher parts of the corrugations, unless very attentively examined by a superior telescope, will only have the re¬ semblance of a mottled surface. “ hen a quantity of empyreal gas, more than what produces only pores in ascending, is formed, it will make itself small openings ; or, meeting perhaps with some resistance in passing upwards, it may exert its action in the production of ridges and nodules. “ Lastly, If still further an uncommon quantity of this gas should be formed, it will burst through the pla¬ netary regions of clouds, and thus will produce great openings; then, spreading itself above them, it will oc¬ casion large shallows, and, mixing afterwards gradual¬ ly with other superior gases, it will promote the in¬ crease, and assist in the maintenance, of the general lu¬ minous phenomena. “ If this account of the solar appearances should be well founded, we shall have no difficulty in ascertain¬ ing the actual state of the sun, with regard to its ener¬ gy in giving light and heat to our globe ; and nothing will now remain, but to decide the question which will naturally occur, whether there be actually any considerable difference in the quantity of light and heat emitted from the sun at different times.” This question he decides in the affirmative, considering the great number of spots as a proof that the sun is emit- ting a great quantity of light and heat, and the want of spots as the contrary. The first is connected with a warm and good season ; the second, on the contrary, produces a bad one *. Chap. II. Of the Moon. Next to the sun, the most conspicuous of all the heavenly bodies is the moon. The changes which it undergoes are more striking and more frequent than those of the sun, and its apparent motions much more rapid. Hence they were attended to even before those of the sun were known ; a fact which explains why the first inhabitants of the earth reckoned their time by the moon’s motions, and of course followed the lunar instead of the solar year. In considering the moon, we shall iollow the same plan that we observed with respect to the sun. We shall first give an account of her apparent motions ; and, secondly, of her nature as far as it has been ascertained. These topics shall oc¬ cupy the two following sections. Appareii Up Motion! |M of the I o Heaven; |le Bodies. IB ' y—u- i Via 1301] i EM1'] * P/i /L Trans. 18 part ii. p. 365. .t£ *b!:t Sect. JS:?'mrent Slot. I. t'th« ’■ a.T.e^ feavenly '’Hiei Bodies. ti: art II. Motijux of the ASTRONOMY. O f the Apparent Motions of the Moon. 35 79 The moon, like the sun, has a peculiar motion from east to west. If vve observe her any evening when she is situated very near any fixed star, we shall find her, in 24 hours, about 130 to the east of that star j and loon’s rao-her distance continually increases, till at last, after a tm in her certain number of days, she returns again to the same star from the west, having performed a complete revo¬ lution in the heavens. l]y a continued series of obser¬ vations it has been ascertained, that the moon makes a complete revolution in 27.32166118036 days, or 27 days 7 hours 43' 11" 35"". Such at least was the duration of its revolution at the commencement of 1700. But it does not remain always the same. From a comparison between the observations of the ancients (and those of the moderns, it appears, that the mean motion of the moon in her orbit is accelerating. This acceleration, but just sensible at present, will gradually become more and more obvious. It is a point of great importance to discover, whether it will always conti¬ nue to increase, or whether, after arriving at a certain maximum, it will again diminish. Observations could be of no service for many ages in the resolution of this question ; but the Newtonian theory has enabled astro¬ nomers to ascertain that the acceleration is periodi¬ cal. I The moon’s motion in her orbit is still more unequal than that of the sun. In one part of her orbit she moves faster, in another slower. By knowing the time of a complete revolution, we can easily calculate the mean motion for a day, or any given time ; and this mean motion is called the mean anomaly. The true motion is called the true anomaly : the diflerence between the two is called the equation. Now the moon’s equation some¬ times amounts to 6° 18' 32". Her apparent diameter varies with the velocity of her angular motion. When she moves fastest, her dia¬ meter is largest; it is smallest when her angular motion is slowest. When smallest, the apparent diameter is 0.489420°; when biggest, it is 0.558030°. Hence it follows, that the distance of the moon from the earth varies. By following the same mode of reasoning, which we have detailed in the last chapter, Kepler as¬ certained that the orbit of the moon is an ellipse, having the earth in one of its foci. Her radius vector describes equal areas in equal times ; and her angular motion is inversely proportional to the square of her distance from the earth. The eccentricity of the elliptic orbit of the moon, has been ascertained to amount to 0.0550368, (the mean distance of the earth being represented by unity) ; or the greater axis is to the smaller, nearly as 100,000 to 99,848. lhat point of the moon’s orbit which is nearest the earth, is called the perigee; the opposite point is the apogee. I he line which joins these opposite points, is Even the elliptical orbit of the moon represents but Apparent imperfectly her real motion round the earth ; for that Motions luminary is subjected to a great number of irregularities, ot tlie evidently connected with the positions of the sun, which {^(nT^nRly considerably alter the figure of her orbit. The three <- v ■' t following are the principal of these. 1. The greatest of all, and the one which was first as- The evec- certained, is called by astronomers the moon’s erection, tion. It is proportional to the sine of twice the mean angular distance of the moon from the sun, minus the mean an¬ gular distance of the moon from the perigee of its orbit. Its maximum amounts to 1.3410°. In the oppositions and conjunctions of the sun and moon it coincides with the equation of the centre, which it always diminishes. Hence the ancients, who determined that equation by means of the eclipses, found that equation smaller than it is in reality. g t 2. There is another inequality in the motion of the Variations, moon, which disappears during the conjunctions and oppositions of the sun and moon ; and likewise when these bodies are 90° distant from each other. It is at its maximum when their mutual distance is about 45°, and then amounts to about O.5940. Hence it has been concluded to be proportional to the sine of twice the mean angular distance of the moon from the sun. This inequality is called the variation. It disappears during the eclipses. g. 3. The moon’s motion is accelerated when that of Annual the sun is retarded, and the contrary. This occasionsedies, 89 boon’s 'parei,, Apparent supposing the tabular radius to be 10,000,000, Motions tural sine of 38° l' 53" (the arc Zar) is 6,160,816, and the of the- the natural sine of 46® 4'41" (the arc :s&) is 7,202,821: If"1! ^odles.^ tlle sum of tjotfl these sines is 13,363,637. Say , therefore, As 13,363,637 is to 10,000,000, SO is i° 16' 34" to 57' 18", which is the moon’s horizontal parallax. If the two places of observation be not exactly un¬ der the same meridian, their difference of longitude must be accurately taken, that proper allowance may be made for the moon’s declination whilst she is passing from the meridian of the one to the meridian of the other. From the theory of the parallax we know, that at the distance of the moon from the earth the apparent size of the earth would be to that of the moon as 21,352 to 5823. Their respective diameters must be proportional to these numbers, or almost as 11 to 3. Hence the bulk of the moon is 49 times less than that j>o of the earth. tier phases The different earances, or phases, of the moon *Pain • constitute some of the most striking phenomena of the heavens. When she emerges from the rays of the sun in an evening, she appears after sunset as a small cres¬ cent just visible. The size of this crescent increases continually as she separates to a greater distance from the sun, and when she is exactly in opposition to that luminary, she appears under the form of a complete circle. This circle changes into a crescent as she ap¬ proaches nearer that luminary, exactly in the same man¬ ner it had increased, till at last she disappears altoge¬ ther, plunging into the sun’s rays in the morning at sunrise. The crescent of the moon being always di¬ rected towards the sun, indicates obviously that she bor¬ rows her light from that luminary; while the law of the variation of her phases, almost proportional to the versed side of the angular distance of the moon from the sun, demonstrates that her figure is spherical. Hence it follows, that the moon is an opaque spherical body. Hiese different phases of the moon are renewed af¬ ter every conjunction. They depend upon the excess of the synodical movement of the moon above that of the sun, an excess which is usually termed the synodi¬ cal motion of the moon. The duration of the synodi¬ cal revolution of the moon in the mean period between two conjunctions is 29.530588 days. It is to the tro¬ pical year nearly in the ratio of 19 to 235, that is to say, that 19 solar years consist of about 235 lunar months. Hie points of the lunar orbit, in which the moon is either in conjunction or opposition to the sun are called syzigies. In the first point the moon is said to be new, in the second to be full. The quadratures are those points in which the moon is distant from the sun 90° or 27°*‘ When in these points, the moon is said to be in first and third quarter. One half only of the moon is then illuminated or seen from the earth. As a more particular account of these phases may be deemed ne¬ cessary, we subjoin the following explanation, which will perhaps be better understood by the generality of readers. ffhe moon is an opaque globe like the earth, and shines only by reflecting the light of the sun : there¬ fore, whilst that half of her which is towards the sun is ASTRONOMY. 37 the na- enlightened, the other half must be dark and invisible. Apparent 9* leflects tie tuu’e ;ht. Hence she disappears when she comes between us and Motions the sun ; because her dark side is then towards us. ^ When she is gone a little way forward, we see a little y of her enlightened side : which still increases to our t ■ view as she advances forward, until she comes to be opposite to the sun 3 and then her whole enlightened side is towards the earth, and she appears with a round illuminated orb, which we call the full moon ; her dark side being then turned away from the earth. From the full she seems to decrease gradually as she goes through the other half of her course 3 showing us less and less of her enlightened side every day, till her next change or conjunction with the sun, and then sire disappears as before. The moon has scarce any difference of seasons 3 her axis being almost perpendicular to the ecliptic. What is very singular, one half of her has no darkness at all 3 the earth constantly affording it a strong light in the sun’s absence ; while the other half has a fortnight’s darkness and a fortnight’s light by turns. Our earth is thought to be a moon to the moon 3 Earth ap- waxing and waning regularly, but appearing 13 timesPearsa as big, and affording her 13 times as much light as shemoon to does us. When she changes to us, the earth appears °Ur nl00L full to her; and when she is in her first quarter to us, the earth is in its third quarter to her 5 and vice versa. But from one half of the moon the earth is never seen at all : from the middle of the other half, it is al¬ ways seen over head 5 turning round almost 30 times as quick as the moon does. From the circle which limits our view of the moon, only one half of the earth’s side next her is seen 3 the other half being hid below the horizon of all places on that circle. To her the earth seems to be the biggest body in the universe 3 for it ap¬ pears 13 times as big as she does to us. As the earth turns round its axis, the several conti¬ nents, seas, and islands, appear to the moon’s inhabi¬ tants like so many spots of different forms and bright¬ ness, moving over its surface ; but much fainter at some times than others, as our clouds cover them or leave them. By these spots the lunarians can determine the time of the earth’s diurnal motion, just as we do the motion of the sun : and perhaps they measure their time by the motion of the earth’s spots: for they cannot have a truer dial. The moon’s axis is so nearly perpendicular to thefiow the ecliptic, that the sun never removes sensibly from her hn*ar in- equator 3 and the obliquity of her orbit, which is next habitants to nothing as seen from the sun, cannot cause the suncan to decline sensibly from her equator. Yet her inhabi-*111 tants are not destitute of means for ascertaining the length of their year, though their method and ours must differ. For we can know the length of our year by the return of our equinoxes 3 but the lunarians having al¬ ways equal day and night, must have recourse to an¬ other method 3 and we may suppose, they measure their year by observing when either of the poles of our earth begins to be enlightened, and the other to disappear, which is always at our equinoxes 3 they being conve¬ niently situated for observing great tracts of land about our earth’s poles which are entirely unknown to us. Hence we may conclude, that the year is of the same^ absolute length both to the earth and moon, though veryy 33 ASTRONOMY. Part II Apf/irent Motions of tho Heavenly Bodies. Fig. tz. 95 Her phases exp!aiued. very different as to the number of days j we having 365^ natural days, and the lunarians only lirV* every day and night in the moon being as long as 29J on the earth. The moon’s inhabitants on the side next the earth may as easily find the longitude of their places as we can find the latitude of ours. For the earth keeping constantly, or very nearly so, over one meridian of the moon, the east or west distances of places from that me¬ ridian are as easily found as we can find our distance from the equator by the altitude of our celestial poles. As the sun can only enlighten that half of the earth which is at any moment turned towards him, and, be¬ ing withdrawn from the opposite half, leaves it in dark¬ ness, so he likewise doth to the moon j only with this difference, that as the earth is surrounded by an at¬ mosphere, we have twilight after the sun sets ; but if the moon has none of her own, nor is included in that of the earth, the lunar inhabitants have an immediate transition from the brightest sunshine to the blackest darkness. For, let trksw be the earth, and A, B, C, I), E, F, G, H, the moon in eight different parts of her orbit. As the earth turns round its axis from west to east, when any place comes to t, the twilight begins there, and when it revolves from thence to r the sun S rises •, when the place comes to s the sun sets, and when it comes to w the twilight ends. But as the moon turns round her axis, which is only once a-month, the moment that any part of her surface comes to r (see the moon at G), the sun rises there without any pre¬ vious warning by twilight $ and when the same point comes to s the sun sets, and that point goes into dark¬ ness as black as at midnight. The moon being an opaque spherical body (for her hills take off no more from her roundness than the in¬ equalities on the surface of an orange take off' from its roundness), we can only see that part of the enlighten¬ ed half of her which is towards the earth. And there¬ fore, when the moon is at A, in conjunction with the sun S, her dark half is towards the earth, and she dis¬ appears, as at a, there being no light on that half to render it visible. When she comes to her first octant at B, or has gone an eighth part of her orbit from her conjunction, a quarter of her enlightened side is to¬ wards the earth ; and she appears horned, as at b. When she has gone a quarter of her orbit from be¬ tween the earth and sun to C, she shows us one half of her enlightened side, as at c, and we say she is a quar¬ ter old. At D, she is in her second octant; and by showing us more of her enlightened side she appears gibbous, as at d. At E, her whole enlightened side is towards the earth ; and therefore she appears round, as at e; when we say it is full moon. In her third oc¬ tant at F, part of her dark side being towards the earth, she again appears gibbous, and is on the de¬ crease, as at/. At G, we see just one half of her en¬ lightened side j and she appears half decreased, or in her third quarter, as at g. At H, we only see a quar¬ ter of her enlightened side, being in her fourth octant j where she appears horned, as at h. And at A, ha¬ ving completed her course from the sun to the sun again, she disappears ; and we say it is new moon. Thus, in going from A to E, the moon seems conti¬ nually to incre ue > and in going from E to A, to de- P, Ai1 i M < E crease in the same proportion ; having like phases at Apparent equal distances from A to E, but as seen from the sun Motions S she is always full. of the The moon appears not perfectly round when she is full in the highest or lowest part of her orbit, because » we have not a full view of her enlightened side at that 96 time. When full in the highest part of her orbit, a ^ver ap- small deficiency appears on her lower edge; and the ]>eillJs Per* contrary when full in the lowest part of her orbit. round It is plain by the figure, that when the moon changes to the earth, the earth appears full to the moon ; and vice versa. For when the moon is at A, new to the earth, the whole enlightened side of the earth is towards the moon ; and when the moon is at E, full to the earth, its dark side is towards her. Hence a new moon answers to a full earth, and a full moon to a new earth. The quarters are also reversed to each other. 97 Between the third quarter and change, the moon is Agreeable per frequently visible in the forenoon, even when the sunrel>res®“la* shines; and then she affords us an opportunity of seeingpij"SyS a very agreeable appearance, wherever we find a globu¬ lar stone above the level of the eye, as suppose on the top of a gate. For, if the sun shines on the stone, and we place ourselves so as the upper part of the stone may just seem to touch the point of the moon’s lowermost horn, we shall then see the enlightened part of the stone exactly 'of the same shape with the moon ; horned as she is, and inclined the same way to the horizon. The rea¬ son is plain ; for the sun enlightens the stone the same way as he does the moon : and both being globes, when we put ourselves into the above situation, the moon and stone have the same position to our eyes; and therefore we must see as much of the illuminated part of the one as of the other. The position of the moon’s cusps, or a right line touching the points of her horns, is very differently inclined to the horizon at different hours of the same day of her age. Sometimes she stands, as it were, up¬ right on her lower horn, and then such a line is per¬ pendicular to the horizon : when this happens, she is 9g in what the astronomers call the nonagesii?ial degree which is the highest point of the ecliptic above the ho-mal degm rizon at that time, and is 90° from both sides of the ■noi ■ iWe I Klip horizon where it is then cut by the ecliptic. But this never happens when the moon is on the meridian, except when she is at the very beginning of Cancer or Capricorn. The explanation of the phases of the moon leads us Eclipses of ri,, to that of the eclipses ; those phenomena which former- the moftn. j n, ly were the subjects of dread and error, but which phi¬ losophers have converted to the purposes of utility and instruction. The moon can only become eclipsed by the interposition of an opaque body, which intercepts from it the light of the sun ; and it is obvious that this opaque body is the earth, because the eclipses of the moon never happen except when the moon is in oppo¬ sition, and consequently when the earth is interposed between her and the sun. The globe of the earth pro¬ jects behind it relatively to the motion of the sun a conical shadow, whose axis is the straight line that joins the centres of the earth and sun, and which ter¬ minates at the point when the apparent diameters of these two bodies become equal. The diameter of these bodies seen from the centre of the moon in oppo¬ sition [.he too reriod of her jesi- c-riet art II. ipparent sition, are nearly in the proportion of 3 for the sun and Motions 11 for the earth. Therefore, the conical shadow of the of the earth is at least thrice as long as the distance between Bodies'y t^le eart^ ant* moon* antl its breadth at the point where it is traversed by the moon more than double the dia¬ meter of that luminary. The moon, therefore, would be eclipsed every time that it is in opposition, if the plane of its orbit coincid¬ ed with the ecliptic. But in consequence of the mu¬ tual inclination of these two planes, the moon, when in opposition, is often elevated above the earth’s conical shadow, or depressed below it j and never can pass through that shadow unless when it is near the nodes. If the whole of the moon’s disk plunges into the shadow, the eclipse is said to be total; if only a part of the disk enter the shadow, the eclipse is said to bejMsr- tial. The mean duration of a revolution of the sun rela- eeclipses. tive]y j.0 tjie no(]eg 0f j|ie lunar orbit is 346.61963 days, and is to the duration of a synodical revolution of the moon nearly as 223 to 19. Consequently, after a period of 223 lunar months, the sun and moon return nearly to the same situation relatively to the order of the lunar orbit. Of course the eclipses must return in the same order after every 223 lunations. This gives us an easy method of predicting them. But the ine¬ qualities in the motions of the sun and moon occasion sensible differences j besides the return of the two lumi¬ naries to the same points relatively to the nodes not be¬ ing rigorously true, the deviations occasioned by this want of exactness alter at last the order of the eclipses observed during one of these periods. The following explanation of the lunar eclipses be¬ ing more particular, may be acceptable to some of our readers. That the moon can never be eclipsed but at the time of her being full, and the reason why she is not eclipsed at every full, has been shown already. In fig. 13. let S be the sun, E the earth, RR the earth’s shadow, and B the moon in opposition to the sun: In this situation the earth intercepts the sun’s light in its way to the moon ; and when the moon touches the earth’s shadow at v, she begins to be eclipsed on her eastern limb x, and continues eclipsed until her western limb y leaves the shadow at ; at B she is in the mid¬ dle of the shadow, and consequently in the middle of the eclipse. 'Ilhy th« I he moon, when totally eclipsed, is not invisible if ijDon is vi- she be above the horizon and the sky be clear ; but ap- £l!wden pfarS ^nerally of a dusky colour, like tarnished cop- T ^ ‘ per, which some have thought to be the moon’s native light. But the true cause of her being visible is the scattered beams of the sun, bent into the earth’s sha¬ dow by going through the atmosphere ; which, being more or less dense near the earth than at considerable heights above it, refracts or bends the sun’s rays more inward, the nearer th&y are passing by the earth’s sur¬ face, than those rays which go through higher parts of the atmosphere, where it is less dense according to its height, until it be so thin or rare as to lose its refrac¬ tive power. Let the circle/, g, h, i, concentric to the earth, include the atmosphere whose refractive power vanishes at the height /"and i; so that the rays Wy*w and \ * v go on straight without suffering the least re¬ ASTRONOMY. 39 lot fraction: but all those rays which enter the atmosphere Apparent between /"and k, and between i and /, on opposite sides Motions of the earth, are gradually more bent inward as they of the go through a greater portion of the atmosphere, until IIea^en,y the rays W k and V l touching the earth at m and n, , Ijof‘tes- are bent so much as to meet at q, a little short of the moon ; and therefore the dark shadow of the earth is contained in the space m 0 p q n, where none of the sun’s rays can enter ; all the rest, R, R, being mixed by the scattered rays which are refracted as above, is in some measure enlightened by them ; and some of those rays falling on the moon, give her the colour of tarnished copper or of iron almost red hot. So that if the earth had no atmosphere, the moon would be as invisible in total eclipses as she is ivhen new. If the were so near the earth as to go into its dark sh acjow, suppose about joo, she would be invisible du¬ ring her stay in it; but visible before and after in the fainter shadow RR. When the moon goes through the centre of the earth’s shadow she is directly opposite to the sun ; yet the moon has been often seen totally eclipsed in the ho¬ rizon, when the sun was also visible in the opposite part of it j for the horizontal refraction being almost 34 minutes of a degree, and the diameter of the sun and moon being each at a mean state but 32 minutes, the refraction causes both luminaries to appear above the horizon when they are really below it. When the moon is full at 12 degrees from either of her nodes, she just touches the earth’s shadow, but en¬ ters not into it. In fig. 14. let GH be the ecliptic, ef the moon’s orbit where she is 12 degrees from the node at her full, c d her orbit where she is 6 degrees from the node, a b her orbit where she is full in the node, AB the earth’s shadow, and M the moon. When the moon describes the line ef, she just touches the shadow, but does not enter into it; when she de¬ scribes the line c d, she is totally, though not centrally, immersed in the shadow ; and when she describes the line a b, she passes by the node at M in the centre of the shadow, and takes the longest line possible, which is a diameter, through it: and such an eclipse being both total and central, is of the longest duration, name- ly, 3 b* 57 6 sec. from the beginning to the end, if the moon be at her greatest distance from the earth $ and 3 h. 37 m. 26. sec. if she be at her least distance. The reason of this difference is, that when the moon is farthest from the earth, she moves slowest 5 and when nearest to it, quickest. The moon’s diameter, as well as the sun’s, is suppo¬ sed to be divided into 12 equal parts, called fftgzV.?; and so many of these parts as are darkened by the earth’s shadow, so many digits is the moon eclipsed. All that the moon is eclipsed above 12 digits, shows how far the shadow of the earth is over the body of the moon, on that edge to which she is nearest at the middle of the eclipse. It is difficult to observe exactly either the beginning or ending of a lunar eclipse, even with a good telescope, eclipse* because the earth’s shadow is so faint and ill-defined difficultly about the edges, that when the moon is either iust°^selve^* touching or leaving it, the obscuration of her limb is scarce sensible ; and therefore the nicest observers can hardly be certain to four or five seconds of time. But both , 40 Apparent Motions of the Heavenly Bodies. 103 Eclipses of the san. 104 Number of eclipses in a year. both the beginning and ending of solar eclipses are vi¬ sibly instantaneous : for the moment that the edge of the moon’s disk touches the sun’s, his roundness seems a little broke on that part: and the moment she leaves it, he appears perfectly round again. The eclipses of the sun only take place during the conjunctions of the sun and moon, or when the moon is placed between the sun and the earth. They are owing to the moon concealing the sun from the earth, or to the earth being plunged in the shadow of the moon. The moon is indeed much smaller than the sunj but it is so much nearer to the earth that its apparent diameter does not differ much from the diameter of that luminary : and, in consequence of the changes which take place in the apparent diameter of these bodies, it happens that sometimes the apparent diame¬ ter of the moon is greater than that of the sun. If we suppose the centres of the sun and moon in the same straight line with the eye of a spectator placed on the earth, he will see the sun eclipsed. If the apparent dia¬ meter of the moon happens to surpass that of the sun, the eclipse will be total: but if the moon’s diameter be smallest, the observer will see a luminous ring, formed by that part of the sun’s disk which exceeds that of the moon’s, and the eclipse will in that case be annular. If the centre of the moon is not in the same straight line which joins the observer and the centre of the sun, the eclipse can only be partial, as the moon can only conceal apart of the sun’s disk. Hence there must be a great variety in the appearance of the solar eclipses. We may add also to these causes of variety the eleva¬ tion of the moon above the horizon, which changes its apparent diameter considerably. For it is well known, that the moon’s diameter appears larger when she is near the horizon than when she is elevated far above it. Now, as the moon’s height above the horizon varies according to the longitude of the observer, it follows, that the solar eclipses will not have the same appearance to the obser¬ vers situated in different longitudes. One observer may see an eclipse which does not happen relatively to another. In this respect the solar differ from the lunar eclipses, which are the same to all the inhabitants of the earth. In any year, the number of eclipses of both lumi¬ naries cannot be less than two, nor more than seven} the most usual number is four, and it is very rare to have more than six. For the sun passes by both the nodes but once a-year, unless he passes by one of them in the beginning of the year ; and, if he does, he will pass by the same node again a little before the year be finished 5 because, as these points move 19^- degrees backwards every year, the sun will come to either of them 173 days after the other. And when either node is within 17 degrees of the sun at the time of new moon, the sun will be eclipsed. At the subsequent opposition, the moon will be eclipsed in the other node, and come round to the next conjunction again ere the former node be 17 degrees past the sun, and will there¬ fore eclipse him again. When three eclipses fall about either node, the like number generally falls about the opposite ; as the sun comes to it in 173 days afterwards ; and six lunations contain but four days Thus, there may be two eclipses of the sun ASTRONOMY. Part II. when the moon changes in either of the nodes, she Apparent PP cannot be near enough the other node at the next full to be eclipsed ; and in six lunar months afterwards she will change nearer the other node; in these cases, there ^odies^ ' can be but two eclipses in a year, and they are both of the sun. A longer period than the above mentioned, for com¬ paring and examining eclipses which happen at long in¬ tervals of time, is 557 years, 21 days, 18 hours, 30 mi¬ nutes, 11 seconds; in which time there are 6890 mean lunations; and the sun and node meet again so nearly as to be but 11 seconds distant; but then it is not the same eclipse that returns, as in the shorter period above mentioned. IQ^ Eclipses of the sun are more frequent than of the tyhy n]0re moon, because the sun’s ecliptic limits are greater than eclipses of the moon’s; yet we have more visible eclipses of the the moon and one of the moon about each of her nodes. But moon than of the sun, because eclipses of the moon arelilan of ‘J16 r sun are ob« seen from all parts of that hemisphere of the earth which serve(j is next her, and are equally great to each of those parts : but the sun’s eclipses are visible only to that small portion of the hemisphere next him whereon the moon’s shadow falls. The moon’s orbit being elliptical, and the earth in one of its focuses, she is once at her least distance from the earth, and once at her greatest in every lunation. ^ When the moon changes at her least distance from the Total and earth, and so near the node that her dark shadow falls ani}ular upon the earth, she appears big enough to cover theec^^*es" whole disk of the sun from that part on which her shallow falls ; and the sun appears totally eclipsed there for some minutes : but, when the moon changes at her greatest distance from the earth, and so near the node that her dark shadow is directed towards the earth, her diameter subtends a less angle than the sun’s; and therefore she cannot hide his whole disk from any part of the earth, nor does her shadow reach it at that time ; and to the place over which the point of her shadow hangs, the eclipse is annular, the sun’s edge appearing like a luminous ring all round the body of the moon. When the change happens within 17 degrees of the node, and the moon at her mean distance from the earth, the point of her shadow just touches the earth and she eclipseth the sun totally to that small spot whereon her shadow falls ; but the darkness is not of a moment’s continuance. The moon’s apparent diameter, when largest, ex¬ ceeds the sun’s, when least, only 1 minute 38 seconds of a degree ; and in the greatest eclipse of the sun that can happen at any time and place, the total darkness continues no longer than whilst the moon is going 1 minute 38 seconds from the sun in her or¬ bit, which is about 3 minutes and 13 seconds of an hour. The moon’s dark shadow covers only a spot on the Extent of earth’s surface about 180 English miles broad, when the moon’s the moon’s diameter appears largest, and the sun’s least; shadow am and the total darkness can extend no farther than the Penumb^a• dark shadow covers. Yet the moon’s partial shadow or penumbra may then cover a circular space 4900 miles in diameter, within all which the sun is more or less eclipsed, as the places are less or more distant from the centre of the penumbra. When the moon changes exactly 107 ■ -ent am! H irt II. pparcnt lotions of the ^arenly Bodies. I3‘ exactly in the node, the penamhra is circular on the earth at the middle of the general eclipse ; because at that time it falls perpendicularly on the earth’s surface j but at every other moment it falls obliquely, and will therefore be elliptical; and the more so, as the time is longer before or after the middle of the general eclipse ; and then much greater portions of the earth’s surface are involved in the penumbra. When the penumbra first touches the earth, the ge¬ neral eclipse begins ; when it leaves the earth, the ge¬ neral eclipse ends : from the beginning to the end the sun appears eclipsed in some part of the earth or other. When the penumbra touches any place, the eclipse be¬ gins at that plate, and ends when the penumbra leaves it. When the moon changes in the node, the pe¬ numbra goes over the centre of the earth’s disk as seen from the moon j and consequently, by describing the longest line possible on the earth, continues the longest upon it $ namefy, at a mean rate, 5 hours, 50 minutes ; more, if the moon be at her greatest distance from the earth, because she then moves slowest; less if she be at her least distance, because of her quicker motion. To make several of the above and other phenomena jdainer, let S be the sun, E the earth, M the moon, and AMP the moon’s orbit. Draw the right line W e from the western side of the sun at W, touching the western side of the moon at c, and the earth at e : draw also the right line V r/, from the eastern side of the sun at V, touching the eastern side of the moon at r/, and the earth at e : the dark space c e d included between those lines is the moon’s shadow, ending in a point at e, where it touches the earth ; because in this Case the moon is supposed to change at M in the middle between A the apogee, or farthest point of her orbit from the earth, and P the perigee, or nearest point to it. For, had the point P been at M, the moon had been nearer the earth : and her dark shadow at e would have covered a space upon it about 180 miles broad, and the sun would have been totally dark¬ ened, with some continuance : but had the point A been at M, the moon would have been farther from the earth, and her shadow would have ended in a point a little above e, and therefore the sun would have ap¬ peared like a luminous ring all around the moon. Draw the right lines WX dh and VX eg, touching the con- trary sides of the sun and moon, and ending on the earth at a and b ; draw also the right line SXM, from the centre of the sun’s disk, through the moon’s cen- tie to the earth 5 and suppose the two former lines WX d h and VX agio revolve on the line SXM as an axis, and their points a and b will describe the limits of the penumbra T. F on the earth’s surface, including the laige space aba; within which the sun appears more or less eclipsed, as the places are more or less di¬ stant from the verge of the penumbra a b. Draw the right line 5/ 12 across the sun’s disk, per¬ pendicular to SXM the axis of the penumbra j then divide the line y \2 into twelve equal parts, as in the figure, for the twelve digits or equal parts of the sun’s diameter; and at equal distances from the centre of the penumbra at e (on the earth’s surface YY) to its edge ab, draw twelve concentric circles, marked with the numeral figures 1234, and remember that VOL. HI. Part I. . ASTEONOMY. 41 the moon’s motion in her orbit AMP is from west to Apparent east, as from s to t. Then, To an observer on the earth at b, the eastern limb Motions of the of the moon at t/ seems to touch the western limb of {lodges ^ the sun at WT, when the moon is at M j and the sun’s eclipse begins at b, appearing as at A, fig. 15. at the left hand j but at the same moment of absolute time, to an observer at a in fig. 14. the western edge of the moon ate leaves the4eastern edge of the sun at V, and the eclipse ends, as at the right hand C, fig. 15. At the very same instant, to all those who live on the circle marked I on the earth A, in fig. 14. the moon M cuts off or darkens a twelfth part of the sun S, and eclipses him one digit, as at 1 in fig. 15.: to those who live on the circle marked 2 in fig. 14. the moon cuts off two twelfth parts of the sun, as at 2 in fig. 15. : to those on the circle 3, three parts ; and so on to the centre at 12 in fig. 14. where the sun is centrally eclipsed, as at B in the middle of fig. 15. j under which figure there is a scale of hours and mi¬ nutes, to show at a mean state how long it is from the beginning to the end of a central eclipse of the sun on the parallel of London; and how many digits are eclipsed at any particular time from the beginning at A to the middle at B, or the end at C. Thus, in 16 minutes from the beginning, the sun is two digits eclipsed ; in an hour and five minutes, eight digits 5 and in an hour and 37 minutes, 12 digits. By fig. 14. it is plain, that the sun is totally or centrally eclipsed but to a small part of the earth at any time, because the dark conical shadow e of the moon M falls but on a small part of the earth ; and that the partial eclipse is confined at that time to the space included by the circle a b, of which only one half can be projected in the figure, the other half being supposed to be hid by the convexity of the earth E\ and likewise, that no part of the sun is eclipsed to the large space YY of the earth, because the moon is not between the sun and any of that part of the earth ; and therefore to all that part the eclipse is invisible. The earth turns eastward on its axis, as from g to h, which is the same way that the moon’s shadow moves ; but the moon’s motion is much swifter in her orbit from st; and therefore, although eclipses of the sun are of no longer duration on account of the earth’s motion on its axis than they would be if that motion was stopped, yet in four minutes of time at most, the moon’s swifter motion carries her dark shadow quite over any place that its centre touches at the time of greatest obscuration. The motion of the shadow on the earth’s disk is equal to the moon’s motion from the sun, which is about 30!- minutes of a degree every hour at a mean rate : but so much of the moon’s orbit is equal to 30^ degrees of a great circle on the earth ; and therefore the moon’s shadow goes 30!- degrees, or 1830 geographical miles on the earth in an hour, or 30* miles in a minute, which is almost four times as swift as the motion of a cannon-ball. As seen from the sun or moon, the earth’s axis ap¬ pears differently inclined every day of the year, on ac¬ count of keeping its parallelism throughout its annual course. In fig. 16. let EDON be the earth at the two equinoxes and the two solstices, NS its axis, N the north pole, S the south pole, iEQ the equator, F t 42 Apparent T the tropic of Cancer, t the tropic of Capricorn, and Motions ABC the circumference of the earth’s enlightened disk of the a3 seen from the sun or new moon at these times. The ^Bodies^ eart^’s ax‘s ^ias the position NES at the vernal equinox, > ^ ' . lying towards the right hand, as seen from the sun or new moon *, its poles N and S being then in the cir¬ cumference of the disk 5 and the equator and all its pa¬ rallels seem to be straight lines, because their planes pass through the observer’s eye looking clown upon the earth from the sun or moon directly over E, where the ecliptic EG intersects the equator 7E. At the summer solstice the earth’s axis has the position NDS j and that part of the ecliptic EG, in which the moon is then new, touches the tropic of Cancer T at D. The north pole N, at that time inclining 23^ degrees towards the sun, falls so many degrees within the earth’s enlight¬ ened disk, because the sun is then vertical to I) 234 degrees north of the equator or iEQ 5 and the equator, with all its parallels, seem elliptic curves bending down- ward, or towards the south pole, as seen from the sun 5 which pole, together with 23I degrees all round it, is bid behind the disk in the dark hemisphere of the earth. At the autumnal equinox, the earth’s axis has the position NOS, lying to the left hand as seen from the sun or new moon, which are then vertical to O, where the ecliptic cuts the equator AEQ. Both poles now lie in the circumference of the disk, the north pole just going to disappear behind it, and the south pole just entering into it j and the equator with all its parallels seem to be straight lines, because their planes pass through the observer’s eye, as seen from the sun, and very nearly so as seen from the moon. At the winter solstice, the earth’s axis has the position NNS, when its south pole S inclining 23^- degrees towards the sun, falls 23J degrees within the enlightened disk, as seen from the sun or new moon, which are then verti¬ cal to the tropic of Capricorn t, 23^ degrees south of the equator iEQ 5 and the equator, with all its paral¬ lels, seem elliptic curves bending upward j the north pole being as far hid behind the disk in the dark hemi¬ sphere as the south pole is come into the light. The nearer that any time of the year is to the equinoxes or solstices, the more it partakes of the phenomena relat¬ ing to them. Thus it appears, that from the vernal equinox to the autumnal, the north pole is enlightened : and the equa¬ tor and all its parallels appear elliptical as seen from the sun, more or less curved as the time is nearer to, or far¬ ther from, the summer solstice 5 and bending down¬ wards, or towards the south pole ) the reverse of which happens from the autumnal equinox to the vernal. A little consideration will be sufficient to convince the reader, that the earth’s axis inclines towards the sun at the summer solstice 5 from the sun at the winter sol¬ stice } and sidewise to the sun at the equinoxes : but towards the right hand, as seen from the sun at the vernal equinox j and towards the left hand at the au¬ tumnal. From the winter to the summer solstice, the earth’s axis inclines more or less to the right hand, as seen from the sun •, and the contrary from the summer to the winter solstice. The different positions of the earth’s axis, as seen from the sun at different times of the year, affect solar eclipses greatly with regard to particular places : yea, so far as would make central eclipses which fall at one Part I time of the year invisible if they fell at another, even Apparer though the moon,should always change in the nodes, Motion and at the same hour of the day 5 of which indefinitely various affections, we shall only give examples for the ^(^j|es< times of the equinoxes and solstices. 1 ... In the same diagram, let EG be part of the eclip- 109 tic, and IK, ik, ik, t k, part of the moon’s orbit;-^c''Pses both seen edgewise, and therefore projected into right tjfcC lines ; and let the intersections NODE be one and the 0f the same node at the above times, when the earth has the earth’s forementioned different positions j and let the spaces*1*!5* included by the circles Yppp be the penumbra at these times, as its centre is passing over the centre of the earth’s disk. At the winter solstice, when the earth’s axis has the position NNS, the centre of the penumbra P touches the tropic of Capricorn £ in N at the middle of the general eclipse j but no part of the penumbra P touches the tropic of Cancer T. At the « summer solstice, when the earth’s axis has the position NDS (7DA: being then part of the moon’s orbit whose node is at D), the penumbra p has its centre at D, on the tropic of Cancer T, at the middle of the general eclipse, and then no part of it touches the tro¬ pic of Capricorn t. At the autumnal equinox, the earth’s axis has the position NOS (7 O A: being then part of the moon’s orbit), and the penumbra equally includes part of both tropics T and t, at the middle of the general eclipse : at the vernal equinox it does the same, because the earth’s axis has the position NES j but, in the former of these two last cases, the penum¬ bra enters the earth at A, north of the tropic of Can¬ cer T, and leaves it at m south of the tropic of Capri¬ corn t, having gone over the earth obliquely southward, as its centre described the line A.Om: whereas, in the latter case, the penumbra touches the earth at n, south of the equator ALQ, and describing the line nTL q (si¬ milar to the former line KOm in open space), goes ob¬ liquely northward over the earth, and leaves it at y, north of the equator. In all these circumstances the moon has been sup¬ posed to change at noon in her descending node : Had she changed in her ascending node, the phenomena would have been as various the contrary way, with re¬ spect to the penumbra’s going northward or southward over the earth. But because the moon changes at all hours, as often in one node as in the other, and at all distances from them both at different times as it hap¬ pens, the variety of the phases of eclipses are almost innumerable, even at the same places j considering also how variously the same places are situated on the enlightened disk of the earth, with respect to the pen¬ umbra’s motion, at the diflerent hours when eclipses happen. When the moon changes 17 degrees short of her de¬ scending node, the penumbra P 18 just touches the northern part of the earth’s disk, near the north pole N j and as seen from that place, the moon appears to touch the. sun, but hides no part of him from sight. Had the change been as far shcrt of the ascending node, the penumbra would have touched the southern , part of the disk near the south pole S. When the moon itooi changes 12 degrees short of the descending node, more 1 1U6' than a third part of the penumbra P 12 falls on the northern parts of the earth at the middle of the gene¬ ral eclipse : Had she changed as far past the same node, as ASTRONOMY. :s' Bodies. II. Pari II. A S T R em Apparent as muc^ of the other sitle of the penumbra about P 'ns Motions would have fallen on the southern parts of the earth ; e oftlie all the rest in the expansum, or open space. When ^ie 131<)011 changes 6 degrees from the node, almost the whole penumbra P 6 falls on the earth at the middle of the general eclipse. And, lastly, when the moon changes in the node at N, the penumbra PN takes the longest course possible on the earth’s disk: its centre falling on the middle thereof, at the middle of the ge¬ neral eclipse. The farther the moon changes from ei¬ ther node, within 17 degrees of it, the shorter is the penumbra’s continuance on the earth, because it goes over a less portion of the disk, as is evident by the no figure. Duration The nearer that the penumbra’s centre is to the hi ddferent e four, and every other mountain of any eminence; and if other persons, who are furnished with good tele¬ scopes and micrometers, would take the quantity of the projection of the lunar mountains, 1 make no doubt hut that we would be nearly as well acquainted with their heights, as we are with the elevation of our own. One caution I would beg leave to mention to those Caution to who may use the excellent 3^ feet refractors of MrbGobse,,wi Dollond. The admirable quantity of light, which on s most occasions is so desirable, will probably give the tdescopes. measure of the projection somewhat larger than the true, if not guarded against by proper limitations placed before the object-glass. I have taken no notice of any allowance to be made for the refraction a ray of light must suffer in passing through the atmosphere of the moon, when it illuminates the top of the mountain, whereby its apparent height will be lessened, as we are too little acquainted with that atmosphere to take it into consideration. It is also to be observed, that this would equally affect the conclusions of Hevelius, and therefore the difference in our inferences would still re¬ main the same.” In the continuation of his observations, Dr Her- sehel informs us that he had measured the height of one of the mountains that had been measured by He¬ velius. “ Antitaurus (says he), the mountain mea¬ sured by Hevelius, was badly situated : because Mount Moschus and its neighbouring hills cast a deep shadow, which may be mistaken for the natural convexity of the moon. A good, full, but just measure, 25.105’'; in miles, 29.27: therefore LM 31.7 miles, and the perpendicular height not quite half a mile. As great exactness was desired in this observation, it was repeat¬ ed with very nearly the same result. Several other mountains were measured by the same method; and all h is observations concurred in making the height of the lunar mountains much less than what former astro¬ nomers had done. Mount Lipulus was found to be near two-thirds of a mile; one of the Apennine mountains, between Lacus Thrasimenus and Pontus Euxinus, mea¬ sured a mile and a quarter; Mons Armenia, near Taur rus, two-thirds of a mile ; Mons Leucoptera three quar¬ ters of a mile. Mons Sacer projected 45.625"; ‘ but (says he) I am almost certain that there are two very considerable cavities, or places where the ground de¬ scends below the level of the convexity, just before these mountains; so that these measures must of course be a good deal too large ; but supposing them to be just, it follows, that on is 50.193 miles, LM=64 miles, and the perpendicular height above one mile and three- fourths.’ x As the moon has on its surface mountains and valT Volcanoes leys in common with the earth, some modern astrono-discovered mers have discovered a still greater similarity, viz. that*11 t*ie some of these are really volcanoes, emitting fire as those m0°n’ on earth do. An appearance of this kind was disco¬ vered some years ago by Don Ulloa in an eclipse of the sun. It was a small bright spot like a star near the margin of the moon, and which he at that time supposed to have been a hole with the sun’s light shinn¬ ing . 45 ASTRONOMY. Apparent mg through it. Succeeding observations, however, Motions have induced astronomers to attribute appearances of Heavcnl • t^1’S eruPti°n of volcanic lire ; and Dr Bodies. Herschel has particularly observed several eruptions of '.j the lunar volcanoes, the last of which he gives an ac¬ count ol in the Phil. Trans, for 1787. “ April 19. 10 h. 36 m. sidereal time. I perceive (says he) three volcanoes in different places of the dark part of the new moon. Two of them are either already nearly extinct, or otherwise in a state of going to break out ; which perhaps may be decided next lunation. The third shows an actual eruption of fire or luminous mat¬ ter. I measured the distance of the crater from the northern limb of the moon, and found it 3' 57.3" ; its light is much brighter than the nucleus of the comet which M. Mechain discovered at Paris the 10th of this month. “ April 20. 10 h. 2 m. sidereal time. The volcano burns with greater violence than last night. Its dia¬ meter cannot be less than 3 sec. by comparing it with that of the Georgian planet: as Jupiter was near at hand, I turned the telescope to his third satellite, and estimated the diameter of the burning part of the vol¬ cano to be equal to at least twice that of the satellite; whence we may compute that the shining or burning matter must be above three miles in diameter. It is of an irregular round figure, and very sharply defined on the edges. The other two volcanoes are much far¬ ther towards the centre of the moon, and resemble large, pretty faint nebulse, that are gradually much brighter in the middle ; but no well defined luminous spot can be discerned in them. These three spots are plainly to be distinguished from the rtst of the marks upon the moon ; for the reflection of the sun’s rays from the earth is, in its present situation, sufiiciently bright, with a ten feet reflector, to show the moon’s spots, even the darkest of them ; nor did I perceive any similar phenomena last lunation, though I then viewed the same places with the same instrument. “ The appearance of what I have called the actual Jlre, or eruption of a volcano, exactly resembled a small piece of burning charcoal when it is covered by a very thin coat of white ashes, which frequently ad¬ here to it when it has been some time ignited j and it had a degree of brightness about as strong as that with which such a coal would be seen to glow in faint day¬ light. All the adjacent parts of the volcanic moun¬ tain seemed to be faintly illuminated by the eruption, and were gradually more obscure as they lay at a greater distance from the crater. This eruption re¬ sembled much that 'which I saw on the 4th of May in the year 1783, but differed considerably in magnitude and brightness j for the volcano of the year 1783, though much brighter than that which is now burning, was not nearly (SO large in the dimensions of its erup¬ tion : the former seen in the telescope resembled a star of the fourth magnitude as it appears to the naked eye ; this, on the contrary, show’s a visible disk of lu¬ minous matter very different from the sparkling bright- 120 ness of star light.” Conjectures Concerning the nature of the moon’s substance there concerning have been many conjectures formed. Some have ima- 8taDc'e>" ?ine(i> that, besides the light reflected from the sun, the moon hath also some obscure light of her own, by which she would be visible without being illuminated Part I of the Heavenl Bodies, by the sunbeams. In proof of this it is urged, that Apparen during the time of even total eclipses the moon is still Motion visible, appearing of a dull red colour, as if obscured by a great deal of smoke. In reply to this it hath been advanced, that this is not always the case 5 die moon sometimes disappearing totally in the time of an eclipse, so as not to be discernible by the best glas¬ ses, while little stars of the fifth and sixth magnitudes were distinctly seen as usual. This phenomenon was observed by Kepler twice, in the years 1580 and 158:3 ; and by Hevelius in 1620. Ricciolus and other Je¬ suits at Bologna, and many people throughout Hol¬ land, observed the same on April 14. 1642: yet at Venice and Vienna she was all the time conspicuous. In the year 1703, Dec. 23. there was another total obscuration. At Arles, she appeared of a yellowish brown ; at Avignon, ruddy and transparent, as if the sun had shone through her j at Marseilles, one part W’as reddish and the other very dusky $ and at length, though in a clear sky, she totally disappeared. The general reason for her appearance at all during the time of eclipses shall be given afterwards : but as for these particular phenomena, they have not yet, as far as we know, been satisfactorily accounted for. Different conjectures have also been formed concern¬ ing the spots on the moon’s surface. Some philosophers have been so taken with the beauty of the brightest places observed in her disk, that they have imagined them to be rocks of diamonds j and others have com¬ pared them to pearls and precious stones. Dr Keill and the greatest part of astronomers now are of opi¬ nion, that these are only the tops of mountains, which by reason of their elevation are more capable of re¬ flecting the sun’s light than others which are low’er. The duskish spots, he says, cannot be seas, nor any thing of a liquid substance; because, when examined by the telescope, they appear to consist of an infinity of caverns and empty pits, whose shadows fall wdthin them, which can never be the case with seas, or any liquid substance: but, even within these spots, bright¬ er places are also to be observed ; which, according to bis hypothesis, ought to be the points of rocks standing- up within the cavities. Dr Dong, however, is of opi¬ nion, that several of the dark spots on the moon are really water. May not the lunar seas and lakes (savs he) have islands in them, wherein there may be pits and caverns ? And if some of these dark parts be brighter than others, may not that be owing to the seas and lakes being of different depths, and to their having rocks in some places and flats in others ? It has also been urged, that if all the dark spots ob¬ served' on the moon’s surface were really the shadows of mountains, or of the sides of deep pits, they could not possibly be so permanent as they are found to be : but would vary according to the position of the moon with regard to the sun, as we find shadows on earth are varied according as the earth is turned towards or from the sun. Accordingly it is pretended, that va¬ riable spots are actually discovered on the moon’s disk and that the direction of these is always opposite to the sun. Hence they are found among those parts which are soonest illuminated in the increasing moon, and in the decreasing moon lose their light sooner than the intermediate ones ; running round, and appearing sometimes longer, and sometimes shorter. The per¬ manent Part II. Apparent manent dark spots, therefore, it is said, must be some Motions .matter which is not fitted for reflecting the rays of the ofthe sun so much as the bright parts do : and this property, ^Botbes V we kno'v by experience, belongs to water rather than . ‘ j land; whence these philosophers conclude, that the moon, as well as our earth, is made up of land anti seas. Whether It ^as been a matter of dispute whether the moon the moon has any atmosphere or not. The following argu~ 1ms any at- ments have been urged by those who take the negative mosphere. s|(]e> I. The moon constantly appears with the same brightness when there are no clouds in our atmosphere ; which could not be the case if she were surrounded with an atmosphere like ours, so variable in its density, and so frequently obscured by clouds and vapours. 2. In an appulse of the moon to a star, when she comes so near it that part of her atmosphere is interposed be¬ tween our eye and the star, refraction would cause the latter to seem to change its place, so that the moon would appear to touch it later than by her own mo¬ tion she would do. 3. Some philosophers are of opi¬ nion, that because there are no seas or lakes in the moon, there is therefore no atmosphere, as there is no water to be raised up in vapours. All these arguments, however, have been answered by other astronomers in the following manner. 1. It is denied that the moon appears always with the same brightness, even when our atmosphere appears equally clear. Hevelius relates, that he has several times found in skies perfectly clear, when even stars of the sixth and seventh magnitude were visible, that at the same altitude of the moon, and the same elongation from the earth, and with one and the same telescope, the moon and its maculae do not appear equally-lucid, clear, and conspicuous at all times j hut are much brighter and more distinct at some times than at others. From the circumstances of this observation, say they, it is evi¬ dent that the reason of this phenomenon is neither in our air, in the tube, in the moon, nor in the spectator’s eye ; hut must be looked for in something existing about the moon. An additional argument is drawn from the different appearances of the moon already mentioned in total eclipses, which are supposed to be owing to the different constitutions of the lunar atmo¬ sphere. To the second argument Dr Long replies, that Sir Isaac Newton has shown (Princip. prop. 3'7. cor. 5.), that the weight of any body upon the moon is but a third part of what the weight of the same would be hythe upon the earth; now the expansion of the air is reci- ht it not procally as the weight that compresses it: the air, "racted therefore, surrounding the moon, being pressed toge- oon’t at a or ,je‘ng attracted towards the centre jtosphere." .t*le moon ^7 a I°rce eflual only to one-third of that which attracts our air towards the centre of the earth, it thence follows, that the lunar atmosphere is only one-third as dense as that of the earth, which is too little to produce any sensible refraction of the stars light. Other astronomers have contended that such refraction was sometimes very apparent. M. Cassini says that he frequently observed Saturn, Jupiter, and the fixed stars, to have their circular figure changed in¬ to an elliptical one, when they approached either to the moon’s dark or illuminated limb 3 though they 47 own, that in other occultations no such change could Apparent be observed. With regard to the fixed stars, indeed, Motions it has been urged, that granting the moon to have ofthe an atmosphere of the same nature and quantity as ours, Keenly no such effect aS a gradual diminution of light ought, . to take place j at least, that we could by no means be capable of perceiving it. Our atmosphere is found to be so rare at the height of 44 miles as to be incapable of refracting the rays of light. This height is the 180th part of the earth’s diameter j but since clouds are never observed higher than four miles, we must conclude that the vaporous or obscure part is only one 1980th. The mean apparent diameter of the moon is 31' 29", or 1889 seconds ; therefore the obscure parts ol her atmosphere, when viewed from the earth, must subtend an angle of less than one second j which space is passed over by the moon in less than two seconds of time. It can therefore hardly be expected that obser¬ vation should generally determine whether the supposed obscuration takes place or not. The third argument is necessarily inconclusive, be¬ cause we know not whether there is any water in the moon or not ; nor though this could be demonstrated, would it follow that the lunar atmosphere answers no other purpose than the raising of water into vapour. I here is, however, a strong argument in favour of the existence of a lunar atmosphere, taken from the *23 appearance of a luminous ring round the moon in the I:uminoiiE time of solar eclipses. In the eclipse of May 1. 1706, Captain Stanyan, from Bern in Switzerland, writes, the mooif that “ the sun was totally darkened there for the in total space of four minutes and a half: that a fixed star andecliPses' planet appeared very bright: that his getting out of the eclipse was preceded by a blood-red streak of light from his left limb, which continued not longer than six or seven seconds of time j then part of the sun’s disk appeared all on a sudden, brighter than Venus was ever seen in the night 5 and in that very instant gave light and shadow to tilings as strong as moon light uses to do.” The publisher of this account observes that the red streak of light preceding the emersion of the sun’s body, is a px-oof that the moon has an atmosphere j and its short continuance of five or six seconds shows that its height is not more than the five or six hundredth part of her diameter. Fatio, who observed the same eclipse at Geneva, tells us, that “ there was seen during the whole time of the total immersion, a whiteness which seemed to break out from behind the moon, and to encompass her on all sides equally : this whiteness was not well defined on its outward side, and the breadth of it was not a twelfth part of the diameter of the moon. The planet appeai-ed very black, and her disk very well de¬ fined within the whiteness which encompassed it about, and was of the same colour as that of a white crown or halo, of about four or five degrees in diameter, which accompanied it, and had the moon for its centre. A little after the sun had begun to appear again, the whiteness, and the crown which had encompassed the moon, did entirely vanish.” “ I must add (says Dr Long), that this description is a little perplexed, ei¬ ther through the fault of the author or of the trans¬ lator j for I suppose Fatio wrote in Fi’ench : however, it plainly appears by it that the moon’s atmosphere was visible, surrounded by a light of larger extent, which u ASTRONOMY. 4B A S T B O A pj) are at 1 think must be that luminous appearance (the zodiacal Motions light) mentioned from Cassini.” Flamstead, who pub¬ lished tins account, takes notice, that, according to these observations, the altitude of the moon’s atmo¬ sphere cannot be well supposed less than 180 geogra¬ phical miles; and that probably this atmosphere was never discovered before the eclipse, by reason of the smallness of the refraction, and the want of proper ob¬ servations. An account of the same eclipse, as it appeared at Zurich, is given by Dr Scheuchzer, in the following words : “ We had an eclipse of the sun, which was both total and annular; total, because the whole sun was covered by the moon ; annular, not what is pro- perly so called, but by refraction : for there appeared round the moon a bright shining, which was owing to the rays of the sun refracted through the atmosphere of the moon.” Dom. Cassini, from a number of accounts sent him from different parts, says, that in all those places where it was total, during the time of total darkness, there was seen round the moon a crown or broad circle of pale light, the breadth whereof was about a 12th part of the moon’s diameter : that at Montpelier, where the observers were particularly attentive to see if they could distinguish the zodiacal light already mentioned, they took notice of a paler light of a larger extent, which surrounded the crown of light before mentioned, and spread itself on each side of it, to the distance of four degrees. He then mentions Kepler’s opinion, that the crown of light which appears round the moon du¬ ring the total darkness in an eclipse of the sun is caused by some celestial matter surrounding the moon, of suffi¬ cient density to receive the rays of the sun and send them to us; and that the moon may have an atmo¬ sphere similar to that of our earth, which may refract the sun’s light. A total eclipse of the sun was observed on the 22d of April O. S. in the year 1715, by Dr Halley at Lon¬ don, and by M. Louville of the Academy of Sciences at Paris. Dr Halley relates, that “ when the first part of the sun remained on his east side, it grew very faint, and was easily supportable to the naked eye even through the telescope, for above a minute of time before the total darkness; whereas, on the contrary, the eye could not endure the splendour of the emerging beams through the telescope even from the first moment. To this, two causes perhaps concurred : the one, that the pupil of the eye did necessarily dilate itself during the dark¬ ness, which before had been much contracted by look¬ ing on the sun : the other that the eastern parts of the moon, having been heated with a day near as long as 30 of ours, must of necessity have that part of its atmosphere replete with vapours raised by the so long continued action of the sun ; and, by consequence, it was more dense near the moon’s surface, and more capable of obstructing the aim’s beams ; whereas at the same time the western edge of the moon had suf¬ fered as long a night, during which there might fall in dew's all the vapours that were raised in the preceding long day ; and for that reason, that that part of its atmosphere might be seen much more pure and trans¬ parent. “ About two minutes before the total immersion, the remaining part of the sun was reduced to a very ROM Y. Part II 124. Dr Halley's account of a solar eclipse in fine horn, whose extremities seemed to lose their acute- Apparent ness, and to become round like stars ; and for the Motions space of about a quarter of a minute a small piece of of the the southern horn of the eclipse seemed to be cut off" ^j^iies^ from the rest by a good interval, and appeared like an > t oblong star rounded at both ends ; which appearance would proceed from no other cause but the inequalities of the moon’s surface; there being some elevated parts thereof near the moon’s southern pole, by whose inter¬ position part of that exceedingly fine filament of light was intercepted. A few seconds before the sun was totally hid, there discovered itself round the moon a luminous ring, about a digit, or perhaps a tenth part of the moon’s diameter in breadth. It was of a pale white¬ ness, or rather of a pearl colour, seeming to me a little tinged with the colour of the iris, and to be concentric with the moon; whence I concluded it the moon’s at¬ mosphere. But the great height of it, far exceeding that of our earth’s atmosphere, and the observations of some who found the breadth of the ring to increase on the west side of the moon as the emersion approached, together with the contrary sentiments of those whose judgments I shall always revere, make me less con¬ fident, especially in a matter to which I gave not all the attention requisite 125 “ Whatever it was, the ring appeared much brighter Flashes of and whiter near the body of the moon than at a di- ap- stance from it; and its outward circumference, w^‘c^ from was ill defined, seemed terminated only by the extreme tjie rarity of the matter of which it was composed, and in moon, all respects resembled the appearance of an enlightened atmosphere seen from far : but whether it belonged to the sun or moon, I shall not pretend to determine. During the whole time of the total eclipse, I kept my telescope constantly fixed on the moon, in order to ob¬ serve what might occur in this uncommon appearance ; and I saw perpetual flashes or coruscations of light, which seemed for a moment to dart out from behind the moon, now here, now there, on all sides, but more especially on the western side, a little before the emersion ; and about two or three seconds before it, on the same western side, where the sun was just coming out, a long and very narrow streak of dusky but strong red light seemed to colour the dark edge of the moon, though nothing like it had been seen immediately after the immersion. But this instantly vanished after the ap¬ pearance of the sun, as did also the aforesaid lumi¬ nous ring.” Mr Louville relates, that a luminous ring of a silver Mr Lou- colour appeared round the moon as soon as the sun was ville's ob- entirely covered by her disk, and disappeared the mo-serTat*cas‘ ment he recovered his light; and this ring was bright¬ est near the moon, and grew gradually fainter towards its outer circumference, where it was, however, de¬ fined ; that it was not equally bright all over, but had several breaks in it: but he makes no doubt of its be¬ ing occasioned by the moon’s atmosphere, and thinks that the breaks in it were occasioned by the mountains of the moon ; he says also, that this ring had the moon, and not the sun, for its centre, during the whole time of its appearance. Another proof brought by him of the moon having an atmosphere is, that, to¬ wards the end of the total darkness, there was seen on that side of the moon on which the sun was going to appear, a piece of a circle, of a lively red, which might be tie atirn Part IL Apparent be owing to the red rays that are least refrangible be- Motions ing transmitted through the moon’s atmosphere in the of the greatest quantity : and that he might be assured this 1 Bodies ? re^ness not proceed from the glasses of his telescope, ' - he took care to bring the red part into the middle of his glasses ASTRONOMY. 49 without the luminous stfeaks or flashes of lightning Apparent above-mentioned $ it is even taken notice of by Plutarch: Mo:ions however, some members of the academy at Paris have 01 **ie. endeavoured to account for both these phenomena Bodies, without having recourse to a lunar atmosphere ; and f See N° 14. et geq Lightning Pie lays great stress on the streaks of light which he TtTuentSaw ^art instantaIieousIy from different places of the nthe'1”611 moon during the time of total darkness, but chiefly [noon. near the eastern edge of the disk : these he takes to be lightning, such as a spectator would see flashing from the dark hemisphere of the earth, if he were placed Upon the moon, and saw the earth come between him¬ self and the sun. “ Now (says Dr Long) it is highly probable, that if a man had, at any time, a view of that half of the earth where it is night, he would see lightning in some part of it or other.” Louville farther observes, that the most mountainous countries are most liable to tempests j and that mountains being more fre¬ quent in the moon, and higher, than on earth*, thun¬ der and lightning must be more frequent there than with us 5 and that the eastern side of the moon would be most subject to thunder and lightning, those parts having been heated by the sun for half the month immediately preceding. It must here be observed, that Halley, in mentioning these flashes, says they seemed to come from behind the moon ; and Louville, though he says they came sometimes from one part and some¬ times from another, owns, that he himself only saw them near the eastern part of the disk ; and that, not knowing at that time what it was that he saw, he did not take notice whether the same appearance was to be seen on other parts of the moon or not. He tells us, however, of an English astronomer, who presented the Royal Society with a draught of what he saw in the moon at the time of this eclipse 5 from which Lou¬ ville seems to conclude, that lightnings had been ob¬ served by that astronomer near the centre of the moon’s disk. “ Now (says Mr Long) thunder and lightning would be a demonstration of the moon having" an at¬ mosphere similar to ours, Avherein vapours and exhala¬ tions may be supported, and furnish materials for clouds, storms, and tempests. But the strongest proof brought by Louville of the moon having an atmosphere is this, that as soon as the eclipse began, those parts of the sun which were going to be hid by the moon grew sensibly palish as the former came near them, suffering beforehand a kind of imperfect eclipse or diminution of light j this would be owing to nothing else but the atmosphere of the moon, the eastern part whereof going before her reached the sun before the moon did. As to the great height of the lunar atmosphere, which from the breadth of the luminous ring, being about a whole digit, would upon a calculation come out 180 128 I'eat light of He lunar ‘mosphere ‘counted miles» above three times as high as the atmosphere of the earth, Louville thinks that no objection ; since if the moon were surrounded with an atmosphere of the same nature with that which encompasses the earth, the gravitation thereof towards the moon would be but one third of that of our atmosphere toxvards the earth $ and consequently its expansion would make the height of it three times as great from the moon as is the height of our atmosphere from the earth.” • The same luminous ring has been observed in other total eclipses, and even in such as are annular, though Vol. III. Part I. f for this purpose they made the following experiments: I2p The image of the sun coming through a small hole in-These phe- to a darkened room, was received upon a circle of wood nomena or metal of a diameter a good deal larger than that °^ccounted the sun’s image ; then the shadow of this opaque circle for< was cast upon whitepaper, and there appeared round it, on the paper, a luminous circle such as that which sur¬ rounds the moon. The like experiment being made with a globe of wood and with another of stone not po¬ lished, the shadows of both these cast upon paper were surrounded xvith a palish light, most vivid near the shadows, and gradually more diluted at a distance from them. They observe also, that the ring round the moon was seen in the eclipse of 1706 by Wurzelbaur, who cast her shadow upon white paper. The same appear¬ ance was observed on holding an opaque globe in the sun, so as to cover his whole body from the eye ; for, looking at it through a smoked glass, in order to pre¬ vent the eye from being hurt by the glare of light it would otherwise be exposed to, the globe appeared xvith a light resembling that round the moon in a total eclipse of the sun. Thus they solve the phenomenon of the ring seen round the moon by the inflection, or diffraction as they call it, of the solar rays passing near an opaque sub¬ stance. As for the small streaks of light above-men¬ tioned, and which are supposed to be lightning, they explain these by an hypothesis concerning the cavities of the moon themselves ; which they consider as con¬ cave mirrors reflecting the light of the sun nearly to the same point; and as these are continually changing their situation with great velocity by the moon’s motion from the sun, the light which any one of them sends to our eye is seen but for a moment. This, however, will not account for the flashes, if any such there are, seen near the centre of the disk, though it does, in no very satisfactory manner, account for those at the edges. It has already been observed, that the occupations ofOcculta- the fixed stars and planets by the moon, in general hap-dons of the pen without any kind of refraction of their light bv®xc<^ stars the lunar atmosphere. The contrary, however, has^0^e sometimes been observed, and the stars have been seen manifestly to change their shape and colour on going behind the moon’s disk. An instance of this happen¬ ed on the 28th of June N. S. in the year 1715, xvhen an occupation of Venus by the moon happened in the day-time. Some astronomers in France observing this with a telescope, saw Venus change colour for about a minute before she was hid by the moon ; and the same change of colour was observed immediately after her emersion from behind the disk. At both times the edge of the disk of Venus that was nearest the moon appeared reddish, and that which was most distant of a bluish colour. These appearances, hoxvever, which might have been taken for proofs of a lunar atmo¬ sphere, were supposed to be owing to the observers ha¬ ving directed the axis of their telescopes toxvards the moon. This would necessarily cause any planet or star near the edge of the moon’s disk to be seen through those parts of the glasses which are near their circum- G fei ence, 50 ASTRONOMY. Part I Apparent Motions of the Heavenly Bodies. Moon has no sensible atmosphere *32 Turns round her 133 Libration of the uioaa. ference, and consequently to appear coloured. This was evidently the case from other observations of an occultation of Jupiter by the moon the same year, when no such appearance of refraction could be per- j ceived while he was kept in the middle of the tele¬ scope. Maraldi also informs us, that he had observed before this two other occultations of Venus and one of Jupiter 5 and was always attentive to see whether those planets changed their figure or colour either up¬ on the approach of the moon to cover them, or at their first coming again into sight j but never could perceive any such thing. Nor could he, in a great number of occultations of the fixed stars, perceive the smallest apparent change in any of them, except¬ ing once that a fixed star seemed to increase its di¬ stance a little from the moon as it was going to be co¬ vered by her j but this, he suspected, might be owing to his telescope being directed so as to have the star seen too far from the middle of its aperture. He con¬ cludes, therefore, that the moon has no atmosphere : and he remarks, that at Montpelier, perhaps because the air is clearer there than at London, the luminous ring round the moon appeared much larger than at London j that it was very white near the moon, and gradually decreasing in brightness, formed round her a circular area of about eight degrees in diameter. If, says he, this light was caused by the atmosphere of the moon, of what a prodigious extent must that at¬ mosphere be ? We have related all these opinions at full length, in order to put our readers in possession of the arguments 'that have been advanced upon this subject j but it is now generally admitted, and indeed, scarcely can be denied, that the atmosphere of the moon, if it really has any, is almost entirely insensible. From the spots upon the moon’s disk it has been as¬ certained, that the same hemisphere of that luminary is always directed towards the earth. Hence it follows that she turns round her axis once during every revolu¬ tion round the earth. F.xact observations have ascertained that slight va¬ rieties take place respecting the appearances of the moon’s disk. The spots are observed alternately to approach towards and recede from the edge of the moon. Those that are very near the edge appear and disappear alternately, making periodical oscillations, which are'distinguished by the name of the libration of the moon. To form a precise idea of the nature of this libration, we must consider that the disk of the moon, seen from the centre of the earth, is terminated by the circumference of a great circle of the moon, perpendi¬ cular to a line drawn from the earth’s centre to that of the moon. The lunar hemisphere is projected upon the plane of this circle turned towards the earth, and its appearances are due to the movements of ro¬ tation of that body relative to its radius vector. If the moon did not revolve round her axis, this radius vector would describe a great circle on the moon’s surface, all the points of which would present themselves succes¬ sively to us. But the moon, revolving in the same time that this radius vector describes the great circle, always keeps the same point of the circle nearly upon the ra¬ dius, and of course the same hemisphere turned towards the earth. The inequalities of her motion produce the slight variations in her appearance : for the rotation Apparer of the moon does not partake sensibly of these irregula- Motion of the Heaven] Bodies. rities. Hence it varies somewhat relatively to the ra¬ dius vector, which accordingly cuts successively differ¬ ent points of the surface. Of course the globe of the moon makes oscillations relatively to that radius corre¬ sponding to the inequalities of her motions, which al¬ ternately conceal from our view and discover to us some parts of her surface. Farther : the axis of rotation of the moon is not ex¬ actly perpendicular to the plane of her orbit. If we suppose the position of this axis fixed, during a revolu¬ tion of the moon it inclines more or less to the radius vector, so that the angle formed by these two lines is acute during one part of her revolution, and obtuse du¬ ring another part of it. Hence the poles of rotation are alternately visible from the earth, and those parts of her surface that are near these poles. Besides all this, the observer is not placed at the centre of the earth, but at its surface. It is the radius drawn from his eye to the centre of the moon, which determines the middle point of her visible hemisphere. But in consequence of the lunar parallax, it is obvious that this radius must cut the surface of the moon in points sensibly different according to the height of that luminary above the horizon. All these causes concur to produce the libration of the moon, a phenomenon which is merely optical, and not connected with her rotation, which relatively to us is perfectly equable, or at least if it be subjected to any irregularities, they are too small to be observed. ^ This is not the case with the variations in the plane Theory of of the moon’s equator. While endeavouring to de-it* termine its position by the lunar spots, Cassini was led to this remarkable conclusion, which includes the whole astronomical theory of the real libration of that lumi¬ nary. Conceive a plane passing through the centre of the moon perpendicular to her axis of rotation, and of course coinciding with the plane of her equator $ con¬ ceive a second plane, parallel to the ecliptic, to pass through the same centre j and also a third plane, which is the mean plane of the lunar orbit: these three planqs have a common intersection ; the second, placed be¬ tween the two others, forms with the first an angle of l°.503, and with the third an angle of 50.14692’, therefore the intersections of the lunar equator with the ecliptic coincide always with the mean nodes of the lunar orbit, and like them have a retrograde motion, which is completed in the period of 6793.3009 days. During that interval the two poles of the equator and lunar orbit describe small circles parallel to the eclip¬ tic, enclosing between them the pole of the ecliptic, so that these three poles are constantly upon a great circle of the heavenly sphere. His till Chap. III. Of the Planets. Amidst the infinite variety of stars which occupy a place in the sphere of the heavens, and which occupy nearly the same relative position with respect to each other, there are eight which may he observed to move in a very complicated manner, but following cer¬ tain precise laws, for they always commence the same motions again after every period. The motions of these 111 Part II. Apparent Motions of the Heavenly Bodies. ASTRONOMY. . is appar it motion these stars, called planets, constitute one of the princi¬ pal objects of astronomy. These planets are called 1. Mercury. 5. Pallas. 2. Venus. 6. Jupiter. 3. Mars. 7. Saturn. 4. Ceres. 8. Herschel. Mercury and Venus never separate from the sun farther than certain limits j the rest separate to all the possible angular distances. The movements of all these bodies are included in a zone of the heavenly sphere called the zodiac. This zone is divided into two equal parts by the ecliptic. Its breadth was formerly considered as only about i6°j but it must be much increased if the orbits of Ceres and Pallas, the two newly discovered planets, are to be comprehended in it, It will be pro¬ per to consider the motions and appearances of each of these planets. This will be the subject of the follow¬ ing sections. Sect. I. Of Mercury. Mercury is a small star, but emits a very bright white light: though, by reason of his always keeping near the sun, he is seldom to be seen ; and when he does make his appearance, his motion towards the sun is so swift, that he can only be discerned for a short time. He appears a little after sunset, and again a little before sunrise. Mercury never goes to a greater distance from the '•sun than about so that he is never longer in setting after the sun than an hour and 50 minutes 5 nor does he ever rise sooner than 1 hour and 50 mi¬ nutes before that luminary. Very frequently, he goes so near the sun as to be lost altogether in his rays. "When he begins to make his appearance in the even¬ ing after sunset, he can scarcely at first be distinguish¬ ed in the rays of the twilight. But the planet disen¬ gages itself more and more, and is seen at a greater di¬ stance from the sun every successive evening 3 and hav¬ ing got to the distance of about 22°.5, it begins to re¬ turn again. During this interval, the motion of Mer¬ cury referred to the stars is direct 3 but when it ap¬ proaches within 18° of the sun it appears for some time stationary 5 and then its motion begins to be retro¬ grade. The planet continues to approach the sun, and at last plunges into his rays in the evening, and disap¬ pears. Soon after, it may be perceived in the morn¬ ing, before sunrise, separating farther and farther from the sun, his motion being retrograde, as before he dis¬ appeared. At the distance of i8°it becomes station¬ ary, and assumes a direct motion, continuing, however, to separate till it comes to 22.5° of distance 3 then it re¬ turns again to the sun, plunges into his rays, and ap¬ pears soon after in the evening, after sunset, to repeat the same career. The angular distance from the sun, which the planet reaches on both sides of that lumina¬ ry, varies from 160 to nearly 28°. The duration of a complete oscillation, or the inter¬ val of time that elapses before the planet returns again to the point from which it set out, varies also from 100 to 130 days. The mean arc of his retrogradation is about 13^°; its mean duration 23 days. But the quantity differs greatly in difl’erent retrogradations. In general, the laws of the movements of Mercury are very complicated 3 he does not move exactly' in the 51 plane of the ecliptic 3 sometimes he deviates from it Apparent more than 50. Motions Some considerable time must have elapsed before ^ie astronomers suspected that the stars which were seen ^ approaching the sun in the evening and in the morning y—, were one and the same. The circumstance, however, ol the one never being seen at the same time with the other would gradually lead them to the right conclu¬ sion. , I "ZO The apparent diameter of Mercury varies as well as Diametsr, that of the sun and moon, and this variation is obvious¬ ly connected with his position relatively to the sun, and with the direction of his movement. The diameter is at its minimum when the planet plunges into the solar rays in the morning, or when it disengages itself from them: it is at its maximum when the planet plunges into the solar rays in the evening, or when it disenga¬ ges itself from them in the evening 3 that is to say, when the planet passes the sun in its retrograde mo¬ tion, its diameter is the greatest possible 3 when it pas¬ ses the sun in its direct motion, it is the smallest pos¬ sible and the mean length of the appai’ent diameter of Mercury is 11". Sometimes, when the planet disappears during its Nature, retrograde motion, that is to say, when it plunges into the sun’s rays in the evening, it may be seen crossing the sun under the form of a black spot, which describes a chord along the disk of the sun. This black spot is recognised to be the planet by its position, its apparent diameter, and its retrograde motion. These transits of Mercury, as they are termed, are real annular eclipses of the sun : they demonstrate that the planet is an opaque body, and that it borrows its light from the sun. When examined by means of telescopes magni¬ fying about 200 or 300 times, he appears equally lu¬ minous throughout his whole surface, without the least dark spot. But he exhibits the same difference of phases with the moon, being sometimes horned, sometimes gib¬ bous, and sometimes shining almost with a round face, though not entirely full, because his enlightened side is never turned directly towards us 3 but at all times per¬ fectly well defined without any ragged edge, and perfect¬ ly bright. Like the moon, the crescent is always turn¬ ed towards the sun. Ihese different phases throw con¬ siderable light on the orbit of Mercury. Sect. II. Of Venus. Venus, the most beautiful star in the heavens, known by the names of the morning and evening stur^ likewise keeps near the sun, though she recedes from him al¬ most double the distance of Mercury. She is never seen in the eastern quarter of the heavens when the sun is in the western 3 but always seems to attend him in the evening, or to give notice of his approach in the morning. The planet Venus presents the same phenomena with Mercury ; but her different phases are much more sen¬ sible, her oscillations wider, and of longer duration. Her greatest distance from the sun varies from 43° to nearly 48°, and the mean duration of a complete oscil¬ lation is 584 days. Venus has been sometimes seen moving across the He/appai- sun’s disk in the form of a round black spot, with anentmotions. apparent diameter of about yf. A few days after this has been observed, Venus is seen in the morning, G % west 52 A S T K Apparent Motions of the west of the sun, in the form of a fine crescent, with the convexity turned toward the sun. She moves gra- Heavenl westward with a retarded motion, and the cres- Bodies/ ce,1t becomes more full. In about ten weeks she lias " " v~" ■' niovefi 46° west of the sun, and is now a semicircle, and her diameter is 26". She is now stationary. She then moves eastward with a motion gradually accele¬ rated, and overtakes the sun about 9-J months after having been seen on his disk. Some time after, she is seen in the evening, east of the sun, round, but very small. She moves eastward, and increases in diame¬ ter, but loses of her roundness, till she gets about 46° east of the sun, when she is again a semicircle. She now moves westwards, increasing in diameter, but be¬ coming a crescent like the waning moon ; and, at last, after a period of nearly 584 days, comes again into conjunction with the sun with an apparent diameter of 59". I he mean arc of her retrogradation is about 16°, and its mean duration is 42 days. She does not move exactly in the plane of the ecliptic, but deviates from it several degrees. Like Mercury, she sometimes cros¬ ses the sun’s disk. The duration of these transits, as ob¬ served from different parts of the earth’s surface, are very different : this is owing to the parallax of Venus, in consequence of which different observers refer to dif¬ ferent parts of the sun’s disk, and see her describe dif¬ ferent chords on that disk. In the transit which hap- pened in 1769, the difference of its duration, as ob¬ served at Otaheite and at Wardhuys in Lapland, a- mounted to 23 m. 10 sec. This difference gives us the parallax of Venus, and of course her distance from the earth during a conjunction. The knowledge of this parallax enables us, by a method to be afterwards de¬ scribed, to ascertain that of the sun, and consequently to discover its distance from the earth. The great variations of the apparent diameter of Venus demonstrates that her distance from the earth is exceedingly variable. It is largest when the planet passes over the surface of the sun. Her mean apparent diameter is 58". From the movement of certain spots upon the sur¬ face of Venus, it has been concluded that she revolves round her axis once in 24 hours ; but this requires to be corrected by future observations. It is extremely difficult to perceive or examine these spots in our cli¬ mate. The subject merits the attention of astrono¬ mers farther to the south, in more favourable circum¬ stances. The following detail will show the uncer¬ tainty which has prevailed among astronomers respect- 140 these spots. Spots when Dr Long informs us, that the earliest account he first disco- had met with of any spots seen by means of the tele- scope on the disk of Venus was in a collection of let- Venus! °f ters Printed at Pari3 in in one of which Mr Auzout relates his having received advice from Poland that Mr Burratini had, by means of large telescopes, seen spots upon the planet Venus similar to those upon the moon. In 1667, Cassini, in a letter to Mr Petit, mentions his having for a long time carefully observed Venus through an excellent telescope made by Campa- ni, in order to know whether that planet revolved on its axis or not, as he had before found Jupiter and Mars to do. But though he then observed some spots upon her, he says, that even when the air was quiet a. 1.19 Revolution round her axis. vered on the dis Venus. 141 Cassini’ observa lions. O N O M Y. Part I and clear, they appeared faint, irregular, and not well Apparet defined ; so that it was difficult to have such a distinct Motion view of any of them as to be certain that it was the 01 th same spot which was seen again in any subsequent ob- Heaverr servation j and this-difficulty was increased, in the first. ° 1 ^ place, when Venus was in her inferior semicircle ; be¬ cause at that time she must be viewed through the thick vapours near the horizon ; though otherwise it was most proper, on account of her being then nearest to us. In the second place, if we would observe her at some height above those vapours, it could only be for a short time $ and thirdly, when she is low in her inferior circle, and at that time nearest the earth, the enlightened part of her is too small to discover apy motion in it. He was therefore of opinion, that he should succeed better in his observations when the pla¬ net was about its mean distance from us, showing about one half of her enlightened hemisphere 5 at which time also he could observe her for a much longer time above the gross atmospherical vapours. His first appearance of success was October 14. 1666, at three quarters past five in the evening j when he saw a bright spot (fig. 37.), but could not then view that spot long enough to draw any inference concerning the planet’s motion. He had no farther success till the 20th of April the following year ; when, about a quarter of an hour be¬ fore sunrise, he began again to perceive on the disk of Venus, now about half enlightened, a bright part near the section, distant from the southern horn a little more than a fourth part of the diameter of the disk, and near the eastern edge. He took notice also of a darkish oblong spot nearer to the northern than the southern horn : at sunrise the bright part was advanced farther from the southern horn than when he first observed it; I4? but though he was pleased to find that he had now a Sp0ts ,c‘‘ convincing proof of the planet’s motion, he was sur-tomove prised that the spots moved from south to north in thefr°m s°ut lower part ol the disk, and from north to south in thetonort^’ upper part 5 a kind of motion of which we have no ex¬ ample except in the librations of the moon. This, how¬ ever, was occasioned by the situation of the planet’s axis. Cassini expected to have found the rotation of Venus similar to that of Jupiter and Mars, both of which have their axis perpendicular to their respective orbits, and turn round according to the order of the signs; so that in each of them the motion of the inferior half of their respective globe, or that part next the sun, is from east to west * in the superior half from west to east 3 but in Venus, whose axis is inclined 75 degrees towards her orbit, the coincidence is so near, that one half of her disk appears to move from south to north, the other from north to south. On the 21st of April, at sunrise, the bright part parlieuJai was a good way off the section, and about a fourth account« part of the diameter distant from the southern horn. lhe appea When the sun was eight degrees six minutes high, jtaRcesoft! seemed to be got beyond the centre, and was cutp^.31^ through by the section. At the time the sun was seven time”, degrees high, the section cut it in the middle, which showed its motion to have some inclination towards the centre. May 9. a little before sunrise, the bright spot was seen near the centre, a little to the northward, with two obscure ones situated between the section and the circumference, at a distance from each other, equal ta that rt Part II. A S T R 144 'assini’s 145 Apparent that of each of them from the nearest angular point or Motions horn of the planet. The weather being at that time ,a . oftlie clear, he observed for an hour and half a quarter the odie' y raot‘oa tlie bright spot, which seemed to he exactly from south to north, without any sensible declination to east or west. A variation was at the same time percei¬ ved in the darkish spot, too great to be ascribed to any optical cause. The bright spot was also seen on the 10 and 13th days of May before sunrise between the northern horn and the centre, and the same irregular change of darkish spots was taken notice of; but as the planet removed to a greater distance from the earth, it became more difficult to observe these appearances. The above phenomena are represented as they occurred, in fig. 19. to 25. But though, from the appearances just now related, •oncernin^ ^ ^assini was of opinion that Venus revolved on her he revolu- axis, he was by no means so positive in this matter as ion of Ve-with regard to Mars and Jupiter. “ The spots on ms on her these (says he) I could attentively observe for a whole ais' night, when the planets were in opposition to the sun : I could see them return to the same situation, and con- sider their motion during some hours, and judge whe¬ ther they were the same spots or not, and what time ... they took in turning round: but it was not the same )lffic“Hies with the spots of Venus ; for they can be observed on- hese ob? ^ ^or 80 s*lort a t‘me’ tllHt ^ much more difficult to ervations. know with certainty when they return into the same situation. I can, however, supposing that the bright spot which I observed on Venus, and particularly this year, was the same, say that she finishes her motion, whether of rotation or libration, in less than a day ; so that, in 23 days nearly, the spot comes into the same situation on nearly the same hour of the day, though not without some irregularity. Now (supposing the bright spot observed to be always the same) whether this motion is an entire turning round, or only a libration, is what I dare not positively affirm.” In 1669, M. Cassini again observed Venus through a telescope, but could not then perceive any spots up¬ on her surface ; the reason of which Du Hamel con¬ jectures to have been the fluctuation of the vapours near the horizon, which prevented them from being 146 visible. However, we hear nothing more of any spots lanchini’* being seen on her disk till the year 1726; when, on jpserva- tije 0f February, Bianchini, with some of Cam- pani’s telescopes of 90 and 100 Roman palms, began to observe the planet at the altitude of 40° above the horizon, and continued his observation till, by the motion of several spots, he determined the position of her axis to be inclined as above mentioned, that the north pole pointed at a circle of latitude drawn through the 20th degree of Aquarius, elevated 150 or 20° abo ve the orbit of Venus. He delineated also the figures of several spots which he supposed to be seas, and com¬ plimented the king of Portugal and some other great men by calling-them by their names. Though none of Bianchini’s observations were continued long enough to know whether the spots, at the end of the period assigned for the rotation of the planet, would have been in a different situation from what they were at the beginning of it; yet, from observations of two and of four days, he concluded the motion of the spots to be at the rate of 130 per day; at which advance the planet must turn round either once in 24 days or 142 / tie iieeM ove 1 soul irtb. oils. O N O M Y. 53 in 23 hours; but without farther observation it could Apparent not be determined which of the two was the period of Motions revolution : for if an observer should at a particular ot the hour, suppose seven in the evening, mark exactly the place of a spot, and at the same hour next evening . ‘ , find the spot advanced 150, he Would not be able to 147 determine whether the spot bad advanced only 150, or Doubts had gone once quite round with the addition of j concerning more in part of another rotation. Mr Bianchini, how-^ ever, supposes Venus to revolve in 24 days eight hours; in revol- the principal proof adduced for which is an observation ving- round of three spots, ABC, being situated as in fig. 26. when ^C1 ax*s* they were viewed by himself, and several persons of di¬ stinction, for about an hour, during which they could not perceive any change of place. The planet being then hid behind the Barbarini palace, they could not have another view of her till three hours after, when the spots still appeared unmoved. “ Now (says Mr Bian¬ chini) if her rotation were so swift as to go round in 23 hours, in this second view, three hours after the former, the spots must have advanced near 50 degrees ; so that the spot C would have been gone off at li, the spot B would have succeeded into the place of C, the spot A into the place of B, and there would have been no more but two spots, A and B, to have been seen.” . 0 „ . . 1 . t 148 Cassini, the son, in a memoir for 1732, denies the Dispute bc- conclusion of Bianchini to be certain. He says, that tween Cas- during the three hours interval, the spot C might bes*”iail4 . gone off the disk, and the spot B got into the place BIanclun1’ thereof, where, being near the edge, it would appear less than in the middle. That A, succeeding into the place of B, would appear larger than it had done near the edge, and that another spot might come into the place of A ; and there were other spots besides these three on the globe of the planet, as appears by the fi¬ gures of Bianchini himself, particularly one which would naturally come in the place of A. That if the rotation of Venus be supposed to be in 23 hours, it will agree with Bianchini’s observations, as well as with those of his father; but that, on the other supposition, the latter must be entirely rejected as erroneous : and he concludes witli telling us, that Venus had frequent¬ ly been observed in the most favourable times by Mr Maraldi and himself with excellent telescopes of 80 and 100 feet focus, without their being able to see any di¬ stinct spot upon her disk. “ Perhaps (says Dr Long) those seen by Bianchini had disappeared, or the air in I ranee was not clear enough ; which last might be the reason why his father could never see those spots in France which he had observed in Italy, even when he made use of the longest telescopes.” Neither of these astronomers take notice of any indentings in the curve which divides the illuminated part from the dark in the disk of Venus, though in some views of that planet by Fontana and Ricciolus, the curve is indented; and it has from thence been concluded, that the surface of the planet is mountainous like that of the moon. This had also been supposed by Burratini, already mention¬ ed ; and a late writer has observed, that, “ when the air is in a good state for observation, mountains like those of the moon may be observed with a very power¬ ful telescope.” Cassini, besides the discovery of the spots on the disk CassiaWli - of Venus, by which he was enabled to ascertain her re-covers her. volution yalelliU. . r54 Apparent volution on an axis, had also a view of her satellite or Motions moon, of which he gives the following account.— He a Yen 1 ** ^ 1 August 28th, at 15 minutes after four Bodies/ t*ie morning, looking at Venus with a telescope of 1—34 feet, I saw, at the distance of one-third of her dia¬ meter eastward, a luminous appearance, of a shape not well defined, that seemed to have the same phase with Venus, which was then gibbous on the western side. The diameter of this phenomenon was nearly equal to a fourth part of the diameter of Venus. I observed it attentively for a quarter of an hour, and having left off looking at it for four or five minutes, I saw it no more j but daylight was then advanced. I had seen a like phenomenon which resembled the phase of Venus, Jan. 25th, A. D. 1672, from 52 minutes after six in the morning to two minutes after seven, when the brightness of the twilight made it disappear. Venus was then horned \ and this phenomenon, the diameter whereof was nearly a fourth part of the diameter of Aenus, was of the same shape. It was distant from the southern horn of Venus, a diameter of the planet, on the western side. In these two observations, I was in doubt whether it was not a satellite of Venus of such a consistence as not to be very well fitted to reflect the light of the sun ; and which, in magnitude, bore near¬ ly the same proportion to Venus as the moon does to the earth, being at the same distance from the sun and the earth as Venus was, the phases whereof it resem¬ bled. Notwithstanding all the pains I took in looking for it after these two observations, and at divers other times, in order to complete so considerable a discovery, I was never able to see it. I therefore suspended my judgment of this phenomenon. If it should return of¬ ten, there will he these two epochas, which, compared with other observations, may be of use to find out the periodical time of its return, if it can be reduced to j;g any Discovered A similar observation was made by Mr Short on the also by Mr 23d of October 1740, about sunrise. He used at this Short. tjme a reflecting telescope of about 16.5 inches, which magnified between 50 and 60 times, with which he perceived a small star at about 10' distance from Ve¬ nus, as measured by the micrometer j and, putting on a magnifying power of 240 times, he found the star put on the same appearance with the planet herself. Its diameter w as somewhat less than a third of that of the primary, but its light was less vivid, though ex¬ ceedingly sharp and well defined. The same appear¬ ance continued with a magnifying power of 140 times. A line, passing through the centre of Venus and it, made an angle of 18 or 20 degrees with the equator : he saw it several times that morning for about the space of an hour, after which he lost sight of it, and could never find it again. From this time the satellite of Venus, though very frequently looked for by astronomers, could never be perceived, which made it generally believed that Cassi¬ ni and Mr Short had been mistaken j but as the tran¬ sits of the planet over the sun in 1761 and 1769 seem¬ ed to promise a greater certainty of finding it, the sa¬ tellite was very carefully looked for by almost every one who had an opportunity of seeing the transit, but generally without success. Mr Baudouin at Paris had provided a telescope of 25 feet, in order to observe the passage of the planet over the sun, and to look for its 2 Part I * satellite ; but he did not succeed either at that time or Apparer in the months of April and May following. Mr Mon- ^lotion; taigne, however, one of the members of the Society of } Limoges, had belter success. On the 3d of May Bodies. 1761, he perceived, about half an hour after nine at'—v— u night, at the distance of 20' from Venus, a small cres- I5I cent, with the horns pointing the same way as those ®jen b7P r of the planet j the diameter of the former being about ce, one-fourth of that of the latter ; and a line drawn from sit in Venus to the satellite making an angle with the verti- ^ cal of about 20° towards the south. But though he repeated this observation several times, some doubt re¬ mained whether it was not a small star. Next day he saw the same star at the same hour, distant from Venus about half a minute or a minute more than before, and making with the vertical an angle of io° below on the north side j so that the satellite seemed to have described an arc of about 30°, whereof Venus was the centre, and the radius 20'. The two following nights were hazy, so that Venus could only be seen $ but on the 7th of May, at the same hour as before, he saw the satellite again above Venus, and on the north side, at the distance of 25' or 26' upon a line which made an angle of about 450 with the vertical towards the right hand. The light of the satellite was always very weak, but it had the same phases with its primary, whether viewed together with it in the field of his telescope or by itself. The telescope was nine feet long, and mag¬ nified an object between 40 and 50 times, but had no micrometer ; so that the distances above mentioned are only from estimation. Fig. 27. represents the three observations of Mr Montaigne. \ is the planet Venus ; ZN the vertical. EC, a parallel to the ecliptic, making them an angle with the vertical of 45* ; the numbers, 3, 4, 7, mark the situations of the satellite on the respective days. Irom the figure it appears that the points 3 and 7 ■would have been diametrically opposite, had the satel¬ lite gone 150 more round the point V at the last obser¬ vation j so that in four days it went through 1550. Then, as 1550 is to four days or 96 hours, so is 360 to a fourth number, which gives 9 days 7 hours for the whole length of the synodical revolution. Hence Mr Baudouin concluded that the distance of this sa¬ tellite was about 60 of the semidiameters of Venus from its surface 5 that its orbit cut the ecliptic nearly at right angles $ had its ascending node in 22° of Vir¬ go and was in its greatest northern digression on the 7th at nine at night; and he supposed that at the tran¬ sit of the primary the satellite would be seen accompa¬ nying it. By a subsequent observation, however, on the nth of May, he corrected his calculation of the periodical time of the satellite, which he now enlarged to 12 days $ in consequence of which he found that it would not pass over the disk of the sun along with its primary, but go at the distance of above 20' from his southern limb $ though if the time of its revolution should be 15 hours longer than 12 days, it might then IS2 pass over the sun after Venus was gone off. He ima-Why this gined the reason why this satellite was so difficult tosate]flte's be observed might be, that one part of its globe was80 crusted over with spots, or otherwise unfit to reflect10 e 8e£ni the light of the sun. By comparing the periodical time of this satellite with that of our moon, he com¬ puted the quantity of matter in Venus to be nearly equal ASTRONOMY. tlfPart II. ASTRO Apparent equal to that in our earth 5 in which case it must have Motions considerable influence in changing the obliquity of the IleaTenl ec^P^c> the latitudes and longitudes of stars, &c. Bodies. It is novv known that this supposed satellite of Cassi¬ ni was merely an optical deception. *53 In the Philosophical Transactions for 1761, Mr Hirst bserva- gjves an account of his having observed an atmosphere etra rerningdieroun^ the planet Venus. The observations were made i ijfj itmosphere at Fort St George j and looking attentively at that tf Venus, part of the sun’s disk where he expected the planet would enter, he plainly perceived a faint shade or pe¬ numbra j on which he called out to his two assistants, “ ’Tis a coming!” and two or three seconds after, the first external contact took place, in the moment where¬ of all the three agreed j but he could not see the pe¬ numbra after the egress j and of the other two gentle¬ men, one had gone home, and the other had lost the planet out of the field of his telescope. Mr Dunn at Chel¬ sea saw a penumbra, or small diminution of light, that grew darker and darker for about five seconds before the internal contact preceding the egress j from whence he determines that Venus is surrounded with an at¬ mosphere of about 50 geographical miles high. His observations, he tells us, were made mith an excellent six-feet Newtonian reflector, with a magnifying power of IIO, and of 220 times ; he had a clear dark glass next his eye, and the sun’s limb appeared well defined 5 but a very narrow waterish penumbra appeared round Venus. The darkest part of the planet’s phasis was at the distance of about a sixth part of her diameter from its edge 5 from which an imperfect light increased to the centre, and illuminated round about. In the northern parts of Europe this penumbra could not be seen. Mr Wargentin, who communica¬ ted several observations of the first external contact, says, that he could not mark the time exactly, be¬ cause of the undulation of the limb of the sun j but thought it very remarkable that, at the egress, the N O M Y. 5-3- ring of a deep yellow near the place that appeared in Apparent the form of a crescent, which was much brighter at Motions the going off than coming upon the sun ; and that, du- oft5le ring the whole time the disk of Venus was upon the y sun, he saw nothing of it. The time of total ingress was instantaneous like a flash of lightning 5 but at the egress the limb of the sun began to be obscured three seconds before the interior contact. Some of the French astronomers attributed this luminous ring round Venus to the inflection of the sun’s rays, as they also do the light seen round the moon in solar eclipses $ but Mr Chappe supposes it to have been owing to the sun enlightening more than one half of the planetary globe, though he owns this cause not to be altogether suffi¬ cient. Mr Fouchy, who observed the transit at La Muette in France, perceived, during the whole time, a kind of ring round Venus, brighter than the rest of the sun, which became fainter the farther it went from the planet, but appeared more vivid in proportion as the sun was clearer. Mr Ferner, who observed at the same place, confirms the testimony of Mr Fouchy. “ During the whole time (says he) of my observing with the telescope, and the blue and green glasses, I perceived a light round about Venus, which followed her like a luminous atmosphere, more or less lively ac¬ cording as the air was more or less clear. Its extent altered in the same manner 5 nor was it well termi¬ nated, throwing out, as it were, some feeble rays on all sides.” i54 “ I am not clear (says Dr Long) as to the mean-Dr Long’s ing of the luminous circle here mentioned; whether, °P‘n‘on 011 when the whole planet was upon the sun, they saw a th(j?e obser" ring of light round it, distinct from the light of theVa UmS“ sun; or whether they mean only the light which sur¬ rounded that part of Venus that was not upon the sun.” Mr Chappe takes this and other accounts of the observations made in France in this latter sense ; and though he sometimes called the luminous part of limb of Venus that was gone off the sun showed itself the crescent that surrounded the part of the planet not with a faint light during almost the whole time of imnn tlip* cnn » r*!»-*r«- K/-* LI~ 1 £* *.i._i. i i* i emersion. Mr Bergman, who was then at the obser¬ vatory at Upsal, begins his account at the time when three-fourths of the disk of the planet was entered up¬ on that of the sun ; and he says, that the part which was not come upon the sun was visible though dark, and surrounded by a crescent of faint light, as in fig. 28.: but this appearance was much more remarkable at the egress ; for as soon as any part of the planet was got off. the sun, that part was visible with a like crescent, but brighter, fig. 29. As more of the planetary disk went off that of the sun, however, that part of the crescent which was farthest from the sun grew fainter, and vanished, until at last only the horns could be seen, as in fig. 30. The total ingress was not instan¬ taneous ; but, as two drops of water, when about to part, form a ligament between them ; so there was a dark swelling stretched out between Venus and the sun, as in fig. 31.; and when this ligament broke, the planet appeared to have got about an eighth part of her diameter from the nearest limb of the sun, fig. 32.: he saw the like appearance at going off, but not so di¬ stinct. fig. 33. Mr Chappe likewise took notice, that the part of Venus which was not upon the sun was vi¬ sible during part of the time of ingress and egress; that it was farther surrounded by a small luminous upon the sun a ring, he explains himself that he did so, because at the coming upon the sun he perceived it at one side of the planet, and on the opposite side on its going oft’: for which reason he supposed that it surrounded it on all sides. S(* fig. 34, 33. Sect. III. Of Mars. The two planets which we have just described, ap¬ pear to accompany Tthe sun like satellites, and their mean motion round the earth is the same with that lu¬ minary. The remaining planets go to all the possible angular distances from the sun. But their motions have obviously a connection with the sun’s position. Mars is of a red fiery colour, and always gives a much duller light than Venus, though sometimes he equals her in size. He is not subject to the same li¬ mitation in his motions as Mercury or Venus ; but ap¬ pears sometimes very near the sun, and sometimes at a great distance from him ; sometimes rising when the sun sets, or setting when he rises. Of this planet it is remarkable, that when he approaches any of the fixed stars, which all the planets frequently do, these stars change their colour, grow dim, and often become totally invisible, though at some little distance from the body of the planet: but Dr Herschel thinks this has been ex¬ aggerated by former astronomers.. Mars, 56 ASTRONOMY. Apparent Motions of the Heavenly Bodies. *55 Spots when first seen on Mars. Mars appears to move from west to east round the earth. The mean duration of his sidereal revolution is 686.979579 days. His motion is very unequal. Mhen we begin to perceive this planet in the morning when he begins to separate from the sun, his motion is direct and the most rapid possible. This rapidity dimi¬ nishes gradually, and the motion ceases altogether when the planet is about 1370 distant from the sun ; then his motion becomes retrograde, and increases in rapidity till he comes into opposition with the sun. ft then gra¬ dually diminishes again, and becomes nothing when Mars approaches within 1370 of the sun. Then the motion becomes direct after having been retrograde for 73 days, during which interval the planet described an arch of about 160. Continuing to approach the sun, the planet at last is lost in the evening in the rays of that luminary. All these different phenomena are re¬ newed after every opposition of Mars j but there are considerable differences both in the extent and duration of his retrogradations. Mars does not move exactly in the plane of the eclip¬ tic, but deviates from it several degrees. His apparent diameter varies exceedingly. His mean apparent dia¬ meter is 27", and it increases so much, that when the planet is in opposition, the apparent diameter is Si". Then the parallax of Mars becomes sensible, and about double that of the sun. I he disk of Mars changes its form relatively to its position with regard to the sun, and becomes oval. Its phases show that it derives its light from that luminary. 1 he spots observed on its surface have informed astrono¬ mers that it moves round its axis from west to east in 1.02733 days, and its axis is inclined to the ecliptic at an angle of about 59.7*. They were first observed in 1666 by Cassini at Bo¬ logna with a telescope of Campani about 16J feet long-, and continuing to observe them for a month, he found they came into the same situation in 24 hours and 40 minutes. The planet was observed by some astronomers at Rome with longer telescopes made by Eustachio Divini *, but they assigned to it a rotation in 13 hours only. This, however, was afterwards shown by Mr Cassini to have been a mistake, and to have arisen from their not distinguishing the opposite sides of the planet, which it seems have spots pretty much alike. He made further observations on the spots of this planet in 1670; from whence he drew' an additional confirmation of the time the planet took to revolve. The spots were again observed in subsequent oppositions; particularly for several days in 1704 by Maraldi, who took notice that they were not always well defined, and that they not only changed their shape frequently in the space between two oppositions, but even in the space of a month. Some of them, however, continued of the same form long enough to ascertain the time of the planet’s revolution. Among these there appeared this year an oblong spot, resem¬ bling one of the belts of Jupiter when broken. It did not reach quite round the body of the planet; but had, not far from the middle of it, a small protuberance to¬ wards the north, so well defined that he was thereby enabled to settle the period of its revolution at 24 hours 39 minutes ; only one minute less than what Cassini had determined it to be. See fig. 45. The near approach of Mars to the earth in 1719, Part i gave a much better opportunity of viewing him than Appare had been obtained before ; as he was then within 24° Motioi of his perihelion, and at the same time in opposition oftbe to the sun. His apparent magnitude and brightness were thus so much increased, that he was by the vul¬ gar taken for a new star. His appearance at that time, as seen by Maraldi through a telescope of 34 feet long, is represented in fig. 37. There was then a long belt that reached half way round, to the end of which ano¬ ther shorter belt was joined, forming an obtuse angle with the former, as in fig. 38. This angular point was observed on the 19th and 20th of August, at 11 hours 15 minutes, a little east of the middle of the disk ; and 37 days after, on the 25th and 26th of Sep¬ tember, returned to the same situation. This interval, divided by 36, the number of revolutions contained in it, gives 24 hours 40 minutes for the period of one re¬ volution; which was verified by another spot of a tri¬ angular shape, one angle whereof was towards the north pole, and the base towards the south, which on the 5th and 6th of August appeared as in fig. 39. and after 72 revolutions returned to the same situation on the 16th and 17th of October. The appearances of Mars, as delineated by Mr Hook, when viewed through a 36 feet telescope are represented in fig. 40. He ap¬ peared through this instrument as big as the full moon. Some of the belts of this planet are said to be parallel to his equator ; but that seen by Maraldi was very much inclined to it. ^ Besides these dark spots former astronomers took Bright notice that a segment of his globe about the south pole sPots al)0 exceeded the rest of his disk so much in brightness, that it appeared beyond them as if it were the segment of a larger globe. Maraldi informs us, that this bright spot had been taken notice of for 60 years, and was more permanent than the other spots on the planet. One part of it is brighter than the rest, and the least bright part is subject to great changes, and has some¬ times disappeared. A similar brightness about the north pole of Mars was also sometimes observed ; and these observations now confirmed by Herschel, who has viewed site jest _i5 and it will be found by placing any one of these connected circles in such a manner as to have its contents in a similar situation with the fi¬ gures rtl Pparei, lolioi! of tl« Part II. ASTRONOMY. Apparent gures in the single representation, which bears the Motions same number, that there is a sufficient resemblance be- eavtn Hearenl ^ween them ; though some allowance must undoubted- Jodiei Uodies. ^ mat^e ^or the distortions occasioned by this kind of projection. 15S With regard to the bright spots themselves, Dr Her- aases of Jnforms US) tliat tlie p0|es 0f t[ie p|anets are not neceaaodal'exact^ ‘n ^le rn'^<^e °f them, though nearly so. 57 ijd fin sabo ^59 wards some point of the heavens, between 9s 240 3^ and os 70 15'; because the change of the situation of the pole from left to right, which happened in the time the planet passed from one place to the other, is a plain indication of its having gone through the node of its axis. Next, we may also conclude, that the node must be considerably nearer the latter point of the ecliptic than the former ; for whatever be the inclination of the axis, it will be seen under equal angles at equal distances from the node. But by a trigono¬ metrical process of solving a tew triangles, we soon dis¬ covered both the inclination of the axis, and the place where it intersects the ecliptic at rectangles (which, for want of a better term, I have perhaps improperly called its node). Accordingly I find by calculation, that the node is in 170 47' of Pisces, the north pole of Mars being directed towards that part of the heavens ; and that the inclination of the axis to the ecliptic is 590 40'. By further calculations we find that the pole of Mars on the ryth of April I777> was ^en actually 8l° 27' inclined to the ecliptic, and pointed towards the left as seen from the sun. “ The inclination and situation of the node of the axis of Mars, with respect to the ecliptic, being found, may be thus reduced to the orbit of the planet him¬ self. Let EC (fig. 66.) be a part of the ecliptic, OM part of the orbit of Mars, PEO a line drawn from P, the celestial pole of Mars, through E, that point which has been determined to be the place of Vol. III. Part I. f the node of the axis of Mars in the ecliptic, and con- Apparent tinued to O, where it intersects his orbit. Now, if, Motions according to M. de la Lande, we put the node of of’tlie the orbit of Mars for 1783 in Is 170 58', we have from IIeHve,lly isappear- $< From the appearance and disappearance (says he) of nee of the bright north polar spot in the year 1781, we col- liese spot*, lect that the circle of its motion was at some consider¬ able distance from the pole. By calculation, its lati¬ tude must have been about 76° or 770 north j for I find that, to the inhabitants of Mars, the declination of the sun, June 25th, 12I1. 15m. of our time was about 90 56' south *, and the spot must have been so far removed from the north pole as to fall a few degrees within the enlightened part of the disk to become visible to us. The south pole of Mars could not be many degrees from the centre of the large bright southern spot of the year 1781 5 though this spot was of such a magnitude as to cover all the polar regions farther than the 70th or 65th degree ; and in that part which was on the me¬ ridian, July 3d, at 10 h. 54 minutes, perhaps a little farther. “ From the appearances of the south polar spot in 1781, we may conclude that its centre was nearly po¬ lar. We find it continued visible all the time Mars revolved on his axis •, and to present us generally with a pretty equal share of the luminous appearance, a spot which covered from 450 to 6o° of a great circle on the globe of the planet, could not have any consi- rtheeK- derable polar distance. From the observations and t position calculations made concerning the poles of Mars, we Mars.0'68 may conclu(le that his north pole must be directed to- the place of the node of the axis, that is, i js 170 47', 1 ' ‘C!" . to the place of the node of the orbit, an arch EN of 6o° n'. In the triangle NEO, right-angled at E, there is also given the angle ENO, according to the same author, i° 51', which is the inclination of the orbit of Mars to the ecliptic. Hence we find the angle EON 89° 5', and the side ON 6o° 12'. Again, when Mars is in the node of its orbit N, we have by calculation the angle PNEr^0 7'; to which adding the angle ENOzri0 51', we have PNO=64° 58': from which two angles, PON and PNO, with the distance ON, we obtain the inclination of the axis of Mars, and place of its node with respect to its own orbit j the inclination being 6i° 18', and the place of the node of the axis 38° 31' preceding the intersection of the ecliptic with the orbit of Mars, or in our 190 28' of Pisces.” Our author next proceeds to show how the seasons Of the sea- in this planet may be calculated, &c. Which con-sons in jectures, though they belong properly to the next sec- Mars* tion, yet are so much connected with what has gone before, that we shall insert here what he says upon the subject. “ Being thus acquainted with what the inhabitants of Mars will call the obliquity of their ecliptic, and the situation of their equinoctial and solstitial points, we are furnished with the means of calculating the seasons on that planet, and may account, in a manner which I think highly probable, for the remarkable appearance about its polar regions. “ But first, it may not be improper to give an in¬ stance how to resolve any query concerning the Mar¬ tial seasons. Thus, let it be required to compute the declination of the sun on Mars, June 25. 1781, at midnight of our time. If tys 8 , n, 35, &c. (fig. 67), represent the ecliptic of Mars, and CY), 25, the ecliptic of out planet, A ^ B the mutual intersection of the Martial and terrestrial ecliptics ; then there is given the heliocentric longitude of Mars, m~ 9s 10 30'; then taking away six signs, and ^ ^ or CY> a—Is iyu 38', there remains b m~\* 22° 32' From this arch, with the given inclination i° 31' of the orbits to each other, we have cosine of inclination to radius, as tangent of bin to tangent of B M— Is 22° 33'. And taking away B jo 29', which is the complement to y? B (or 25 A, already shown to be Is 28° 3I0> there will remain Ti Mrr: 0s 21° 4', the place of Mars in its own orbit; that is, on the time above mentioned, the sun’s longitude on Mars will be 6s 2i° 4'; and the obliquity of the Martial ecliptic, 28° 42', being also given, we find, by the usual method, the sun’s declination 90 c6' south. “ The analogy between Mars and the earth is per- Consider- haps by far the greatest in the whole solar system, able reserra- 7 heir diurnal motion is nearly the same ; the obliqui- Mance be- ty of their respective ecliptics not very different : 0f tvv*xl t^le all the superior planets, the distance of Mars from the aB<1 sun is by far the nearest alike to that of the earth ; H,S’ nor will the length of the Martial year appear very II different 58 ASTRONOMY. Part II. Apparent Motions of the Heavenly Bodies. i6i White spots about the poles of Mars, sup¬ posed to be occasioned by snow. 163 Of the spheroidical form of Mars. 164 Difference between the equato¬ rial and po¬ lar diame¬ ter of Mars, different from what \ye enjoy, when compared to the surprising duration of the years of Jupiter, Saturn, and the Georgium Sidus. It we then find that the globe we inhabit has its polar region frozen and co¬ vered with mountains of ice and snow that only partly melt when alternately exposed to the sun, I may well be permitted to surmise, that the same causes may pro¬ bably have the same effect on the globe of Mars ; that the bright polar spots are owing to the vivid reflection of light from frozen regions j and that the reduction of those spots is to be ascribed to their being exposed to the sun. In the year lySt, the south polar spot was extremely large, which we might well expect, as that pole had but lately been involved in a whole twelve¬ month’s darkness and absence of the sun $ but in I7^3> I found it considerably smaller than before, and it de¬ creased continually from the 20tb of May till about the middle of September, when it seemed to be at a stand. During this last period the south pole had already been above eight months enjoying the benefit of summer, and still continued to receive the sun-beams, though, towards the latter end, in such an oblique direction as to be but little benefited by them. On the other hand, in the year 1781, the north polar spot, which had then been its twelvemonth in the sunshine, and was but lately re¬ turning into darkness, appeared small, though undoubt¬ edly increasing in size. Its not being visible in the year 1783, is no objection to these phenomena, being owing to the position of the axis, by which it was re¬ moved out of sight. “ That a planetary globe, such as Mars, turning on an axis, should be of a spheroidical form, will easily find admittance, when two familiar instances in Jupiter and the earth, as well as the known laws of gravitation and the centrifugal force of rotatory bodies, lead the way to the reception of such doctrines. 80 far from creating difficulties, or doubts, it will rather appear singular, that the spheroidical form of this planet has not al¬ ready been noticed by former astronomers j and yet, reflecting on the general appearance of Mars, we soon find, that oppoi'tunities of making observations on its real form cannot be very frequent: for when it is near enough to view it to an advantage, we see it generally • gibbous, and its appositions are so scarce, and of so short a duration, that in more than two years time, we have not above three or four weeks for such observa¬ tions. Besides, astronomers being generally accustom¬ ed to see this planet distorted, the spheroidical form might easily be overlooked. “ September 25. 1783. At ph. 50 m. the equatorial diameter of Mars measured 2i'/ 53w j the polar diame¬ ter 21" \ full measure; that is, certainly not too small. This difference of the diameters was shown, on the 28th of the same month, to Mr Wilson of Glasgow, who saw it perfectly well, so as to he convinced that it was not owing to any defect or distortion occasioned by the lens; and because I wished him to be satisfied of the reality of the appearance, I reminded him of several precautions j such as causing the planet to pass directly through the centre of the field of view, and judging of its figure when it was most distinct and best defined, &c. Next day the difference between the two diameters was shown to Dr Blagden and Mr Au- bert. The former not only saw it immediately, but thought the flattening almost as much as that of Jupi¬ ter. Mr Aubert also saw it very plainly, so as to en- Apparent tertain no manner of doubt about the appearance. Motions “ September 30th, loh. 52m. the equatorial diame- oi liHS ter was 22" 9'", with a magnifying power of 278. By a second measure it was 22// 31"', full large *, the polar diameter, very exact, was 21" 26". On the first of October, at loh. 50m. the equatorial diameter measured 103 by the micrometer j and the polar 98; the value of the divisions in seconds and thirds not being well determined, on account of some changes lately made in the focal length of the object metals of the tele¬ scope. On the 13th, the equatorial diameter was ex¬ actly 22" 3 s'": the polar diameter 21" 35/".” In a great number of succeeding observations, the same ap¬ pearance occurred j but on account of the quick changes in the appearance of this planet, Dr Herschel thought proper to settle the proportion betwixt the equatorial and polar diameters from those which were made on the very day of the apposition, and which were also to be preferred on account of their being repeated with a very high power, and in a fine clear air, with two different instruments of an excellent quality. From these he de¬ termined the proportions to be as 103 to 98, or 1355 to 1272. 165 It lias been commonly related by astronomers, that Of the at- the atmosphere of this planet is possessed of such strong mosPllere refractive powers, as to render the small fixed stars near which it passes invisible. Dr Smith relates an ob¬ servation of Cassini, where a star in the water of xYqua- rius at the distance of six minutes from the disk of Mars, became so faint before its occultation, that it could not be seen by the naked eye, nor with a three- feet telescope. This would indicate an atmosphere of a very extraordinary size and density : but the follow¬ ing observations of Dr Herschel seem to show that it is of much smaller dimensions. “ 1783, Oct. 26th. There are two small stars preceding Mars, of difterent sizes ; with 460 they appear both dusky red, and are pretty unequal; with 218 they appear considerably unequal. The distance from Mars of the nearest, which is also the largest, with 227 measured 3' 26" 20,,,. Some time after, the same evening, the distance was 3' 8" 55"', Mars being retrograde. Both of them were seen very distinctly. They were viewed with a new 20 feet reflector, and appeared very bright. Oc¬ tober 27th, the small star is not quite so bright in pro¬ portion to the large one as it was last night, being a good deal nearer to Mars, which is now on the side of the small star-, but when the planet was drawn aside, or out of view, it appeared as plainly as usual. The di¬ stance of the small star was 2' 5" sy"7. The largest of the two stars (adds he), on which the above obser¬ vations were made, cannot exceed the I2tb, and the smallest the 13th or 14th magnitude *, and I have no reason to suppose that they were any otherwise affected by the approach of Mars, than what the brightness of its superior light may account for. From other pheno¬ mena it appears, however, that this planet is not without a considerable atmosphere j for besides the permanent spots on its surface, I have often noticed occasional changes of partial bright belts, and also once a darkish one in a pretty high latitude ; and these alterations we can hardly ascribe to any other cause than the variable disposition of clouds and vapours floating in the atmo¬ sphere of the planet.” Sect. Part II. A S T Pt O AppwrcRt Motions of the Heavenly Bodies. Sect. IV. Of Jupiter. \66 Belts of Jii- rered. pear ja. them. 168 Account of N O M Y. disappeared, thougl 59 Jupiter is the brightest of all the planets except Venus. lie moves from west to east in a period of 4332.602208 days, exhibiting irregularities similar to those of Mars. Before he comes into opposition, and when distant from the sun about 1150, his motion be¬ comes retrograde, and increases in swiftness till he comes into opposition. The motion then becomes gradually slower, and becomes direct when the planet advances within 1150 of the sun. The duration of the retrograde motion is about 1 21 days, and the arch of retrogradation described is about io°. But there is a considerable dif¬ ference both in the amount and in the duration of this retrograde motion. Jupiter has the same general appearance with Mars, piter when only that the belts on his surface are much larger and fust disco- more permanent. Their general appearance, as described by Dr Bong, is represented fig. 68—71.; but they are not to be seen but by an excellent telescope. They are said to have been first discovered by Fontana and two other Italians ; but Cassini was the first who gave a good account of them. Their number is very variable, as sometimes only one, and at others no fewer than eight, may be perceived. They are generally parallel to one another, but not always so j and their breadth is likewise variable, one belt having been observed to grow' narrow, while another in its neighbourhood has increased in breadth, as if the one had flowed into the other: and in this case Dr Long observes, that a part of an oblique belt lay between them, as if to form a communication for this purpose. The time of their continuance is very uncertain, sometimes remaining unchanged for three months; at others, new belts Spots some-have been formed in an hour or two. In some of times ap- these belts large black spots have appeared, which moved swiftly over the disk from east to west, and returned in a short time to the same place j from whence the rotation of this planet about its axis has been determined. On the 9th of May 1664, Dr Hook, with a good 12 feet telescope, observed a small spot in the biggqst of the three obscure belts of Jupiter 5 and observing it from time to time, found that in two hours it had moved from east to west about half the visible diameter of the planet. In 1665, Cassini observed a spot near the largest belt of Jupiter which is most fre¬ quently seen. It appeared round, and moved with the greatest velocity when in the middle, but appeared narrower, and moved slower, the nearer it was to the circumference. “ These circumstances (says Dr Long) showed that the spot adhered to the body of Jupiter, and was carried round upon it. It continued there¬ on till the year following •, long enough to determine the periodical time of Jupiter’s rotation upon his axis to be 9 h. 56 m.” This principal, or ancient spot one of theseas‘s called, is the largest, and of the longest con- spots. tinuance of any hitherto known, and has appeared and vanished no fewer than eight times between the years 1665 and 1708 j from the year last mentioned it was invisible till 17x3. The longest time of its con¬ tinuing to be visible was three years ; and the longest time of its disappearing was fyom 1708 to 1713 : it seems to have some connection with the principal sou¬ thern belt j for the spot has never been seen when that 1 that belt has often been visible Apparent without that spot. Besides this ancient spot, Cassini, Motions in the year 1669, saw one of less stability that did not ot ^ie continue of the same shape or dimensions, but broke into several small ones, whereof the revolution was but < v~— 9 h. 51 m. ; and two other spots that revolved in 9 h. 52^-m. The figure of Jupiter is evidently an oblate spheroid, the longest diameter of his disk being to the shortest as 13 to 12. His rotation is from west to east, like that of the sun, and the plane of his equator is i()C> very nearly coincident with that of his orbit; so that No differ- there can scarcely be any difference of seasons in that ence.°*sea* planet. His rotation has been observed to be some- sons in Ju¬ piter. what quicker in his aphelion than his perihelion. The axis of rotation is nearly perpendicular to the plane of the ecliptic, and the planet makes one revolution in 0.41377 day, or about 9 h. 33' and 37'/. The changes in the appearance of these spots, and the difference in the time of their rotation, make it probable that they do not adhere to Jupiter, but are clouds transported by the winds with different velocities in an atmosphere subject to violent agitations. The apparent diameter of this planet is a maximum during his opposition to the sun, it is then equal to about 46" j when in conjunction it is smaller, being only about 3 x" : his mean apparent diameter is equal to 36". 170 Four little stars are observed around Jupiter, which Is attended constantly accompany him. Their relative situation by f°UF is continually changing. They oscillate on both sidesmoolls;' of the planet, and their relative rank is determined by the length of these oscillations. That one in which the oscillation is shortest is called the first satellite, and so on. These satellites are analogous to our moon. See fig. 18. and 186. They are all supposed to move in ellipses j though the eccentricities of all of them are too small to be measured, excepting that of the fourth j and even this amounts to no more than 0.007 of its mean distance from the primary. The orbits of these planets were thought by Galileo to be in the same plane with that of their primary : but Mr Cassini has found that their orbits make a small angle with it ; and, as he did not find any difference in the place of their nodes, he concluded that they were all in the same place, and that their ascending nodes were in the middle of Aquarius. After observing them for more than 36 years, he found their greatest latitude, or deviation from the plane of Jupiter’s orbit, to be 2° 55'. The first of these Distances satellites revolves at the distance of 5.697 of Jupiter’s a?d Pei'J°- semidiameters, or l' 51" as measured by proper instru-t/'ne,s mentsj its periodical time is 1 d. x8 h. 27' 34,/. The^100l^tcl ’ next satellite revolves at the distance of 9.017 semidia¬ meters, or 2' 56", in 3d. 13 h. 1^' 43,/; the third at the distance of 14.384 semidiameters, or 4' 42,/, in 7 d. 3 h. 42' 36"; and the fourth at the distance of 25.266, or 8' 16", in 16 d. 16 h. 32' 09". Since the time of Cassini it has been found that the nodes of Jupiter’s satellites are not in the same place ; and from the different points of view in which we have an opportunity of observing them from the earth, we see them sometimes apparently moving in straight lines, and at other times in elliptic curves. All of them, by reason of their immense distance, seem to keep near their primary, and their apparent motion is a kind of oscillation like that of a pendulum, going alternate- H 2 ly 6d ASTRONOMY. Apparent Motions of the Heavenly Uodies. Occult a- tions and eclipses of Jupiter’s satellites. '73 The satel¬ lites.some¬ times ap¬ pear as dark spots. l74 Why they vary in their light and appa¬ rent mag¬ nitude. ly from their greatest distance on one side to the greatest distance on the other, sometimes in a straight line, and sometimes in an elliptic curve. When a sa¬ tellite is in its superior semicircle, or that half of its • orbit which is more distant from the earth than Jupi¬ ter is, its motion appears to us direct, according to the order of the signs ; but in its inferior semicircle, when it is nearer to us than Jupiter, its motion ap¬ pears retrograde ; and both these motions seem quicker the nearer the satellites are to the centre of the prima¬ ry, slower the more distant they are, and at the greatest distance of all they appear for a short time to be sta¬ tionary. Jrom this account of the system of Jupiter and his satellites, it is evident, that occultations of them must frequently happen by their going behind their primary, or by coming in betwixt us and it. The former takes place when they proceed towards the middle of their up¬ per semicircle j the latter, when they pass through the same part of their inferior semicircle. Occultations of the former kind happen to the first and second satellite; at every revolution, the third very rarely escapes an oc- cultation, but the fourth more frequently by reason of its greater distance. It is seldom that a satellite can be discovered upon the disk of Jupiter, even by the best telescopes, excepting at its first entrance, when by rea¬ son of its being more directly illuminated by the rays ot the sun than the planet itself, it appears like a lucid spot upon it. Sometimes, however, a satellite in pas¬ sing over the disk, appears like a dark spot, and is easily to be distinguished. This is supposed to be ow¬ ing to spots on the body of these secondary planets; and it is remarkable, that the same satellite has been known to pass over the disk at one time as a dark spot, and at another so luminous that it could not he distin¬ guished from Jupiter himself, except at its coming on and going off. To account for this, we must say, that either the spots are subject to change ; or if they be permanent like those of our moon, that the satellites at different times turn different parts of their globes to¬ wards us. Possibly both these causes may contribute to produce the phenomena just mentioned. For these reasons also both the light and apparent magnitude of the satellites are variable ; for the fewer spots there are upon that side which is turned towards us, the brighter it will appear; and as the bright side only can be seen, a satellite must appear larger the more of its bright side it turns towards the earth, and the less so the more it happens to be covered with spots. The fourth satellite, though generally the smallest, sometimes ap¬ pears bigger than any of the rest: the third sometimes seems least, though usually the largest; nay, a satellite may be so covered with spots as to appear less than its shadow passing over the disk of the primary, though we are certain that the shadow must he smaller than the body which casts it. To a spectator placed on the surface of Jupiter, each of these satellites would put on the phases of the moon ; but as the distance *of any ot them from Jupiter is but small when compared with the distance of that planet from the sun, the satellites are therefore illuminated by the sun very nearly in the same manner with the primary itself; hence they ap¬ pear to us always round, having constantly the greatest part of their enlightened half turned towards the earth : stud indeed they are so small, that were they to put on 5 Part I] the phases of the moon, these phases could scarce be Apparem discerned through the best telescopes. Motions When the satellites pass through their inferior semi- the circles, they may cast a shadow upon their primary, * and thus cause an eclipse of the sun to his inhabitants - 0^lL*‘ if there are any; and in some situations this shadow 175 may be observed going before or following the satel- Their sha lite. On the other hand, in passing through their ^.ows som<; superior semicircles, the satellites may be eclipsed in ble on'thj! the same manner as our moon by passing through the disk of J11 shadow of Jupiter: and this is actually the case withpiter. the first, second, and third of these bodies ; but the , 176 fourth, by reason of the largeness of its orbit, passes sometimes above or below the shadow, as is the case moons1 * with our moon. The beginnings and endings of these eclipsed in eclipses are easily seen by a telescope when the earth ev near the apposition, only the immersions of the satel- lites into his shadow, or the beginnings of the eclipses, tellites are are visible ; at the apposition, only the occultations of visible, the satellites, by going behind or coming before their primary, are observable ; and from the apposition to the conjunction, only the emersions, or end of the eclipses, are to be seen. This is exactly true in the first satellite, of which we can never see an immersion with its immediately subsequent emersion: and it is hut rarely that they can be both seen in the second; as in order to their being so, that satellite must be near one of its limits, at the same time that the planet is near his perihelion and quadrature with the sun. With re¬ gard to the third, when Jupiter is more than 46 de¬ grees from conjunction with, or apposition to, the sun, both its immersions and immediately subsequent emer¬ sions are visible ; as they likewise are in the fourth, when the distance of Jupiter from conjunction or ap¬ position is 24 degrees. When Jupiter is in quadrature with the sun, the eaith is farthest out of the line that passes through the centres ol the sun and Jupiter, and therefore the shadow of the planet is then most exposed to our view: but even then the body of the planet will hide from us one side of that part of the shadow which is nearest to it, through which the first satellite passes; which is the reason that though we see the entrance of that satellite into the shadow, or its coming out from thence, as the earth is situated on the east or west side thereof, we cannot see them both ; whereas the other satellites going through the shadow at a greater distance from Jupiter, their ingress anil- egress are both visible. Sect. V. 0/' Saturn. Saturn is likewise a very conspicuous planet, though not so brilliant as Jupiter. The period of his sidereal revolution round the earth, is 10759.077213 days. He moves from west to east nearly in the plane of the ecliptic, and exhibits irregularities similar to those of Jupiter and Mars. He becomes retrograde both before and after his opposition, when at the distance of about n r* .1 -w-T • 109" from the sun. His retrograde motion continues about 139 days, and during its continuance he describes. an in Part II. Jare"i Apparent a,l0“! Motions fll>e of the wtnlj Heavenly xlies. bodies. '75 I78 rsia. Telescopic one on each sj(ie of a large one ; and he published his ' .AngaraTIPP. • tt .• . . SOffit, s Vlli. »n tin ofJ«. [;6 e of tr’i is sed in ’ rcTo. i. I1 hat the ses, ot. tiom, )fJu. s sa- :sare e. 179 li* ring rst disco- ered by luygens. ASTRO an arc of about 6®. Mis diameter is a maximum at iiis opposition, and his mean apparent diameter is 18". Saturn, when viewed through a good telescope, makes a more remarkable appearance than any of the other planets. Galileo first discovered his uncommon shape, which he thought to be like two small globe N O M Y. 61 the plane of it. When it appears double, the ring Apparent 'Eum.06 (liscovery in a Latin sentence : the meaning of which was, that he had seen him appear with three bodies 5 though, in order to keep the discovery a secret, the letters were transposed. Having viewed him for two years, he was surprised to see him become quite round without these appendages, and then after some time to assume them as before. These adjoining globes were what are now called the ansce of his ring, the true shape of which was first discovered by Huygens about 40 years after Galileo, first with a telescope of 12 feet, and then with one of 23 feet, which magnified objects 100 times. From the discoveries made by him and other astronomers, it appears that this planet is sur¬ rounded by a broad thin ring, the edge of which re¬ flects little or none of the sun’s light to us, but the planes of the ring reflect the light in the same manner that the planet itself does j and if we suppose the dia¬ meter of Saturn to be divided into three equal parts, the diameter of the ring is about seven of these parts. The ring is detached from the body of Saturn in such a manner, that the distance between the innermost part of the ring and the body is equal to its breadth. If we had a view of the planet and his ring, with our eyes, per¬ pendicular to one ot the planes of the latter, we should see them as in fig. '72.: but our eye is never so much ele¬ vated above either plane as to have the visual ray stand at right angles to it, nor indeed is it ever elevated more than about 30 degrees above it; so that the ring, be¬ ing commonly viewed at an oblique angle, appears of an oval form, and through very good telescopes double, as represented fig. 73. and 74. Both the outward and inward rim is projected into an ellipsis, more or less oblong according to the different degrees of obli¬ quity with which it is viewed. Sometimes our eye is in the plane of the ring, and then it becomes invisible; either because the outward edge is not fitted to reflect the sun’s light, or more probably because it is too thin to be seen at such a distance. As the plane of this ring keeps always parallel to itself, that is, its situation in one part of the orbit is alwavs parallel to that in any other part, it disappears twice in every revolution of the planet, that is, about once in 13 years ; and he some¬ times appeals quite round for nine months together. At other times, the distance betwixt the body of the planet and the ring is very perceptible ; insomuch that Mr W luston tells us of Dr Clarke’s father having seen a star through the opening, and supposed him to have been the only person who ever saw a sight so rare, ns the opening, though certainly very large, appears very small to us. When Saturn appears round, if our eye he in the plane of the ring, it will appear as a dark hue across the middle of the planet’s disk; and if our eye be elevated above the plane of the ring, a shadowy belt will be visible, caused by the shadow of the ring as well as by the interposition of part of it betwixt the eye and the planet. The shadow of the ring is broad¬ est when the sun is most elevated, but its obscure parts appear broadest when our eye is most elevated above J _ I £ - . 7 ft next the body of the planet appears brightest ; when Motions the ring appears of an elliptical form, the parts about of tlw the ends of the largest axis are called the ansce, as lias been already mentioned. These, a little before and . after the disappearing of the ring, are of unequal mag¬ nitude: the largest ansa is longer visible before the pla¬ net’s round phase, and appeal's again sooner, than the jSq other. On the first of October 17x4, the largest ansa Ring of Sa- was on the east side, and on the 12th on the west sidetum Pr°- ol the disk ot the planet, which makes it probable that kas a the ring has a rotation round an axis. Herschel has on™ ” axis, demonstrated, that it revolves in its own plane in 10 hours 32' 15.4". The observations of this philosopher have added greatly to our knowledge of Saturn’s ring. According to him there is one single, dark, considera¬ bly broad line, belt, or zone, which he has constant¬ ly found on the north side of the ring. As this dark belt is subject to no change whatever, it is probably owing to some permanent construction of the surface of the ring: this construction cannot be owing to the sha¬ dow of a chain of mountains, since it is visible all round on the ring ; for there could be no shade at the ends of the ring : a similar argument will apply against the opinion of very extended caverns. It is pretty evident that this dark zone is contained between two concentric circles ; for all the phenomena correspond with the projection of such a zone. The nature of the ring Hr Herschel thinks no less solid than that of Sa¬ turn itself, and it is observed to cast a strong shadow upon the planet. The light of the ring is also gene¬ rally brighter than that of the planet; for the ring ap¬ pears sufficiently bright when the telescope affords scarcely light enough for Saturn. The doctor concludes that the edge of the ring is not flat, hut spherical or speroidical. The dimensions of the ring, or of the two rings with the space between them, Hr Herschel gives as below : , Miles. Inner diameter of smaller ring I46345 Outside diam. of ditto 184393 Inner diam. of larger ring 190248 Outside diam. of ditto 204883 Breadth of the inner ring 20000 Breadth of the outer ring 7200 Breadth of the vacant space, or dark zone 1 here have been various conjectures relative to the nature of this ring. Some persons have ima¬ gined that the diameter of the planet Saturn was once equal to the present diameter of the outer rint>>, and that it was hollow; the present body bein^ con¬ tained within the former surface, in like manner as a kernel is contained within its shell: they suppose that, in consequence of some concussion, or other cause, the outer shell all fell down to the inner body, and left only the ring at the greater distance from the centre, as we now perceive it. This conjecture is in some measure corroborated by the consideration, that both the planet and its ring perform their rotations about the same common axis, and in very nearly the same time. But from the observations of Hr Herschel he thus concludes : “ It does not appear to me that there is sufficient ground for admitting the ring of Saturn to be of a very changeable nature, and I guess that its phenomena will hereafter be so fully explained, as to reconcile- 62 Apparent Motions ot the Heavenly Bodies. 1S1 His seven satellites. reconcile all observations. withhold a final judgment of its construction, till we can have more observations. Its division, however, into two very unequal parts, can admit of no doubt.” ' The diameters of Saturn are not equal: that which is perpendicular to the plane of his ring appears less by one-eleventh than the diameter situated in that plane. If we compare this form with that of Jupiter, we have reason to conclude that Saturn turns rapidly round his shorter axis, and that the ring moves in the plane of his equator. Herscbel has confirmed this opinion by actual observation. He has ascertained the duration of a re¬ volution of Saturn round his axis to amount to 0.428 day. Huygens observed five belts upon this planet nearly parallel to the equator. Saturn is still better attended than Jupiter^see fig. 18. and 186.) j having, besides the ring above-mentioned, no fewer than seven moons continually circulating round him. Hie first, at the distance of 2.097 semidiameters of his ring, and 4.893 of the planet itself, performs its revolution in 1 d. 21 h. 18' 57" j the second, at 2.686 semidiameters of the ring, and 6.268 of Saturn, re¬ volves in 2d. 17 h. 41' 22"; the third, at the di¬ stance of 8.754 semidiameters of Saturn, and 3.752 of the ring, in 4 d. 12I1. 25' 12" 5 the fourth, called the Hin/genian satellite, 'at 8.698 semidiameters of the ring, and 20.295 Saturn, revolves in 15 d. 22 h. 41' 12"; while the fifth, placed at the vast distance of 59.154 semidiameters of Saturn, or 25.348 of his ring, does not perform its revolution in less than 79 d. 7 h. 47' 00". The orbits of all these satellites, except the fifth, are nearly in the same plane, which makes an angle with the plane of Saturn’s orbit of about 31° 5 and by reason of their being inclined at such large angles, they cannot pass either across their primary or behind it with respect to the earth, except when very near their nodes 5 so that eclipses of them happen much more seldom than of the satellites of Jupiter. There is, however, an account in the Philos. Transact, of an occultation of the fourth satellite behind the body of Saturn j and there is a curious account by Cassini in the Memoirs of the Royal Academy for 1692, of a fixed star being covered by the fourth satellite, so that Fifth satel-for 13 minutes they appeared both as one star. By times°die' reason extreme smallness, these satellites cannot pears amf *,e 8een lI11^ess ^ie air be very clear; and Dorn. Cassini for several years observed the fifth satellite to grow less and less as it went through the eastern part of its or¬ bit until it became quite invisible; while in the western part it gradually became more and more bright until it arrived at its greatest splendour.—“ This phenomenon (says Dr Long) cannot be better accounted for than by supposing one half of the surface of this satellite to be unfit to reflect the light of the sun in sufficient quantity to make it visible, and that it turns round its axis nearly in the same time as it revolves round its primary; and that, by means of this rotation, and keeping always the same face toward Saturn, we upon the earth may, during one half of its periodical time, be able to see successively more and more of its bright side, and during the other half of its period have more and more of the spotted or dark side turned towards us. In the year 1705, this satellite unexpectedly became visible in all parts of its orbit through the very same 2 ASTRONOMY. Part In the meanwhile Ave must telescopes that were before often made use of to view it in the eastern part without success : this sIioavs the spots upon this satellite, like those upon Jupiter and some other of the primary planets, are not permanent, but JI^aTei subject to change.” . v ^ The two other satellites were discovered by DrHer- Apparc Motioi of th( 1S2 why. schel in 1787 and 1788. They are nearer to Saturn than any of the other five. But in order to prevent con¬ fusion, they have been called the 6th and 7th satellites. The filth satellite has been observed by Dr Herschel to turn once round its axis, exactly in the time in Avliich it revolves round Saturn. In this respect it re¬ sembles our moon. * Sect. VI. 0/' Her schel. The planets hitherto described have been known from the remotest antiquity ; but the planet Herschel, called also the Georgium Sidus, and Uranus, escaped attention of the ancient astronomers. Flamstead, th 183 Mayer, and Le Mounier had observed it as a small star; hut in 1781 Dr Herschel discovered its motion, and ascertained, it to be a planet. Like Mars, Jupi¬ ter, and Saturn, it moves from west to east round the sun. Ihe duration of its sidereal reA'olution is 30689 days. Its motion, Avbich is nearly in the plane of the ecliptic, begins to be retrograde before and after the opposition, Avhen the planet is 103.5° fr°m the sun ; its retrograde motion continues for about 151 days; and the arc of retrogradation amounts to 3.6®. If we judge of the distance of this planet by the slowness of it motions, it ought to be at the very confines of the planetary system. The apparent magnitude of this planet is so small Its satel- that it can seldom be seen Avith the naked eye. It is^tes* accompanied by six satellites : tAvo of them, which Avere discovered by Dr Herschel in 1787, revolve about that planet in periods of 8 d. 17 h. 1 m. 19. sec. and 13 d. 11 h. 5 m. 14 sec. respectively, the angular di¬ stances from the primary being 33" and 44!-" : their orbits are nearly perpendicular to the plane of the ecliptic. The history of the discovery of the other four, Avith such elements as could then be ascertained, are given in the Philosophical Transactions for 1798, Part I. The precise periods of these additional satel¬ lites cannot be ascertained without a greater number of observations than had been made when Dr Herschel sent the account of theirdiscovery to the Royal Society ; hut he gave the following estimates as the most probable which could be formed by means of the data then de¬ termined. Admitting the distance of the anterior satel¬ lite to be 25".5, its periodical revolution veill be 5 d. 21 h. 25 m. It the intermediate satellite be placed at an equal distance bettveen the two old satellites, or at 38"-57j its period Avill be 10 d. 23 h. 4 m. The nearest exterior satellite is about double the distance of the farthest old one; its periodical time Avill therefore be about 38 d. 1 h. 49 m. The most distant satellite is full four times as far from the planet as the old second satellite: it will therefore take at least 107 d. i6h. 40 m. to complete one revolution. All these satellites perform their revolutions in their orbits contrary to the order of the sigtis; that is, their real motion is retro¬ grade. Sect. A S T R Sect. VII. Of Ceres and Pallas. 'I'ljese two planets, lately discovered by Piazza and -Jf—~ ■ Olbers, two foreign astronomers, ought to have follow¬ ed Mars in the order of description, as their orbits are placed between those of Mars and Jupiter j but as they have been observed only for a very short time, we judged it more proper to reserve the account of them till we came to the words Ceres and Pallas, when the elements of their orbits will in all probability be determined with more precision than at present. They are invisible to the naked eye j and Dr Herschel has ascertained that their size is extremely small. For that reason, together with the great obliquity of their orbits, he has proposed to distinguish them from the planets, and to call them asteroids. Chap. IV. Of the Comets. The planets are not the only moving bodies visible in the heavens. There are others which appear at un¬ certain intervals, and with a very different aspect from the planets. These are very numerous, and no fewer than 450 are supposed to belong to our solar system. They are called Comets, from their having a long tail, somewhat resembling the appearance of hair. This, however, is not always the case ; for some comets have appeared which were as well defined, and as round as planets : but in general they have a luminous matter dif¬ fused around them, or projecting out from them, which to appearance very much resembles the Aurora Borea- 183 lis. When these appear, they come in a direct line to¬ wards the sun, as it they were going to fall into his body; and after having disappeared for some time in con¬ sequence of their proximity to that luminary, they fly off again on the other side as fast as they came, project¬ ing a tail much greater and brighter in their recess from him than when they advanced towards him ; but, getting daily at a farther distance from us in the hea¬ vens, tney continually lose of their splendour, and at last totally disappear. Their apparent magnitude is ve¬ ry different; sometimes they appear only of the bigness of the fixed stars ; at other times they will equal the diameter of \ enus, and sometimes even of the sun or moon. So, in 1652, Hevelius observed a comet which seemed not inferior to the moon in size, though it had not so bright a splendour, but appeared with a pale and dun light, and had a dismal aspect. These bodies will also sometimes lose their splendour suddenly, while their apparent bulk remains unaltered. With respect to their apparent motions, they have all the inequalities of the planets ; sometimes seeming to go forwards, sometimes backwards, and sometimes to be stationary. T. he comets, viewed thi’ough a telescope, have a very different appearance from any of the planets. The nu¬ cleus, or star, seems much more dim. Sturmius tells us, that observing the comet of 1680 with a telescope, it appeared like a coal dimly glowing ; or a rude mass of matter illuminated with a dusky fumid light, less sen¬ sible at the extremes than in the middle; and not at all like a stai, which appears with around disk and a vivid light. Hevelius observed of the comet in 1661, that its lit ar til. ilotioiis of the eavenly If O N O M Y._ 63 body was of a yellowish colour, bright and conspicuous, Apparent but without any glittering light. Jn the middle was a Motions dense ruddy nucleus, almost equal to Jupiter, encom- of tlle passed with a much fainter thinner matter.—February 5th. I he nucleus was somewhat bigger and brighter, > ^ ' ^ . of a gold colour, but its light more dusky than the rest of the stars; it appeared also divided into a number of parts.—I'eb. 6th. 1 he nuclei still appeared, though less than before. One of them on the left side of the lower part of the disk appeared to be much denser and brighter than the rest; its body round, and representing a little lucid star ; the nuclei still encompassed with another kind of matter.—Feb. 10th. The nuclei more obscure and confused, but brighter at top than at bot¬ tom.—l(eb. 13th. The head diminished much both in brightness and in magnitude.—March 2d. Its round¬ ness a little impaired, and the edges lacerated.—March 28th. Its matter much dispersed; and no distinct nu¬ cleus at all appearing. Wiegelius, who saw through a telescope the comet of 1664, tbe moon, and a little cloud illuminated by the sun, at the same time, observed that the moon ap¬ peared of a continued luminous surface, but the comet very different, being perfectly like the little cloud en¬ lightened by the sun’s beams. The comets, too, are to appearance surrounded with At.no- atmospheres of a prodigious size, often rising ten times 8Pheres and higher than the nucleus. They have often likewise dif-phases of ferent phases, like the moon. comets. “ The head of a comet (says Dr Long) to the eye, Dr Dong’s unassisted by glasses, appears sometimes like a cloudy account of star ; sometimes shines with a dull light like that of thethem* planet Saturn : some comets have been said to equal, some to exceed, stars of the first magnitude ; some to have surpassed Jupiter, and even Venus ; and to have cast a shadow as Venus sometimes does. “ The head of a comet, seen through a good tele¬ scope, appears to consist of a solid globe, and an at¬ mosphere that surrounds it. The solid part is fre¬ quently called the nucleus ; which through a telescope is easily distinguished from the atmosphere or hairy ap¬ pearance. “ A comet is generally attended with a blaze or tail, whereby it is distinguished from a star or planet; as it is also by its motion. Sometimes the tail only of a co¬ met has been visible at a place where the head has been all the while under the horizon ; such an appearance is called a beam. lg(5 “ The nucleus of the comet of 1618 is said, a fewAPPear»n- days after coming into view, to have broken into three Ges of the or four parts of irregular figures. One observer com- j^g1 ot pares them to so many burning coals ; and says they changed their situation while he was looking at them, as when a person stirs a fire ; and a few days after were broken into a great number of smaller pieces. Another account of the same is, that on the 1st and 4th of De¬ cember, the nucleus appeared to be a round, solid, and luminous body, of a dusky lead colour, larger than any star of the first magnitude. On the 8th of the same month it was broken into three or four parts of irregu¬ lar figures; and on the 20th was changed into a cluster of small stars. “ As the tail of a comet is owing to the heat of the Pileno,ue; sun, it grows larger as the comet approaches near to, tIleli? and 64 ASTRONOMY. Apparent Motions of the Heavenly Bodies. 18S Difference between the obser¬ vations of Hevelius and Hooke, i5q Account of the comet of x6So. and shortens as it recedes from, that luminary. If the tail of a comet were to continue of the same length, it would appear longer or shorter according to the differ¬ ent views of the spectator j for if his eye be in a line j drawn through the middle of the tail lengthwise, or nearly so, the tail will not be distinguished from the rest ol the atmosphere, but the whole will appear round $ if the eye be a little out of that line, the tail will appear short as in fig. 75.; and it is called a bearded comet, when the tail hangs down towards the horizon, as in that figure. It the tail of a comet be viewed sidewise, the whole length of it is seen. It is obvious to remark, that the nearer the eye is to the tail, the greater will be the apparent length thereof. “ The tails of comets often appear bent, as in fig. 76. and 77. owing to the resistance of the aether 5 which, though extremely small, may have a sensible effect on so thin a vapour as the tails consist of. This bending is seen only when the earth is not in the plane of the orbit of the comet continued. When that plane passes through the eye of the spectator, the tail appears straight, as in fig. 78, 79. “ Longomontanus mentions a comet, that, in 1618, -Dec. 10th, had a tail above 100 degrees in length ; which shows that it must then have been very near the earth. The tail of a comet will at the same time ap¬ pear of different lengths in different places, according as the air in one place is clearer than in another. It need not be mentioned, that in the same place, the dif¬ ference in the eyes of the spectators will be the cause of their disagreeing in their estimate of the length of the tail of a comet. “ Hevelius is very particular in telling us, that he observed the comet of 1665 to cast a shadow upon the tail j for in the middle thereof there appeared a dark line. It is somewhat surprising, that Hooke should be -positive in affirming, on the contrary, that the place where the shadow of the comet should have been, if there had been any shadow, was brighter than any other part of the tail. He was of opinion that comets have some light of their own : His observations were made in a hurry ; he owns they were short and transitory. He- velius’s were made with so much care, that there is more reason to depend upon them. Dom. Cassini observed, ip the tail of the comet of 1680, a darkness in the mid¬ dle ; and the like was taken notice of by a curious ob¬ server in that of 1744. “ There are three comets, viz. of 1680, 1744, and 1759, that deserve to have a farther account given of them. The comet of 1680 was remarkable for its near approach to the sun ; so near, that in its perihelion it was not above a sixth part of the diameter of that lumi¬ nary from the surface thereof. Fig. 77. taken from Newton’s Principia, represents so much of the trajectory of this comet as it passed through while it was visible to the inhabitants of our earth, in going from and return¬ ing to its perihelion. It shows also the tail, as it ap¬ peared on the days mentioned in the figure. The tail, like that of other comets, increased in length and bright¬ ness as it came nearer to the sun ; and grew shorter and fainter as it went farther from him and from the earth, till that and the comet were too far off to be any longer visible. ‘‘ The comet of 1744 was first seen at Lausanne in Part I Appaj-en Motion of the Heaveul Bodies. Switzerland, Dec. 13. 1743, N. S. From that time it increased in brightness and magnitude as it was co¬ ming nearer to the sun. The diameter of it, when at the distance of the sun from us, measured about one minute ; which brings it out equal to three times the diameter of the earth. It came so near Mercury, that, ip0 if its attraction had been proportionable to its magni-Of that 0 tude, it was thought probable it would have disturbed I744* the motion of that planet. Mr Betts of Oxford, how¬ ever, from some observations made there, and at Lord Macclesfield’s observatory at Sherburn, found, that when the comet was at its least distance from Mercury, and almost twice as near the sun as that planet was, it was still distant from him a fifth part of the distance of the sun from the earth 5 and could therefore have no effect upon the planet’s motions. He judged the co¬ met to be at least equal in magnitude to the earth. He says, that in the evening of Jan. 23d, this comet ap¬ peared exceedingly distinct and bright, and the diame¬ ter of its nucleus nearly equal to that of Jupiter. Its tail extended above 26 degrees from its body ; and was in length, supposing the sun’s parallax 10", no less than 23 millions of miles. Dr Bevis, in the month of May 1744, made four observations of Mercury, and found the places of that planet, calculated from correct ta¬ bles, differed so little from the places observed, as to show that the comet had no influence upon Mercury’s motion. “ The nucleus, which had before been always round, on the 10th of February appeared oblong in the di¬ rection of the tail, and seemed divided into two parts, by a black stroke in the middle. One of the parts had a sort of beard brighter than the tail ; this beard was surrounded by two unequal dark strokes, that se¬ parated the beard from the hair of the comet. The odd phenomena disappeared the next day, and nothing was seen but irregular obscure spaces like smoke in the middle of the tail 5 and the head resumed its natural form. February 15th, the tail was divided into two branches ; the eastern part about seven or eight degrees long, the western 24. On the 23d, the tail began to be bent; it shewed no tail till it was as near to the sun as the orbit of Mars $ the tail grew longer as it ap¬ proached nearer the sun ; and at its greatest length was computed to equal a third part of the distance of the earth from the sun. Fig. 76. is a view of this comet, taken by an observer at Cambridge. I remember that, in viewing it, I thought the tail seemed to sparkle, or vibrate luminous particles. Hevelius mentions the like in other comets; and that their tails lengthen and short¬ en while we are viewing. This is probably owing to the motion of our air. “ The comet of 1759 did not make any consider-or I.91 able appearance by reason of the unfavourable situation C° of the earth all the time its tail might otherwise have 1759. been conspicuous; the comet being then too near the sun to be seen by us; but deserves our particular con¬ sideration, as it was the first that ever had its return foretold.” Hevelius gives pictures of comets of various shapes; as they are described by historians to have been like a sword, a buckler, a tun, &c. These are drawn by fancy only, from the description in words. He gives, however, also pictures of some comets, engraved by his rtl 'PSft! otioi 'ftllt iaveu odiet ?il 190 that 4- Part IT. y tele- ;.'opes. Apparent f1*3 °wn nand from the views he had of them through Motion* a very long and excellent telescope. In these we find of the changes in the nucleus and the atmosphere of the same Bodies/ comet• Th® nucleus of the comet of 1661, which in ■ -y— > one observation appeared as one round body, as it is represented in fig. 87. in subsequent views seemed to consist of several smaller ones separated from one ano¬ ther, as in fig. 86. The atmosphere surrounding the nucleus, at different times, varied in the extent thereof; as did also the tail in length and breadth. The nuclei of other comets, as has already been ob¬ served, have sometimes phases like the moon. Those of 1744 I7^9 both this kind of appearance. Chap. V. Of the Fixed Stars. dumber of Tke parallax of the stars is insensible. When viewed xed stars through the best telescopes, they appear not at all mag- ucreascd nified, but rather diminished in bulk ; by reason as is thought by some, that the telescope takes off that twinkling appearance they make to the naked eye ; but by others, more probably, that the telescope tube excludes a quantity of the rays of light, which are not only emitted from the particular stars themselves, but by many thousands more, which falling upon our eye¬ lids and the aerial particles about us, are reflected into our eyes so strongly as to excite vibrations, not only on those points of the retina where the images of the stars are formed, but also in other points at the same distance round about. Ibis, without the telescope, makes us ima¬ gine the stars to be much bigger than when we see them only by a few rays coming directly from them, so as to enter our eyes without being intermixed with others. The smallness of their apparent diametejr is proved by the suddenness with which they disappear on their oc- cultations by the moon. The time which they take does not amount to one second, which shows their ap¬ parent diameter not to exceed 4". The vivacity of their light, compared with their small diameter, leads us to suppose them at a much greater distance than the planets, and to consider them as luminous bodies like our sun, instead of borrowing their light from that lu- l93 minary like the planets. lilfferent -The stars, on account of their apparently various mag- |, with north latitude i° 56k These two seem to be of a di¬ stinct species from the rest, and nothing like them has appeared since. “ But between them, viz. in the year 1596, we have the first account of the wonderful star in Colit) Ceti, Apparent seen by David Fabricius on the third of August st. vet. Motions as bright as a star of the 3d magnitude, which has been since found to appear and disappear periodically ; Bodies, its period being precisely enough seven revolutions in -y—..v six years, though it returns not always with the same lustre. Nor is it ever totally extinguished, but may at all times be seen with a six feet tube. This was singu¬ lar in its kind, till that in Collo Cygni was discovered. It precedes the first star of Aries i° 40', with 150 57' south latitude. “ Another new star was first discovered by William Jansonius in the year 1600, in pectore, or rather in eductione^ Colli Cygni, which exceeded not the third magnitude. This having continued some years, became at length so small, as to be thought by some to have disappeared entirely 5 but in the years 1657, and 1659, again rose to the third magnitude 5 though soon after it decayed by degrees to the fifth or sixth magnitude, and at this day is to be seen as such in 9s 18° 38' a im* * , with 550 29' north latitude. “ A fifth new star was first seen by Hevelius in the year 1670, on July 15. st. vet. as a star of the third magnitude, but by the beginning of October was scarce to be perceived by the naked eye. In April following it was again as bright as before, or rather greater than of the third magnitude, yet wholly disappeared about the middle of August. The next year, in March 1672, it was seen again, but not exceeding the sixth magni¬ tude : since when, it has been no further visible, though we have frequently sought for its return j its place is 9s 3° 17' a iraa * , and has lat. north 470 28'. “ The sixth and last is that discovered by Mr G. Kirch in the year 1686, and its period determined to be of 404!- days j and though it rarely exceeds the fifth magnitude, yet it is .very regular in its returns, as we found in the year 1714. Since then we have watched, as the absence of the moon and clearness of the weather would permit, to catch the first beginning of its appear¬ ance in a six feet tube, that, bearing a very great aper¬ ture, discovers most minute stars. And on June 15. last, it was first perceived like one of the very least te- lescopical stars j but in the rest of that month and July, it gradually increased, so as to become in August visible to the naked eye : and so continued till the month of September. After that, it again died away by degrees : and on the 8th of December, at night, was scarcely discernible by the tube; and, as near as could be gues¬ sed, equal to what it was at its first appearance on June 25th : so that this year it has been seen in all near six months, which is but little less than half its period ; and the middle, and consequently the greatest brightness, falls about the 10th of September.” 20r Concerning the changes which happen among the Mr Mouta- fixed stars, Mr Montanere, professor of mathematics atnere’s ac- Bononia, gave the following account, in a letter to the count Royal Society, dated April 30th 1670. “ There areama^es* now wanting in the heavens two stars of the second the fixed magnitude in the stern of the ship Argo, and its yard ; stars. Bayerus marked them with the letters /3 and %. I and others observed them in the year 1664, upon the oc¬ casion of the comet that appeared that year : when they disappeared first, I know not: only I am sure that in the year 1668, upon the 10th of April, there was not the least glimpse of them to be seen j and yet the I 2 rest 68 ASTRO Apparent Motion's of the Heavenly Bodies. aoa Mr Bigot’s remarks on the ac¬ counts of variable stars. *03 Star in Gol lo Ceti. 304 Algol. rest about them, even of the third and fourth magni¬ tudes, remained the same. I have observed many more changes among the fixed stars, even to the number of a hundred, though none of them are so great as those I have showed.” I he late improvements in astronomy, and particu¬ larly those in the construction of telescopes, have now given astronomers an opportunity of observing the changes which take place among the stars with much greater accuracy than could be formerly done. In a paper in the 76th volume of the Philosophical Trans¬ actions, Mr Pdward Pigot gives a dissertation on the stars suspected by the astronomers of last century to be changeable. For the greater accuracy in the investi¬ gation of his subject, he divides them into two classes j one containing those which are undoubtedly change¬ able, and the other those which are only suspected to be so. The former contains a list of 12 stars, from the first to the fourth magnitude j including the new one which appeared in Cassiopeia in 1572, and that in Ser- pentarius in 1604 : the other contains the names of 38 stars of all magnitudes, from the first to the seventh. He is of opinion, that the celebrated new star in Cassio¬ peia is a periodical one, and that it returns once in 150 years, Mr Keill is of the same opinion : and Mr Pigot thinks, that its not being observed at the expiration°of each period is no argument against the truth of that opi¬ nion ; “ since (says he), perhaps, as with most of the variables, it may at different periods have different de¬ grees of lustre, so as sometimes only to increase to the ninth magnitude 5 and if this should be the case, its pe¬ riod is probably much shorter.” For this reason, in September 1782, he took a plan of the small stars near the place where it formerly appeared, but in four years had observed no alteration. The star in the neck of the Whale had also been ex¬ amined by Mr Pigot from the end of 1782 to 1786} but he never found it exceed the sixth magnitude 5 though Mr Goodricke had observed it on the 9th of August to be of the second magnitude, and on the 3d of September the same year it was of the third magni¬ tude. Mr Pigot deduced its period from its apparent equality with a small star in the neighbourhood, and thence found it to be 320, 328, and 337 days. I he most remarkable of these changeable stars is that called Algol, in the head of Medusa. It had long been known to be variable ; but its period was first ascertained by Mr Goodricke of York, who began to observe it in the beginning of 1783. It changes con¬ tinually from the first to the fourth magnitude j and the time taken up from its greatest diminution to its least is found, at a mean, to be 2 d. 20 h. 49 m. and 3 sec. During four hours it gradually diminishes in lustre, which it recovers during the succeeding four hours \ and in the remaining part of the period it in¬ variably preserves its greatest lustre, and after the ex¬ piration of the term its diminution again commences. According to Mr Pigot, the degree of brightness of this star when at its minimum is variable in different periods, and he is of the same opinion with regard to its brightness when at its Fill; but whether these dif¬ ferences return regularly or not, has not been deter¬ mined. The 420th of Mayer’s catalogue, in Leo, has lately been shown to be variable by Mr Koch. Some years Part I] of the Heavenl Bodies. r i N O M Y. before 1782, that gentleman perceived it undoubtedly Apparent L smaller than the 419th of the same catalogue. In Fe- Motions bruary that year, it was of the same brightness with the 419th, that is, of the seventh magnitude. In April 17831 it was of the ninth magnitude j and in the same month 1784, it was of the tenth. Mr Pigot could never observe this star, though he frequently looked for it with a night-glass, and on the fifth of April 1785 with a three feet achromatic transit instru¬ ment. In 1704, Maraldi observed a variable star in Hydra, Variable whose period he settled at about two years, though star in Hy with considerable variations : but from the observationsdra’ even of Maraldi, Mr Pigot concludes, that its period was then only 494 days 5 and from some others made by himself, he thinks that now it is only 487 days j so that since the time of Maraldi it has shortened seven days. The particulars relating to this star are as fol¬ low. 1. When at its full brightness it is of the fourth magnitude, and does not perceptibly change for a fort¬ night. 2. It is about six months in increasing from the tenth magnitude and returning to the same : so that it may be considered as invisible during that time. 3. It is considerably more quick, perhaps one half more so, in its increase than in its decrease. 4. Though when at its full it may always be styled a star of the fourth magnitude, it does not constantly attain the same degree of brightness, but the differences are very small. rl his star is the 30th of Hydra in Hevelius’s catalogue, and is marked by him of the sixth magni¬ tude. The new star in Serpentarius, observed by Kepler, seems to have been of the same nature with that of Cassiopeia ; and Mr Pigot therefore looks upon it also to be a periodical one, though, after taking a plan of the nearest stars in that part of the heavens, in the year 1782, he could, in lour years time, perceive no altera- tion. 1 he variation of the star /3 Lyras was discovered by Swan’* Mr Goodricke above-mentioned, who suspects its pe-Head. nod to be six days nine hours} which coincides with the opinion of Mr Pigot. The new star near the Swan’s Head, observed by Don An th el me in December 1669, soon became of the third magnitude, and disappeared in 1672. Mr Pigot has constantly looked for it since November 1781, but without success. He is of opinion, that had it only in¬ creased to the 10th or nth magnitude, he would have seen it, having taken a plan of all the neighbouring small stars. The next variable star in IMr Pigot’s catalogue is the jj Antinoi, whose variation and period he disco¬ vered in 1785. From his corrected observations, he concludes that it continues at its greatest brightness 40 hours without decreasing; it is 66 hours after it begins to decrease before it comes to its full diminu¬ tion ; alter which it continues stationary for 30 hours more, and then increases for 36 hours. In every pe¬ riod it seems to acquire its full brightness, and to be equally decreased. I he variable star in the Swan’s Neck was observed Swan’s for three years. The period of this star had been Neck, settled hy Maraldi and Cassini at 405, and by M. le Gentil at 405.3 days ; but from a mean of the ob¬ servations of Mr Pigot, it appears to be only 392. “ Perhaps y-g-pg f 'U1 art II. ASTRONOMY. Ipparent lotions of the °5 able! in Hj. 20S an’s east. “ Perhaps (says he) its period is irregular; to deter¬ mine which several intervals of 15 years ought to be taken ; and I am much inclined to believe that it will Jodies y f°und only 396 days 21 hours.” The particulars relating to this star are, 1. When at its full bright¬ ness it undergoes no perceptible change for a fortnight. 2. It is about three months and a half in increasing from the nth magnitude to its full brightness, and the same in decreasing ; for which reason it may be considered as invisible during six months. 3. It does not always attain the same degree of lustre, being some¬ times of the fifth and sometimes of the seventh mag¬ nitude. In 1600, G. Jansonius discovered a variable star in the breast of the Swan, which was afterwards observed by different astronomers, and supposed to have a period of about 10 years. The results of Mr Pigot’s calcu¬ lations from the observations of former astronomers are, 1. That it continues in full lustre for five years. 2. It decreases rapidly for two years. 3. It is invisible to the naked eye for four years. 4. It increases slowly during seven years. All these changes are com¬ pleted in 18 years. 6. It was at its minimum at the end of the year 1663. 7. It does not always increase to the same degree of brightness, being sometimes of the third, and at others only of the sixth, magnitude. “ I am entirely ignorant (says Mr Pigot) whether it is subject to the same changes in this century, having not met with any series of observations on it; but if the above conjectures are right, it will be at its minimum in a very few years. Since November 1781 I have con¬ stantly seen it of the sixth magnitude. Sometimes I have suspected that it has decreased within these two last years, though in a very small degree.” The last star in Mr Pigot’s first class is the 5 Cephei, whose variation was discovered by Mr Goodricke. Its changes are very difficult to be seen, unless it is observed at the times of its greatest and least brightness. The re¬ sult of the observations hitherto made upon it are, that its period consists of 5 days 8 hours 37'on a mean. The following observations relate to some stars of the second 1 °P itus, va- ifi-m of vltii is e»eer- taiii class. x. Hevelius’s 6th Cassiopeiae was missing in 1782, nor could Mr Pigot find it in 1783 and 1784. 2. | or 46 Andromedae, said to be variable, but the evidence is not convincing to Mr Pigot. 3. Flamstead’s 50, 52, rAndromedge, and Hevelius’s 41 Andromedae. The position and characters of these stars differ considerably in different catalogues, and some of them are said by Cassini to have disappeared and re¬ appeared. Mr Pigot therefore gives their comparative brightness as observed in the years 1783, 1784, and 1785, during which time he does not mention any par¬ ticular change. 4. Tycho’s 20th Ceti. “ This (says Mr Pigot) must be the star which Hevelius said had disappeared, being Tycho’s second in the Whale’s Belly. There can hard¬ ly be any doubt that it is the misplaced by Tycho. This £ is of the fourth or fifth magnitude. 5. cr, or the 17th Eridani of Ptolemy and Ulug Beigh. Flamstead says he could not see this star in 1691 and 1692; but in 1782, 1783, and 1784, Mr Pigot observed in that place one of the seventh magni¬ tude, which appeared always of the same lustre. 6. Flamstead’s 41 Tauri was supposed by Cassini to be either a new or variable star j but Mr Pigot thinks there is no reason to he of that opinion. “ That it is not new (says he) is evident, since it is Ulug Beigh’s 26th and Tycho’s 43d. 7. A star about 2i° north of 53 Eridani, and 47 Eri¬ dani. Cassini supposed the first of these stars to be a new one, and that it was not visible in 1664. He mentions another star thereabouts, which he also esteemed a new one. 8. y Canis Majoris. Maraldi could not see this star in 1670 j but in 1692 and 1693 it appeared of the fourth magnitude. Mr Pigot made frequent observa¬ tions upon it from 1782 to 1786, but could perceive no variation. 9. « /3 Geminorum. “ If any of these stars (says our author) have changed in brightness, it is probably the (J. _ In 1783, 1784, and 1785, the 0 was undoubt¬ edly brighter than 10. | Leonis. According to Montanan', this star was hardly visible in 1693. In 1783, 1784, and 1785, it was of the fifth magnitude. By Tycho, Flamstead, Mayer, Bradley, &c. it is marked of the fourth. 11. Eeonis. This star is said to have disappeared before the year 1667 ; but according to Mr Pigot’s observations, was constantly of the fifth or sixth magni¬ tude since 1783. 12. 25th Eeonis. In 17^3? 0ur author first per¬ ceived that this star was missing, and could not per¬ ceive it in 1784 aa^ eveQ with a transit instru¬ ment. 13. Bayer’s * Leonis, or Tycho’s 16 Leonis was not visible in 1709, nor could it be seen in .1785. It is a different star from the i Leonis of the other cata¬ logues, though Tycho’s description of its place is the same. 14. S Ursae Majoris. This star is suspected to change in brightness, on account of its being marked by Tycho, the prince of Hesse, &c. of the second magnitude, while Hevelius, Bradley, and others, have marked it of the third. In 1786, and for three years before, it appeared as a bright star of the fourth magni¬ tude. 15. «i Virginis. This is supposed to be variable, be¬ cause Flamstead, on the 2 7th of January 1680, could not see it $ but he observed it in 1677, and some years afterwards. Mr Pigot observed it frequently in 1784 and 1785, and found it a star of the sixth magnitude without any perceptible change. 16. Bayer’s star of the sixth magnitude i° south ofg Virginis. “ This star (says Mr Pigot) is not in any of the nine catalogues that I have. Maraldi looked for it in vain j and in May 1785 I could not see the least appearance of it.” It certainly was not of the eighth magnitude. 17. A star in the northern thigh of Virgo, marked by Ricciolus of the sixth magnitude, could not be seen by Maraldi in 1709J nor was it of the ninth magni¬ tude, if at all visible in 1785. 18. The 91 and 92 Virginis. In 1685, one of these stars, probably the 91, was missing: the remain¬ ing one is of the sixth or seventh magnitude. 19. « Draconis. Mr Pigot coincides in opinion with Dr Herschel, that this star is variable. Bradley, Flam¬ stead, &c. mark it of the second magnitude, but in 1786 it was only a bright fourth. It was, frequently examined 69 Apparent M otions of the Heavenly Bodies. 7° ASTRONOMY. Part m Apparent examined by Mr Pigot from the fourth of October 1782, Motions but without any alteration being perceived. Heay16 ] 20’ ^ayer’s star the west scale of Libra. Ma- Bodies/ ra^‘ could not see this star, and it was likewise invisible —Y—j to Mr Pigot in 1784 and 1785. 21. N° 6 of Ptolemy, and Ulug Beigh’s unformed in Libra. This star is not mentioned in any other cata¬ logues than the above. Mr Pigot frequently observed a little star of the seventh magnitude very near its place 22 k Librae. This star is thought to be variable, but Mr Pigot is not of that opinion, though “ certainly (says he) it is rather singular, that Hevelius, whose at¬ tention was directed to that part of the heavens to find Tycho’s nth, did not find the * $ and the more so, as he has noticed two much smaller stars not far from it. During these three years I have found the * constantly of the fifth magnitude.” 23. Tycho’s nth Librae. Mr Pigot is of opinion that no such star as this ever existed ; and that it is no other than the * with an error of 2 degrees of longi¬ tude. 24. 33 Serpentis. This star was missing in 1784J nor could it be perceived with a night-glass in 1785. 25. A star marked by Bayer near s Ursae majoris. Phis star could not be seen by Cassini ; nor was Mr Pigot able to discover it with a night-glass in 1782. 26. I he g, or Ptolemy and Ulug Beigh’s 14th Ophi- uchi, or Flamstead’s 36th. Mr Pigot has no doubt tiiat this is the star which is said to have disappeared before the year 1695 ; and it is evident that it was not seen by Hevelius. In 1784 and 1785 Mr Pigot found it of the lourth or fifth magnitude 5 but he is far from being certain of its having undergone any change, espe¬ cially as it has a southern declination of 26 degrees 5 for which reason great attention must be paid to the state of the atmosphere. 27. Ptolemy’s 13th and 18th Ophiuchi, fourth mag* nitude. Mr Pigot is of opinion that these stars are misplaced in the catalogues. The 18th of Ptolemy he thinks ought to be marked with a north latitude instead of a south, which would make it agree nearly with Ilamstead’s 58th j and he is also of opinion that the 13th of Ptolemy is the 40th of Flamstead. 28. f tlie [fa,t l:aveuly liodj ;odie& " '<^V t it MWxy, or ‘"uilfr-way. known star, which is to be brought into the centre or common intersection of all the wires. The relative positions of such other stars as appear within the field are to be judged of by the eye ; whether at 4, or 4, -» from the centre towards the circumference, or vice versa; and so with regard to the nearest wire respec¬ tively. These, as one sees them, are to be noted down with a black-lead pencil upon a large message-card held in the hand, upon which a circle similarly divided is ready drawn. One of thi’ee inches diameter seems most convenient. The motion of the heavenly bodies in such a telescope is so slow, and the noting down of the stars so quickly done, that there is commonly full time for it without moving the telescope. When that is wanted, the principal star is easily brought back again into the centre of the field at pleasure, and the work resumed. After a little practice, it is astonishing how near one can come to the truth in this way : and though neither the right ascensions nor the declinations are laid down by it, nor the distances between the stars measured ; yet their apparent situations being pre¬ served in black and white, with the day and year, and hour, if thought necessary, written underneath, each card then becomes a register of the then appearance of the heavens ; which is easily re-examined at any time with little more than a transient view j and which will yet show, on the first glance, if there should have hap¬ pened in it any alteration of consequence.” Fig. 80. shows part of the Corona Borealis delineated in this manner, and which was afterwards fully taken down by making the stars y, e, £, *, g, o-, and t, successively central; and these were joined with some of the stars of Bootes, for the sake of connecting the whole, and united into one map, as represented in fig. 8r. In observing in this way, it is evident, that the places of such stars as happen to be under or very near any of the wires, are more to be depended upon than those which are in the intermediate spaces, especially if towards the edges of the fields j so also those which are nearest to the centre, because better defined, and more within the reach of one wire or another. For this rea¬ son, different stars of the same set must successively be made central, or brought towards one of the wires, where any suspicion arises of a mistake, in order to an- proach nearer to a certainty; but if the stand of the telescope be tolerably well adjusted and fixed, this is soon done. In such a glass it is seldom that light sufficient for discerning the wires is wanting. When an illuminator is required, a piece of card or white pasteboard pro¬ jecting on one side beyond the tube, and which may be brought forward occasionally, is better than any other. By cutting across a small segment of the object-glass, it throws a sufficient light down the tube though the candle be at a great distance, and one may lose sight of the false glare by drawing back the head, and moving the eye a little to one side, when the small stars will be seen as if no illuminator was there. See a delineation of the principal fixed stars, with the apparent path of the sun among them, in figures 82 and 83. A very remarkable appearance in the heavens is that called the galaxy, or milky-way. This is a broad circle, sometimes double, but for the most part single, surround- 71 N O M Y. ing the whole celestial concave. We perceive also in Apparent different parts of the heavens small white spots, which Motions appear to be of the same nature with the milky-way. 01 T-hese spots are called nebulae. Heavenly We shall subjoin in this place, for the entertainment > of the reader, the theories of Mr Michell and Dr Her- schel, concerning the nature and position of the fixed stars. “ J he very great number of stars (says Mr Mi- chell) that have been discovered to be double, triple, chelt’s con- &c. particularly by Mr Herschel, if we apply the doc-jectares trine of chances, as I have heretofore done in my in_ conceri'ing quiry into the probable parallax, &c. of the fixed stars, ^et?atfureI published in the Philosophical Transactions for the year stars.6 ' ^ 1767, cannot leave a doubt with any one who is pro¬ perly acquainted with the force of those arguments, that by far the greatest part, if not all of them, are systems of stars so near each other, as probably to be liable to be affected sensibly by their mutual gravita¬ tion ; and it is therefore not unlikely, that the periods ol the revolutions ot some of these about their princi¬ pals (tlie smaller ones being, upon this hypothesis, to be considered as satellites to the other) may some time or other be discovered.” Having then shown in what manner the magnitude of a fixed star, if its density were known, would affect the velocity of its light, he concludes at last, that “ if the semidiameter of a sphere jn whit of the same density with the sun were to exceed his in cases light the proportion of 500 to I, a body falling from an in- may be finite height towards it (or moving in a parabolic supPose<* to curve at its surface) would have acquired a greater ve-^bod^ locity than that of light; and consequently, supposing that emits light to be attracted by the same force in proportion it- to its vis inertice with other bodies, all light emitted from such a body would be made to return towards it by its own proper gravity. But if the semidiameter of a sphere, of the same density with the sun, was of any other size less than 497 times that of the sun, though the velocity of light emitted by such a body would never be wholly destroyed, yet it would always suffer some diminution, more or less according to the magnitude of the sphere. The same effects would like¬ wise take place if the semidiameters were different from those already mentioned, provided the density was great¬ er or less in the duplicate ratio of these semidiameters inversely. After proceeding jn his calculations, in order to find Compara- the diameter and distance of any star, he proceeds live bright- thus : “ According to Mr Bouguer the brightness ofness of the the sun exceeds that of a wax-candle in no less a pro-pUQ ,all<1 portion than that of 8000 to 1. If therefore the ed stars* brightness of any of the fixed stars should not exceed that of our common candles, which, as being some¬ thing less luminous than wax, we will suppose in round numbers to be only one ten thousandth part as bright as the sun, such a star would not be visible at more than one hundredth part of the distance at which it would be seen if it were as bright as the sun. Now, because the sun would still, I apprehend, appear as bright and luminous as the star Sirius, if removed to 400,000 times his pr-esent distance, such a body, if no brighter than our common candles, would only appear equally luminous with that star at 4000 times the di¬ stance of the sun ; and we might then be able, with the best telescopes, to distinguish some sensible ap¬ parent 73 A S T Pt Apparent parent diameter of it : but the apparent diameters Motions of the stars of lesser magnitudes would still be too of the small to be distinguishable even with our best telescopes, ■ un^ess they were yet a good deal less luminous •, which - - - —" - may possibly, however, be the case with some of them : for though we have indeed very slight grounds to go upon with regard to the specific brightness of the fixed stars, compared with that of the sun at present, and can therefore form only very uncertain and random conjectures concerning it; yet from the infinite variety which we find in the works of the creation, it is not unreasonable to suspect, that very possibly some of the fixed stars may have so little natural brightness in pro¬ portion to their magnitude, as to admit of their dia¬ meters having some sensible apparent size when they shall come to be more carefully examined, and with larger and better telescopes than have been hitherto in common use. With respect to the sun, we know that his whole VS Xmninous appearance surface extremely luminous, a very small and tern- su ^ Porary interruption sometimes, from a few spots, ex- '' ‘ cepted. This universal and excessive brightness of the proceed from an at- whole surface is probably owing to an atmosphere, mosphere. which being luminous throughout,- and in some mea¬ sure also transparent, the light proceeding from a con¬ siderable depth of it, all arrives at the eye, in the same manner as the light of a great number of candles would do if they were placed one behind another, and their flames were sufficiently transparent to permit the light of the more distant ones to pass through those that were nearer without interruption. “ How far the same constitution may take place in the fixed stars we do not know: probably, however, it may still do so in many ; but there are some appear¬ ances, with regard to a few of them, which seem to make it probable that it does not do so universally. Now, if I am right in supposing the light of the sun to proceed from a luminous atmosphere which must necessarily diffuse itself equally over the whole surface, and I think there can be very little doubt that this is really the case, this constitution cannot well take place in those stars which are in some degree periodically 216 more and less luminous, such as that in Collo Ceti, Of the va- &c. It is also not very improbable, that there is some liable stars, difference from that of the sun in the constitution of those stars which have sometimes appeared and disap¬ peared, of which that in the constellation of Cassiopeia is a notable instance. And if these conjectures are well founded which have been formed by some philoso¬ phers concerning stars of this kind, that they are not wholly luminous, or at least not constantly so, but that all, or by far the greatest part of their sur¬ faces, is subject to considerable changes, sometimes becoming luminous, at other times extinguished; it is amongst stars of this sort that we are most likely to meet with instances of a sensible apparent diameter, their light being much more likely not to be so great in proportion as that of the sun, which if removed to 217 0 N 0 M Y. Part | 400,000 times his present distance, would still appear, Appar I apprehend, as bright as Sirius, as I have observed MotiJ above ; whereas it is hardly to be expected, with any telescope whatsoever’, that we should ever be able to di¬ stinguish a well-defined disk of any body of the same size with the sun at much more than 10,000 times his present distance. “ Hence the greatest distance at which it would be possible to distinguish any sensible apparent diameter of a body as dense as the sun, cannot well greatly exceed five hundred times ten thousand ; that is, five million times the distance of the sun ; for if the diameter of such a body was not less than 500 times that of the sun, its light, as has been shown above, could never arrive at us.” Dr Herschel, improving on Mr Michell’s idea ofDrHerJ the fixed stars being collected into groups, and as- -hel’st; sisted by his own observations with the extraordinary moII.coi*-' telescopic powers already mentioned, has suggested a^on^trol theory concerning the construction of the universe en-tionofi tirely new and singular. It had been the opinion of universt former astronomers, that our sun, besides occupying the centre of the system which properly belongs to him, occupied also the centre of the universe : but Dr Herschel is of a very different opinion. “ Hither¬ to (says he) the sidereal heavens have, not inadequate¬ ly for the purpose designed, been represented by the concave surface of a sphere, in the centre of which the eye of the observer might be supposed to be placed. It is true, the various magnitudes of the fixed stars even then plainly suggested to us, and would have bet¬ ter suited, the idea of an expanded firmament of three dimensions ; but the observations upon which I am now going to enter, still farther illustrate and enforce the ne¬ cessity of considering the heavens in this point of view. In future therefore we shall look upon those regions in¬ to which we may now penetrate by means of such large telescopes (a), as a naturalist regards a rich extent of ground or chain of mountains containing strata various¬ ly inclined and directed, as well as consisting of very different materials. A surface of a globe or map there¬ fore will but ill delineate the interior parts of the hea¬ vens.” With the powerful telescope mentioned in the note, His obse Dr Herschel first began to survey the Via Lactea, and vaiionsc found that it completely resolved the whitish appear- V'a ance into stars, which the telescopes he formerly used ctead had not light enough to do. The portion he first ob¬ served was that about the hand and club of Orion; and found therein an astonishing multitude of stars, whose number he endeavoured to estimate by counting many fields (b), and computing from a mean of these how many might be contained in a given portion of the milky-way. In the most vacant place to be met with in that neighbourhood he found 63 stars ; other six fields contained no, 60, 70, 90, 70, and 74 stars; a mean of all which gave 79 for the number of stars to each field; and thus he found, that by allowing 15 minutes I! i. 218 !« Jth *1 iih'.u f fears 1 Ktl, (a) Dr Herschel’s observations, on which this theory is founded, were made with a Newtonian reflector of 20 feet focal length, and an aperture of 18 inches. (b) By this word we are to understand the apparent space in the heavens he could see at once through his te¬ lescope. art irt II. ASTRONOMY. iparent minutes for the diameter of his field of view, a belt of lotions .15 degrees long and two broad, which lie had often of the seen pass before his telescope in an hour’s time, could todies^ not conta'n ^ess ^lan 50>°30 stars, large enough to be distinctly numbered ; besides which, he suspected twice as many more, which could be seen only now and then by faint glimpses for want of sufficient light. the9 The success he had within the milky-way soon indu- jl®. ced him to turn his telescope to the nebulous parts of the heavens, of which an accurate list had been publish¬ ed in the Connoisance des Temps for 1783 and 1784. Most of these yielded to a Newtonian reflector of 20 feet focal distance and 12 inches aperture j which plain¬ ly discovered them to be composed of stars, or at least to contain stars, and to show every other indication of y are consisting of them entirely. “ The nebulae (says he) aged are arranged into strata, and run on to a great length 5 •trata. and some of them I have been able to pursue, and to guess pretty well at their form and direction. It is probable enough that they may surround the whole starry sphere of the heavens, not unlike the milky-way, which undoubtedly is nothing but a stratum of fixed stars : And as this latter immense starry bed is not of equal breadth or lustre in every part, nor runs on in one straight direction, but is curved, and even divided into tw’o streams along a very considerable portion of it j we may likewise expect the greatest variety in the strata of the clusters of stars and nebulae. One of these nebulous beds is so rich, that, in passing through a |t?I- section of it in the time of only 36 minutes, I have itiiety of detected no less than 31 nebulae, all distinctly visible fines as- upon a fine blue sky. Their situation and shape, as well as condition, seem to denote the greatest variety imaginable. In another stratum, or perhaps a differ¬ ent branch of the former, I have often seen double and treble nebulae variously arranged ; large ones with small seeming attendants ; narrow, but much extended lucid nebula; or bright dashes ; some of the shape of a fan, resembling an electric brush issuing from a lucid point 5 others of the cometic shape, with a seeming nucleus in the centre, or like cloudy stars, surrounded with a ne¬ bulous atmosphere : a different sort again contain a ne¬ bulosity of the milky kind, like that wouderful inex¬ plicable phenomenon about 4 Orionis ; while others shine with a fainter mottled kind of light, which de¬ notes their being resolvable into stars. “ It is very probable that the great stratum called the milky-ivay, is that in which the sun is placed, though perhaps not in the very centre of its thickness. We gather this from the appearance of tire galaxy, which seems to encompass the whole heavens, as it certainly must do if the sun is within the same. For suppose a number of stars arranged between two parallel planes, indefinitely extended every way, but at a given consi¬ derable distance from one another, and calling this a sidereal stratum, an eye placed somewhere within it will see all the stars in the direction of the planes of the stratum projected into a great circle, which will appear lucid on account of the accumulation of the stars, while the rest of the heavens at the sides will on¬ ly seem to be scattered over with constellations, more or less crowded according to the distance of the planes or number of stars contained in the thickness or sides of the stratum. Vol. III. Part I. + 73 ;uied by hi'i, '-JL122 w the aii y-way spftars to r.B)Hund ‘iwuea- Apparent Motions of the Heavenly Bodies. 223 “ Thus in fig. 83. an eye at S within the stratum a b, will see the stars in the direction of its length a b, or height ed> with all those in the intermediate situation, projected into the lucid circle ABCD 5 while those in the sides m c, n w, will be seen scattered over the re¬ maining part of the heavens at MVNW. “ If the eye were placed somewhere without the stra-Celestial turn, at no very great distance, the appearance of the stars within it would assume the form of one of the lesserVt circles of the sphere, which would be more or less con-Hersehel’s tracted to the distance of the eye j and if (his distance hypothesis, were exceedingly increased, the whole stratum might at last be drawn together into a lucid spot of any shape, ac¬ cording to the position, length, and height of the stratum. “ Let us now suppose, that a branch or smaller stra¬ tum should run out from the former in a certain direc¬ tion, and let it also be contained between two parallel planes extended indefinitely onwards, but so that the eye may be placed in the great stratum somewhere be¬ fore the separation, and not far from the place where the strata are still united j then will this second stratum not be projected into a bright circle like the former, but will be seen as a lucid branch proceeding from the first, and returning to it again at a certain distance less than a semicircle. Thus, in the same figure, the stars in the small stratum 7?g will be projected into a bright arch at TRRP, which after its separation from the circle CBD, unites with it again at P. “ What has been instanced in parallel planes may easily be applied to strata irregularly bounded, and run¬ ning in various directions; for their projection will of consequence vary according to the quantities of the va¬ riations in the strata and the distance of the eye from the same. And thus any kind of curvatures, as well as various degrees of brightness, may be produced in the projections. 2,4 “ From appearances, then, as I observed before, we Of the sun’# may infer, that the sun is most likely placed in one 0fPlacein tl:ic the great strata of the fixed stars, and very probably univers®‘ not far from the place where some smaller stratum branches out from it. Such a supposition will satis- factorily, and with great simplicity, account for all the phenomena of the milky-way j which according to this hypothesis, is no other than the appearance of the projection of the stars contained in this stratum and its secondary branch. As a farther inducement to look on the galaxy in this point of view, let it be consider¬ ed, that we can no longer doubt of its whitish appear¬ ance arising from the mixed lustre of the numberless stars that compose it. Now, should we suppose it to be an irregular ring of stars, in the centre nearly of which we must then suppose the sun to be placed, it will appear not a little extraordinary, that the sun, being a fixed star, like those which compose this ima¬ gined ring, should just be in the centre of such a mul¬ titude of celestial bodies, without any apparent reason for this singular distinction; whereas, on our supposition, every star in this stratum, not very near the termination of its length or height, will be so placed as also to have its own galaxy, with only such variations in the form and lustre of it as may arise from the particular situa¬ tion of each star. *25 “ Various methods may be taken to come to a^ethocTo* knowledge of the sun’s place in the sidereal stratum, ™aeu^ng the K one heaven*. 7+ ASTRONOMY. Apparent one of wliicli I Iiave already begun to put in practice : I call it gauging the heavens; or the star-s;auge. It Heavenly cons’sts !n repeatedly taking tbe number of stars in ten Bodies, fields or view of my reflector very near each other; and w—-v~—by adding their sums, and cutting off one decimal on Part sidereal stratum. tiie right, a mean of tbe contents of tbe heavens in all tbe parts which are thus gauged are obtained. Thus it appears that the number of stars increases very much as we approach the milky-way ; for in the parallel from 92 to 94 degrees north polar distance, and right ascen¬ sion 15 h. TO', the star-gauge runs up from 9.4 stars in tbe field to 18.6 in about an hour and a half; whereas in the parallel from 78 to 80 degrees north polar dis¬ tance, and R. A. 11, 12, 13, and 14 hours, it very seldom rises above 4. We are, however, to remember, that, with different instruments, the account of the gauges will be very different, especially on our supposi¬ tion of the sun in a stratum of stars. For let a b fig. 84. be the stratum, and suppose the small circle g h l k lo represent the space into which, by the light and power oi a given telescope, we are enabled to penetrate, and let GHLK be the extent of another portion which we are enabled to visit by means of a larger aperture and power, it is evident, that the gauges with the latter in¬ strument will differ very much in their account of stars contained at MN and at KG or LH, when with the former they will hardly be affected with the change from zzS m n to kg or Ik. findVie sltuat*on ffi® sun in tbe sidereal stratum place ofthewIU be found considering in what manner the star- sun in the £aufte agrees with the length of a ray revolving in se¬ veral directions about an assumed point, and cut off by the bounds of the stratum. Thus, in fig. 85. let S be the place of an observer: Srrr, Srrr, lines in the plane r S r, r S r, drawn from S within the stratum to one of the boundaries here represented by the plane AB. Then, since neither the situation of S nor the form of the limiting surface AB is known, we are to assume a point, and apply to it lines proportional to the several gauges that have been obtained, and at such angles from each other as they may point out: then will the termi¬ nation of these lines delineate the boundary of the stra¬ tum, and consequently manifest the situation of the sun within the same. “ In my late observations on nebulae, I soon found, that I generally detected them in certain directions ra¬ ther than in others: that the spaces preceding them were generally quite deprived of their stars, so as often to afford many fields without a single star in it: that the nebulae generally appeared some time after among stars of a certain considerable size, and but seldom among very small stars : that when I came to one ne- btila, I generally found several more in the neighbour¬ hood : that afterwards a considerable time passed before I came to another parcel. These events being often repeated in different altitudes of my instrument, and some of them at considerable distances from each other, it occurred to me that the intermediate spaces between the sweeps might also contain nebulae; and finding this to hold good more than once, I ventured to give notice to my assistant at the clock, that I ‘ found my¬ self on nebulous ground.’ But how far these circum¬ stances of vacant places preceding and following the nebulous strata, and their being as it were contained in a bed of stars sparingly scattered between them, may 227 Observa lions on nebulas. hold good in more distant portions of the heavens, and ApparJ which I have not been yet able to visit in any regular Motior manner, I ought by no means to hazard a conjecture. thf I may venture, however, to add a few particulars about *ieavH |3je: the direction of some of the capital strata or their U(lei “ branches. The well-known nebula of Cancer, visible 228 to the naked eye, is probably one belonging to a cer- Directioi iJ?> JI31 ! lute* ufora tain stratum, in which I suppose it to be so placed as to0fsoine lie nearest to us. This stratum I shall call that oftil?I*jf3 ^ Cancer. It runs from t Cancri towards the south, over the 67th nebula of the Connoissance des Temps, which is a very beautiful and pretty much compressed cluster of stars, easily to be seen by any good telescope; and in which I have observed above 200 stars at once in the field of view of my great reflector with a power of 157. This cluster appearing so plainly with any good common telescope, and being so near to the one which may be seen with the naked eye, denotes it to be pro¬ bably the next in distance to that within the quartile formed by y, »i, 0. From the 67th nebula the stratum of Cancer proceeds towards the head of Hydra ; but I have not yet had time to trace it farther than the equa¬ tor. “ Another stratum, which perhaps approaches nearer to the solar system than any of the rest, and whose situ¬ ation is nearly at rectangles with the great sidereal stratum in which the sun is placed, is that of Coma Berenices, as I shall call it. I suppose the Coma it¬ self to be one of the clusters in it, and that on account of its nearness it appears to be so scattered. It has many capital nebulae very near it: and in all probability this stratum runs out a very considerable way. It may perhaps even make the circuit of the heavens, though very likely not in one of the great circles of the sphere ; for unless it should chance to intersect the great sidereal stratum of the milky-way before mentioned, in the very place in which the sun is stationed, such an appearance would hardly be produced. However, if the stratum of Coma Berenices should extend so far as I apprehend it may, the direction of it towards the north lies pro¬ bably, with some windings, through the Great Bear onwards to Cassiopeia, thence through the girdle of Andromeda and the Northern Fish, proceeding towards Cetus; while towards the south it passes through the Virgin, probably on to the tail of Hydra and Centan- rus.” By a continued series of observations, Hr Herschel became confirmed in his notions ; and in a succeeding paper * has given a sketch of his opinions concerning* Phil, the interior construction of the heavens. “ That the Tram. milky-way (says he) is a most extensive stratum ofTOfi*xxr' stars of various sizes, admits no longer of the Ifast Qf doubt; and that our sun is one of the heavenly bodies terior co* belonging to it is as evident. I have now viewed and struction gauged this shining zone in almost every direction, andthe liea‘ find it composed of shining stars, whose number, byvens‘ the account of those gauges, constantly increases and decreases in proportion to its apparent brightness to the naked eye. But in order to develope the ideas of the universe that have been suggested by my late ob¬ servations, it will be best to take the subject from a point of view at a considerable distance both of space and time. “ Let us then suppose numberless stars of various sizes scattered over an indefinite portion of space, in such |i ica- •(Hu oftl ■- iea. ft ASTRONOMY. PP»®parent such a manner as to be almost equally distributed lotions through the whole. The laws of attraction, which no t*16 doubt extend to the remotest regions of the fixed stars, will operate in such a manner as most probably to pro¬ duce the following remarkable effects. “ I. It will frequently happen, that a star, being equen-considerably larger than its neighbouring ones, will attract them more than they will be attracted by others that are immediately around them j by which means they will be in time, as it were, condensed about a centre : or, in other words, form themselves into a cluster of stars of almost a globular figure, more or less regularly so according to the size and original di¬ stance of the surrounding stars. The perturbations of these mutual attractions must undoubtedly be very intricate, as we may easily comprehend, by considering what Sir Isaac Newton has said, Princip. lib. I. prop. 38. et seq. : but in order to apply this great author’s reasoning of bodies moving in ellipses to such as are here for a while supposed to have no other motion than what their mutual gravity has imparted to them, we must suppose the conjugate axes of these ellipses inde¬ finitely diminished, whereby the ellipses will become straight lines. “ II. The next case, which will happen almost as frequently as the former, is where a few stars, though not superior in size to the rest, may change to be ra¬ ther nearer each other than the surrounding ones j for here also will be formed a prevailing attraction in the combined centre of gravity of them all, which will oc¬ casion the neighbouring stars to draw together; not, indeed, so as to form a regular globular figui’e, but, however, in such a manner as to be condensed towards the common centre of gravity of the whole irregular cluster. And this construction admits of the utmost variety of shapes, according to the number and situa¬ tion of the stars which first gave rise to the condensa¬ tion of the rest. “ III. From the composition and repeated conjunc¬ tion of both the foregoing forms, a third may be de¬ rived, when many large stars, or combined small ones, are situated in long extended regular or crooked rows, hooks, or branches ; for they will also draw the sur¬ rounding ones so as to produce figures of condensed stars coarsely similar to the former, which gave rise to these condensations. “ IV. We may likewise admit of still more exten¬ sive combinations •, when, at the same time that a cluster of stars is forming in one part of space, there may be another collecting in a different, but perhaps not far di¬ stant quarter, which may occasion a mutual approach towards their common centre of gravity. “ V. In the last place, as a natural consequence of the former cases, there will be great cavities or vacan¬ cies formed by the retreat of the stars towards the vari¬ ous centres which attract them $ so that, upon the whole, there is evidently a field of the greatest variety for the mutual and combined attractions of the heavenly bodies to exert themselves in. “ From this theoretical view of the heavens, which has been taken from a point not less distant in time than in space, we will now retreat to our own retired station, in one of the planets attending a star in its great combination with numberless others: and in or¬ der to investigate what will be the appearances from M 1 M III I It || jit Jr ’ Vacicies, >ilhey aoill in ' the ifea- reaii this contracted situation, let us begin with the naked eye. The stars of the first magnitude, being in all pro¬ bability the nearest, will furnish us with a step to begin our scale. Setting olf, therefore, with the distance of Sirius or Arcturus, for instance, as unity, we wi at present suppose, that those of the second magnitude are at double, those of the third at treble, the distance, &c. Taking it for granted, then, that a star of the seventh magnitude (the smallest supposed visible with the naked eye) is about seven times as far as one of the first, it follows, that an observer who is enclosed in a globular cluster of stars, and not far from the centre, will never be able with the naked eye to see to the end of it 3 for since, according to the above estimations, he can only extend his view to above seven times the distance of Sirius, it cannot be expected that his eyes should reach the borders of a cluster which has perhaps not less than 50 stars in depth everywhere around him. The whole universe to him, therefore, will be comprised in a set of constellations richly ornamented with scattered stars of all sizes : Or, if the united brightness of a neighbouring cluster of stars should, in a remarkable clear night, reach his sight, it will put on the appearance of a small, faint, whitish, nebulous cloud, not to be perceived without the greatest atten¬ tion. Let us suppose him placed in a much extended stratum or branching cluster of millions of stars, such as may fall under the third form of nebulae already con¬ sidered. Here also the heavens will not only be richly scattered over with brilliant constellations, but a shi¬ ning zone or milky-way will be perceived to surround the whole sphere of the heavens, owing to the com¬ bined light of these stars which are too small, that is, too remote, to be seen. Our observer’s sight will be so confined, that he will imagine this single collection of stars, though he does not even perceive the thousandth part of them, to be the whole contents of the heavens^ Allowing him now the use of a common telescope, he begins to suspect that all the milkiness of the bright path which surrounds the sphere may be owing to stars. He perceives a few clusters of them in various parts of the heavens, and finds also that there are a kind of nebulous patches : but still his views are not extended to reach so far as to the end of the stratum in which he is situated 3 so that he looks upon these patches as belonging to that system which to him seems to comprehend every celestial object. He now in¬ creases his power of vision ; and, applying himself to a close observation, finds that the milky-way is indeed no other than a collection of very small stars. He perceives, that those objects which had been called nebulce, are evidently nothing but clusters of stars. Their number increases upon him ; and when he re¬ solves one nebula into stars, he discovers ten new ones which he cannot resolve. He then forms the idea of immense strata of fixed stars, of cluster's of stars, and of nebulae 3 till, going on with such interesting obser¬ vations, he now perceives, that all these appearances must naturally arise from the confined situation in which we are placed. Covjlned it may justly be called, though in no less a space than what appear¬ ed before to be the whole region of the fixed stars, but which now has assumed the shape of a crookedly branching nebula 3 not indeed one of the least, but per¬ haps very far from being the most considerable, of those K. 2 numberless? 75 Apparent Moti< ns of the Heavenly B idles. *33 How the stars must appear to us accord¬ ing to this hypothesis. 76 ASTRONOMY. Apparent Motions of the 234 Arguments are {0 in favour of the fore- seevations on nebulte. numlierless clusters that enter into the construction of the heavens.” Heaven! ^ur au^lor now proceeds to show that this theoreti- JBodies. ca^ v^ew ^ie heavens is perfectly consistent with facts, and seems to be confirmed by a series of observations. Many hundreds of nebulae of the first and second forms be seen in the heavens; and their places, be says, will hereafter be pointed out j many of the third going theo-form described, and instances of the fourth related j ry from ob-a few of the cavities mentioned in the fifth particula¬ rized, though many more have been already observed: so that, “ upon the whole (says he), I believe it will be found, that the foregoing theoretical view, with all its consequential appearances, as seen by an eye enclo¬ sed in one of the nebulae, is no other than a drawing from nature, wherein the features of the original have been closely copied : and I hope the resemblance will not be called a bad one, when it shall be considered how very limited must be the pencil of an inhabitant of so small and retired a portion of an indefinite system in attempting the picture of so unbounded an extent.” Dr Herschel next presents us with a long table of star-gauges, or accounts of the number of stars at once men- tjie 0f jjjg telescope, which go as high as 588 $ heavens. eafter which he proposes the following Problem. Part! 235 Method of measuring the dimen- “ The stars being supposed nearly equally scattered, and their number, in a field of view of a known angular diameter, being given j to determine the length of the visual ray. “ Here, the arrangement of the stars not being fix¬ ed upon, we must endeavour to find which way they may be placed so as to fill a given space most equally. Suppose a rectangular cone cut into frustula by many equidistant planes perpendicular to the axis j then, if one star be placed at the vertex and another in the axis at the first intersection, six stars may be set around it so as to be equally distant from one another and from the central star. These positions being carried on in the same manner, we shall have every star within the cone surrounded by eight others at an equal distance from that star taken as a centre. Fig. 100. contains four sections of such a cone distinguished by alternate shades; which will be sufficient to explain what sort of arrange¬ ment I would point out. “ The series of the number of stars contained in the several sections will be I, 7, 19, 37, 61, 91, &c. which continued to n terms, the sum of it, by the • • • 7l~- X 72, ~ X differential method, will be na-\-n.- a n- —2 d’\ &c. where a is the first term, d!, d", d'", &c. the first, second, and third differences. Then, since d'zs.6, d"—6, d'"=zO, the sum of the series will be n3. Let S be the given number of stars ; 1 the diameter of the base of the field of view; and B the diameter of the great rectangular cone ; and by trigonometry we shall have „ .Now, since the field of view Tang. 4 field’ of a telescope is a cone, we shall have its solidity to that of the great cone of the stars formed by the above construction, as the square of the diameter of the base of the field of view, to the square of the diameter > 2 237 of the great cone, the height of both being the same ; App and the stars in each cone being in the ratio of the so- Motk - ofti hdity, as being equally scattered, we have -y/B’S; Ileav{: and the length of the visual ray ~n—1, which was to be determined.” Another solution of this problem, on ' r' the supposition of another arrangement of stars, is given; but Dr Herschel prefers the former. ^ From the data now laid down, Dr Herschel next en-Proof 0 deavours to prove that the earth is i the planet ofaoul'sid< star belonging to a compound nebula of the third form.’ ^S)8* “ I shall now (says he) proceed to show, that the stu-nebula? pendous sidereal system we inhabit, this extensive stra¬ tum, and its secondary branch, consisting of many mil¬ lions of stars, is in all probability a detached nebula. In order to go upon grounds that seem to me to be capable of great certainty, they being no less than an actual sur¬ vey of the boundaries of our sidereal system, which I have plainly perceived as far as I have yet gone round it, everywhere terminated, and in most places very nar¬ rowly too, it will be proper to show the length of my sounding line, if I may so call it, that it may appear whether it was sufficiently long for the purpose. “ In the most crowded parts of the milky-way, I Length} have had fields of view that contained no fewer thantllc.line 588 stars, and these were continued for many mi-^“cM nutes : so that in one quarter of an hour’s time there measmt passed no less than 116,000 stars through the field ofthe hea. view of my telescope. Now, if we compute the lengthvens. of the visual ray, by putting 8=588, and the diame¬ ter of the field of view 15 minutes, we shall find 3 «=N/BiS=498; so that it appears the length of what I have called my Sounding Line, or n—1, was not probably less than 497 times the distance of Sirius from the sun. “ It may seem inaccurate that we should found an argument on the stars being equally scattered, when, in all probability, there may not be any two of them in the heavens whose mutual distance shall be equal to that of any other two given stars : but it should be considered, that when we take all the stars collectively, there will be a mean distance which may be assumed as the general one ; and an argument founded on such a supposition will have in its favour the greatest pro- g bability of not being far short of truth. And here I Cluster c must observe, that the difl’erence between a crowded stars de¬ place and a cluster (none of the latter being put intofined‘ the gauge table), may easily be perceived by the ar¬ rangement as well as the size and mutual distance of the stars ; for in a cluster they are generally not only resembling each other pretty nearly in size, but a cer¬ tain uniformity of distance also takes place : they are more and more accumulated towards the centre, and put on all the appearances which we should naturally expect from a number of them collected into a group at a certain distance from us. On the other hand, the rich parts of the milky-way, as well as those in the distant broad parts of the stratum, consist of a mixture of stars of all possible sizes, that are seemingly placed without any particular apparent order. Perhaps, we might re¬ collect, that a greater condensation towards the centre of our system than towards the borders of it should be taken into consideration ; but with a nebula of the third form containing such various and extensive com¬ binations Moti0l . oftli, learei Bodij t3< roof of ir sidt. alsjn :inSa :bula, 237 Ellgtl elk lich I ersclf :asutt c h ns. 239 Sxtent of < Part II. ASTRO Apparent binations as I have found to take place in ours, this Motions circumstance, -which in one of the first form would be of the of considerable moment, may, I think, be safely ne- ^Bodks17 g,ected* , “ If some other high gauge be selected from the table, such as 472 or 344, the length of the visual ray will be found 461 and 415. And although, in conse¬ quence of what has been said, a certain degree of doubt may be left about the arrangement and scatter¬ ing of the stars, yet when it is recollected, that in those parts of the milky-way, where these high gauges were taken, the stars were neither so small nor so crowded as they must have been, on a suppostion of a much farther continuance of them, when certainly a milky or nebulous appearance must have come on, I need not fear to have overrated the extent of my visual ray j and indeed every thing that can be said to shorten it will only contract the limits of our nebula, as it has in most places been of sufficient length to go far beyond the bounds of it. Thus in the sides of our stratum, opposite to our situation in it, where the gauges often eju OI run below 5, our nebula cannot extend to 100 times nebula. ^ie distance of Sirius j and the same telescope which, could show 588 stars in a field of view of 15 minutes, must certainly have presented me also with the stars in these situations, had they been there. If we should answer this by observing, that they might be at too great a distance to be perceived, it will be allowing that there must at least be a vacancy amounting to the length of a visual ray, not short of 400 times the distance of Sirius ; and this is amply sufficient to make our nebula a detached one. It is true, that it would not be consistent confidently to affirm that we were on an island, unless we had found ourselves everywhere bounded by the ocean ; and therefore I shall go no far¬ ther than the gauges will authorize ; but considering the little depth of the stratum in all those places which have been actually gauged, to which must be added all the intermediate parts that have been viewed and found to be much like the rest, there is but little room to ex¬ pect a connection between our nebula and any of the neighbouring ones. A telescope, with a much larger aperture than my present one, grasping together a greater quantity of light, and thereby enabling us to see farther into space, will be the surest means of com¬ pleting and establishing the arguments that have been used : for if our nebula is not absolutely a detached one, I am firmly persuaded that an instrument may be made large enough to discover the places where the stars continue onwards. A very bright milky nebulo¬ sity must there undoubtedly come on, since the stars in a field of view will increase in the ratio of n3 greater than that of the cube of the visual ray. Thus, if 588 stars in a given field of view are to be seen by a ray of 497 times the distance of Sirius, when this is length¬ en jd to 1000, which is but little more than double the former, the number of stars in the same field of view will be no less than 4774 j for when the visual ray r is 71 2 will be ; where given, the number of stars S ) and a telescope with a threefold power of extending into space, or with a ray of 1500, which I think may easily be constructed, will give us 16,096 stars. Nor would these be so close, but that a good power applied to such an instrument might easily di? Heavenly Bodies N O M Y. 77 stinguish them j for they need not, if arranged in re- gular squares, approach nearer to each other than Molious 6".27 ; but the milky nebulosity I have mentioned, would be produced by the numberless stars beyond them, which, in one respect, the visual ray might also be said to reach. l.o make this appear, we must re¬ turn to the naked eye : which, as we have before esti¬ mated, can only see the stars of the seventh magnitude so as to distinguish them: but it is nevertheless very evident, that the united lustre of millions of stars, such as I suppose the nebula in Andromeda to be, will, reach our sight in the shape of a very small faint nebu¬ losity } since the nebula of which I speak may easily be seen in a fine evening. In the same manner, my. present telescope, as I have argued, has not only a visual ray that will reach the stars at 497 times the distance of Sirius, so as to distinguish them, and pro¬ bably much farther, but also a power of showing the united lustre of the accumulated stars that compose a milky nebulosity at a distance far exceeding the former limits: so that from these considerations it appears again highly probable, that my present telescope not showing such a nebulosity in the milky-way, goes al¬ ready far beyond its extent 5 and consequently much more would an instrument, such as I have mentioned, remove all doubt on the subject, both by showing the stars in the continuation of the stratum, and by expo¬ sing a very strong milky nebulosity beyond them, that could no longer be mistaken for the dark ground of the heavens. “ To these arguments, which rest on the firm basis Analogical of a series of observation, wre may add the following arguments considerations drawn from analogy. Among the greatin f^V0Br number of nebulae which I have now already seen,^** do** amounting to more than 900, there are many which in all probability are equally extensive with that which we inhabit 5 and yet they are all separated from each other by very considerable intervals. Some, indeed, there are that seem to be double and treble j and though with most of these it may be that they are at a very great distance from each other, yet we allow that some such conjunctions really are to be found j nor is this what we mean to exclude: But then these compound or double nebulae, which are those of the third and fourth forms, still make a detached link in the great chain. It is also to be supposed, that there may be some thinly scattered solitary stars between the large interstices of nebulae ; which being situated so as to be nearly equally attracted by the several clusters when they were forming, remain unassociated : and though we cannot expect to see those stars on account of their vast distance, yet we may well presume that their num¬ ber cannot be very considerable in comparison to those that are already drawn into systems j which conjecture is also abundantly confirmed in situations where the ne¬ bulae are near enough to have their stars visible; for they are all insulated, and generally to be seen upon a very clear and pure ground, without any star near them that might be thought to belong to them. And though I have often seen them in beds of stars, yet from the size of these latter we may be certain, that they were much nearer to us than those nebulae, and belong un¬ doubtedly to our own system.” Having thus determined that the visible system of nature, by us called the universe, consisting of all the celestial ^8 Apparent Motions of the Heavenly Bodies. 241 How the figure of our nebula may be de¬ lineated. A S T B celestial bodies, and many more than can be seen by the naked eye, is only a group of stars or suns with their planets, constituting one of those patches called a nebula, and perhaps not one ten-thousandth part of what is really the universe, Dr Herschel goes on to delineate the tigure of this vast nebula, which he is of opinion may now be done ; and for this purpose he gives a table, calculating the distances of the stars which form its extreme boundaries, or the length of the vi¬ sual ray in different parts, by the number of stars con¬ tained in the field of his telescope at diiferent times, according to the principles already laid down. He does not, however, as yet attempt the whole nebula, hut ol a particular section, represented fig. 160. “I have taken one (says he) which passes through the poles of our system, and is at rectangles to the con¬ junction ol the branches, which l have called its/ewg-fA. The name of poles seems to me not improperly ap¬ plied to those points which are 90 degrees distant from a circle passing along the milky-way j and the north pole is here supposed to be situated in right ascension 186°, and polar distance (that is from the pole com¬ monly so called) ^8°. The section is one which makes an angle of 350 with our equator, crossing it in 1 24^0 ar'd ^ celestial globe, adjusted to the latitude of 550 north, and having r Ceti near the meridian, will have the plane of this section pointed out by the horizon. The visual rays are to be project¬ ed on the plane of the horizon of the latitude just mentioned, which may be done accurately enough by a globe adjusted in the manner directed. The stars in the border, which are marked larger than the rest, are those pointed out by the gauges. The intermediate parts are filled up by smaller stars, arranged in straight lines between the gauged ones. From this figure, which I hope is not a very inaccurate one, we may see that our nebula, as we observed before, is of the third form 5 that is, a very extensive, branching, compound congeries of many millions of stars, which most pro¬ bably owes its origin to many remarkably large, as well as pretty closely scattered, small stars, that may have drawn together the rest. Now, to have some idea of the wonderful extent of this system, I must observe, that this section of it is drawn upon a scale where the distance of Sirius is no more than the 80th part of an inch $ so that probably all the stars, which in the finest nights we are able to distinguish with the naked eye, may be comprehended within a sphere drawn round the large star near the middle, representing our situa¬ tion in the nebula, of less than half a quarter of an inch radius.” Dr Herschel now proceeds to offer some further thoughts on the origin of the nebulous strata of the heavens : in doing which he gives some hints concern¬ ing the antiquity of them. “ If it were possible (says he) to distinguish between the parts of an indefinitely extended whole, the nebula we inhabit might be said to be one that has fewer marks of antiquity than any of the rest. To explain this idea perhaps more clearly, We should recollect, that the condensation of clusters of stars has been ascribed to a gradual approach } and whoever reflects on the number of ages that must have passed before some of the clusters that are to he found in my intended catalogue of them could be so far con¬ densed as we find them at present, will not wonder if O N O M Y. . Parti, I ascribe a certain air of youth and vigour to many Apparti very regularly scattered regions of our sidereal stratum. Motioi There are, moreover, many places in it in which, if we of 1,1 may judge from appearances, there is the greatest rea- HeavelJr son to believe that the stars are drawing towards secon- < dary centres, and will in time separate into clusters, so 242 as to occasion many subdivisions. Hence me may sur-Of the ». raise, that when a nebulous stratum consists chiefly ofcay an<*e nebulae of the first and second forms, it probably owes C£mf,os,]'<,n its origin to what may he called the decay of a great ° ncbu ' compound nebula of the third form; and that the sub¬ divisions which happened to it in length of time, occa¬ sioned all the small nebulae which sprung from it to lie in a certain range, according as they were detached from the primary one. In like manner, our system, after numbers of ages, may very possibly become divid¬ ed, so as to give rise to a stratum of two or three hundred nebulae ; for it would not be difficult to point out so many beginning or gathering clusters in it. This throws a considerable light upon that remarkable collection of many hundreds of nebulae which are to be seen in what I have called the nebulous stratum, in Coma Berenices. It appears, from the extended and branching figure of our nebula, that there is room for the decomposed small nebulae of a large reduced former great one to approach nearer to us in the sides than in any other parts. Nay, possibly there might originally be another very large joining branch, which in time became separated by the condensation of the stars ; and this may be the reason of the little remaining breadth of our system in that very place j for the ne¬ bulae of the stratum of the Coma are brightest and most crowded just opposite to our situation, or in the pole of our system. As soon as this idea was suggested, I tried also the opposite pole ; where accordingly I have met with a great number of nebulae, though "under a much more scattered form. Some parts of our system indeed seem already to have sustained greater ravages 'of time than others j for instance, in the body of the Scorpion is an open¬ ing or hole, which is probably owing to this cause, it is at least four degrees broad ; but its height I have not yet ascertained. It is remarkable, that the 80th Nebuleuse sans Etoiles of the Connoissance des Temps, which is one of the richest and most compressed clu¬ sters of small stars I remember to have seen, is situated just on the west border of it, and would almost autho¬ rize a suspicion that the stars of which it is composed were collected from that place, and had left the vacancy. VVnat adds not a little to this surmise is, that the same phenomenon is once more repeated with the fourth cluster of the Connoissance des Temps; which is also on the western border of another vacancy, and has more¬ over a small miniature cluster, or easily resolvable nebu¬ la, of about 24 minutes in diameter north, following it at no very great distance. 0 There is a remarkable purity or clearness in the heavens when we look out of our stratum at the sides- that is, towards Leo, Virgo, and Coma Berenices on one hand, and towards Cetus on the other ; whereas the ground of the heavens becomes troubled as we ap¬ proach towards the length or height of it. These troubled appearances are easily to be explained by ascribing them to some of the distant straggling stars that yield hardly light enough to be distinguished. And art Part II. ■Ppar 'lolioi °f thi Jeave liodi , 54i the i y and foposii ncbul 243 Universe composed jf nebulas. STa/. Phil. ASTRONOMY. Bodies. Apparent And I have indeed often experienced this to be the cause, Motions by examining these troubled spots for a long while toge- ofthe ther, when at last I generally perceived the stars which Heavenly occasione(l them. But when we look towards the poles of our system, where the visual ray does not graze along the side, the straggling stars will of course be very few in number : and therefore the ground of the heavens will assume that purity which I have always observed to take place in those regions.” Thus, then, according to Dr Herschel, the universe consists of nebulce, or innumerable collections of innu¬ merable stars, each individual of which is a sun not on¬ ly equal, but much superior to ours : at least if the words of Mr Nicholson have any weight ; for he tells ip5, 196. us, that “ each individual sun is destined to give light to hundreds of worlds that revolve about it, but which can no more be seen by us, on account of their great distance, than the solar planets can be seen from the fixed stars.” “ Yet (continues he), as in this unex¬ plored, and perhaps unexplorable, abyss of space, it is no necessary condition that the planets should be of the same magnitudes as those belonging to our system, it is not impossible but that planetary bodies may be discovered among the double and triple stars.” Though in the above extracts from Dr Herschel’s papers, the words condensations, clusters, &c. of stars frequently occur, we are by no means from thence to imagine that any of the celestial bodies in our nebula are nearer to one another than we are to Sirius, whose distance is supposed not to be less than 400,000 times that of the sun from us, or 38 millions of millions of miles. The whole extent of the nebula being in some places near 500 times as great, must be such, that the light of a star placed at its extreme boundary, suppo¬ sing it to fly with the velocity of 12 millions of miles every minute, must have taken near 3000 years to reach us. Dr Herschel, however, is by no means of opinion, that our nebula is the most considerable in the, universe. “ As we are used (says he) to call the appearance of the heavens, where it is surrounded with a bright zone, the milky.way, it may not be amiss to point out some other very remarkable nebulae, which cannot well be less, but are probably much larger, than our own system ; and being also extended, the inhabi¬ tants of the planets that attend the stars which compose them, must likewise perceive the same phenomena : for which reason they may also be called milky-ways, bv way of distinction. “ My opinion of their size is grounded on the fol¬ lowing observations : There are many round nebulae of the first form, of about five or six minutes in diameter, the stars of which I can see very distinctly ; and on comparing them with the visual ray calculated from some of my long gauges, I suppose by the appearance of the small stars in those gauges, that the centres of these round nebulae may be 600 times the distance of Sirius from us.”—He then goes on to tell us, that the stars in such nebulae are probably twice as much con¬ densed as those of our system 5 otherwise the centre of it would not be less than 6000 times the distance of Sirius from us ; and that it is possibly much under¬ rated by supposing it only 600 times the distance of that star. “ Some of these round nebulae (says Dr Herschel) have others near them, perfectly similar in form, colour, 79 Apparent Motions of the Heavenly Bodies. and the distribution of stars, but of only half the dia¬ meter : and the stars in them seem to be doubly crowd¬ ed, and only at about half the distance from each other. The y are indeed so small, as not to be visible without the utmost attention. I suppose these miniature nebulce ■ to be at double the distance of the first. An instance equally remarkable and instructive is a case where, in the neighbourhood of twm such nebulae as have been mentioned, I met with a third similar, resolvable, but much smaller and fainter nebula. The stars of it are no longer to be perceived ; but a resemblance of colour with the former two, and its diminished size and light, may well permit us to place it at full twice the di¬ stance of the second, or about four or five times the distance of the first. And yet the nebulosity is not of the milky kind 5 nor is it so much as difficultly re¬ solvable or colourless. Now in a few of the extend¬ ed nebulae, the light changes gradually, so as from the resolvable to approach to the milky kind ; which appears to me an indication, that the milky light of nebulae is owing to their much greater distance. A nebula, therefore, whose light is perfectly milky, can- nob-well be supposed to be at less than six or eight thousand times the distance of Sirius ; and though the numbers here assumed are not to be taken otherwise than as very coarse estimates, yet an extended nebula, which an oblique situation, where it is possibly fore¬ shortened by one-half, two-thirds, or three-fourths of its length, subtends a degree, or more in diameter, cannot be otherwise than of a wonderful magnitude, and may well outvie our milky-way in grandeur.” Dr Herschel next proceeds to give an account of se-Vastlenglh veral remarkable nebulse, and then concludes thus : of time re- “ Now, what great length of time must be required lf a clock whose dial plate is divided into 360°, instead of twelve hours, be ordered in such a manner! that the index may pass round the whole circle in the interval which a star requires to come to the same meri¬ dian again and another index be so managed as to point out the sexagesimal parts: then, when the sun is on the meridian, let the indices of the clock be put to Vol. Ill, Part I. r , f N O M Y. 8t his right ascension at noon that day ; and when the star Apparent conies to the meridian, its right ascension will be shown Motions by the clock, without any kind of reduction. of the The stars are referred likewise to the ecliptic as well J^0T.enIy as to the equator. In that case the terms longitude and latitude are used. I he longitude of any of the heavenly bodies is an Longitude arc of the ecliptic contained between the first point ofofthehea. Aries, and a secondary to the ecliptic or circle of lati-ven^T tude, passing through the body ; it is always measured ^oc'^es’ according to the order of the signs. If the body be supposed seen from the centre of the earth, it is called geocentric longitude 5 but if it be supposed seen from the centre of the sun, then is the longitude heliocen¬ tric. . Tke latitude of a heavenly body is its distance from j at?tude& the ecliptic, measured upon a secondary to the eclip¬ tic drawn through the body. If the latitude be such as is seen from the earth’s centre, it is called geocen- t> cc latitude 5 but if it be supposed seen from the centre of the sun, it is heliocentric* i he equator being the principal circle which re¬ spects the earth, the latitudes and longitudes of terres¬ trial objects are referred to it; and, for a similar reason (the sun’s motion in the ecliptic rendering that the principal of the celestial circles), the situations of hea¬ venly objects are generally ascertained by their lati¬ tudes and longitudes referred to the ecliptic : it has therefore become a useful problem to find the latitudes and longitudes of the stars, &c. having their declina¬ tions,, and. right ascensions, with the obliquity of the ecliptic, given. One of the best methods of perform- mg this problem has been thus investigated: Let How found. » be the place of the body (fig. 88.), EC the ecliptic, EQ the equator: and SL and SR being re¬ spectively perpendicular to EC and EQ, ER will re¬ present the right ascension, SR the declination, EL the longitude, and SL the latitude ; then, by spherics S SR:co-ta”ff- SER; and SER_4_CEQ_SEL. Also, co-sine SER : rad :: tamr ER : tang. ES; and rad. : co-sine SEL :: tang. ES : tang. EL; therefore, co-sine SER : co-sine SEL : : tang. ER • tang. EL; whence we readily get co-sine SLL X tang. ER c^TSER" = the tangeQt of EL, the longitude. Then, rad. : sine of EL :: tang. SEL : tang. SL, the latitude. But the same thing may be performed very expedi- tion.sly by means of the following excellent rule, given by Hr Maskelyne, the present worthy astronomer royal: 1. The sine of the right ascension -f co-tang, de¬ clination—10 =r co-tang. of arc A, which call north. or according as the declination is north or south. 2. Call the obliquity of the ecliptic south in the six mst signs of right ascension, and north in the six last. Let the sum of are A, and obliquity of ecliptic, ac¬ cording to their titles, —arc B with its proper title, tit one be north and the other south, the proper title is that which belongs to the greater; and in this case arc B is their differwice.] 3, The arithmetical com! plement or co-sine arc A + co-sine arc B X tang, right ascension =: tangent of the longitude: this is of the same kind as the right ascension, unless arc B be more than 90 , when the quantity found of the same kind as h the 82 Apparent Motions of the Heavenly Bodies. ASTRO the right ascension must he subtracted from 12 signs, or 360°. 4. The sine" of longitude -{- tang, arc B — 10 —tang, of the required latitude, of the same title as arc IT Note, If the longitude be found near 0° or near 180°, for the sine of longitude, in the last operation, substitute tang, longitude -J- co-sine longi¬ tude — 10; and then the last operation will be tang, longitude -J- co-sine longitude -f- tang, arc B — 20 — tang, latitude. By sine, tang. &c. are meant logarithm sine, log. tang. &c. This rule may be exemplified by inquiring what are the latitude and longitude of a star whose declination is I2° 59' north, and right ascension 4s 290 38', the obli¬ quity of the ecliptic being 290 28'? Here, sine of right ascension 4s 290 38' Co-tang, of declination 12 59 Co-tang, of arc A, north 24 Obliquity of ecliptic south 23 Arc B, north - 1 Arith. comp, of co-sine arc A Tangent of right ascension 31 28 9-7o37486 10-6372126 1034069612 cos. 9-9999271 0-0410347 9-7678344 Tangent of longitude 1470 15' 26" 9-8087962 Or 4s 270 13' 26", answering to 270 13' 26" of Leo. Then, sine of longitude - - 9'7334843 8-2631153 Tangent of arc B 254 Sttars vary in right a- scension and decli¬ nation. 255 Observa¬ tions of the Asiatic shepherds. 256 To deter¬ mine the time of the sun’s occu¬ pying the equinoctial points. Tang, of latitude, north, 34' 6" 7'99^S99^ Astronomers have observed that the stars vary in right ascension and in declination, but keep the same latitude: hence.it was concluded that their variations in declination and right ascension were owing to the revolution ot the celestial sphere round the poles of the ecliptic. Or they may be accounted for by supposing that the poles of the equator revolve slowly round those of the ecliptic. This revolution is called the preces¬ sion ol the equinoxes. A more particular account of it will be necessary'. By a long series of observations, the shepherds of Asia were able to mark out the sun’s path in the heavens ; he being always in the opposite point to that which comes to the meridian at midnight, with equal but op¬ posite declination. Thus they could tell the stars among which the sun then was, although they could not see them. They discovered that this path was a great circle of the heavens, afterwards called the Ecliptic j which cuts the equator in two opposite points, dividing it, and being divided by it, into two equal parts. They farther observed, that when the sun was in either of those points of intersection, his circle of diurnal revolution coincided with the equa¬ tor, and therefore the days and nights were equal. H ence the equator came to be called the Equinoc¬ tial line, and the points in which it cuts the eclip¬ tic were called the Equinoctial points, and the sun was then said to be in the equinoxes. One of these was called the Vernal and the other the Autumnal Equinox. It was evidently an important problem in practical astronomy to determine the exact moment of the sun’s occupying these stations-, for it was natural to compute the course of the year from that moment. Accordingly this has been the leading problem in the astronomy of 3 Motioi ofthe Heave Bodie N O M Y. Part ] all nations. It is susceptible of considerable precision, Appare without any apparatus of instruments. It is only ne¬ cessary to observe the sun’s declination on the noon of two or three days before and after the equinoctial day. On two consecutive days of this number, bis declination must have changed from north to south, or from south to north. If his declination on one day was observed to be 11' north, and on the next 5' south, it follows that his declination was nothing, or that he was in the equi¬ noctial point about 23 minutes after 7 in the morning of the second day. Knowing the precise moments, and knowing the rate of the sun’s motion in the ecliptic, it is easy to ascertain the precise point of the ecliptic in which the equator intersected it. By a series of such observations made at Alexandria Hippar- between the years 161 and 127 before Christ, Hippar-Aws’s di elms, the father of our astronomy, found that the pointcovenes’ of the autumnal equinox was about six degrees to the eastward of the star called Spica virginis. Eager to determine every thing by multiplied observations, be ran¬ sacked all the Chaldean, Egyptian, and other records, to which Itis travels could procure him access, for obser¬ vations of the same kind; but he does not mention bis having found any. He found, however, some observa¬ tions ol Aristillus and Timochares made about 1 50 years before. From these it appeared evident that the point of the autumnal equinox was then about eight degrees east of the same star. He discusses these observations with great sagacity and rigour ; and, on their authority, he asserts that the equinoctial points are not fixed in the heavens, but move to the westward about a degree in 75 years or somewhat less. This motion is called the PRECESSION OF THE Equi- w- 258 < NOXES, because by it the time and place of the sun’s the'prece equinoctial station precedes the usual calculations: it issiouoftli fully confirmed by all subsequent observations. In 1750 equinoxa the autumnal equinox was observed to be 20° 2i' west¬ ward ot Spica Virginis. Supposing the motion to have been uniform during this period of ages, it follows that the annual precession is about 50"-^ j that is, if the ce¬ lestial equator cuts the ecliptic in a particular point on any day of this year, it will on the same day of the fol¬ lowing year cut it in a point 50"! to the west of it, and the sun will come to the equinox 2o' 23" before be has completed his round of the heavens. Thus the equinoctial or tropical year, or true year of seasons, is so much shorter than the revolution ofthe sun or the sidereal year. It is this discovery that has chiefly immortalized the name of Hipparchus, though it must be acknow-of the dis- ledged that all his astronomical researches have been covery. conducted with the same sagacity and intelligence. It was natural therefore lor him to value himself highly for the discovery. It must be acknowledged to be one of the most singular that has been made, that the re¬ volution of the whole heavens should not be stable, but its axis continually changing. For it must be ob¬ served, that since the equator changes its position, and the equator is only an imaginary circle, equidistant from the two poles or extremities of the axis ; these poles and this axis must equally change their positions. The equinoctial points make a complete revolution in about 25’745 years, the , equator being all the while inclined to the ecliptic in nearly the same angle. Therefore the poles of this diurnal revolution must describe a circle BStei j (inf ( iM Irict ikr i 161 Uotii oftlk art II. ppiirciit circle round the poles of the ecliptic at the distance of .lotions about 23J degrees in 25,745 years; and in the time of . Holt*ie I imochares the north pole of the heavens must have y been 30 degrees eastward of where it now is. -v-—> Hipparchus has been accused of plagiarism and insin- 260 cerity in this matter. It is now very certain that the iparclius precession of the equinoxes was known to the astrono- bcen ^ mers ot India many ages before the time of Hipparchus, n It appears also that the Chaldeans had a pretty accurate rrom their saros we ASTRONOMY. 8j described by the pole of the equator during one revolu- Apparent tion of the equinoctial points. Let P be the place of Motions this last-mentioned pole at some given time. Round *iee Du- Isur le ague knowledge of the year of seasons. deduce their measure of this year to be 365 days 5 hours 49 minutes and 11 seconds, exceeding the truth only by 26", and much more exact than the year of Hippar¬ chus. They had also a sidereal year of 365 days 6 hours 11 minutes. Now what could occasion an atten¬ tion to two years, if they did not suppose the equi¬ noxes moveable ? The Egyptians also had a knowledge of something equivalent to this : for they had discover¬ ed that the dog-star was no longer the faithful fore- Warner of the overflowing of the Nile : and they com- d&Egyp- bined him with the star Fomalhaset * in their mystic ca- !u., Mem. lendar. This knowledge is also involved in the precepts d<> Acad. 0f t|ie Chinese astronomy, of much older date than the torn;,, time of Hipparchus. bifalscly. Hut all these acknowledged facts are not sufficient for depriving Hipparchus of the honour of the disco¬ very, or fixing on him the charge of plagiarism. This motion was a thing unknown to the astronomers of the Alexandrian school, and it was pointed out to them by Hipparchus in the way in which he ascertained every other position in astronomy, namely, as the ma¬ thematical result of actual observations, and not as a thing deducible from any opinions on other subjects re¬ lated to it. We see him, on all other occasions, eager to confirm his own observations, and his deductions from them, by every thing he could pick up from other astro¬ nomers ; and he even adduced the above-mentioned practice of the Egyptians in corroboration of his doc¬ trine. It is more than probable then that he did not know any thing more. Had he known the Indian pre¬ cession of 54" annually, he had no temptation whatever to withhold him from using it in preference to one which he acknowledges to be inaccurate, because dedu¬ ced from the very short period of 150 years, and from the observations of Timochares, in which he had no great confidence. Small periodical irregularities in the inclination of the equator to the ecliptic, and in the precession of the equinoxes, were discovered and examined by Bradley with great sagacity. He found that the pole described an epicycle, whose diameter was about 18", having for its centre that point of the circle round the pole of the ecliptic in which the pole would have been found inde¬ pendent of this new motion. He also observed, that the period of this epicyclical motion was 18 years and seven months. It struck him, that this was precisely the period of the revolution of the nodes of the moon’s orbit. He gave a brief account of these results to Lord Macclesfield, then president of the Royal Society, m 1747. Mr Machin, to whom he also communicated the observations, gave him in return a very neat mathe¬ matical hypothesis, by which the motion might be cal¬ culated. Let E (fig. 89.) be the pole of the ecliptic, and SPQ a circle distant from it 230 28', representing the circle of the P describe a circle ABCD, whose diameter AC is 187. I he real situation of the pole will be in the circumfer- . , v ence of this circle; and its place, in this circumference, 262 depends on the place of the moon’s ascending node. Mathema- Draw EPF and GPL perpendicular to it ; let GL bef'.c^ t^eory the colure of the equinoxes, and EF the colure of the equa. solstices. Dr Bradley’s observations showed that the tor be sup- pole was in A when the node was in L, the vernal equi-posed to nox. If the node recede to H, the winter solstice, the d.escribe a pole is in B. When the node is in the autumnal equi-circle‘ nox at G, the pole is at C ; and when the node is in F, the summer solstice, the pole is in D. In intermediate situations of the moon’s ascending node, the pole is in a point of the circumference ABCD, three signs or 90° more advanced. Dr Bradley, by comparing together a great number More exact of observations, found that the mathematical theory,if an ell}Pse and the calculation depending on it, would correspond much better with the observations, if an ellipse were tb^circle. substituted for the circle ABCD, making the longer axis AC 18", and the shorter, BD, 16". M. d’Alem¬ bert determined, by the physical theory of gravitation, the axis to be 18" and I3".4. 2(j4 These observations, and this mathematical theory, These ob- rnust be considered as so many facts in astronomy, and servations we must deduce from them the methods of computing a.nd ^llis the places of all celestial phenomena, agreeable to the are • i • i • • . icieis universal practice ot determining every point of the hea-astronomy, vens by its longitude, latitude, right ascension, and de¬ clination. „ , It is evident, m the first place, that the equation of Obliquity the pole’s motion makes a change in the obliquity ofol'.tlie e~ the ecliptic. The inclination of the equator to the cllPtie' ecliptic is measured by the arch of a great circle inter¬ cepted between their poles. Now, if the pole be in O instead of P, it is plain that the obliquity is measured by EO instead of EP. If EP be considered as the mean obliquity of the ecliptic, it is augmented by 9" when the moon’s ascending node is in the vernal equi¬ nox, and consequently the pole in A. It is, on the contrary, diminished 9" when the node is in the autum¬ nal equinox, and the pole in C ; and it is equal to the mean when the node is in the colure of the solstices. This change of the inclination of the earth’s axis to the plane of the ecliptic was called the nutation of the axis by Sir Isaac Newton. Dr Bradley also discovered a general and periodical motion in all the stars, which alter a little their relative situations. To form an idea of this motion, let us sup¬ pose that each star describes annually a small circum¬ ference parallel to the ecliptic, whose centre is the mean position of the star, and whose diameter, as seen from the earth, subtends an angle of about 40"; and that it was in that circumference as the sun in its orbit, but so that the sun always precedes it by 6o°. .This circum¬ ference, projected upon the surface of the celestial sphere, appears under the form of an ellipse, more or less flat¬ tened according to the height of the star above the equa¬ tor, the smaller axis of the ellipse being to the greater axis as the sine of that height to radius. These periodi¬ cal movements of the stars have received the name of aberrations of thefixed stars. L 2 Besides 8+ ASTRO Apparent Besides these general motions, particular motions Motions have been detected in several stars, excessively slow in- of the deed, but which a long succession of ages has rendered Bodies/ sens^le. These motions have been chiefly observed in t Sirius and Arcturus. But astronomers suppose that all the stars have similar motions, which may become evi- I(S5 dent in process of time. Distance of No method of ascertaining the distance of fixed stars the fixed bath hitherto been found out. Those who have formed measurable. conjectures concerning them, have thought that they ’ were at least 400,000 times farther from us than we are from the sun. They are said to be fixed, because they have been ge¬ nerally observed to keep at the same distances from each Part II other ; their apparent diurnal revolutions being caused I r M. 1. _____ Why they solely by the earth’s turning on its axis. They appear seem so of a sensible magnitude to the bare eye, because the re- naked e”1 t'na a^ectet^ not on*y by the rays of light which are ‘ t>c' emitted directly from them, but by many thousands more, which falling upon our eyelids, and upon the aerial particles about us, are reflected into our eyes so strongly as to excite vibrations not only in those points of the retina where the real images of the stars are formed, but also in other points at some distance round about. This makes us imagine the stars to be much bigger than they would appear, if we saw them only by the few rays which come directly from them, so as to enter our eyes without being intermixed with others. Any one may be sensible of this, by looking at a star of the first magnitude through a long narrow tube ; which, though it takes in as much of the sky as would hold 1000 such stars, yet scarcely renders that one vi¬ sible. The more a telescope magnifies, the lesff is the aper¬ ture through which the star is seen } and consequently, the fewer rays it admits into the eye. Now, since the stars appear less in a telescope which magnifies 200 times, than they do to the bare eye, insomuch that they seem to be only indivisible points, it proves at once that the stars are at immense distances from us, and that they shine by their own proper light. If they shone by borrowed light, they would be as invisible without tele¬ scopes as the satellites of Jupiter are ; for these satel¬ lites appear bigger when viewed with a good telescope than the largest fixed stars do. Dr Herschel has proposed a method of ascertaining the parallax of the fixed stars, something similar, but more complete, than that mentioned by Galileo and others •, for it is by the parallax of the fixed stars that we should be best able to determine their distance. The method pointed out by Galileo, and first attempt¬ ed by Hooke, Flamstead, Molineux, and Bradley, of taking distances of stars from the zenith that pass very near it, has given us a much juster idea of the immense distance of the stars, and furnished us with an approxi¬ mation to the knowledge of their parallax, that is much nearer the truth than we ever had before. But Dr Herschel mentions the insufficiency of tlfeir instru¬ ments, which were similar to the present zenith sec¬ tors, the method of zenith distances being liable to considerable errors on account of refraction, the change of position of the earth’s axis arising from nutation, precession of the equinoxes, and other causes, and the aberration of the light. The method of his own is by 26S Parallax of the fixed stars. N O M Y. means of double stars j which is exempted from these Apparent errors, and of such a nature, that the annual parallax, Motions even if it should not exceed the tenth part of a second, of the may still become more visible, and be ascertained, at Heavfnlj least to a much greater degree of approximation than . it has ever been done. This method is capable of every improvement which the telescope and mechanism of micrometers can furnish. The method and its theory will be seen by the following investigation, extracted p. S?. from his paper on the subject. Let O, E, (fig. 90.) be two opposite points in the annual orbit, taken in the same plane with two stars, a, b, of unequal magni¬ tudes. Let the angle a O b be observed, when the earth is at O, and a E & be observed when the earth is at E. From the difference of these angles, if there should be any, we may calculate the parallax of the stars, according to the theory subjoined. These two stars ought to be as near each other as possible, and also to differ as much in magnitude as we can find them. Dr Herschel’s theory of the annual parallax of double stars, with the method of computing from thence what is generally called the parallax of the fixed stars, or of single stars of the first magnitude, such as are nearest to us, supposes, first, that the stars, one with another, are about the size of the sun $ and, secondlijy that the difference of their apparent magnitudes is ow¬ ing to their different distances ; so that the star of the second, third, or fourth magnitude, is two, three, or four times as far off as one of the first. These princi¬ ples which he premises as postulata, have so great a probability in their favour, that they will hardly he objected to by those who are in the least acquainted with the doctrine of chances. Accordingly, let OE (fig. 91.) be the whole diameter of the earth’s an¬ nual orbit, and let a, b, c, be three stars situated in the ecliptic, in such a manner that they may be seen all in one line O ab c, when the earth is at O. Let the line Q abc be perpendicular to OE, and draw PE parallel to c 0 ; then, if O o, a b, b c, are equal to each other, a will be a star of the first magnitude, b of the second, and c of the third. Let us now suppose the angle O a E, or parallax of the whole orbit of the earth to be 1" of a degree j then we have PE a~0 a Ezzi" : and because very small angles, having the same subtense OE, may be taken to be in the inverse ratio of the lines O a, Ob, O c, &c. we shall have O b E~4-,/, O c E~y,/, &c. Now when the earth is removed to E, we shall have PE £r=E b o=£", and PE a—PE b=za E b—\u, L e. the stars a, b, will ap¬ pear to be y distant. We also have PE c=Ec 0= and PE a—PE enra E c=r|-,/ j i. e. the stars a, c, will appear to be distant when the earth is at E. Now, since we have b EP=4", and c EP—there- r Li fore b EP—c EV=b E c~y—y=y J i. e. the stars b, c, will appear to be only y" removed from each other when the earth is at E. Whence we may de¬ duce the following expression, to denote the parallax that will become visible in the change of distance be¬ tween the two stars, by the removal of the earth from one extreme of ks orbit to the other. Let P express- the total parallax of a fixed star of the first magnitude, M the magnitude of the largest of the two stars, m the magnitude of the smallest, and jp the partial parallax ta 2 rt II. ASTRONOMY. parent o^served by the change in the distance of a dou- ’thg5 hie star; then will -P ; and jo, being found avenly *P\r °^ies' , by observation, will give us Pzz:—E. G, Sup¬ pose a star of the first magnitude should have a small star of the twelfth magnitude near it j then will the • t I 2 X I P partial parallax we are to expect to see be , or •J4 the total parallax of a fixed star of the first mag¬ nitude ; and if we should, by observation, find the partial parallax between two such stars to amount to l", we shall have the total parallax P~Y*~-1 * 1 2 — 12—i P'.opop. If the stars are of the third and twenty- fourth magnitude, the partial parallax will be ——- 3X24 21 =—P 5 and if, by observation, p is found to be a 72 tenth of a second, the whole parallax will come out .1 X 3 X 24 „ 0 2;=0'/.2428. 24—3 ^ Farther, suppose the stars, being still in the ecliptic, to appear in one line, when the earth is in any other part of its orbit between O and E ; then will the pa¬ rallax still be expressed by the same algebraic formula, and one of the maxima will still lie at O, the other at E 5 but the whole effect will be divided into two parts, which will be in proportion to each other as radius — sine to radius -f- sine of the stars distance from the nearest conjunction or opposition. When the stars are anywhere out of the ecliptic, situated so as to appear in one line O a be perpendicu¬ lar to OE, the maximum of parallax will still be ex¬ pressed by —-P ; but there will arise another ad¬ ditional parallax in the conjunction and opposition, which will be to that which is found 90° before or af¬ ter the sun, as the sine (iS*) of the latitude of the stars seen at O is to the radius (R) ; and the effect of this parallax will be divided into two parts ; half of it ly¬ ing on one sidy of the large star, the other half on the other side of it. This latter parallax, moreover, will be compounded with the former, so that the distance of the stars in the conjunction and opposition will then be represented by the diagonal of a parallelogram, whereof the two semiparallaxes are the sides •, a general expression for which will be s -iVL 2MP X SS BR +15 for the stars will apparently describe two ellipses in the heavens, whose transverse axes will be to each other in the ratio of M to tn (fig. 93.), and A «, B £, C c, I) d, will be the cotemporary situations. Now, if Z»Q be drawn parallel to AC, and the parallelogram b (j BQ be completed, we shall have £ Q CA 4 ca~\ C c=z\p, or semiparallax 90° before or after the sun, and B£ may be resolved into, or is compound¬ ed of, b Q and b q ; but b q=^ BD—£ b dzz the se¬ miparallax in the conjunction or opposition. We also have R t S :: : bq— therefore the distance B b (or D 85 X p s Tr the value ofp in this expression, we obtain y m—M 2 M SS ; and by substituting iiotTon"/ of the Heavenly- Bodies. as above. When the stars- are in the pole of the ecliptic, bq will become equal to b Q, and B b will be 7071 Again, let the stars be at some distance, e. g, 5" from each other, and let them both be in the ecliptic. This case is re¬ solvable into the first j for imagine the star a (fig. 92.) to stand at a?, and in that situation the stars .v, b, c} will be in one line, and their parallax expressed by m—M J M m ^Ut tie an8^e °Ea? may be taken to be equal to aOx; and as the foregoing formula gives- us the angles a?E & a? E c, we are to add oi E .v or 3^J to a# E and we shall have a E A In general, let the distance of the stars be d, and let the observed distance at E be E, then will i)~d-^-p, and therefore the whole parallax of the annual orbit will be expressed by, l)M;n—c?M m m—M Suppose the two stars now to differ only in latitude, one being in the ecliptic, the other, e. g. 5 north when seen at O. This case may also be resolved by the former; for imagine the stars b, c, (fig. 91.) to be elevated at right angles above the plane of the fi¬ gure, so that a Ob, or aOc, may make an angle of 5,/ at O ; then, instead of the line O a b c, E a, E b, E c, EP, imagine them all to be planes at right angles to the figure ; and it will appear that the parallax of the stars in longitude must be the same as if the small star had been without latitude. And since the stars b, c, by the motion of the earth from O to E, will not change their latitude, we shall have the following con¬ struction for finding the distance of the stars a b, ac, at E, and from thence the parallax B. Let the tri¬ angle a b (fig. 94.) represent the situation of the stars ; a & is the subtense of j", the angle under which they are supposed to be seen at O. The quantity b, by the former theorem, is found ^—P, which is m JV1 the partial parallax that would have been seen by the earth’s moving from O to E, if hath stars had been in the ecliptic, but on account of the difference in lati¬ tude, it will be now represented by a/3, the hypothe- - nuse of the triangle a bp-, therefore, in general, put- Y7xm m. -M ting a l—d, and a,S=D, we have r:P. Hence I) being taken by observation, and r/, M,5 and m, given, we obtain the total parallax. If the stuation of the stars differs in longitude as well as latitude, we may resolve this case by the following method. Let the triangle (fig. 169.) represent the situation of the stars, a b—d being their distance seen at O, a/3=I> their distance seen at E. That the change h /3, which is produced by the earth’s motion will be truly expressed by ^jA-P may be; proved as before, by supposing the star a. to have been placed at Apparent u. Now let the angle of position £ o « be taken by s Aio n;as micrometer, or by any other method sufficiently exact; Heavenly t^en» ^7 solving the triangle aba, we shall have the lon- Bodies. gitudinal and latitudinal ditferences a a and b a of the two stars. Putca~.r, b a—y, and it will be .r-}-^/3 — ay, whence D -MP V'D*—-y* x Ma/w—M m m—M M + yy i and :P. If neither of the stars should be in the ecliptic, nor have the same longitude or latitude, the last theorem will still serve to calculate the total parallax whose maximum will lie in E. There will, moreover, arise another parallax, whose maximum will be in the con¬ junction and opposition, which will be divided, and lie on different sides of the large star 5 but as we know the whole parallax to be exceedingly small} it will not be necessary to investigate every particular case of this kind ; for by reason of the division of the parallax, which renders observations taken at any other time, except where it is greatest, very unfavourable, the for¬ mulae wrould be of little use. Dr Herschel closes his account of this theory with a general observation on the time and place where the maxima of parallax will happen. Vf hen two unequal stars are both in the ecliptic, or, not being in the ecliptic, have equal latitudes, north or south, and the largest star has most longitude ; the maximum of the apparent distance will be when the sun’s longitude is 90 degrees more than the stars, or when observed in the morning ; and the minimum when the longitude of the sun is 90 degrees less than that 0! the stars, or w’hen observed in the evening. When the small star has most longitude, the maximum and minimum, as well as the time of observation, will be the reverse of the former' W hen the stars differ in latitudes, this makes no alteration in the place of the maximum or minimum, nor in the time of observa¬ tion ; i. e. it is immaterial whether the largest star has the least or the greatest distance of the two stars. Chap. VI. Oj the Figure of the Earth. Having now described the apparent motions of the heavenly bodies, let us return to the earth, in order to examine the information which has been collected con- 269 cerning its figure. Earthsphe- We have seen already, that the earth is spherical. The force of gravity constantly directed towards its centre retains bodies on its surface, though situated'on places diametrically opposite, or though antipodes to each other. The sun and stars appear always above the earth j for above and below are merely relative to the 27° direction of gravity. howTscer-8 As S00n tlle sPlierical figure of the earth was dis- taineeb " covered> curiosity naturally led men to endeavour to measure its dimensions. Hence it is probable, that at¬ tempts of that nature were made in very ancient times. The reference which several of the ancient measures have to the size of the globe is a confirmation of this. But among the moderns, Picard was the first who exe¬ cuted the task with any degree of success. He mea¬ sured a degree of the meridian in France about the middle of the 17th century. Since a meridian, or any other circle on a sphere, may be conceived to be divided into 360 equal parts, called degrees, and these into minutes and seconds, as explained by the writers on trigonometry, the circum¬ ference of the earth, and thence its diameter, may be determined by measuring the length of a degree on the meridian or any other great circle. To perform this important problem, there have been various methods invented by different philosophers of early and later times ; one of these methods, which unites consider¬ able accuracy with great facility, will be readily under¬ stood from fig. 95. where PB and ST represent two mountains or very high buildings, the distance PS between which-must be very nicely determined by longimetry : then, by measuring the angles HBT and Kf'B with an accurate instrument, their sum taken from 1800 leaves the angle BRT, which is measured also by the arc PS ; whence PS is known in parts of the whole circle. Thus, if the angle BTR be 89° AS' 32"> t,,e ang^e TBR 89° 54' 28", and the distance PS 23tV English miles ; then the angle R or arc PS being equal to 1800-—89° 45' 32" +89° 54' 28"= 20' it will be, as 20' : 60' or i° :: 23^ : 69! English miles, length of a degree. Plence the circumference of the earth is (according to this example) 24912 miles, and its diameter nearly 7930 miles.—A material advantage attending this method is, that there is no oc¬ casion to measure the altitudes of the mountains, an object which can seldom be attained without consider¬ able difficulty. 1 he method which is given above is, it must be confessed, as well as all the other methods which aim at the measurement of a degree without having re¬ course to the heavenly bodies, liable to some inaccu¬ racy 5 for, by reason of the changes in the state of the atmosphere, distant terrestrial objects never appear in their true places j they always seem more or less ele¬ vated or distant, according to the nature of the season, and the time of the day. On this account—and be¬ cause it could not escape observation, that as persons changed their situation on the earth by moving towards the north or the south, the stars and other heavenly bodies either increased or decreased their apparent alti¬ tudes proportionally—the measurement of a degree was attempted even by the earliest philosophers, by means of known fixed stars. Every person who is ac¬ quainted with plane trigonometry will admit, that the distance of two places, north and south of each other, may be accurately measured by a series of triangles ; for if we measure the distance of any two objects, and take the angles which each of them make with a third, the triangle formed by the three objects will become known ; so that the other two sides may be as truly determined by calculation, as if they had been actu¬ ally measured. And by making either of these sides the base of a new triangle, the "distances of other ob¬ jects may be found in the same manner 5 and thus by a series of triangles, properly connected at their bases, ive might measure any part of the circumference of the earth. And if these distances were reduced to the north and south, or meridian line, and the altitude of some star was measured at the extremities of the distance, iart II. Oft ifaitj Boiiiil A S T It O Moti' r)|)iireHt distance, the difference of the altit udes would he equal Viotions to the length of the grand lines in degrees, minutes, &c. of the whence the length of a degree would be known. This dlifdies^ meti10d was5 we helieve, first practised by Eratosthenes ' |[ ‘ i in Egypt j and has been frequently used since with greater and greater accuracy, in proportion as the in¬ struments for taking angles became, by gradual im¬ provements, more exact and minute. By this method, or some others not widely different, and which it is needless here to explain, the length of a degree has been measured in different parts of the earth ; the results of the most noted of these admeasure¬ ments it may be proper to give. Snell found the length of a degree by two different methods : by one method he made it 57064 Paris toises, or 342384 feet; and by the other 57057 toises, or 342342 feet. M. Picard, in 1669, f°and by mensuration from A- miens to Malvoisin, the quantity of a degree to be 57060 toises, or 342360 feet ; being nearly an arith¬ metical mean between the numbers of Snell. Our countryman Norwood, about the year 1635, by measuring between London and York, determined a degree at 367196 English feet, or 57300 Paris toises, or 69 miles 288 yards. Muschenbroek, in 1700, with a view of correcting the errors of Snell, found by particular observations that the degree between Alcmaer and Bergen-op zoom con¬ tained 57033 toises. Messrs Maupertuis, Clairaut, Monnier, and others from France, were sent on a northern expedition, and began their operations in July 1736; they found the length ol a degree in Sweden to he 57439 toises, when reduced to the level of the sea. About the same time Messrs Godin, Bougucr, and Condamine, from France, with some philosophers from Spain, were sent to South America, and measured a degree in the province of Quito in Peru ; the medium ot their results gives about 56750 toises for a degree. M. de la Caille, being at the Cape of Good Hope in 1752, found the length of a degree on the meridian there to be 57037 toises. In 1755 Father Boscovich found the length of a degree between Rome and Rimini in Italy to be 56972 toises. In 1764, F. Beccaria measured a degree near Turin ; from his measurement he deduced the length of a de¬ gree there 57024 toises. At Vienna the length ol a degree was found 57091 toises. ■ And in 1766 Messrs Mason and Dixon measured a degree in Maryland and Pennsylvania, North America, which they determined to he 363763 English feet, or 56904^ Paris toises. I he difference of these measures leads us to conclude that the earth is not exactly spherical, but that its axis ' which passes through the poles, is shorter than that which passes through the equator. But the observa- Itions which have been made to determine the magni¬ tude and figure of the earth, have not hitherto led to results completely satisfactory. They have indeed de¬ monstrated the compression or oblateness of the terre¬ strial spheroid, but they have left an uncertainty as to the quantity ol that compression, extending from about the 170th, to the 330th part of the radius of the equa¬ tor. Between these two quantities, the former of which is nearly double of the latter, most of the re- 87 N O M Y. suits are placed, but in such a manner that those best Apparent entitled to credit are much nearer to the least extreme Motions than to the greatest. S;r Isaac Newton, as is well 01 ll|e known, supposing the earth to be of uniform density, F^'dvV1,y assigned for the compression at the poles 230 nearly a mean between the two limits just mentioned ; and it is probable, that, if the compression is less than this, it is owing to the increase of the density toward the centre. Boscovich, taking a mean from all the mea¬ sures ol degrees, so as to make the positive and nega¬ tive errors equal, found the difference of the axis of the meridian ■^-g. By comparing the degrees mea¬ sured by Father Leisganic in Germany, with eight others that have been measured in different latitudes, I ind, suppressing the degree in La Labde finds •—•, 311 Lapland, which appears to err iu excess, A— for the 331 compression. La Place makes it 321 Sejour 3°7 and lastly, Carouge and La Lande . 300 These anomalies have induced some astronomers, Supposed especially M. de la Place, to give up the spheroidal fi-figure of gure of the earth altogether, to suppose that it is notAie eai^u a solid of revolution, and that its surface is a curve of double curvature. Mr Playfair, on the other hand, in an excellent dissertation on the subject, published in the fifth volume of the Edinburgh Transactions, sup¬ poses, that the anomalies may be owing to the differ¬ ent densities of the strata fiear the surface where the degrees were measured, occasioning errors in the mea¬ surement. The position of the different places on the earth’s sur- j^tj/udes face is determined by their distance from the equator, and longi- called their latitude, and from a first meridian called tudes how their longitude. The latitude is easily ascertained by oh-foun(l- serving the height of the pole: The longitude is calcu¬ lated by observing some celestial phenomenon, as an eclipse of Jupiter’s satellites at the same instant in two places situated in different meridians. The difference in point of apparent time in the two places, gives their di¬ stance east or west from each other, and consequently the difference of their longitude ; for it is not noon at the same time in all the different parts of the earth’s sur¬ face. When it is noon at London, it is only eleven o’clock in all the places 150 west from London, while it is one o’clock in all places 150 east from London. Every 150 east or west causes the difference of an hour. Hence the difference in time, when any celestial pheno¬ menon. is observed, gives us the distance east and west, or in longitude, between the places where it is obser- ved. The eclipses of Jupiter’s satellites are of the greatest service in determining the longitude of places on this earth, astronomers therefore have been at great pains to calculate tables for the eclipses of these satellites by their primary, for the satellites themselves have never been observed to eclipse one another. The construc- tioa e SB Apparent Motions of the Heavenly Codies. Fig. <>?• Philosophi¬ cal Maga¬ zine, vol. xv. p. 97. 274 Mr Lowe’s method of finding the longitude. A S T B tlon of such tallies is indeed much easier for these sa¬ tellites than of any other celestial bodies, as their mo¬ tions are much more regular. The English tables are calculated for the meridian 1 of Greenwich, and by these it is very easy to find how many degrees of longitude any place is distant either east or west from Greenwich j for, let an observer, who has these tables, with a good telescope and a well- regulated clock at any other place of the earth, ob¬ serve the beginning or ending of an eclipse of one of Jupiter’s satellites, and note the precise moment of time that he saw the satellite either immerge into, or emerge out of, the shadow, and compare that time with the time shown by the tables for Greenwich : then 15 degrees dift’erence of longitude being allowed for every hour’s difference of time, will give the longitude of that place from Greenwich 3 and if there be any odd minutes of time, for every minute a quarter of a degree, castor west, must be allowed, as the time of observation is later or earlier than the time shown by the tables. Such eclipses are very convenient for this purpose at land, be¬ cause they happen almost every day 3 but are of no use at sea, because the rolling of the ship hinders all nice telescopical observations. To explain this by a figure, let J be Jupiter, K, L, M, N, his four satellites in the respective orbits, 1, 2, 3, 4 3 and let the earth be at F (suppose in November, although that month is no otherwise material than to find the earth readily in this scheme, where it is shown in eight difierent parts of the orbit). Let Q be a place on the meridian of Greenwich, R a place on some other meridian eastward from Greenwich. Let a person at R observe the instantaneous vanishing of the first satellite K. into Jupiter’s shadow, suppose at three o’clock in the morning; but by the tables he finds the immersion of that satellite to be at midnight at Greenwich ; he then can immediately determine, that as there are three hours difference of time between Q and K, and that R is three hours forwarder in rec¬ koning than Q, it must be 45 degrees of east longitude from the meridian of Q. Were this method as practi¬ cable at sea as at land, any sailor might almost as easily, and with equal certainty, find the longitude as the lati¬ tude. From its impracticability, the seaman is obliged to have recourse to other celestial phenomena, and the most useful are the motions of the moon. On this sub¬ ject we shall satisfy ourselves with inserting the follow¬ ing observations of Mr Lowe, who has pointed out a very simple method of ascertaining the longitude on land. Although the method of determining the difference of longitude at sea from the lunar observations has been accurately laid down by Dr Maskelyne and other able nautical astronomers, it has, however, happened that several writers on longitude and astronomy have, in the course of the last twenty years, given rules for finding the difference of longitude at land from the moon’s transits, either so erroneous or imperfect, that the adoption thereof might do a serious injury both to navigation and geography : they have given examples-, but no demonstrations 3 or at least such obscure and imperfect ones, as prove that they had not a clear con¬ ception of the matter. O N O M Y. Part If It is for these reasons that the following demonstra- Appard tion of a rule both easy and accurate for finding the Motion’ difference of longitude is now proposed. The data are 0< ^ the observed increase of the moon’s right ascension in passing from the first to the second meridian, and the increase of the sun’s and moon’s right ascension in twelve hours apparent time, which may be had from the Nautical Almanack. Demonstration.—Let the circle ABC represent the Fig. 97. equator, P its pole, and A PD the first meridian, as that of Greenwich. Suppose that the centres of the sun, the moon, and a fixed star, are on that meridian at the same moment of time as represented at A, and that they move from thence to the westward with their re¬ spective velocities, the earth being considered as at rest. Then, after twelve hours apparent time, the sun will be at D, the opposite point to A, or 180° distant from it 3 but the fixed star, moving in appearance over a greater space than 1800 in twelve hours apparent time, will be at E ; while the moon, with a motion appa¬ rently slower than the sun and the star, will appear af¬ ter twrelve hours at the point B, or on a meridian BP. But ED is the distance of the sun from the star after an interval of twelve hours apparent time, and EB the distance of the moon, or, in other words, the increase of their respective right ascensions: and since ED and EB are known from the Nautical Almanack, if we subtract the first from the last, we have DB, equal to the difference between the increase of the sun’s and moon’s right ascension in twelve hours apparent time. Now the difference of longitude between the two me¬ ridians AP and BP is the arc A ,3 B, equal to A /3 D less the arc DB 3 that is, equal to 18o° less the difl’er- ence between the increase of the sun’s and moon’s right ascension in twelve hours 3 and, since the increase of the moon’s right ascension from the time of its passing the meridian AP to the time of its passing BP is known from observation, and equal to EB, we can make the following proportion for finding the difference of longi¬ tude between any other two meridians, AP and /2 P, from the observed increase of the moon’s right ascen¬ sion t fi. As EB : A /3 D—DB :: s /3 : A ,3 the difference of longitude ; or, in more familiar language, as the in¬ crease of the moon’s right ascension in twelve hours ap¬ parent time is to 1800 or 12 h. less the difference be¬ tween the increase of the sun’s and moon’s right ascen¬ sion in that time :: so is any other observed increase of the moon’s right ascension between two meridians : to their difference of longitude. If the increase of the moon’s right ascension in 12 hours were uniform, or such that equal parts of it would be, produced in equal times, the above rule would be strictly accurate 3 but as that increase arises from a motion continually accelerated or retarded, and seldom uniform but for a short space of time, it will therefore be necessary to find the mean increase of the moon’s right ascension when it is at the intermediate point between A and /3, in order to determine their dif¬ ference of longitude with the greatest precision ; and for that purpose, Taylor’s Tables of Second Difference are very useful. Ao-w^/e.-—April the 8th, 1800, the transit of the moon’s first limb was observed at the royal observato¬ ry IL ASTRO A isrcnt ^ C^) > and, allowance being made for the error of Mions the clock, its right ascension was Add the time that the moon’s semi- ■diameter took to pass the meridian H. 12 M. 35 Sec. lS.22 8.38 Right ascension of the moon’s centre 12 36 26.6 On a meridian (/3) far to the west¬ ward, the transit of the moon’s first limb was observed the same day, and being reduced to the centre, its right ascen¬ sion was - _ . 12 47 56.7 Increase of right ascension between A and /3. - - _ _ The increase of the moon’s right as¬ cension in 12 hours apparent time per l he Nautical Almanack was The increase of the sun’s in the same time - - _ 11 30.1 26 3 49^5 Difference - - . o 24 13.35 And 12 hours minus this difference is = 11 h. 35 m. 46.65 sec. j therefore, as 26 m. 3 sec. : 11 h. 35 m. 46.65 sec. :: 11 m. 30.1 sec.: to 5 h. 7 m. 12 sec. the correct difference of longitude between A and /3. By reducing the three terms to seconds, and using logarithms, the operation is much shortened. In a book published by Mr Mackay on longitude about 15 or 16 years ago, there is a rule given, and also an example, for finding the difference of longitude at land from the transits of the moon, but no demon¬ stration.^ Ihe rule, when divested of its high-sounding enunciation, runs thus: ° As the increase of the moon’s right ascension in 12 'hours apparent time : is to 180° :: so is any other ob¬ served increase between two meridians : to their differ¬ ence of longitude. It follows from this, that the moon as well as the sun would, in 12 hours apparent time pass over an arc of 1800, although the apparent mo¬ tion of the moon to the westward in 12 hours, or 1800 of space, be less than that of the sun by six or seven degrees; and so much error would this method pro¬ duce, if the two places differed about 180° in loim. tude. 0 The above example, wrought according to Mac- kay’s rule, would come out thus : \ s It- M. Sec. As 26 m. 3 sec.: 12 li. :: 11 m. 30.1 sec. to 5 17 53.7 But the correct difference as above is 5 712 Error o 10 41.7 which amounts to more than 2^°, or 150 miles, in a difference of longitude little exceeding five hours. Mr Edward Bigot adopts the very same rule-for de- termimng the difference of longitude between Green- wich and York, and states the result in the Philoso¬ phical transactions for 1785, p. 417. Mr \ ince has inserted this rule and example in his leatise of Practical Astronomy ; but we have to re¬ gret that they were not accompanied with a strict de¬ monstration. N O M Y. g9 Fasciculus Astronomicus, published two or three years Apparent ago, has given a rule, without demonstration or ex- Motions ample, for finding the difference of longitude from the of the moon’s transits, which produces the same error as I^ayeilly Mackay’s and Pigot’s, although worded differently from theirs. Mr Wollaston makes the first term of his proportion apparent, and the third mean time? this renders the result erroneous. Since the motions of the sun, moon, and planets are computed for apparent time, and given so in the Nautical Almanack, mean time is not at all requisite for resolving the difference of longitude either at sea or at land. We shall there¬ fore endeavour to apply Mr Wollaston’s rule, accord¬ ing to its literal meaning, for finding the difference of longitude from the above observations. . Th6 right ascension of the moon’s centre on the me¬ ridian of Greenwich being known, we can easily de¬ duce the mean and apparent time corresponding to it j and in like manner the mean and apparent time at the distant meridian /3. The apparent and mean time of the transits of the moon’s centre over the meridians of A and ,8, when strictly computed, were as follows: Apparent Time. Mean Time. . H- M. Sec. H. M. Sec. ff 7- ‘ ’ H2647.81 112833.5 ^ " ‘ 11 37 29-5 11 39 11.4 Time later at /3 than at A Erom the increase of the moon’s right ascen¬ sion in 12 hours Subtract the increase of the sun’s right ascen¬ sion in that time O 10 41.69 o 10 37.9 26 49-65 retarda- 24 13*35 moon’s retardation m 12 to the The Rev. Mr Wollaston, in the appendix to his VoL. Ill, Part I. + The moon’s tion in 12 hours l hen, “ As twice the hours : is to 24 hours :: “ So is the mean time later at £ than at A difference of longitude west from A.” . tAftf,r doulding 24 m. 13.25 sec. and also 12, which is totally unnecessary, as the result would be the same tion • St00Cl S1Dsle’ We State tIie ft>1Ilowing propor- As 48 m. 26.7 sec. : 34 h. :: 10 m. 37.9 sec. to 5I1. 15 m. 1.3 sec. the difference of longitude between A and /3. . But as the third term is improperly reduced to mean time, we shall take the apparent time above found, and then 48 m. 26.7 sec. : 24 h. :: 10 m. 41.69 sec. to 5 h. 17 m. 53.7 sec.; the same as results from Mac¬ kay’s and Pigot’s rules. We shall only remark, that 5 h. 17 m. 53.7 sec. is the apparent time that the moon took in passing from the meridian of A to the meridian of /3 ; but from what has been demonstrated, the apparent time at /3 will be equal to the difference between the increase of the sun’s and moon’s right ascension in that interval of apparent time; for DB, or 24 m. 13.35 sec. is the difference tor 12 hours, and therefore by proportion 2/3, or 10 m. 41.69 sec. will be the difference for 5 h. 17 m. 53.7 sec.* subtracting the former from the latter, we have 5 h! 7 m. 12 sec. the difference of longitude as before, and M 90 ASTRONOMY. Part of the Heavenly Bodies. Apparent a clear proof that the authors above mentioned have Motions omitted to deduct the apparent time at the distant place or station /3, from the apparent time at Greenwich. A very important fact relative to the earth has been ascertained by astronomers, namely, that the weight of bodies does not continue the same when carried to dif¬ ferent parts of it. It is impossible to ascertain this va¬ riation by the balance, because it affects equally the bodies weighed and the weight by which wTe estimate its gravity. But the pendulum affords a certain me¬ thod of detecting every such change 5 because the num¬ ber of oscillations made by a given pendulum in a given time depends upon the force of gravity. The smaller that force, the fewer vibrations will it make. Therefore, if the force of gravity diminish, the pendulum will move slower; if it decreases, it will oscillate with Appar« more celerity. In different pendulums the slowness of Motior vibration is proportional to the length of the pendulum : of the If a pendulum be lengthened it moves slower, if it be shortened it moves swifter than before. Mr Richer ■ ^ ^ in a voyage made to Cayenne, found that the pendu¬ lum of his clock did not vibrate so frequently there, as it did when at Paris; but that it was necessary to short¬ en it by about the eleventh part of an inch to make it vibrate in exact seconds. The nearer the equator a pen¬ dulum is placed it vibrates the slower, the nearer the pole it is placed it vibrates the faster. Hence it fol¬ lows that the force of. gravity is greatest at the poles, and that it gradually diminishes as we approach the equator, where it is smallest. 'limp inn tin ilia! ■anc' ! Mr- 275 Argument for the earth’s mo tion from its spheroi¬ dal figure. PART III. OF THE REAL MOTIONS OF THE HEAVENLY BODIES. WE have now enumerated and explained the ap¬ parent motions of the heavenly bodies. Nothing can appear more intricate and perplexed, or more remote from what we are accustomed to consider as the sim¬ plicity of nature. Hence mankind have in all ages been tempted to consider them as merely apparent, and not real; and the object of astronomers has always been to detect the real motions of the heavenly bodies from those which they exhibit to the eye of a spectator on the earth. Neither industry nor address was spared to gain this desirable end. Hypothesis was formed after hypothesis ; every new supposition was a step towards the truth ; and at last the real motions have not only been ascertained but demonstrated in the most satisfac¬ tory manner. It shall be our object in this part of our treatise to lay before our readers the result of these dis- Chap. I. Of the Rotation of the Earth. lar regions : for as the equatorial parts move quickest, they will recede farthest from the axis of motion, and enlarge the equatorial diameter. That our earth is really of this figure, is demonstrable from the unequal vibrations of a pendulum, and the unequal lengths of degrees in different latitudes. Since then the earth is higher at the equator than at the poles, the sea, which naturally runs downward, or towards the places which are nearest the centre, would run towards the polar re¬ gions, and leave the equatorial parts dry, if the cen¬ trifugal force of these parts, by which the waters were carried thither, did not keep them from returning. The earth’s equatorial diameter is 36 miles longer than its axis. Bodies near the poles are heavier than those towards yygfght the equator, because they are nearer the earth’s centre, bodies where the whole force of the earth’s attraction is accu-nicreasi mulated. They are also heavier, because their centri-t0,jvar^ 276 fugal force is less, on account of their diurnal motion poles. We find that the sun, and those planets on which there are visible spots, turn round their axis: for the spots move regularly over their disks (b). Fronl hence we may reasonably conclude, that the other planets on which we see no spots, and the earth, which is likewise a planet, have such rotations. But being incapable of leaving the earth, and viewing it at a distance, and its rotation being smooth and uniform, we can neither see it move on its axis as we do the planets, nor feel our¬ selves affected by its motion. Yet there is one effect of such a motion, which will enable us to judge with cer¬ tainty whether the earth revolves on its axis or not. All globes which do not turn round their axis will be perfect spheres, on account of the equality of the weight of bodies on their surfaces 5 especially of the fluid parts. But all globes which turn on their axis will be oblate spheroids 5 that is, their surfaces will be higher or far¬ ther from the centre in the equatorial than in the po- being slower. For both these reasons, bodies carried from the poles towards the equator gradually lose their weight. Experiments prove, that a pendulum which vibrates seconds near the poles vibrates slower near the equator, which shows that it is lighter or less attracted there. To make it oscillate in the same time it is found necessary to diminish its length. By com¬ paring the different lengths of pendulums swinging seconds at the equator and at London, it is found that a pendulum must be ‘I-ttsSo lines shorter at the equator than at the poles. A line is a twelfth part of an inch. If the earth turned round its axis in 84 minutes 43 seconds, the centrifugal force would be equal to the powrer of gravity at the equator j and all bodies there would entirely lose their weight. If the earth revolved quicker, they would all fly off and leave it. A person on the earth can no more be sensible of its undisturbed motion on its axis, than one in the cabin of (b) This, however, must be understood with some degree of limitation, as will evidently appear from what has been already said concerning the variable motion both of the spots of the sun and planets. bn •after * !ctiou " wete, irtFft III. ASTRO :77 Eiih’s mo- eal of a ship on smooth water can be sensible of the ship’s lli (lotions motion, when it turns gently and uniformly round. It the js therefore no argument against the earth’s diurnal mo- R8 Tdies^ ^on ^ia*' we no^ ^ ’ nor ^ie aPParent revolu- ■ tions of the celestial bodies every day a proof of the rea¬ lity of these motions ; for whether we or they revolve, the appearance is the very same. A person looking through the cabin windows of a ship, as strongly fancies the objects on land to go round when the ship turns as if they were actually in motion. If we could translate ourselves from planet to planet, tio: proved we should still find that the stars would appear of the rro: the same magnitudes, and at the same distances from each 3«tialap-0ther as they do to us here ; because the width of the ISdiffer- remotest planet’s orbit bears no sensible proportion to ;nt<’lanets. the distance of the stars. But then the heavens would seem to revolve about very dilFerent axes ; and conse¬ quently, those quiescent points, which are our poles in the heavens, would seem to revolve about other points, which, though apparently in motion as seen from the earth, would be at rest as seen from any other planet. Thus the axis of Venus, which lies at right angles to the axis of the earth, would have its motionless poles in two opposite points of the heavens lying almost in our equinoctial, where the motion appears quickest* because it is seemingly performed in the greatest circle : and the very poles, which are at rest to us, have the quickest motion of all as seen from Venus. To Mars and Jupiter the heavens appear to turn round with very dilFerent velocities on the same axis, whose poles are about 234 degrees from ours. Were we on Jupi¬ ter, we should be at first amaied at the rapid motion of the heavens $ the sun and stars going round in 9 hours 56 minutes. Could we go from thence to Venus, we should be as much surprised at the slowness of the hea¬ venly motions ; the sun going but once round in 584 hours, and the stars in 540. And could we go from Venus to the moon, we should see the heavens turn round with a yet slower motion 5 the sun in 708 hours, the stars in 655. As it is impossible these various cir¬ cumvolutions in such different times, and on such dif¬ ferent axes, can be real, so it is unreasonable to suppose the heavens to revolve about our earth more than it does about any other planet. When we reflect on the vast distance of the fixed stars, to which 190,000,000 of miles, the diameter of the earth’s orbit, is but a point, we are filled with amazement at the immensity of the distance. But if we try to frame an idea of the extreme rapidity with which the stars must move, if they move round the earth in 24 hours, the thought becomes so much too big for our imagination, that we can no more conceive it than we do infinity or eternity. If the sun was to go round the earth in 24 hours, he must travel upwards of 300,000 miles in a minute: but the stars being at least 400,000 times as far from the sun as the sun is from us* those about the equator must move 400,000 times as quick. And all this to serve no other purpose than what can be as fully and much more simply obtained by the earth’s turning round eastward as on an axis, eveiy 24 hours, causing there¬ by an apparent diurnal motion of the sun westward, and bringing about the alternate returns of day and ^ J*8 night. jetton ^ common objections against the earth’s s.n»wrej motion on its axis, they are all easily answered and set >! N O M Y. aside. That it may turn without being seen or felt by us to do so, has been already shown. But some are apt to imagine, that if the earth turns eastward (as it certainly does if it turns at all), a ball fired perpen¬ dicularly upward in the air must fall considerably west¬ ward of the place it was projected f rom. The objec¬ tion which at first seems to have some weight, will be found to have none at all, when we consider that the gun and ball partake of the earth’s motion j and there¬ fore the ball being carried forward with the air as quick as the earth and air turn, must fall down on the same place. A stone let fall from the top of a main¬ mast, if it meets with no obstacle, falls on the deck as near the foot of the mast when the ship sails as when it does not. If an inverted bottle full of liquor be hung up to the ceiling of the cabin, and a small hole be made in the cork, to let the liquor through on the floor, the drops will fall just as far forward on the floor when the ship sails as when it is at rest. And gnats or flies can as easily dance among one another in a moving cabin as in a fixed chamber. As for those Scripture expres¬ sions which seem to contradict the earth’s motion, this general answer may be made to them all, viz. it is plain from many instances, that the Scriptures were ne¬ ver intended to instruct us in philosophy or astronomy; and therefore on those subjects expressions are not al¬ ways to be taken in the literal sense, but for the most part as accommodated to the common apprehensions of mankind. Men of sense in all ages, when not treat¬ ing of the sciences purposely, have followed this me¬ thod : and it would be in vain to follow any other in addressing ourselves to the vulgar, or bulk of any com¬ munity. Chap. II. Of the Revolution of the Planets round the Sun. The apparent motions of the planets lead us to con¬ clude that they all move in orbits nearly circular round the sun, while the sun moves round the earth : that the orbits of Venus and Mercury are nearer the sun than the earth; but the orbits of the other planets include the earth within them. All the apparent motions are reconcilable to this opinion, and lead us to form it. It removes all the inexplicable intricacy of their apparent motions. But the earth itself is a planet, and bears a very exact resemblance to the rest. Shall we suppose all the other planets to revolve round the sun while it alone remains stationary P Or shall we suppose that the earth, like the other planets, revolves round the sun in the course of a year ? The phenomena in both cases will be exactly the same, but the motion of the earth will reduce the whole system to the greatest simplicity, whereas the motion of the sun carrying with it the revolving planets would leave the whole complicated and involved. Various opinions on this subject have been maintained by astro¬ nomers. Concerning the opinion of the very first astronomers about the system of nature, we are necessarily as igno¬ rant as we are of those astronomers themselves. "What¬ ever opinions are handed down to us, must be of a vast¬ ly later date than the introduction of astronomy a- mong mankind. If we may hazard a conjecture, how¬ ever, we are inclined to think that the first opinions M 2 on 9t Real Motions of the Heavenly Bodies. 92 Real Motions of the, Heavenly Bodies. 279 on this subject were much more just than those that were held afterwards for many ages. We are told that Pythagoras maintained the motion of the earth, which is now universally believed, but at that time appears to have been the opinion of only a few detach- ^ individuals of Greece. As the Greeks borrowed Pythasore- many things from the Egyptians, and Pythagoras had ^ c 1 travelled into Egypt and Phenice, it is probable he might receive an account of this hypothesis from thence 1 but whether he did so or not, we have now no means of knowing, neither is it of any im¬ portance whether he did or not. Certain it is, how¬ ever, that this opinion did not prevail in his days, nor for many ages after. In the second century after Christ, the very name of the Pythagorean hypothesis was sup- 280'' pressed by a system erected by the famous geographer Suppressed and astronomer Claudius Ptolemaeus. This system, t»y the Pto- which commonly goes by the name of the Ptolemaic, ASTRONOMY. 281 Ptolemy’s system in¬ sufficient. he seems not to have originally invented, but adopted as the prevailing one of that age j and perhaps made it somewhat more consistent than it was before. He supposed the earth at rest in the centre of the universe. Round the earth, and the nearest to it of all the hea¬ venly bodies, the moon performed its monthly revolu¬ tions. Next to the moon was placed the planet Mer¬ cury j then Venus ; and above that the sun, Mars, Ju¬ piter, and Saturn, in their proper orbits 5 then the sphere of the fixed stars •, above these, two spheres of what he called crystalline heavens j. above these was the primum mobile, which, by turning round once, in 24 hours, by some unaccountable means or other, car^ ried all the rest along with it. This primum mobile was encompassed by the empyrean heaven, which was of a cubic form, and the seat of angels and blessed spirits. Besides the motions of all the heavens round the earth once in 24 hours, each planet was supposed to have a particular motion of its own ; the moon, for instance, once in a month, performed an additional revolution, the sun in a year, Sec. See fig. 98. It is easy to see, that, on this supposition, the con¬ fused motions of the planets already described could never be accounted for. Had they circulated uniform¬ ly round the earth, their apparent motion ought always to have been equal and uniform, without appearing either stationary or retrograde in any part of their courses. In consequence of this objection, Ptolemy was obliged to invent a great number of circles, inter¬ fering with each other, which he called epicycles and eccentrics. These proved a ready and effectual salvo for all the defects of his system ; as, whenever a planet was deviating from tlie course it ought on his plan to have followed, it was then only moving in an epicycle or an eccentric, and would in due time fall into its proper path. As to the natural causes by which the planets were directed to move in. these epicycles and eccentrics, it is no wonder that he found himself much at a loss, and was obliged to have recourse to divine power for an explanation, or, in other words, to own that his system was unintelligible. This system continued to be in vogue till the begin- rean system ning of the 16th century, when Nicolaus Copernicus, revived by a native of Thorn (a city of Regal Prussia), and a man opeuucus. great abilities, began to try whether a more satis¬ factory manner of accounting for the apparent motions of ^the heavenly bodies could not he obtained than was 1 282 Pythago- Rea] Motion! of tlie he 'S Part II afforded by the Ptolemaic hypothesis. He had recourse to every author upon the subject, to see whether any bad been more consistent in explaining the irregular mo¬ tions of the stars than the mathematical schools : but he received no satisfaction, till he found first from Cicero, that Nicetas the Syracusan had maintained the motion of the earth 5 and next from Plutarch, that others of the ancients had been of the same opinion. From the small hints he could obtain from the ancients, Coperni¬ cus then deduced a most complete system, capable of solving every phenomenon in a satisfactory manner. ■From him his system hath ever afterwards been called the Copernican, and is represented fig. 99. Here the sun is supposed to be in the centre j next him revolves the planet Mercury ; then Venus ; next, the Earth, with the Moon : beyond these, Mars, Jupiter, and Sa¬ turn j and far beyond the orbit of Saturn, he supposed the fixed stars to be placed, which formed the bound¬ aries of the visible creation. g Though this hypothesis afforded the only natural andTychonic satisfactory solution of the phenomena which so muebsystem. perplexed Ptolemy’s system, it met with great opposi¬ tion at first j which is not to be wondered at, consider¬ ing the age in which he lived. Even the famous astro¬ nomer Tycho Brahe could never assent to the earth’s motion, which was the foundation of Copernicus’s scheme. He therefore invented another system, where-Fig. 100, by he avoided the ascribing of motion to the earth, and at the same time got clear of the difficulties with which Ptolemy was embarrassed. In this system, the earth was supposed the centre of the orbits of the sun and moon j but the sun was supposed to be the centre of the orbits of the five planets ; so that the sun with all the planets were by Tycho Brahe supposed to turn round the earth, in order to save the motion of the earth round its axis once in 24 hours.. This system was never much followed, the superiority of the Copernican scheme being evident at first sight. The sun is so immensely bigger and heavier than the earth, that, if he was moved out of his place, not only the earth, but all the other planets, if they were united into one mass, would be carried along with the sun as the pebble would be with the mill-stone. By considering the law of gravitation, which takes From the place throughout the solar system, in another light, it proportion' will lie evident that the earth moves round the sun in aal decreas year, and not the sun round the earth. It has been ^ gra1"tj! observed, that the power of gravity decreases as the&C' square of the distance increases ; and from this it fol¬ lows with mathematical certainty, that when two or more bodies move round another as their centre of mo¬ tion, the squares of their periodic times will be to one another in the same proportion as the cubes of their distances from the central body. This holds precisely with regard to the planets round the sun, and the sa¬ tellites round the planets 5 the relative distances of all wlneh are well known. But, if we suppose the sun to. move round the earth, and compare its period with the moon’s by the above rule, it will be found that the sun would take no less than 173.510 days to move round the earth 5 in which case ©ur year would be 475 times as long as it now is. To this we may add, that the aspects of increase and decrease of the planets, the times of their seeming to stand still, and to move direct and retrograde, answer precisely to the earth’s motion •, but Fa lie* Ik djectii 8 Son ired. 284 Real Motions of the :eavenly Bodies. 'art III. bat not at all to the sun’s without introducing the most absurd and monstrous suppositions, which would destroy all harmony, order, and simplicity, in the system. Moreover, if the earth be supposed to stand still, and j the stars to revolve in free spaces about the earth in 24 hours, it is certain that the forces by which the stars revolve in their orbits are not directed to the earth, but to the centres of the several orbits ; that is, of the se¬ veral parallel circles which the stars on different sides of the equator describe every day ; and the like infe¬ rences may be drawn from the supposed diurnal mo¬ tion of the planets, since they are never in the equinoc¬ tial but twice in their courses with regard to the starry heavens. But, that forces should be directed to no central body, on which they physically depend, but to innumerable imaginary points in the axis of the earth produced to the poles of the heavens, is an hypo¬ thesis too absurd to be allowed of by any rational creature. And it is still more absurd to imagine that these forces should increase exactly in proportion to the distances from this axis •, for this is an indication of an increase to infinity j whereas the force of attrac¬ tion is found to decrease in receding from the fountain from whence it flows. But the farther any star is from the quiescent pole, the greater must be the orbit which it describes j and yet it appears to go round in the same time as the nearest star to the pole does. And if we take into consideration the twofold motion observed in the stars, one diurnal round the axis of the earth in 24 hours, and the other round the axis of the ecliptic in 25>920 years, it would require an explication of such a perplexed composition of forces, as could by no means be reconciled with any physical theory, si , T!ie strongest objections that can be made against X e ^ eart^’s motion round the sun is, that in opposite ASTRONOMY. when the eye comes to A, is at C when the eye is at Real 9? 28s Orations niton an- pomts of the earth’s orbit, its axis, which always keeps *wied S6 Rail’s nioibn de- mowrated fromthe alienation •t' blit. a parallel direction, would point to different fixed starsj which is not found to be fact. But this objection is easily removed, by considering the immense distance of the stars in respect of the diameter of the earth’s orbit $ the latter being no more than a point when compared to the former. If we lay a ruler on the side of a table, and along the edge of the ruler view the top of a spire at tei> miles distance j then lay the ruler on the oppo¬ site side of the table in a parallel situation to what it had before, and the spire will still appear along the edge of the ruler 5 because our eyes, even when assisted by the best instruments, are incapable of distinguishing so small a change at so great a distance. Dr Bradley, our late astronomer-royal, found by a long series of the most accurate observations, that there is a small apparent motion of the fixed stars, occasioned by the aberration of their light j and so exactly an¬ swering to an annual motion of the earth, as evinces the same, even to a mathematical demonstration. He considered this matter in the following manner: he imagined CA, fig. 101. to be a ray of light falling per¬ pendicularly upon the line BD j that, if the eye is at rest at A, the object must appear in the direction AC, whether light be propagated in time or in an instant. But if the eye is moving from B towards A, and light is propagated in time, with a velocity that is to the velocity of the eye as CA to BA j then light mo¬ ving from C to A, whilst the eye moves from B to A, that particle of it by which, the object will be discerned B. Joining the points BC, he supposed the line CB Motions to be a tube, inclined to the line BD in the angle °rtIie DBC, of such diameter as to admit but one particle ^odies^ of light. Then it was easy to conceive, that the par- ■ 'Y■■ tide ot light, at C, by which the object must be seen, when the eye, as it moves along, arrives at A, would pass through the tube BC, if it is inclined to BD, in the angle DBC, and accompanies the eye in its mo¬ tion from B to A j and that it could not come to the eye placed behind such a tube, if it had any other in¬ clination to the line BD. If, instead of supposing CB so small a tube, we imagine it to be the axis of a lar¬ ger , then, for the same reason, the particle of light at C wrould not pass through the axis, unless it is inclined, to BD in the angle CBD. In like manner, if the eye moved the contrary way, from D towards A, with the same velocity, then the tube must be inclined ia the angle BCD. Although, therefore, the true or real place ol an object is perpendicular to the line in which the eye is moving, yet the visible place will not be so j. since that, no doubt, must be in the direction of the tube j hut the difference betw’een the true and appa¬ rent place w'ill be cceteris? paribus greater or less, ac¬ cording to the different proportion between the velo¬ city of light and that of the eye. So that, if we could suppose that light was propagated in an instant, then there would be no difference between the real and vir sible place of an object, although the eye was in mo¬ tion , for in that case, AC being infinite with respect to AB, the angle ACB, the difl’erence between the true and visible place, vanishes. But if light be pro¬ pagated in time, it is evident, from the foregoing con¬ siderations, that there will be always a- difference be¬ tween the real and visible place of an object, unless. the eye is moving either directly towards or from the object. And in all cases the sine of the difference be¬ tween the real and visible place of the object will be to the sine of the visible inclination of the object to the- line in which the eye is moving, as the velocity of the eye is to the velocity of light. Pie then shows,, that if the earth revolve round the sun annually, and the velocity of light be to the velo¬ city ol the earth’s motion in its orbit, as 1000 to 1, that a star really placed in the very pole of the ecliptic would, to an eye carried along with the earth, seem to change its place continually j and, neglecting the small difference on the account of the earth’s diurnal ! levolution on its axis, would seem to describe a circle round that pole every way distant from it 3J J so that its longitude would be varied through all the points of the ecliptic every year, but its latitude would always remain the same. Its right ascension would also change 5. and its declination, according to the different situation, of the sun with respect to the equinoctial points, and. its apparent distance from the north pole of the equa¬ tor, would be 7' less at the autumnal than at the vernal equinox. _ ^ By calculating exactly the quantity of aberration Telocity of of the fixed stars from their place, he found that light^U came from the sun to us in 8' 13" 5 so that its velo¬ city is to the velocity of the earth in its orbit as I0,2QX.ErrOrsfa ° t ’ 1 , * the obser- It must here be taken notice of, however, that Mr vation of Nevil Maskelyne, in attempting to find the parallax ofimal1 aE'*‘ Sirius, 94 ASTRONOMY Part HI Real Motions of the Heavenly Bodies- 289 Another objection against the earth’s mo¬ tion an¬ swered. 290 Diurnal motion of the earth, and differ¬ ent chan¬ ges of the seasons il¬ lustrated by experi¬ ment. Fig. ro2. Sirius, with a ten-feet sector, observed, that by the fric¬ tion of the plummet-line on the pin which suspended it, an error of 10", 20", and sometimes 30", was committed. The pin was ^ of an inch diameter j and though he re¬ duced it to of an inch, the error still amounted to 3". All observations, therefore, that have hitherto been made in order to discover the parallax of the fixed stars are to be disregarded. It is also objected, that the sun seems to change his place daily, so as to make a tour round the starry hea¬ vens in a year. But whether the sun or earth moves, this appearance will be the same ; for when the earth is in any part of the heavens, the sun will appear in the opposite. And, therefore, this appearance can be no objection against the motion of the earth. It is well known to every person who has sailed on smooth water, or been carried by a stream in a calm, that, however fast the vessel goes he does not feel its progressive motion. The motion of the earth is in¬ comparably more smooth and uniform than that of a ship, or any machine made and moved by human art; and therefore it is not to be imagined that we can feel its motion. The following experiment will give a plain idea of the diurnal or annual motions of the earth, together with the different length of days and nights, and all the beautiful variety of seasons, depending on those motions. Take about seven feet of strong wire, and bend it into a circular form, as a b c d, which being viewed obliquely appears elliptical, as in the figure. Place a lighted candle on a table ; and having fixed one end of a silk thread K to the north pole of a small terrestrial globe H, about three inches diameter, cause another person to hold the wire circle, so that it may be paral¬ lel to the table, and as high as the flame of the candle I, which should be in or near the centre. Then hav¬ ing twisted the thread as towards the left hand, that by untwisting it may turn the globe round eastward, or contrary to the way that the hands of a watch move, hang the globe by the thread within this circle, al¬ most contiguous to it j and as the thread untwists, the globe (which is enlightened half round by the candle as the earth is by the sun) will turn round its axis, and the difterent places upon it will be carried through the light and dark hemispheres, and have the appearance of a regular succession of days and nights, as our earth has in reality by such a motion. As the globe turns, move your hand slowly, so as to carry the globe round the candle according to the order of the letters abed, keeping its centre even with the wire circle ; and you will perceive, that the candle, being still perpendicular to the equator, will enlighten the globe from pole to pole in its whole motion round the circle ; and that every place on the globe goes equally through the light and the dark, as it turns round by the untwist¬ ing of the thread, and therefore has a perpetual equi¬ nox. The globe thus turning round, represents the earth turning round its axis : and the motion of the globe round the candle represents the earth’s annual motion round the sun*, and shows, that if the earth’s orbit had no inclination to its axis, all the days and nights of the year would be equally long, and there would be no different seasons. Hence also it appears why the planets Mars and Jupiter have a perpetual 3 equinox, namely, because the axis is perpendicular to the plane of their orbit, as the thread round which the globe turns in this experiment is perpendicular to the plane of the area enclosed by the wire.—But now de¬ sire the person who holds the wire to hold it obliquely in the position ABCD, raising the side as just as much as he depresses the side >j>, that the flame may be still in the plane of the circle; and twisting the thread as before, that the globe may turn round its axis the same way as you carry it round the candle, that is, from west to east j let the globe down into the lowermost part of the wire circle at yf : and, if the circle be pro¬ perly inclined, the candle will shine perpendicularly on the tropic of Cancer} and the frigid zone, lying within the arctic or north polar circle, will be all in tbe light, as in the figure ; and will keep in the light, let the globe turn round its axis ever so often. From the equator to the north polar circle, all the places have longer days and shorter nights } but from the equator to the south polar circle, just the reverse. The sun does not set to any part of the north frigid zone, as shown by the candle’s shining on it, so that the motion of the globe can carry no place of that zone into the dark ; and at the same time the south frigid zone is involved in darkness, and the turning of the globe brings none of its places into the light. If the earth w*ere to continue in the like part of its orbit, the sun would never set to the inhabitants of the north frigid zone, nor rise to those of the south. At the equator it would be always equal day and night j and as places are gradually more and more distant from the equator to¬ wards the arctic circle, they would have longer days and shorter nights ; while those on the south side of the equator would have their nights longer than their days. In this case, there would be continual summer on the north side of the equator, and continual winter on the south side of it. But as the globe turns round its axis, move your hand slowly forward, so as to carry the globe from H towards E, and the boundary of light and darkness will approach towards the north pole, and recede from the south pole 5 the northern places will go through less and less of the light, and the southern places through more and more of it $ showing how the north¬ ern days decrease in length and the southern days in¬ crease, whilst the globe proceeds from H to E. When the globe is at E, it is at a mean state between the lowest and highest parts of its orbit; the candle is di¬ rectly over the equator, the boundary of light and dark¬ ness just reaches to both the poles, and all places on the globe go equally through the light and dark hemi¬ spheres, showing that the days and nights are then equal at all places of the earth, the poles only excepted ; for the sun is then setting to the north pole and rising to the south pole. Continue moving the globe forward, and as it goes through the quarter A, the north pole recedes still far¬ ther into the dark hemisphere, and the south pole ad¬ vances more into the light, as the globe comes nearer to ss : and when it comes there at F, the candle is directly over the tropic of Capricorn ; the days are at the shortest and nights at the longest, in the northern hemisphere, all the way from the equator to the arctic circle ; and the reverse in the southern hemisphere from the equator to the antarctic circle j within which circles Real I R( Motions M01 of the I of Heavenly Bodies, 191 Feren .bBS[ silarly lake alak I 5. 10! iflirt III. ASTRONOMY. Keal circles it is dark to the north frigid zone, and light to lotions 'At : of the the south. Continue both motions; and as the globe moves 3(li' through the quarter B, the north pole advances to- ■y> ic—y—wards the light, and the south pole recedes towards the dark ; the days lengthen in the northern hemisphere and shorten in the southern j and when the globe conies to G, the candle will be again over the equator (as when the globe was at E), and the days and nights will again be equal as formerly 5 and the north pole will be just coming into the light, the south pole going out of it. Thus we see the reason why the days lengthen and shorten from the equator to the polar circles every year; why there is sometimes no day or night for many turnings of the earth, within the polar circles ; why there is but one day and one night in the whole year at the poles j and why the days and nights are equally long all the year round at the equator, which, is always equally cut by the circle bounding light and darkness. The inclination of an axis or orbit is merely relative, because we compare it with some other axis or orbit which we consider as not inclined at all. Thus, our horizon being level to us, whatever place of the earth we are upon, we consider it as having no inclination j and yet, if we travel 90 degrees from that place, we shall then have a horizon perpendicular to the former j but it will still be level to us. Let us now take a view of the earth in its annual sat •L,ei us now taKe a view ot the earth in its annual Bpar-course round the sun, considering its orbit as having no ly inclination j and its axis as inclining 23J degrees from 291 n'ereat se.oBs _ tiorlarly f & ^ ^ cxlamed' a line perpendicular to the plane of its orbit, and keep ing the same oblique direction in all parts of its annual course 5 or, as commonly termed, keeping always pa- t rallel to itself. Ioa’ Let g, b, r, d, e, f g, h, be the earth in eight differ¬ ent parts of its orbit, equidistant from one another,; N s its axis, N its north pole, s its south pole, and S the sun nearly in the centre of the earth’s 01 bit. As the earth goes round the sun according to the order of the letters abed, &c. its axis N s keeps the same ob¬ liquity, and is still parallel to the line MN s. When the earth is at a, its north pole inclines towards the sun S, and brings all the northern places more into the light, than at any other time of the year. But when the earth is at e in the opposite time of the year, the north pole declines from the sun, which occasions the northern places to be more in the dark than in the light, and the reverse at the southern places ; as is evi¬ dent by the figure which is taken from Dr Long’s astronomy. When the earth is either at c or g, its axis inclines not either to or from the sun, but lies side- wise to him, and then the poles are in the boundary of light and darkness ; and the sun, being directly over the equator, makes equal day and night at all places. When the earth is at b, it is half-way between the summer solstice and harvest equinox ; when it is at d it is half-way from the harvest equinox to the winter solstice ; at^, half- way from the winter solstice to the spring equinox ; and at h, half-way from the spring equinox to the summer solstice. From this oblique view of the earth’s orbit, let us suppose ourselves to be raised far above it, and placed just over its centre S, looking down upon it from its north pole ; and as the earth’s orbit differs but very little from a circle, we shall have its figure in such a view represented by the circle ABCDEFG. Let us suppose this circle to be divided into 12 equal parts, called signs, having their names affixed to them ; and each sign into 30 equal parts, called degrees, number¬ ed 10, 20, 30, as in the outermost circle of the figure, which represents the great ecliptic in the heavens. Hie earth is shown in eight different positions in this circle ; and in each position AE is the equator, T the tropic of Cancer, the dotted circle the parallel of Lon¬ don, U the artic or north polar circle, and P the north pole, where all the meridians or hour-circles meet. As the earth goes round the sun, the north pole keeps constantly towards one part of the heavens, as it keeps in the figure towards the right-hand side of the place. When the earth is at the beginning of Libra, name¬ ly on the 20th of March, in this figure the sun S as seen from the earth, appears at the beginning of A- ries in the opposite part of the heavens, the north pole is just coming into the light, and the sun is vertical to the equator; which/ together with the tropic of Can¬ cer, parallel of London, and arctic circle, are alt equally cut by the circle bounding light and darkness, coinciding with the six-o’clock hour-circle, and there¬ fore the days and nights are equally long at all places: for every part of the meridian AETL a comes into the light at six in the morning, and, revolving with the earth according to the order of the hour-letters, goes into the dark at six in the evening. There are 24 me¬ ridians or hour-circles drawn on the earth in this figure, to show the time of sun-rising and setting at different seasons of the year. As the earth moves in the ecliptic according to the order of the letters ABCD, &c. through the signs Libra, Scorpio, and Sagittarius, the north pole P comes more and more into the light; the days increase as the nights decrease in length, at all places north of the equator JE.; which is plain by viewing the earth at b on the 5th of May, when it is in the 15th degree of Scorpio, and the sun as seen from the earth appears in the 15th degree of Taurus. For then the tropic of Cancer T is in the light from a little after five in the morning till almost seven in the evening ; the parallel of London, from half an hour past four till half an hour past seven ; the polar circle U, from three till nine ; and a large tract round the north pole P has day all the 24 hours, for many rotations of the earth on its axis. When the earth comes to c (fig. 104.) at the be¬ ginning of Capricorn, and the sun as seen from the earth appears at the beginning of Cancer, on the 21st of June, as in this figure, it is in the position C in fig. 103. ; and its north pole inclines towards the sun, so as to bring all the north frigid zone into the light, and the northern parallels of latitude more into the light than the dark from the equator to the polar cir¬ cle ; and the more so as they are farther from the equa¬ tor. The tropic of Cancer is in the light from five in the morning till seven at night, the parallel of London from a quarter before four till a quarter after eight ; and the polar circle just touches the dark, so that the sun has only the lower half of his disk hid from the in¬ habitants on that circle for a few minutes about mid- night,; Fig. 103. gS ASTRO Real Motions of the Heavenly Bodies. igz Effects of irigiit, supposing no Inequalities in the horizon, and no refractions. A bare view of the figure is enough to show, that as the earth advances from Capricorn towards Aries, and the sun appears to move from Cancer towards Libra, the north pole recedes from the light, which causes the days to decrease and the nights to increase in length, till the earth comes to the beginning of Aries, and then they are equal as before j for the boundary of light and darkness cuts the equator and all its parallels equally or in halves. The north pole then goes into the dark, and continues therein until the earth goes half¬ way round its orbit; or, from the 23d of September till the 20th of March. In the middle between these times, viz. on the 22d of December, the north pole is as far as it can be in the dark, which is 23I- degrees, equal to the inclination of the earth’s axis from a per¬ pendicular to its orbit: and then the northern paral¬ lels are as much in the dark as they were in the light on the 21st of June •, the winter nights being as long as the summer days, and the winter days as short as the summer nights. Here it must be noted, that of all that has been said of the northern hemisphere, the contrary must be understood of the southern : for on different sides of the equator the seasons are contrary, because, when the northern hemisphere inclines towards the sun, the southern declines from him. Taking it for granted, then, that the earth revolves the earth’s round the sun, let us see what effect that motion has thif a mar uPon ^ie aPParent motions of the other planets. For ances^of tlie e better comprehending of these motions, however, planets. we have hitherto supposed the earth to stand still in some part of its orbit, while they go round the sun in theirs : but as this is not the case, it now remains to consider the changes which take place in consequence of the earth’s motion. Were the earth to stand still in any part of its orbit, as at A, the places of conjunction both in the superior and inferior semicircle, as also of the greatest elongation, and consequently the places of direct and retrograde motion, and of the stations of an inferior planet, would always be in the same part of the heavens. Thus, in fig. 105. upon this supposition, the places of Mercury’s stations would always be the points P and JR, the arc of his motion PR, and of his retrograde motion RP 5 whereas, on account of the earth’s motion, the places where these appearances happen are continually advancing forward in the eclip¬ tic according to the order of the signs. In fig. 106. let ABCD be the orbit of the earth ; efg h that of Mercury ; © the sun ; GKI an arch of the ecliptic ex¬ tended to the fixed stars. When the earth is at A, the sun’s geocentric place is at F: and Mercury, in order to a conjunction, must be in the line AF 5 that is, in bis orbit be must be at j^or h. Suppose him to be at f in his inferior semicircle : if the earth stood still at A, his next conjunction would be when he is in his superior semicircle at h ; the places of his greatest elongation also would be at e and g, and in the eclip¬ tic at E and G : but supposing the earth to go on in its orbit from A to B j the sun’s geocentric place is now at K } and Mercury, in order to be in conjunction, ought to be in the line BK at m. As by the motion of the earth, the places of Mercury’s conjunctions with the sun are thus continually carried round in the eclip¬ tic in consequence, so the places of his utmost elonga- N O M Y. Part Illijt] tions must be carried in consequence also. Thus, when the earth is at A, the places of his longest elongation from the sun are in the ecliptic E and G ; the motion of the earth from A to B advances them forward from G to L and from E to I. But the geocentric mo¬ tion of Mercury will best be seen in fig. 107. Here we have part of the extended ecliptic marked ol' the HeavesilH It would be exceedingly easy to ascertain the posi¬ tion of the planets for any given time, if their orbits were, circular and uniform. But they exhibit very sen¬ sible inequalities in this respect, the laws of which are exceedingly important in astronomy, as furnishing the only clue which can lead us to the theory of the celes¬ tial motions. To ascertain, these irregularities, and de¬ tect their laws, it is necessary to abstract from their apparent motions the effects produced by the motion of the earth. In the first place then, we must determine the nature and dimensions of the earth’s orbit. We have seen formerly that the sun apparently moves round the earth in an ellipse, having the earth in the focus. We have only to reverse the position to obtain the orbit of the earth. It moves round the sun in an ellipse, having that luminary in the focus 5 so that its radius vector describes areas proportional to the times. In general, all the remarks made formerly on the supposed orbit of the sun relative to its eccentri¬ city, &c. apply accurately to the real orbit of -the earth. The figure of the earth’s orbit being thus ascertain¬ ed, let us see how astronomers have been able to deter¬ mine that of the other planets. Let us take the pla¬ net Mars as an example, which, from the great eccen¬ tricity of its orbit, and its nearness to the earth, fur¬ nishes an excellent medium for discovering the laws of the planetary motions. The motion of Mars round the sun and his orbit would be known, if we had at any given time, the angle formed by its radius vector, and a fixed straight line passing through the centre of the sun, together with the length of that radius vector. To simplify the pro¬ blem, a time is chosen when one of these quantities may be had separately from the other. This happens at the oppositions, when we see the planet in the same point of the ecliptic to which it would be referred by a spectator in the sun. The difference in the velocity and periodic times of the earth and Mars causes the planet to appear when in opposition in different points of the ecliptic successively. By comparing together a great number of such oppositions, the relation which sub¬ sists between the time and the angular motion of Mars round the sun, (called heliocentric), maybe discovered. Different methods present themselves for that purpose. But in the present case the problem is simplified by con¬ sidering that the principal inequalities of Mars return¬ ing in the same manner at every sidereal revolution, the whole of them may be expressed by a rapidly con¬ verging series of the sines of the angles multiplied by its mean motion. The relative changes in the length of the radius vector, may be determined by comparing together observations made about the quadrature when the planet being about 90° from the sun, that radius presents itself under the greatest angle possible. In the triangle formed by the straight lines which join the centres of the earth, the sun, and Mars, the angle at the earth is obtained by observation, that at the sun is ascertained by the law of Mars’s heliocentric motion. Hence the radius vector is deduced in parts of the earth’s j’adius vector. By comparing together a num¬ ber tlBrt III. 1(1 (leai ber of such radii vectores determined in this manner, oti Unions the law of their variations, corresponding to the angles 1 f the which they make with a straight line fixed in position, ^ may be determined. In this manner Kepler determin- „ ■ ed the orbit of Mars, and found it to be an ellipse with the sun in the focus. He inferred that the other planets moved likewise in ellipses round the sun, and this'inference has been confirmed by actual examina- j96 tion. Htocen- To a spectator placed in the sun, all the planets triicircles wou]([ appear to describe circles annually in the hea- ofite pla- veng . j-or tJjQygh tlie;r niotions are really elliptical, the eccentricity is so small, that the difference between them and true circles is not easily perceived even on earth ; and at the sun, whether great or small, it would entirely vanish. These circles, which in such a situa¬ tion would appear to be annually described among the fixed stars, are called the heliocentric circles of the pla- !nets j and if we suppose the orbits of the planets to be extended to the extreme bounds of the creation, they would describe among the fixed stars those circles just mentioned. To a spectator in the sun, the comets, though moving in the most eccentric orbits, would also appear to describe circles in the heavens : for though their orbits are in reality very long ellipses, the planes iof them extended to the heavens would mark a great circle thereon, whereof the eye would be the centre ; only, as the real motion is in an ellipsis, the body would appear to move much more slowly in some part of the circle than another, and to differ excessively in magnitude. To an inhabitant of any planet, how¬ ever, the sun appears to go round in its own heliocen¬ tric circle, or to describe in the heavens that same curve which the planet would appear to do if seen from the sun. Thus (fig. 114.), when the earth is at c, if we draw a line from a through the sun at S, the point G, in the sphere of the heavens where the line termi¬ nates, is the place where the sun then appears to an inhabitant of the earth. In a month’s time the earth will be got from a \.o b ; draw a line then through the sun, and its extremity at H will point out his apparent place at that time. In like manner, if we draw lines from the earth in the twelve several situations in which it is represented for the twelve months of the year, the sun’s apparent place will be found as above, and so it would be found by a spectator placed in Venus or any other planet. The geocentric latitude of a superior planet may be understood from fig. 115. Let AB be the orbit of the earth, CD that of Mars, both viewed with the eye in their common section continued, by which they ap¬ pear in straight lines. Let E and F be opposite points of the ecliptic, and suppose Mars to be in the south limit at C. If he were at that time viewed from S, the I centre of the sun, he would appear in the sphere of the heavens at the point H j in which case his heliocentric latitude would be FH : But when viewed in C from the earth, or from its centre, which in this case is sup¬ posed to be the station of the spectator, he will appear to be in different places of the heavens according to 99 the position of the earth. When the earth, for in- R^i stance, is at B, the place of Mars will appear to be at Motions g-, and his geocentric latitude will be F g. When the t!‘^ earth is at A, his apparent place will be in G, and {j0^leg ^ his geocentric latitude FG t and in like manner, sup-——v-- posing the earth to be in any other part of its orbit, as in I or K, it is easy to see, that his apparent places, as well as geocentric latitudes at those times, will be different. 297 The two points where the heliocentric circle of any Nodes of a planet cuts the ecliptic, are called its nodes ; and thatP-anef’ which the planet passes through as it goes into north latitude, is called the ascending node, and is marked thus Sb ? and the opposite to this is called the descending node, and is marked IS. A line drawn from one node to the other is called the line of the nodes of the planet, which is the common section of the plane of the eclip¬ tic, and that of the planet produced on each side to the fixed stars. The deviation of the orbit from a circle is called the eccentricity of the orbit $ the point where it is farthest distant from the sun is called its aphelion ; and where nearest, the perihelion. The motion of the planets is swiftest at the perihelion when the radius vector is shortest: it diminishes as the radius vector increases, and is at its minimum at the aphelion. When Kepler compared these two quanti¬ ties in the planet Mars, he observed that the velocity of the planet was always proportional to the square of the radius vector, so that the product of that velocity multiplied into the square of the radius vector is a constant quantity!. This product is double the area described by the radius vector in the given time. Hence that area, supposing the radius vector to set out from a fixed line, increases as the time. This Kepler announced by saying, that the areas described by the radius vector are proportional to the times. These laws are precisely those followed by the earth in her motion round the sun. Hence Kepler established as the funda¬ mental laws of the motions of the planets the two fol¬ lowing : 1. The orbits of the planets are ellipses, having the sun in their focus. 2. The areas described by the radius vector of each planet are proportional to the times of describing them. These laws suffice for determining the motions of the planets round the sun : But it is necessary to know for each of the planets seven quantities, called the elements of their elliptical motion. Five of these elements re¬ lative to the motion of the ellipse are, 1. The duration of the sidereal revolution. 2. Half the greater axis or the mean distance of the planet from the sun. 3. The eccentricity of the orbit. 4. The mean longitude of the planet at a given time. 5. The longitude of its perihelion at the same epoch. The other two elements relate to the position of the orbits. They are, 6. The longitude of the nodes of the orbit at a given epoch, or the points where the orbit intersects the ecliptic. 7. The inclination of the orbit to the plane of the ecliptic. The following table exhibits a view of these elements. ASTRONOMY. ICO ASTRONOMY. Part 11 Mercury Venus Earth Mars Jupiter Saturn Herschel Sidereal revolu¬ tions. Days. 87. 224. 365' 686. 4332' I075V 30689, 969255 700817 256384 979579 602208 °772I3 000000 Mean di¬ stances. 0.387100 O.723332 I.OOOOOO I.523693 5.202792 9.540724 19.183620 Eccentrici¬ ty in 175c. O.205513 0.006885 0.016814 0.093088 0.048077 O.056223 O.046683 Secular variation in the eccentri¬ city. O.OOOOO3369 0.000062905 O.OCOO45572 O.OOCO90685 O.OOOI34245 0.000261553 O.OOOO26228 Mean lon¬ gitude in 17S0' 281.3104 5i-4963 311.1218 24.4219 4.1201 257.0438 353.961° Longitudes of the peri¬ helion in Sidereal and secular mo¬ tion of the perihelion. 81.7401 I4I*9759 3°9-5790 368.3006 11.5012 97.9466 185.1262 I735'5° --699.07 3671.63 4834-57 2030.25 4967.64 759-85 Inclina¬ tion of the orbits to the ecliptic in 17 50. 7.7778 3.7701 0.0000 2.0556 M636 2.7762 0.8599 Secular variation in the in¬ clination to the ecliptic. 55.09 13.80 0.00 -4.45 —67.40 ■47.87 9*38 Longitudes of the a- scending nodes in 175°- 50.3836 82.7093 0.0000 52.9377 108.8062 123.9327 80.7015 Sidereal at secular mot; of the node —2332 —5673 0.C —7027.4 —45°9-j —5781.5 —10608.C The sign — denotes a retrograde motion. In this table, drawn up by M. de La Place, the decimal notation is employed ; the circle beine divided into 400° the degree into too' the minute into too", and so on ■ we did not alter it, in order to give the reader a specimen of this notation, and because the usual notation is employed m the following table. We think it proper to subjoin here Dr Maskelyne’s view of the planetary system for 1801, Dec. i. Pi! The The Pali; iatu: - Ters II. III. IV. V. VI. VII. VIII. IX. X. ■ere The Sun Mercury Venus The Earth The Moon Mars Ceres Pallas Jupiter Saturn Herschel Apparent mean dia¬ meters, as seen from the earth. 32' i",5 IO 58 31 8 27 1 °>5 39 18 3 54 Mean di¬ ameters as seen from the tun. 16" 30 17,2 4,6 10 37 16 Mean dia¬ meters in English miles. Mean distances from the sun in round num hers of miles. 883246 3224 7687 79II>73 2180 4189 160 80 89170 79042 35H2 37000000 68000000 95000000 95000000 144000000 26000000c 266000000 49000000c 900000000 1800000000 More accu¬ rate propor¬ tional num¬ bers of the preceding mean di¬ stances. Densities to that of water, which is 1. S8?10 72333 100000 ICOOOO 152369 273550 279100 520279 954072 1908352 TT 9i 5tx 4^ 5i 34 O-J-TT Propor- tions of the quantities of matter. 333928 0,1654 0,8899 I 0,025 0,0875 3 * 2,1 97>76 16,84 Inclinations of orbits to the ecliptic in 1780. 7 o' o" 3 23 35 000 5 9 3 at a mean. 1 51 o 10 37 56,6 in 1801. 34 5° 4° in 1801. 1 18 56 in 1780. 2 29 50 in 1780. o 46 20 in 1780. Inclinations of axes to orbits. 82° 44' O" 66 32 88 17 59 22 90 nearly. 60 probably. Rotations diurnal or round their own axes. 25d I4h 8m 0s O 23 21 I 29 17 44 3 o 24 39 22 0 9 55 37 o 10 16 2 j1 tlie 1 i tnu t * aiieti, 195 IfiJtull c inioii j: nc(tI i The Sun l)ll I Mercury : /enus The Earth rhe Moon dars t Part III. ASTRONOMY. xr. XII. XIII. XIV. XV. XVI. XVII. ’eres alias upiter iiturn Tropical revolutions. 87d 23h I4m 32,7s 224 16 41 27,5 365 5 48 49 686 22 18 27,4 1681 12 9 o Sidereal revolutions. 87d 23h I5m 43)6 224 46 49 10,6 365 6 9 12 686 23 30 35,6 Places of Aphelia, January 1800. 4330 H 39 2 10746 19 16 15,5 [erachel 130637 400 1703 16 48 o 4332 14 27 10,8 10759 1 51 11,2 30737 18 o o 8s 40 20' 50" 10 7 59 1 9 8 40 12 5 2 24 15 10 2s 57 14 in 1802. 6 11 8 20 in 1800. 8 29 4 11 in 1800. ti 16 30 31 in 1800. Secular mo¬ tions of the Aphelia. 1 33 45 12 1 O o 19 35 I 51 40 1 34 33 1 50 7 1 29 2 Eccentrici¬ ties; the mean dis¬ tances being 100000. 7955-4 498 1681,395 14183,7 8x40,64 24630 25OI3>3 53640,42 90804 Greatest equa¬ tions of the centres. Longitudes of St, i or places of ascending nodes in 1750. 230 40' o" O 47 20 1 55 3°,9 x o 40 40 9 20 8 5 3° 38 6 26 42 5 27 16 Is 150 20' 43" 2 14 26 18 I7 38 38 20 58 40 in 1802. 22 28 57 in 1802. 7 55 32 in 1750. 21 32 22 in 1750. 12 47 in 1788 j 198 Shposed b> the an- eiiU to be pneU. 199 A[ itoile’s 0[ iioil cwcerning tJk From the above tables it appears that this time of the revolution of the planets increases with their di¬ stance from the sun. This induced Kepler to suspect that some relation existed between them. After many attempts continued for 17 years, he at last discovered that the squares of the periodic times of the planets are proportional to the cubes of the greater axis of their orbits. Chap. IV. Of the Orbits of the Comets, Of all the celestial bodies, comets have given rise to the greatest number of speculations and conjectures. Their strange appearance has in all ages been a mat¬ ter of terror to the vulgar, who uniformly have looked upon them to be evil omens and forerunners of war, pe¬ stilence, &c. Others, less superstitious, supposed them to be meteors raised in the higher regions of the air. But we find that some part of the modern doctrine con¬ cerning them had been received into the ancient Italic and Pythagorean schools: for they held them to be so far of the nature of planets, that they had their periodi¬ cal times of appearing ; that they were out of sight for a long time, while they were carried aloft at an immense distance from the earth, but became visible when they descended into the lower regions of the air, when they were nearer to us. Tliese opinions were probably brought from Egypt, from whence the Greeks borrowed great part of their learning. However, it seems not to have been gene¬ rally received; for Aristotle, who mentions it, asserted that the heavens were unchangeable, and not liable to generation or corruption. Comets, therefore, which he believed to be generated when they first made their appearance, and destroyed when they vanished from our sight, he maintained could not be heavenly bodies, but rather meteors or exhalations raised into the upper regions of the atmosphere, where they blazed out for a while, and disappeared when the matter of which they were formed was consumed. Seneca, who lived in the first century, mentions Apollonius of Myndus, a very careful observer of natural causes, to have been of the same sentiments with the most ancient Greek philosophers with regard to comets. He himself had seen two; one in the reign of Claudius, the other in that of Nero; besides another which he saw while a boy, before the death of Augustus. He plainly inti¬ mates, that he thought them above the moon ; and argues strongly against those who supposed them to be meteors, or held other absurd opinions concerning them : declaring his belief that they were not fires suddenly kindled, but the eternal productions of na¬ ture.^ He points out also the only way to come’at a certainty on this subject, viz. by collecting a number of observations concerning their appearance, in order to discover whether they return periodically or not, “ Eor this purpose (says he) one age is not sufficient; but the time will come when the nature of comets and their magnitudes will be demonstrated, and the routes they take, so different from the planets, explained. Posterity will then wonder that the preceding ages should be ignorant of matters so plain and easy to be known.” For a long time this prediction of Seneca seemed very unlikely to be fulfilled. The great authority which Aristotle maintained for many ages, determined them to be nothing but meteors casually lighted up in the air; though they were manifestly at a great height, not only above the clouds, but subject to the diurnal revolution, of the earth. In> the dark and su¬ perstitious ages, they were held to be the forerunners of every kind of calamity, and were supposed to.have dif¬ ferent degrees of malignity according to the shape they assumed ;. from whence also they were differently deno¬ minated. Thus, some were said to be bearded, some hairy 4 some to represent a beam, sword or spear; others Si * X Id XVIII. Secular mo¬ tions of nodes. 1° 12' XO7 o 51 40 o 46 40 o 59 30 0 55 30 1 44 35 102 ASTRONOMY. Part III, 300 Only osie species of them exists. others a target, &c.; whereas modern astronomers ac¬ knowledge only one species of comets, and account for their different appearances from their different situations from the sun and earth. It was not till some time after people began to throw off the fetters of superstition and ignorance which had so long held them, that any rational hypo¬ thesis was formed concerning comets. Kepler, in 20t other respects a very great genius, indulged the most Kepler and extravagant conjectures, not only concerning comets. Bodin’s opi-but the whole system of nature in general. The pia- nion of them. 302 Bernoulli’s opinion. 3°3 True doc¬ trine con¬ cerning them re¬ vived by Tycho Brahe. nets he imagined to be huge animals who swam round the sun by means of certain fins acting upon the ethe¬ real fluid, as those of fishes do on the water : and agree¬ ably to this notion, he imagined the comets to he mon¬ strous and uncommon animals generated in the celestial spaces ; and he explained how the air engendered them by an animal faculty. A yet more ridiculous opinion, if possible, was that of John Bodin, a learned man of France in the 17th century. He maintained that co¬ mets “ are spirits, which have lived on the earth in¬ numerable ages, and being at last arrived on the con¬ fines of death, celebrate their last triumph, or are re¬ called to the firmament like shining stars ! This is fol¬ lowed by famine, plague, &c. because the cities and people destroy the governors and chiefs who appease the wrath of God.” This opinion (he says) he borrow¬ ed from the philosopher Democritus, who imagined them to be the souls of famous heroes : but that being irreconcileable with Bodin’s Christian sentiments, he was obliged to suppose them to be a kind of genii, or spiidts subject to death, like those so much mentioned in the Mahometan fables. Others, again, have denied even the existence of comets, and maintained that they were only false appearances occasioned by the refraction or reflection of light. The first rational conjecture we meet with is that of James Bernoulli, an Italian astronomer, W'ho imagined them to be the satellites of some very distant planet, which was invisible to us on account of its distance^ as were also the satellites, unless when in a certain part of their course. Tycho Brahe was the first who restored the comets to their true rank in the creation. Before his time, several comets had been observed with tolerable exact¬ ness by Regiomontanus, Appian, Fabricius, and others 5 yet they all thought them below the moon. But Ty¬ cho, being provided with much better instruments, set himself with great diligence to observe the famous comet of 15775 and, from many careful observations, deduced that it bad no sensible diurnal parallax 5 and therefore was not only far above the regions of our at¬ mosphere, but much higher than the moon. But though few have come so near the earth as to have any diurnal parallax, all of them have what may be called an annual parallax 5 that is, the revolution of the earth in her orbit causes their apparent motion to be very different from what it would be if viewed from the sun ; and this shows them to be much nearer than the fixed stars, which have no such parallax. Kepler, the disciple of Tycho, not¬ withstanding his ridiculous conjecture already mention¬ ed, was very attentive to the motions of the comets, and found that they did not move in straight lines, as had been supposed. He showed that their paths were con¬ cave towards the sun, and supposed them to move in Real parabolic trajectories. Motions Their true motion, however, was only discovered ot l*le from the observations made by Sir Isaac Newton on ijodie the great comet of 1680. This descended almost per- 1 v—' j pendicularly towards the sun with a prodigious velo- 304 city ; ascending again with the same velocity retarded,^1611 rao‘ as it had been before accelerated. It was seen in the[10'|e^^V morning by a great number of astronomers in different jfed by Sir parts of Europe, from the 4th to the 25th of Novem-Isaac New. ber, in its wav toward the sun 5 and in the evening fromton- the 12th of December to the 9th of March following. The many exact observations made on this comet en¬ abled Sir Isaac Newton to determine that they are a kind of planets which move in very eccentric ellipses 5 and this opinion is now looked upon to be certainly established. It was opposed, however, by M. de la Hire, and some other French philosophers 5 and it is evident that the whole dispute now turned on mere practical observations. If the return of any comet could be predicted, and its periodical time calculated like that of a planet, then the doctrine might be concluded certainly true, but not otherwise. Dr Halley therefore Dr Halley set himself to collect all the observations he could on predicts a comets ; and afterwards calculated the periodical times comet’s re' of 24 of them, on a supposition of their being para-turn’ boles; but afterwards found that they agreed better with the supposition of their motion being performed in very eccentric elliptical orbits. On this he calcu¬ lated a table of their elements 5 from which it was ma¬ nifest that they were not comprehended in the zodiac, some of them making an angle of upwards of 8o° with the ecliptic. By computations founded on these elements, the Periodical Doctor concluded that the comet of 1682 was the times of same which had appeared in 1607 and 1531 5 that it different had a period of 75 or 76 years 5 and be ventured to ^ine.ts ^ foretel that it would return about the year 1758. The iraine comet which appeared in 1661 was supposed to be the same with that of 1532, and to have a period of 129 years ; and from the equality of periods, and similitude of appearances, it was concluded that the great comet of 1680 was the same which had appeared in 1106 in the time of Henry I. in the consulate of Lampadius and Orestes about the year 531, and in the year 44 B. C. before Julius Caesar was murdered 5 and hence conclud¬ ed that its period rvas 575 years. MrDunthorne, how¬ ever, has endeavoured to show from a MS. in Pembroke- hall library, that the comet of 1106 could not be the same with that of 1680: but M. de la Lande thinks the four appearances related by Dr Halley stronger proofs than a single observation, which might be very faulty. Since the time of Dr Halley other astronomers have calculated the elements of 25 other comets 5 all of which, excepting one of three which appeared in 1759, and which differs but little from that of 1531, 1607, and 1682, and is therefore accounted the same, differ very much from each other; so that we cannot help 307 concluding them all to be different, and that the num-c0* ber of these bodies is very great. “ It is not, how-IT,ets “ay Tii, ■fv t . 7 sometimes ever, unlikely (says Dr Long), from the immense inter-be invisiblc val between the orbit of Saturn and the nearest fixed even in stars, that many of them have not descended into the tJiew peri- planetary k6^011. # ice: r.ci Real .lotions of the leavenly Bodies. ||art III. -ASTRO planetary regions since they have been looked upon as celestial bodies, and observed accordingly : besides, it may often happen, that a body may finish its whole pe¬ riod without being observed by us, on account of the unfavourable situation of the earth in her orbit when the comet is in its perihelion. Thus, if the comet be either behind or before the sun, or nearly so, it must be above our horizon in the day time, and consequently in¬ visible, except the sun should at that time be in a total eclipse ; for then the comet might be seen near the sun, as well as the stars and planets are : and this case is said to have happened ; for Seneca relates from Possi- donius, that a comet was seen when the sun was eclips¬ ed, which had before been invisible by being near that luminary.” A greater number of comets are seen in the hemisphere ar seen in towards the sun than in the opposite j the reason of which idere'to" eas*ly appear from fig. 116. wherein S represents wds the the sun, E the earth, ABCD the sphere of the fixed sil than in stars : and because comets either do not reflect light tkoppo- enough to be visible, or emit tails conspicuous enough to attract our notice, till they come within the planeta¬ ry regions, commonly a good way within the sphere of Jupiter, let KLMN be a sphere concentric to the sun, at such a distance from him, that no comet can be seen by us till it come within that distance 5 though E draw the plane BD perpendicular to SE, which will divide the sphere CLMN into two hemispheres, one of which, BCD, is toward the sun, the other, DAB, opposite. Now it is manifest, that the spherical portion LMN, which is in the hemisphere BCD towards the sun, is larger than the portion NKL in the hemisphere oppo¬ site to him : and consequently a greater number of co¬ mets will appear in the hemisphere BCD than in that j marked DAB. cia^dif- Though the orbits of all comets are very eccentric Sac 3rl earth, Distances, its appa- diameters. J 3°S wiy more fetices in ellipses, there are vast difl'erences amongst them ; ex- hcccen- cepting Mercury, there are no great diflerences among dotus, lib. vii. cap. 37. and lib. ix. cap. 70. ; fikewise trities of tliH nlanets. pither as tn tlip f"Pl 1 fltPir* r» K1 fa flic* 1 4- C,-v E "T\ ! ~ 1* _ 1 _ I _ 1 1 * . , 1 N O M Y. planet 5 though this must be attended with some un¬ certainty, as we know not whether the heads of comets reflect the sun’s light in the same manner the planets do. Their distance may be known from their paral¬ lax, in the manner related in a subsequent section. In this manner he found the distance of the comet of 1577 !)e about 210 semidiameters of th or about 840,000 miles distant from us, lent diameter being seven minutes; whence be con-comets eluded, that the true diameter of the comet was to computed, that of the earth as 3 to 14. “ But (says Dr Long) it was the hemisphere of the comet which was then measured.” Hevelius, from the parallax and apparent diameter of the head of the comet in 1652, computed its diameter to be to that of the earth as 52 to 100. By the same method he found the diameter of the head ol the comet of 1664 to be at one time 12 semidiame¬ ters of the earth, and at another not much more than 5- “ That the head of the comet must appear less the farther it is from the earth (says Dr Long) is obvious j but besides this apparent change, there is also a real one in the dimensions of the head of the same comet ; lor, when near the sun, the atmosphere is diminished by the heat raising more of it into the tail ; whereas, at a greater distance, the tail is diminished and the head enlarged.” Hevelius computed the diameter of the nucleus of the comets of 1661 and 1665 to l36 only about a tenth part of that of the earth ; and Cysatus makes the true diameter of the comet of 1618 to be about the same size. Some comets, however, from their apparent magnitude and distance, have been sup¬ posed much larger than the moon, or even equal in magnitude to some of the primary planets j and some have imagined, that by an interposition of these bodies Ec]jp^s betwixt the earth and sun, we might account for those occasioned darknesses which cannot be derived from any interposi-by cornels, tion of the moon. Such are those mentioned by Hero- thnorbits ufjpmets. 310 Ojnion stiPce, the planets, either as to the eccentricity of their orbits, or the inclination of their planes j but the planes of some comets are almost perpendicular to others, and some of their ellipses are much wider than others. The narrow¬ est ellipsis of any comet hitherto observed was that of 1680. There is also a much greater inequality in the motion of the comets than of the planets ; the velocity of the former being incomparably greater in their peri¬ helion than in their aphelion : but the planets are but very little accelerated. Astronomers are now generally agreed, that comets caieraing are opaque bodies, enlightened by the sun. Hevelius, th® 6ub' in a large work, wherein he gives the opinion of vari¬ ous authors on the subject, mentions some who were of the same sentiments with himself, that comets were so far transparent as to let the light of the sun pass through them, which formed their tails. Sir Isaac Newton was of opinion, that they are quite opaque 5 and in confirmation of this, he observes, that if a comet be seen in two parts of its orbit, at equal distances from the earth, but at unequal distances from the sun, it al¬ ways shines brightest in that nearest the sun. They are of very different magnitudes, which may be con¬ jectured from their apparent diameter and brightness. Thus the head of a comet, when of the same bright¬ ness and apparent diameter with Saturn, may be sup¬ posed to be nearly about the same magnitude with that 3, the eclipse mentioned by Dion, which happened a little before the death of Augustus j and it is observable that Seneca saw a comet that year. Some have even at¬ tempted to account in this manner for the darkness which happened at our Saviour’s crucifixion ; and in¬ deed it is certain, that were a comet in its perigee to come between the earth and sun, and to be moving the same way with the earth, it must cause a darkness much more intense, as well as of more considerable duration, than what would take place in any lunar eclipse. ,, , Various conjectures have been formed respecting Conjectures the tails of comets; though it is acknowledged by concerning all, that they depend on the sun somehow or other ; t^ie*r ta^s* and for this plain reason, that they are always turned from him ; but in what manner this is accomplished, we cannot easily determine. Appian, Tycho Brahe, and others, thought the tail was formed by the sun’s rays transmitted through the nucleus of the comet, which they fancied transparent, and was there refracted as in a lens of glass, so as to form a beam of light behind the comet : but this cannot be the case, as well because the figure of a comet’s tail does not answer to such a refraction, as that such refracted light would not he seen by a spectator placed sideways to it, unless it fell upon some substance sufficiently dense to cause a reflection. Descartes and his followers were of opi- 3r4 nion, that the tail of a comet was owing to the refrac- 0pmion 01 tion Descartes. 104 RcjI JVJ(Uion> of the Heavenly Bodies. ASTRONOMY. lion of its head : but if this were the case, the planets and principal fixed stars must have tails also; for the rays from them pass through the same medium as the light from the comets. Sir Isaac Newton was of opinion, that the tail of a comet is a very thin vapour which the head sends out by reason of its heat: that it ascends from the sun just as smoke does from the earth : that as the ascent of smoke is caused by the rarefaction of the air wherein it is entangled, causing such air to ascend and carry the smoke up with it; so the sun’s rays acting upon the coma or atmosphere of the comet, do by rarefaction and refraction heat the same : that this heated atmosphere heats, and by heating rarefies, the ether that is involved therein ; and that the specific gravity with which such ether tends to the sun, is so diminished by its rarefaction, that it will now ascend from him by its relative lightness, and carry with it the reflectingparticles whereof the tail iscomposed. Though the immensely large tails of some comets seem to re¬ quire a great quantity of matter to produce them, this is no objection to the foregoing solution : for every day’s experience shows what a great quantity of smoke is produced from a very little wood or coal ; and New¬ ton has demonstrated, that a cubic inch of air equally rarefied with that at the distance of a semidiameter from the earth’s surface, would fill all the planetary regions to the orbit of Saturn and beyond. Mairan entertained a very different opinion. He supposed the tails of the comets to be formed out of the luminous matter whereof the sun’s atmosphere consists. This he supposes to extend as far as the orbit of the earth, and to furnish matter for the aurora borealis. M. de la Lande is for joining the two last opinions together. Part of the matter which forms the tails of comets he supposes to arise from their own atmosphere rarefied by heat and pushed forward by the force of the light streaming from the sun ; and also that a comet passing through the sun’s atmosphere is drenched therein, and carries away some of it. Mr Howning objects to New¬ ton’s account, that it can hardly be supposed the thin vapour of the tail should go before the more solid body of the comet, when the motion thereof is sometimes so extremely swift, as that of some of the comets is said to be, after the rate, as Sir Isaac Newton calculated the motion of the comet of 1680 to be, of no less than 880,000 miles an hour. He therefore supposes the atmosphere of the comet to extend every wTay round it as far as the tail reaches; and that the part of it which makes the tail is distinguished from the rest, so as to fall thick upon that part of the atmosphere which goes before the comet in its progress along its elliptic orbit. The greatest objection to this is the immense magni¬ tude of the atmospheres; as it must now be supposed to account for the vast lengths of the tails of some comets, which have been said to measure above 80 millions of miles. The many discoveries which, since the time of New¬ ton, Halley, and other celebrated mathematicians, have been made in electricity, having brought in a new element unknown to former ages, and which shows a vast power through every part of the creation with which we are acquainted, it became natural to imagine that it must extend also into those higher re¬ gions which are altogether inaccessible to man. The similarity of the tails of comets to the Aurora Borea¬ Real Motiom of the Heavenly Bodies. 3*5 Part III, lis, which is commonly looked upon to be an electri¬ cal phenomenon, therefore suggested an opinion, at present far from being generally disbelieved, that the tails of comets are streams of electric matter. An hy¬ pothesis of this kind was published by Hr Hamilton of Hublin in a small treatise, entitled, Conjectwes on the Nature of the Aurora Borealis, a n d on the Tails of Co- I >r Hamil. mets. His hypothesis is, that the comets are of use to|.0^ Puk bring back the electric fluid to the planets, which isnj011 °^1' continually discharged from the higher regions of their atmospheres. Having given at length the above-men¬ tioned opinion of Sir Isaac, “ We find (says he) in this account, that Sir Isaac ascribes the ascent of co¬ mets tails to their being rarer and lighter, and moving round the sun more swiftly than the solar atmosphere, with which he supposes them to be surrounded whilst in the neighbourhood of the sun ; he says also, that whatever position (in respect to each other) the head and tail of a comet then receive, they will keep the same afterwards most freely ; and in another place he observes, ‘ That the celestial spaces must be entirely void of any power of resisting, since not only the solid bodies of the planets and comets, but even the exceed¬ ing thin vapours of which comets tails are formed, move through those spaces with immense velocity, and yet with the greatest freedom.’ I cannot help thinking that this account is liable to many difficulties and objec¬ tions, and that it seems not very consistent with itself or with the phenomena. “ I do not know that we have any proof of the ex¬ istence of a solar atmosphere of any considerable ex¬ tent, nor are we anywhere taught how to guess at the limits of it. It is evident that the existence of such an atmosphere cannot be proved merely by the ascent of comets tails from the sun, as that phenomenon may possibly arise from some other cause. However, let ua suppose, for the present, that the ascent of comets tails is owing to an atmosphere suiTounding the sun ; and see how the effects arising from thence will agree with the phenomena. When a comet comes into the solar atmosphere, and is then descending almost direct¬ ly to the sun, if the vapours which compose the tail are raised up from it by the superior density and weight of that atmosphere, they must rise into those parts that the comet has left, and therefore at that time they may appear in a direction opposite to the sun. But as soon as the comet comes near the sun, and moves in a di¬ rection nearly at right angles with the direction of its tail, the vapours which then arise, partaking of the great velocity of the comet, and being specifically lighter than the medium in which they move, and be¬ ing vastly expanded through it, must necessarily softer a resistance immensely greater than what the small and dense body of the comet meets with, and consequently cannot possibly keep up with it, but must be left be¬ hind, or, as it were, driven backwards by the resist¬ ance of that medium into a line directed towards the parts which the comet has left, and therefore can no longer appear in a direction opposite to the sun. And, in like manner, when a comet passes its perihelion, and begins to ascend from the sun, it certainly ought to appear ever after with its tail behind it, or in a direc¬ tion pointed towards the sun ; for if the tail of the co¬ met be specifically lighter than the medium in which it moves with so great velocity, it must be just as im¬ possible irt III. ASTRONOMY. Real Motions of the Jiarenly :odieii. possible it should move foremost, as it is that a torch moved swiftly through the air should project its flame and smoke before it. Since therefore we find that the tail of a comet, even when it is ascending from the sun, moves foremost, and appears in a direction nearly opposite to the sun, I think we must conclude that the comet and its tail do not move in a medium heavier and denser than the matter of which the tail consists, and consequently that the constant ascent of the tail from the sun must be owing to some other cause. For that the solar atmosphere should have density and weight sufficient to raise up the vapours of a comet from the sun, and yet not be able to give any sensible resistance to these vapours in their rapid progress through it, are two things inconsistent with each other : And there¬ fore, since the tail of a comet is found to move as freely as the body does, we ought rather to conclude, that the celestial spaces are void of all resisting matter, than that they are filled with a solar atmosphere, be it ever so rare. “ But there is, I think, a further consideration, which will show that the received opinion, as to the ascent of comets tails, is not agreeable to the pheno¬ mena, and may at the same time lead us to some know¬ ledge of the matter of which these tails consist; which I suspect is of a very different nature from what it has been hitherto supposed to be. Sir Isaac says, the va¬ pours of which the tail of a comet consists, grow hot by reflecting the rays of the sun, and thereby warm and rarefy the medium which surrounds them j which must therefore ascend from the sun, and carry with it IO the reflecting particles of which the tail is formed ; for he always speaks of the tail as shining by reflected light. But one would rather imagine, from the phe¬ nomena, that the matter which forms a comet’s tail has not the least sensible power of reflecting the rays of light. For it appears from Sir Isaac’s observation, which I have quoted already, that the light of the smallest stars, coming to us through the immense thick¬ ness of a comet’s tail, does not suffer the least diminu¬ tion. And yet, if the tail can reflect the light of the sun so copiously as it must do if its great splendour be owing to such reflection, it must undoubtedly have the same effect on the light of the stars ; that is, it must reflect back the light which comes from the stars be¬ hind it, and by so doing must intercept them from out- sight, considering its vast thickness, and how exceed¬ ingly slender a ray is that comes from a small star ; or if it did not intercept their whole light, it must at least increase their twinkling. But we do not find that it has even this small effect; for those stars that appear through the tail are not observed to twinkle more than others in their neighbourhood. Since therefore this fact is supported by observations, what can be a plainer proof that the matter of a comet’s tail has no power of reflecting the rays of light P and consequently, that it must be a self-shining substance. But the same thing will further appear, from considering that bodies leflect and refract light by one and the same power; and therefore if comets tails want the power of refract¬ ing the rays of light, they must also want the power of reflecting them. Now, that they want this re¬ fracting power appears from hence : If that great co¬ lumn of transparent matter which forms a comet’s tail, and moves either in a vacuum or in some medium of a VoL. III. Part I. ^ different density from its own, had any power of re- Rea! fracting a ray of light coming through it from a star Motions to us, that ray must be turned far out of its way in of the passing over the great distance between the comet and Hta,wn,y the earth ; and therefore we should very sensibly per- , Bo^iCS’ . ceive the smallest refraction that the light of the stars might suffer in passing through a comet’s tail. The consequence of such a refraction must be very remark¬ able : the stars that lie near the tail would, in some cases, appear double ; for they would appear in their proper places by their direct rays, and we should see their images behind the tail, by means of their rays which it' might refract to our eyes ; and those stars that were really behind the tail w'ould disappear in some situations, their rays being turned aside from us by refraction. . In short, it is easy to imagine what strange alterations w-ould be made in the apparent pla¬ ces of the fixed stars by the tails of comets, if they had a power of refracting their light, which could not fail to be taken notice of if any such ever happened. But since astronomers have not mentioned any such appa¬ rent changes of place among the stars, I take it for granted that the stars seen through all parts of a comet’s tail appear in their proper places, and with their usual colours ; and consequently I infer, that the rays of light suffer no refraction in passing through a comet’s tail. And thence I conclude (as before), that the matter of a comet s tail has not the power of refracting or reflect¬ ing the rays of light, and must therefore be a lucid or self-shining substance.” ^ But whatever probability the Doctor’s conjecture Sir isaac’s concerning the materials whereof the tails are formed account da- may have in it, his criticism on Sir Isaac Newton’s ac-fended* count of them seems not to be just: for that great phi¬ losopher supposes the comets to have an atmosphere pe¬ culiar to themselves; and consequently in their nearest approaches to the sun, both comet and atmosphere are immersed in the atmosphere of that luminary. In this case, the atmosphere of the comet being prodigiously heated on the side next to the sun, and consequently the equilibrium in it broken, the denser parts will con¬ tinually pour in from the regions farthest from the sun ; for the same reason, the more rarefied part which is be¬ fore will continually fly off opposite to the sun, be¬ ing displaced by that which comes from behind ; for though we must suppose the comet and its atmosphere to be heated on all sides to an extreme degree, yet still that part which is farthest from the sun will be less hot, and consequently more dense, than what is nearest to his body. The consequence of this is, that there must be a constant stream of dense atmosphere descending towards the sun, and another stream of rarefied vapours and atmosphere ascending on the contrary side; just as in a common fire there is a constant stream of dense air ascending, which pushes up another of rarefied air, flame, and smoke. I he resistance of a solar atmos- sphere may indeed be very well supposed to occasion the curvature observable in the tails of comets, and their being better defined in the fore part than be¬ hind ; and this appearance we think Dr Hamilton’s n i}7 •. hypothesis is incapable of solving. We grant, that ton’s hy^o- there is the utmost probability that the tails of comets thesis in- are streams of electric matter; but they who advancesuffirieut* a theory of any kind ought to solve every phenome¬ non, otherwise their theory is insufficient. It was in- ^ curnbeut ic6 ASTRONOMY. Real Motions of the Heavenly Bodies. cumbent on Dr Hamilton, therefore to have explained how this stream of electric matter comes to be bent into a curve 5 and also why it is better defined and brighter on the outer side of the arch than on the in¬ ner. This indeed he attempts in the following man¬ ner : “ But that this curvature was not owing to any resisting matter appears from hence, that the tail must be bent into a curve, though it met with no resistance $ lor it could not be a right line, unless all its particles were projected in parallel directions, and with the same velocity, and unless the comet moved uniformly in a right line. But the comet moves in a curve, and each part of the tail is projected in a direction opposite to the sun, and at the same time partakes of the motion of the comet; so that the different parts of the tail must move on in lines which diverge from each other 5 and a line drawn from the head of a comet to the ex¬ tremity of the tail, will be parallel to aline drawn from the sun to the place where the comet was when that part of the tail began to ascend, as Sir Isaac observes : and so all the chords or lines drawn from the head of the comet to the intermediate parts of the tail, will be respectively parallel to lines drawn from the sun to the places where the comet was when these parts of the tail began to ascend. And, therefore, since these chords of the tail will be of different lengths, and parallel to different lines, they must make different angles with a great circle passing through the sun and comet; and consequently a line passing through their extremities will be a curve. “ It is observed, that the convex side of the tail which is turned from the sun is better defined, and shines a little brighter, than the concave side. Sir Isaac accounts for this, by saying, that the vapour on the convex side is fresher (that is, has ascended later) than that on the concave side ; and yet I cannot see how the particles on the convex side can be thought to have ascended later than those on the concave side which may be nearer to the head of the comet. I think it rather looks as if the tail, in its rapid motion, met with some slight resistance just sufficient to cause a small condensation in that side of it which moves foremost, and which would occasion it to appear a little brighter and better defined than the other side ; which slight re¬ sistance may arise from that subtile ether which is sup¬ posed to be dispersed through the celestial regions, or from this very electric matter dispersed in the same manner, if it he different from the ether.” On the last part of this observation we must remark, that though a slight resistance in the ethereal medium would have served Sir Isaac Newton’s turn, it will by no means serve Dr Hamilton’s ; for though a stream of water or air may be easily destroyed or broken by resistance, yet a stream of electric matter seems to set every obstacle at defiance. If a sharp needle is placed on the conductor of an electric machine, and the ma¬ chine set in motion, we will perceive a small stream of electric matter issuing from the point; but though we blow against this stream of fire with the utmost, vio¬ lence, it is impossible either to move it, or to brighten it on the side against which we blow. If the celestial spaces then are full of a subtile ether capable of thus affecting a stream of electric matter, we may be sure that it also will resist very violently: and we are then as much difficulted to account for the projectile mo- Part III, tion continuing amidst such violent resistance ; for if Reaj the ether resists the tail of the comet, it is impossible Moiiom to prove that it doth not resist the head also. of the This objection may appear to some to be but weak- * ly founded, as we perceive the electric fluid to be en- ^ '_j dowed with such extreme subtility, and to yield to the 318 impression of solid bodies with such facility, that we Electric easily imagine it to be of a very passive nature in aU not cases. But it is certain, that this fluid only shows it-jj^^^*1, self passive where it passes from one body into another, which it seems very much inclined to do of itself. It will also be found, on proper examination of all the phenomena, that the only way we can manage the elec¬ tric fluid at all is by allowing it to direct its own mo¬ tions. In all cases where we ourselves attempt to as¬ sume the government of it, it shows itself the most un- tractable and stubborn being in nature. But these things come more properly under the article Elec¬ tricity, where they are fully considered. Here it is sufficient to observe, that a stream of electric matter resists air, and from the phenomena of electric repul¬ sion we are sure that one stream of electric matter re¬ sists another : from which we may be also certain, that if a stream of electric matter moves in an aerial fluid, such fluid will resist it j and we can only judge of the degree of resistance it meets with in the heavens from what we observe on earth. Here we see the most vio¬ lent blast of air has no effect upon a stream of electric fluid : in the celestial regions, either air or some other fluid has an effect upon it according to Dr Hamilton. The resistance of that fluid, therefore, must be greater than that of the most violent blast of air we can ima- h gme. As to the Doctor’s method of accounting for the curvature of the comet’s tail, it might do very well on Sir Isaac Newton’s principles, but cannot do so on his. There is no comparison between the celerity with which rarefied vapour ascends in our atmosphere, and that whereby the electric fluid is discharged. The velocity of the latter seems to equal that of light 5 of conse¬ quence, supposing the velocity of the comet to be equal to that of the earth in its annual course, and its tail equal in length to the distance of the sun from the earth, the curvature of the tail could only be to a straight line as the velocity of the comet in its orbit is to the velocity of light, which according to the calcu¬ lations of Dr Bradley, is as io,2oi to I. The appa¬ rent curvature of such a comet’s tail, therefore, would at this rate only be t-oVot Pai't °f its visible length, and this would always be imperceptible to us. The veloci-proJjgi#B ty of comets is indeed sometimes inconceivably great, velocity of Mr Brydone observed one at Palermo, in July 1 770, a comet ol which in 24 hours described an arch in the heavens Up.servedby wards of 50 degrees in length; according to which he^o^e ^ supposes, that il it was as far distant as the sun, it must have moved at the rate of upwards of 60 millions of miles in a day. But this comet was attended with no tail, so that we cannot be certain whether the curvature of the tails of these bodies corresponds with their velo¬ city or not. 520 The near approach of some comets to the sun sub-Vehement jects them to intense and inconceivable degrees of heat, heat of tin Newton calculated that the heat of the comet of i68ocomelof must have been near 2000 times as great as that 0fl680, red-hot iron. The calculation is founded upon this principle, lift III. Rea| principle, that the beat of the sun falling upon any lotions body at different distances is reciprocally as the squares of the 0f those distances 5 but it may be observed, that the ef- Itodies^ feet of the heat of the sun upon all bodies near our y ' < earth depends very much on the constitution of those bodies, and of the air that surrounds them. “ The comet in question (says Dr Long) certainly acquired a prodigious heat: but I cannot think it came up to what the calculation makes it: the effect of the strong¬ est burning-glass that has ever been made use of was the vitrification of most bodies placed in its focus. What would be the effect of a still greater heat we can only conjecture) it would perhaps so disunite the parts as to make them fly off every way in atoms. This co¬ met, according to Halley, in passing through its south¬ ern node, came within the length of the sun’s semidia¬ meter of the orbit of the earth. Had the earth then been in the part of her orbit nearest to that node, their mutual gravitation must have caused a change in the plane of the orbit of the earth, and in the length of our year: he adds, that if so large a body, with so rapid a motion as that of this comet, were to strike against the earth, a thing by no means impossible, the shock might reduce this beautiful frame to its original chaos.” We must not conclude this account without observing that Whiston, who, from Flamstead’s measure of its apparent diameter, concluded the nucleus of the comet to be about ten times as big as the moon, or equal to a fourth part of the earth, attributes the universal de¬ luge in the time of Noah to the near approach thereof. His opinion was, that the earth passing through the at¬ mosphere of the comet, attracted therefrom great part of the water of the flood ; that the nearness of the comet raised a great tide in the subterraneous waters, so that the outer crust of the earth was changed from a sphe¬ rical to an oval figure 5 that this could not be done without making fissures and cracks in it, through which the waters forced themselves, by the hollow of the earth being changed into a less capacious form ; that along with the water thus squeezed up on the surface of the earth, much slime or mud would rise ; which, together with the grosser part of the comet’s atmosphere, would, after the subsiding of the water, partly into the fissures and partly into the lower parts of the earth to form the sea, cover all over, to a considerable depth, the antediluvian earth. Thus he accounts for trees and bones of animals being found at a very great depth in the earth. He also held that, before the fall, the earth revolved round the sun in the plane of the eclip¬ tic, keeping always the same points of its surface to¬ wards the same fixed stars. By this means, as every meridian would come to the sun but once in every re¬ volution, a day and a year were then the same : but that a comet striking obliquely upon some part of the earth gave it the diurnal rotation : that the antedilu¬ vian year consisted of 360 days : but that the addition¬ al matter deposited upon the earth from the atmosphere of the comet at the flood, so retarded the revolution thereof round the sun, that it is not now performed in less than 365 days and about a quarter. The same co¬ met he thought would probably, coming near the earth when heated in an intense degree in its perihelion, he the instrumental cause of that great catastrophe, the IO7 general conflagration, foretold in the sacred writings Real and from ancient tradition. .Motions These conjectures lead us to speak somewhat more °r t!ie particularly concerning the nature of comets, and the purposes they may possibly answer in the creation. ’ . Hevelius, in order to account for the various appear- ?2i ances of the nucleus already related, supposed that Conjecture* they were composed of several masses compacted toge-HeveS,us, ther, with a transparent fluid interspersed, but the^ningthe apparent changes in the nucleus maybe only on the nature of surface : comets may be subject to spots as the planets comets, are ; and the vastly different degrees of heat they go through may occasion great and sudden changes’ not only in their surfaces, but even in their internal frame and texture. Newton places all these apparent changes to the atmosphere that environs them ; which must be very dense near their surfaces, and have clouds floating therein. It was his opinion, that the changes mention¬ ed may all be in the clouds, not in the nucleus. This last indeed he looked upon to be a body of extreme so¬ lidity, in order to sustain such an intense heat as the comets are sometimes destined to undergo ; and that, notwithstanding their running out into the immense regions of space, Avhere they were exposed to the most intense degrees of cold, they would hardly be cooled again on their return to the sun. Indeed, accord¬ ing to his calculation, the comet of 1680 must be for ever in a state of violent ignition. He hath com¬ puted that a globe of red-hot iron of the same dimen¬ sions with the earth, would scarce be cool in 50,000 years. If then the comet be supposed to cool 100 times faster than red-hot iron, as its heat was 2000 times greater, it must require upwards of a million of years to cool it. In the short period of 575 years, therefore, its heat will be in a manner scarce dimi¬ nished ) and, of consequence, in its next and every suc¬ ceeding revolution, it must acquire an increase of heat: so that, since the creation, having received a propor¬ tional addition in every succeeding revolution, it must now be in a state of ignition very little inferior to that of the sun itself. Sir Isaac Newton hath farther con¬ cluded, that this comet must be considerably retarded in every succeeding revolution by the atmosphere of the sun within which it enters ; and thus must continually come nearer and nearer his body, till at last it falls in¬ to it. This, he thinks, may be one use of the comets, to furnish fuel for the sun, which otherwuse would be in danger of wasting from the continual emission of its light. He adds, that for the conservation of the water and moisture ol the planets, comets seem absolutely requi¬ site ; from whose condensed vapours and exhalation all the moisture which is spent in vegetation and pu¬ trefaction, and turned into dry earth, &c. may be resupplied and recruited j for all vegetables grow and increase wholly from fluids ) and again, as to their greatest part, turn by putrefaction into earth j art earthy slime being perpetually precipitated to the bot¬ tom of putrefying liquors. Hence the quantity of dry earth must continually increase, and the moisture of the . globe decrease, and be quite evaporated, if it have not a continual supply from some part or other of the uni¬ verse. “ And I suspect (adds our great author), that the spirit which makes the finest, subtilest, and best O 2 part ASTRONOMY. io8 ASTRONOMY. Part III, t Real Motions of the Heavenly Bodies. 322 Mr Bry- done's con jectures pnrt of our air, and which is absolutely requisite for the life and being of all things, comes principally from the comets.” Mr Brydone observes, that the comets without tails seem to be of a very different species from those which have tails : To the latter, he says, they appear to bear a much less resemblance than they do even to planets. He tells us, that comets with tails have sel- comets without tails. 323 Mr Cole’s 3*4 Of the pe¬ riodical times, See. of the comets. earth’s Bodies, concerning ^om been visible but on their recess from the sun : that they are kindled up, and receive their alarming appear¬ ance, in their near approach to this glorious luminary ; but that those without tails are seldom or ever seen but on their way to the sun ; and he does not recollect any whose return has been tolerably well ascertained. “ I remember indeed (says be), a few years ago, a small one, that was said to have been discovered by a telescope after it had passed the sun, but never more be¬ came visible to the naked eye. This assertion is easily made, and nobody can contradict it ; but it does not at all appear probable that it should have been so much less luminous after it had passed the sun than before it approached him: and I will own to you, when I have heard that the return of these comets had escaped the eyes of the most acute astronomers, I have been tempt¬ ed to think that they did not return at all, but were absorbed in the body of the sun, which their violent mo¬ tion towards him seemed to indicate.” Pie then at¬ tempts to account for the continual emission of the sun’s light without waste, by supposing that there are num¬ berless bodies throughout the universe that are attracted into the body of the sun, which serve to supply the waste of light, and which for some time remain ob¬ scure and occasion spots on bis surface, till at last they are perfectly dissolved and become bright like the rest. This hypothesis may account for the dark spots becom¬ ing as bright, or even brighter than the rest of the disk, but will by no means account for the brighter spots becoming dark. Of this comet, too, Mr Brydone re¬ marks, that it was evidently surrounded by an atmo¬ sphere which refracted the light of the fixed stars, and seemed to cause them to change their places as the co¬ met came near them. A very strange opinion we find set forth in a book hypothesis, entitled “ Observations and Conjectures on the Nature and Properties of Light, and on the Theory of Comets, by William Cole.” This gentleman supposes that the comets belong to no particular system $ but were ori¬ ginally projected in such directions, as wmuld successive¬ ly expose them to the attraction of different centres, and thus they would describe various curves of the parabolic and the hyperbolic kind. P'his treatise is written in an¬ swer to some objections thrown out in Mr Brydone’s Tour, against the motions of the comets by means of the two forces of gravitation and projection, which were thought sufficient for that purpose by Sir Isaac Newton: of which we shall treat as fully as our limits will allow in the next section. The analogy between the periodical times of the planets and their distances from the sun, discovered by Kepler, takes place also in the comets. In conse¬ quence of this, the mean distance of a comet from the sun may be found by comparing its period with the time of the earth’s revolution round the sun. Thus the period of the comet that appeared in 1531, 1607, 1682, and 1759, being about 76 years, its mean di- 2 stance from the sun may-be found by this proportion : Real As 1, the square of one year, the earth’s periodical time, Motions is to 5776 the square of 76, the comet’s periodical °Hbe time ; so is 1,000,000 the cube of 100 the mean distance from the sun, to 5,776,000,000 the cube of the comet’s mean distance. The cube root of this last number is 1794 J the mean distance itself in such parts as the mean distance of the earth from the sun contains ICO. If the perihelion distance of this comet, 58 be taken from 3588 double the mean distance, we shall have the aphelion distance, 3530 of such parts as the distance of the earth contains 100 ; which is a little more than 35 times the distance of the earth from the sun. By a like method, the aphelion distance of the comet of 1680 comes out 138 times the mean distance of the earth from the sun, supposing its period to be 575 years : so that this comet, in its aphelion, goes more than 14 times the distance from the sun that Sa¬ turn does. Euler computes the orbit of this comet from three of Flamstead’s observations taken near to¬ gether, compared with a fourth taken at some di¬ stance from the other three, and from thence concludes the period to be a little more than 170 years. “ It seems something surprising (says Dr Long), that, from the same observations which were used by New¬ ton and Halley, he should bring out a period so very different from what these great men have determined : but it is the less to be wondered at, if we consider how small a portion of the comet’s orbit lay between the most distant places used in this computation, or indeed that could be bad for that purpose 5 so small, that the form of the ellipsis cannot be found with precision by this method, except the comet’s places were more ex¬ actly verified than is possible to be done : and that he does not pretend to confirm his determination of the pe¬ riod by pointing out and comparing together any former appearances of this comet j a method which Newton recommended as the only one whereby the periodical times and transverse diameters of the orbits of the co¬ mets can be determined with accuracy.” The period of the comet in 1744 is much longer than even that of 1680. Mr Betts, in attempting to compute the transverse axis of its orbit, found it come out so near infinite, that, though the orbit showed itself in this manner to be a very long one, he found it impossi¬ ble to calculate it without some observations made after its perihelion. Halley, after he had finished hisjQr tables of comets, found such a similitude in the elements calculate* of those.of 1531, 1607, and 1682, that he was induced.the return to believe them to be returns of the same comet in<>f comet*- an elliptic orbit: but as there was such a difference in their periodical times and inclinations of their or¬ bits as seemed to make against this opinion ; and as the observations of the first of them in 1531 by Appian, and the second in 1607 by Kepler, were not exact enough to determine so nice a point when he first pub¬ lished his synopsis in 1705 5 he only mentioned this as a thing probable, and recommended it to posterity to watch for an appearance of the same in 1758. After¬ wards, looking over the catalogue of ancient comets, and finding three others at equal instruments with those now mentioned, he grew more positive in his opi¬ nion •, and knowing a method of calculating with ease a motion in an elliptic orbit, how eccentric soever it might be, instead of the parabolic orbit which he had given Frt III. ASTRONOMY. teal lotions . f the given for the comet of 1682, he set about adapting the plan of that orbit to an ellipsis of a given space and magnitude, having the sun in one ol its foci, so as to l-odies * t^ie observations of that comet made by Flam- stead with great accuracy, by the help of a very large sextant. He likewise corrected the places of the comet of 1531 from Appian, and those of the comet 1607 from Kepler and Longomontanus, by rectifying the places of the stars they had made use of, and found those places agree as well with the motion in such an ellipsis as could be expected from the manner of ob¬ serving of these astronomers, and the imperfections of their instruments. The greatest objection to this theory was some difference in the inclination of the 2<5 orbits, and that there was above a year’s difference be- Wv the tween the two periods. The comet of 1531 was pewdieal its perihelion August 24. 5 that of 1607, October 16, cotitsan(^ ^ia*: September 4. : so that the first of nap hap- the3e periods was more than 76, the latter not quite pent un- 75 years. To obviate this, he reminds his readers of cqelinter-an observation made by him of the periodical revolu¬ tion of Saturn having at one time been about 13 days longer than at another time j occasioned, as he sup¬ posed, by the near approach of Saturn and Jupiter, and the mutual attraction and gravitation of these two planets : and observes, that in the summer of the year 1681, the comet in its descent was for some time so near Jupiter, that its gravitation towards that planet was one-fiftieth part of its gravitation towards the sun* This, he concluded, would cause a change in the in¬ clination of its orbit, and also in the velocity of its motion : for by continuing longer near the planet Ju¬ piter on the side most remote from the sun, its velocity would be more increased by the joint forces of both those bodies, than it would be diminished by them act¬ ing contrarywise, when on the side next the sun where its motion was swiftest. The projectile motion being thus increased, its orbit would be enlarged, and its period lengthened $ so that he thought it probable it would not return till after a longer period than 76 years, about the end of the year 1758, or beginning of 1759* As Halley expressed his opinion modestly, though clearly enough, that this comet would appear again about the end of 1758, or the beginning of the fol¬ lowing year, M. de la Lande pretends he must have been at a loss to know whether the period he foretold would have been of 75 or of 76 years ; that he did not give a decisive prediction, as if it had been the re¬ sult of calculation ; and that, by considering the affair in so loose a manner as Halley did, there was a good deal of room for objecting to his reasoning. After these reflections, he is very large in his commendation of the performance of Clairault j who, he says, not only calculated strictly the effect of the atti'action of Jupiter in 1681 and 1683, when the comet was again near Jupiter, but did not neglect the attraction of that planet when the comet was most distant ; that he con¬ sidered the uninterrupted attractions of Jupiter and Saturn upon the sun and upon the comet, but chiefly the attractions of Jupiter upon the sun, whereby that luminary was a little displaced, and gave different ele¬ ments to the orbit of the comet. By this method he found the comet would be in its perihelion about the middle of April 5 but that* on account of some small ICQ Real Motions of the .Heavenly Bodies. 327 quantities necessarily neglected in the method of ap¬ proximation made use of by him, Mr Clairault de¬ sired to be indulged one month ; and that the comet came just 30 days before the time he had fixed for its appearance. That comets may have their motion disturbed by the planets, especially by the two largest, Jupiter and Sa¬ turn, appears by an instance just now mentioned. They may also affect one another by their mutual gravitation when out of the planetary regions y but of this we can take no account, nor can we estimate the resistance cf the ether through which they pass; and yet both these causes may have some influence on the inclination of their orbits and the length of their periods. Chap. V. Of the Motions of the Satellites. The moon is the satellite which moves round the earth, and as her apparent and real motions are tbs same, we have already given an account of her ellipti¬ cal orbit and irregularities. Jupiter is attended by four satellites. If we repre¬ sent the semidiameters of Jupiter’s equator by unity, then the mean distances of the satellites from Jupiter, will be represented by the following numbers. First satellite 5.697300 semidiameters. Orbits and Second satellite 9.065898 distances Third satellite 14.461628 ter’sTatel- Fourth satellite 25.436000 lites. The durations of their revolutions are respectively, First satellite 1.769137787069931 days. Second satellite 3.551181016734509 Third satellite 7.154552807541524 Fourth satellite 16.689019396008634 If we compare the distances of these satellites with, their periodic times, we observe the same relation point¬ ed out by Kepler between the distances of the planets from the sun and the duration of their revolutions : for the squares of the periodic times of the satellites are proportional to the cubes of their distance from Jupi¬ ter’s centre. The frequent eclipses of these satellites have enabled astronomers to ascertain their motion, with much more precision than could have been attained merely by ob¬ serving their distances from Jupiter. The following points have been ascertained. The orbit of the first satellite is circular, at least its eccentricity is insensible ; it coincides nearly with Ju¬ piter’s equator, which is inclined to the orbit of the planet at an angle of 3.99990. The ellipticity of the orbit of the second satellite isIrregulari- also insensible j its inclination to Jupiter’s orbit varies,ties in their as does also the position of its nodes.. These irregular!-ni0t,0Ils* ties are represented pretty, well, by supposing the incli¬ nation of the orbit to the equator of Jupiter i1-] and that its nodes move retrograde in that plane in a period of 30 years. A small eccentricity is observed in the orbit of the third satellite.. The extremity of its longerjaxis next Jupiter, called the perijove, has a direct motion. The eccentricity of the orbit has been observed to vary con¬ siderably. The equation of the centre was at its maxi¬ mum about the end of the 17th century j it then a-, mounted ASTRONOMY. mounted to about 862" ; it gradually diminished, and in the year 1775 it 'vas at its minimum, and amounted only to about 229.7". inclination of the orbit of this satellite to that of Jupiter, and the position of its nodes, are variable. These different variations are re¬ presented pretty nearly, by supposing the orbit inclin¬ ed to that of Jupiter, at an angle of about 726", and giving to the nodes a retrograde motion in the plane of the equator, completed in the period of 137 years. The orbit of the fourth satellite is very sensibly el¬ liptical. Its perijove has a direct motion, amounting to about 2112". This orbit is inclined to that of Jupiter, at an angle of about 147'. It is in con¬ sequence of this inclination, that the fourth satellite often passes behind the planet relatively to the sun with¬ out being eclipsed. From the first discovery of this planet, till the year 1760, the inclination of its orbit appeared constant : but it has sensibly increased since that period. Besides all these variations, the satellites of Jupiter are subjected to several irregularities, which disturb their elliptical motion, and render their theory very complicated. These irregularities are most conspicuous in the three first satellites. Their mean motions are such, that the mean mo¬ tion of the first satellite, together with twice the mean motion of the third, is nearly equal to thrice the mean motion of the second. The same relation holds in their synodical motions. The mean longitude both sy¬ nodical and sidereal of the first three satellites, seen from the centre of Jupiter, is such that the longi¬ tude of the first, minus thrice that of the second, plus twice that of the third, is nearly equal to the semicir¬ cumference. This relation is so very near the truth, that one is tempted to consider it as rigorous, and to ascribe the supposed errors to the imperfection of ob¬ servations. It will hold at least for a long time to come, and shews us that the three satellites cannot be eclipsed at once. The periods and laws of the principal irregularities of these satellites are the same in all. The irregularity of the first advances or retards its eclipses 20" of time at its maximum. If we compare the changes on this inequality, with the relative positions of the two first satellites, we find that it disappears when these two sa¬ tellites, seen from the centre of Jupiter, are in opposi¬ tion at the same time j that it increases gradually, and acquires its maximum when the first satellite, at the in¬ stant of opposition, is 450 more advanced than the se¬ cond ; that it vanishes when the first is 90° before the second. Beyond that point it becomes negative and retards the eclipses, and increases till the two satellites are 135 degrees from each other, when it acquires its negative maximum. Then it diminishes and disap¬ pears when they are 180° distant. In the second half of the circumference the very same laws are observed as in the first. From these phenomena it has been concluded, that there exists in the motion of the first satellite round Jupiter, an inequality amounting to at its maximum, and proportional to the sine of twice the excess of the mean longitude of the first satellite above that of the second ; which excess is equal to the difference between the mean synodical longitudes of the two satellites. The period of this inequality does not amount to 4 days. How comes it 3 .esv Part 111 |i then, it will be asked, to change into a period of 437.75 Rea] days, with respect to the eclipses of the first satellite ? Motions Let us supposfe, that the first and second satellites set of the out together from their mean opposition to the sun. HeaT.e“l! During every revolution of the first satellite, in conse- , Bodittl quence of its mean synodical motion, it will be in mean ^ opposition. Suppose a fictitious star, whose angular motion is owing to the excess of the mean synodical motion of the first satellite, over that of the second, then twice the difference of the mean synodical motions of the two satellites will in the eclipses of the first be equal to a multiple of the circumference together with the motion of the fictitious star. Of course the sine of this last motion will be proportional to the ine¬ quality of the first satellite in its eclipses, and may re¬ present that inequality. Its period is equal to the dura¬ tion of the revolution of the fictitious star, which ac¬ cording to the mean motion of the two satellites is 437*75 days. Thus it is determined with more preci¬ sion than by direct observation. The irregularity of the second satellite follows a law similar to that of the first 3 but its sign is always con¬ trary. It accelerates or retards the eclipses 932" in time when at its maximum. When compared with the position of the two satellites, weperceivethatitdisappears when they are in opposition to the sun at the same time: that it retards the time of the eclipses more and more, till the two satellites are distant from each other 90° at the time when they take place j then the retardation diminishes and vanishes altogether, when the two satel¬ lites are 1800 from each other at the time of the eclip¬ ses. It then accelerates the eclipses in the other half of the circumference precisely as it had retarded them before. From these observations it has been concluded that there exists in the motion of the second satellite an irregularity of 3647" at its maximum proportional, {but With a contrary sign) to the sign of the excess of the mean longitude of the first satellite above that of the se¬ cond, which excess is equal to the difference of the mean synodical motions of the two satellites. If the two satellites set out together from their mean opposition to the sun j the second satellite will he in mean opposition every time that it completes a synodi* cal revolution. If we suppose, as before, a star whose angular motion is equal to the excess of the mean sy¬ nodical movement of the first satellite, or twice that of the second, then the difference of the two synodical movements of the two satellites will, at the eclipses of the second, equal a multiple of the circumference to¬ gether with the motion of the fictitious star. Of course the inequality of the second during its eclipse will be proportional to the sine of the angular motion of that fictitious star. Hence the reason that the period and law of that irregularity are the same as in the irregularity of the first satellite. If the third satellite produces in the motion of the second an inequality resembling that which the second seems to produce in the motion of the first, that is to say, proportional to the sine of twice the difference of the mean longitudes of the second and third satellite ; that new inequality will coincide with that which is due to the first satellite. For in consequence of the re¬ lation which the mean longitude of the three first satel¬ lites have to each other, the difference of the mean lon¬ gitudes of the two first satellites is equal to the semicir¬ cumference »lite 1 tun 111 Ipirt 111. cal cumference together with ASTRO twice tiie difference of the itiiions mean longitudes of the second and third satellites, so that ♦ the the sine of the hist difference is the same as the sine of ,( double the second difference, but with a contrary sign. y ^ The inequality produced by the third satellite in the motion of the second, will therefore have the same sign, and will follow the same law as the inequality observed in that motion. It is, therefore, very probable that this inequality is the result of two inequalities depending on the first and third satellite. If in the course of ages, the preceding relation between the mean longitudes of these three satellites should cease to exist, these two inequa¬ lities, at present compounded, vmuld separate, and their respective values might be discovered. The inequality relative to the third satellite in its eclipses, compared with the respective positions of the second and third, offers the same relations with the inequality of the second compared with the respective si¬ tuations of the two first. There exists then in the mo¬ tion of the third satellite, an inequality which at its maximum amounts to 268". If we suppose a star whose angular motion is equal to the excess of the mean syno¬ dical motion of the second satellite, above twice the mean synodical motion of the third, the inequality of the third satellite will in its eclipses be proportional to the motion of this fictitious star. But in consequence of the relation which exists between the mean longitude of the three satellites, the sine of this motion is the same (ex¬ cept its sign), with that of the motion of the first ficti¬ tious star which we formerly considered. Therefore the inequality of the third satellite in its eclipses has the same period, and follows the same laws, with the in¬ equalities of the two first satellites : such are the laws of the principal irregularities of the three first satellites of J upiter. Let us now consider the satellites of Saturn, which S*im. are seven in number. The satellites of Saturn have not as yet proved so useful to astronomy or geographv as those of Jupiter; principally because they cannot be seen unlessverypowerful telescopes be used. Five of those satellites were discovered in the year 1685, by Cassini and Huygens, who used telescopes consisting of two simple lenses, but upwards of 100 feet in length ; and those were called 1st, 2d, 3d, &c. reckoning from the planet. Two others were discovered by Dr Herschel in the years 1787 and 1788, and these are smaller and nearer to the planet, on which account they ought to have been called the first and second, at the same time that the other five ought to have been called 3d, 4th, 5th, 6th, and 7th ; but, imagining that this might cre¬ ate some confusion in the reading ol old astronomical books, the five old satellites have been suffered to retain their numerical names, and the two new satellites are now called the 6th and the 7th ; so that the 7th is the nearest to the planet, then comes the 6th, then the 1st ; and this is followed by the 2d, 3d, 4th, and 5th. The inclinations of the orbits of the 1st, 2d, 3d, and 4th satellites, to the ecliptic, are from 30° to 310. Lr9 Sataites N O M Y. That of the 5th is from I 70 to 180. Of all the satel¬ lites of the solar system, none, except the j'.h of Saturn, has been observed to have any spots, from the motion of which the rotation of the satellite round its own axis might be determined. Then the 5th satellite of Saturn, as Dr Herschel has discovered, turns round its own axis; and it is remarkable, that, like our moon, it revolves round its axis exactly in the same time that it revolves round its primary. The following table states the particulars which have been ascertained with respect to the satellites of Saturn. The Satellites of Saturn. Real Motions of the Heavenly Bodies. Satellites. Periods. Seventh Sixth First Second Third Fourth Fifth d. h. m. s. O 22 40 46 1 8 53 9 1 21 l8 27 2 17 41 22 4 12 25 12 IC 22 41 12 79 7 48 o Dist. in Nemi-dia. ofSaturn. 3i 4t 5tt 8 18 54 Di»t. in miles. 107,000 135,o°o 170,000 2I7,OOoj 303,000 704,000 2,050,000 App. diam. of orbits. O I I 1 2 6 l7 57 H 27 52 36 iB 4 The planet Herschel, with its six satellites, have been entirely discovered by Dr Herschel. The planet itself may be seen with almost any telescope ; but its satellites cannot be perceived without the most powerful instru¬ ments, and the concurrence of all other favourable cir¬ cumstances. One of these satellites Dr Herschel found to revolve round its primary in 8d. 17I1. im. 19 sec.; the period of another he found to be 13d. uh. 5m. 1.5 sec. The apparent distance of the former from the planet is 33 ; 5 that of the second 44,,■5'• Their orbits are nearly perpendicular to the plane of the ecliptic. The other four satellites were discovered a consider¬ able time after, and of course Dr Herschel has had less time to make observations upon them. They are alto¬ gether very minute objects; so that the following parti¬ culars must be considered as being not accurate but pro¬ bable. “ Admitting the distance of the interior satel¬ lite to be 25".5, its periodical revolution will be 3d. 2ih. 25m. “ If the intermediate satellite be placed at an equal distance between the two old satellites, or at its period will be lod. 23b. 4m. The nearest exterior satellite is about double the distance of the farthest old one ; its periodical time will therefore be about 388. ih. 49m. The most distant satellite is full four times as far from the planet as the old second satellite ; it will therefore take at least 1078. i6h. 14m. to complete one revolution. All these satellites perform their revolu¬ tions in their mbits contrary to the order of the signs; that is, their real motion is retrograde,” Part Satellites ot Herschel. i 12 ASTRONOMY. Theory of Universal Gravita¬ tion. PART IV. OF THE THEORY OF UNIVERSAL GRAVITATION. Part IH Theory Mif Univers G rarity tiou. [r.i' 33* Motioa. 33* Moving forces. 333 Composi¬ tion forces. HA.VING in the last two parts of this treatise given an account of the apparent and real motions of the heavenly bodies, it only remains for us to compare these motions with the laws established by mathema¬ ticians, in order to ascertain the forces that animate the solar system, and to acquire notions of the general principle of gravitation on which they depend. To de- velope this part of the subject properly, three particu¬ lars claim our attention. We must in the first place lay down the laws of motion as established by mathe¬ maticians •, in the second place, we must apply these laws to the heavenly bodies, which will furnish us with the theory of gravitation ; and, in the third place, we must apply this theory to the planetary system, and demonstrate that the whole motions of the heavenly bo¬ dies are explicable by that theory, and merely cases of it. These particulars shall be the subject of the three following chapters. Chap. I. Of the Laws of Motion* The laws of motion, by which all matter is regula¬ ted, and to which it is subject notwithstanding the variety of phenomena which it continually exhibits, con¬ stitute the first principles of mechanical philosophy. They will claim a separate place hereafter in this work, under the title of Dynamics ; but some notions of them are requisite in order to understand the theory of gravi¬ tation. We shall satisfy ourselves in this place with the following short sketch. A body appears to us to move when it changes its situation with respect to other bodies which we con¬ sider as at rest. Thus in a vessel sailing down a river, bodies are said to be in motion when they correspond successively to different parts of the vessel. But this motion is merely relative. The vessel itself is moving along the surface of the river, which turns round the axis of the earth, while the centre of the earth itself is carried round the sun, and the sun with all its attendant planets is moving through space. This renders it ne¬ cessary to refer the motion of a body to the parts of space, which is considered as boundless, immoveable, and penetrable. A body then is said to be in motion when it corresponds successively to different parts of space. Matter, as far as we know, is equally indifferent to motion or rest. When in motion it moves for ever un¬ less stopt by some cause, and when at rest it remains so, unless put in motion by some cause. The cause which puts matter in motion is called a force. The nature of moving forces is altogether unknown, but we can mea¬ sure their effects. Whenever a force acts upon matter it puts it in mo¬ tion, if no other force prevent this effect $ the straight line which the body describes, is called the direction of the force. Two forces may act upon matter at the same time. If their direction be the same, they increase the motion $ if their direction be opposite they destroy each other j and the motion is nothing if the two forces be equal; it is merely the excess of the one force above the other if the motions be unequal. If the directions of the two forces make with each other any angle whatever, the resulting motion will be in a direction between the two. And it has been demonstrated, that if lines be taken to represent the direction and amount of the forces, if these lines be converted into a parallelogram by drawing parallels to them; the diagonal of that parallelogram will represent the direction and quantity of the resulting motion. This is called the composition of forces. For two forces thus acting together, we may substi¬ tute their result, and vice versa. Hence we may de¬ compose a force into two others, parallel to two axes situated in the same plane, and perpendicular to each other. Thus finding that a body A, fig. liy. has mov¬ ed from A to C, we may imagine either that the body has been impelled by a single force in the direc¬ tion of AC, and proportionate to the length of AC, or that it has been impelled by two forces at once, viz. by one in the direction of AD, and proportionate to the length of AD ; and by another force in the direc¬ tion of AB or DC, and proportionate to AB or DC. Therefore, if two sides of any triangle (as AD and DC) represent both the quantities and the directions of two forces acting from a given point, then the third side (as AC) of the triangle will represent both the quantity and the direction of a third force, which act¬ ing from the same point, will be equivalent to the other two, and vice versa. Thus also in fig. Ii8. finding that the body A has moved along the line AF from A to F in a certain time 5 we may imagine, 1st, that the body has been im¬ pelled by a single force in the direction and quantity re¬ presented by AF ; or 2dly, that it has been impelled by two forces, viz. the one represented by AD, and the other represented by AE ; or thirdly, that it has been impelled by three forces, viz. those represented by AD, AB, and AC } or lastly, that it has been impelled by any other number of forces in any directions ; provided all these forces be equivalent to the single force which is represented by AF. This supposition of a body having been impelled by two or more forces to perform a certain course j or, on the contrary, the supposition that a body has been im¬ pelled by a single force, when the body is actually known to have been impelled by several forces, which are, how¬ ever, equivalent to that single force $ has been called the composition and resolution of forces. The knowledge of these principles gives mathema-ResoluL ticians an easy method of obtaining the result of any of forces, number of forces whatever acting on a body. For every particular force may be resolved into three others, parallel to three axes given in position, and per¬ pendicular to each other. It is obvious, that all the forces parallel to the same axis are equivalent to a single force, equal to the sum of all those which act in one direction, diminished by the sum of those which act ( IfOt 35 ;ity. t!lrt IV. ASTR leery of act in tlie opposite direction. Thus the body will be liiversal acted on by three forces perpendicular to each other: if the direction of these forces be represented by the sides of a parallelepiped, the resulting force will be re¬ presented by the diagonal of that parallelepiped. The indifference of a material body to motion or rest, and its perseverance in either state when put into it, is called the vis inertias of matter. This property is considered as the first law of motion. Hence, when¬ ever the state of a body changes, wTe ascribe the change to the action of some cause: hence the motion of a body when not altered by the action of some new force, must be uniform and in a straight line. In such uniform motions the space passed over is pro¬ portional to the time : but the time employed to de¬ scribe a given space will be longer or shorter according to the greatness of the moving force. This difference in the time of traversing the same space gives us the notion of velocitij, which in uniform motions is the ra¬ tio between the space and the time employed in tra¬ versing it. As space and time are heterogeneous quan¬ tities, they cannot indeed be compared together; it is the ratio between the numbers representing each that constitutes velocity. A unity of time, a second for in¬ stance, is chosen, and in like manner a unity of space, as a foot. Thus, if one body move over 20 feet in one second, and another only 10, then the velocity of the first is double that of the second; for the ratio between 20 and i is twice as great as the ratio* of io to I. When the space, time, and velocity, are represented by numbers, we have the space equal to the velocity mul¬ tiplied by the time, and the time equal to the space di¬ vided by the time. The force by which a body is moved is proportional to the velocity, and therefore is measured by the velo¬ city. This has been disputed by some philosophers, but has been sufficiently established. We shall consi¬ der it, therefore, as a matter of fact, referring the read¬ er for a discussion of the subject to the article Dy¬ namics. lerat- When a body is put in motion by forces which not wiirees. only act at first, but which continue to act uniformly, it will describe a curve line, the nature of which de¬ pends upon the forces which occasion the motion. Gravitation is an instance of a force which acts in this manner. Let us consider it a little. It appears to act in the same manner in a body at rest and in motion. A body abandoned to its action acquires a very small velocity the first instant; the second instant it acquires a new velocity equal to what it had the first instant; and thus its velocity increases every instant in propor¬ tion to the time. Suppose a right-angled triangle, one of the sides of which represents the time, and the other the velocity. The fluxion of the surface of the tri¬ angle being equal to the fluxion of the time multiplied by that of the velocity, will represent the fluxion of the space. Hence the whole triangle will represent the space described in a given time. But the triangle increasing as the square of either of its sides, it is ob¬ vious, that in the accelerated motion produced by gra¬ vitation, the velocities increase with the times, and the heights from which a body falls from rest increase as the squares of the times or of the velocities. Hence, if we denote by i the space through which a body falls Vol. III. Part I, : f O N O M Y. ri3 the first second, it will fall 4 in 2", 9 in 3", and so on ; Theory of so that every second it will describe spaces increasing Universal as the odd numbers 1, 3, 5, 7, &c. This important point will perhaps be rendered more intelligible by the , li°n’ f following diagram. * Let AB, fig. 119. represent the time during which a body is descending, and let BC represent the velocity acquired at the end of that time. Complete the tri¬ angle ABC, and the parallelogram ABCD. Also suppose the time to be divided into innumerable parti¬ cles ei, im, mp, po, &c. and draw ef ik, mn, &c. all parallel to the base BC. Then, since the velocity of the descending body has been gradually increasing from the commencement of the motion, and BC represents the ultimate velocity; therefore the parallel lines e/, ik, mn, &c. will represent the velocities at the ends oi the respective times Ae, Az', Am, &c. Moreover, since the velocity during an indefinitely small particle of time may be considered as uniform ; therefore the right line ef will be as the velocity of the body in the indefinitely small particle of time ei; ik will be as the velocity in the particle of time im, and so forth. Now the space passed over in any time with any velocity is as the velocity multiplied by the time ; viz. as the rectangle under that time and velocity; hence the space passed over in the time ef with the velocity ef, will be as the rectangle if; the space passed over in the time zm with the velocity ik, will be as the rectangle mk ; the space passed over in the time mp with the velocity m 11, will be as the rectangle pn, and so on. Therefore the space passed over in the sum of all those times, will be as the sum of all those rectangles. But since the particles of time are infinitely small, the sum of all the rectangles will be equal to the triangle ABC. Now since the space passed over by a moving body in the time AB with a uniform velocity BC, is as the rectangle ABCD, (viz. as the time multiplied by the velocity) and this rectangle is equal to twice the triangle ABC (Eucl. p. 31. B. I.) therefore the space passed over in a given time by a body falling from rest, is equal to half the space passed over in the same time with an uniform velocity, equal to that which is acquired by the descending body at the end of its fall. Since the space run over by a falling body in the time represented by AB, fig. 120. with the velocity BC is as the triangle ABC, and the space run over in any other time AD, and velocity DE, is represented by the triangle ADE ; those spaces must be as the squares of the times AB AD ; for the similar triangles ABC, and ADE, are as the squares of their homologous sides, viz. ABC is to ADE as the square of AB is to the square of AD, (Eucl. p. 29. B. VI.). When a body is placed upon an inclined plane, the force of gravity which urges that body downwards, acts with a power so much less, than if the body descended freely and perpendicularly downwards, as the elevation of the plane is less than its length. The space which is described by a body descending freely from rest towards the earth, is to the space which it will describe upon the surface of an inclined plane in the same time as the length of the plane is to its eleva¬ tion, or as radius is to the sine of the plane’s inclina¬ tion to the horizon. If upon the elevation BC, fig. 121. of the plane BD, I* as ASTRONOMY. Part IV Theory of as a diameter, the semicircle BEGC be described, the Universal part BE of the inclined plane, which is cut off by the Gravita- semicircle, is that part of the plane dver which a body . u^t1, , will descend, in the same time that another body will descend freely and perpendicularly along the diameter of the circle, viz. from B to C, which is the altitude of the plane, or sine of its inclination to the horizon. The time of a body’s descending along the whole length of an inclined plane, is to the time of its de¬ scending freely and perpendicularly along the altitude of the plane, as the length of the plane is to its alti¬ tude j or as the whole force of gravity is to that part of it which acts upon the plane. A body by descending from a certain height to the same horizontal line, will acquire the same velocity whe¬ ther the descent be made perpendicularly or obliquely, over an inclined plane, or over many successive inclined planes, or lastly over a curve surface. From these propositions, which have been sufficiently established by mathematicians, it follows, that in the circle ABC (fig. 122), a body will fall along the dia¬ meter from A to B, or along the chords CB, DB, in exactly the same line by the action of gravity. When a body is projected in any line whatever not perpendicular to the earth’s surface, it does not conti¬ nue in that line, but continually deviates from it, de¬ scribing a curve, of which the primary line of direc¬ tion is a tangent. The motion of the body relative to this line is uniform. But if vertical lines be drawn from this tangent to the curve, it will be perceived that its velocity is unifor mly accelerated in the direction of these verticals. They are proportional to the squares of the corresponding parts of the tangent. This property shows us that the curve in which the body projected moves is a parabola. Of the The oscillations of the pendulum are regulated like- pendulum. wise by the same law of gravitation. The fundamen¬ tal proportions respecting pendulums are the follow- ing: If a pendulum be moved to any distance from its natural and perpendicular direction, and there be let go, it will descend towards the perpendicular ; then it will ascend on the opposite side nearly as far from the perpendicular, as the place whence it began to descend 5 after which it will again descend towards the perpen¬ dicular, and thus it will keep moving backwards and forwards for a considerable time ; and it would conti- nue to move in that manner for ever, were it not for the resistance of the air, and the friction at the point of suspension, which always prevent its ascending to the same height as that from which it lastly began to de¬ scend. The velocity of a pendulum in its lowest point is as the chord of the arch which it has described in its de¬ scent. The very small vibrations of the same pendulum are performed in times nearly equal 5 but the vibrations through longer and unequal arches are performed in times sensibly different. As the diameter of a circle is to its circumference, so is the time of a heavy body’s descent from rest through half the length of a pendulum to the time of one of the smallest vibrations of that pendulum. It is from these propositions, and the experiments made with pendulums, that the space described by a 3 body falling from rest by the action of gravity has been Theory of ascertained. Universal The late Mr John Whitehurst, an ingenious mem- Gravita. ber of the Royal Society, seems to have contrived and . tl°n’ performed the least exceptionable experiments rela¬ tively on this subject. The result of his experiments shews, that the length of the pendulum which vibrates seconds in London, at 113 feet above the level of the sea, in the temperature of 6o° of Fahrenheit’s thermo¬ meter, and when the barometer is at 30 inches, is 39,1196 inches ; whence it follows that the space which is passed over by bodies descending perpendicularly, in the first second of time, is 16,087 feet. This length of a second pendulum is certainly not mathematically exact, yet it may be considered as such for all common purposes ; for it is not likely to differ from the truth by more than ToVs-th part of an inch. By these propositions, also, the variations of gravity in different parts of the earth’s surface and on the tops of mountains has been ascertained. Newton also has shown, by means of the pendulum, that gravity does not depend upon the surface nor figure of a body. The motion of bodies round a centre affords another of central well known instance of a constant force. As the mo-forces, tion of matter left to itself is uniform and rectilinear, it is obvious that a body moving in the circumference of a curve, must have a continual tendency to fly off at a tangent. This tendency is called a centrifugalforce, while every force directed towards a centre is called a central or centripetal force. In circular motions the central force is equal, and directly contrary, to the centrifugal force. It tends constantly, to bring the body towards the centre, and in a very short interval of time, its effect is measured by the versed sine of the small arch described. Let A (fig. 123.) be the centre of a force. Let a body in B be moving in the direction of the straight line BC, in which line it would continue to move if undisturbed •, but being attracted by the centripetal force towards A, the body must necessarily depart from this line BC; and being drawn into the curve line BD, must pass between the lines AB and BC. It is evi¬ dent, therefore, that the body in B being gradually turned off from the straight line BC, it will at first be convex towards that line, and concave towards A. And that the curve will always continue to have this conca¬ vity towards A, may thus appear: In the line BC, near to B, take any point, as E, from which the line EFG may be so drawn as to touch the curve line BD in some point, as F. Now, when the body is come to F, if the centripetal power were immediately to be suspended, the body would no longer continue to move in a curve line, but, being left to itself, would forth¬ with reassume a straight course, and that straight course would be in the line FG ; for that line is in the direc¬ tion of the body’s motion of the point F. But the cen¬ tripetal force continuing its energy, the body will be gradually drawn from this line FG so as to keep in the line FD, and make that line, near the point F, to be concave towards the point A ; and in this manner the body may be followed in its course throughout the line BD, and every part of that line be shown to he concave towards the point A. Again, the point A (fig. 124.) being the centre of a centripetal force, let a body at B set out in the di¬ rection ft :S Cr firt IV. ASTRONOMY. "neory of rection of the straight line BC, perpendicular to the tuvei-sal jjne jt wjjj jjg eas]]y conceived, that there is no Ira vita- - - tion. other point in the line BC so near to A as the point t B j that AB is the shortest of all the lines which can be drawn from A to any part of the line BC ; all others, as AD or AE, being longer than AB. Hence it fol¬ lows, that the body setting out from it, if it moved in the line BC, would recede more and more from the point A. Now, as the operation of a centripetal force is to draw a body towards the centre of that force, if such a force act upon a resting body, it must neces¬ sarily put that body so into motion as to cause it move towards the centre of the force : if the body were of itself moving towards that centre, it w’ould accelerate that motion, and cause it to move faster down ; but if the body were in such a motion that it would of itself recede from the centre, it is not necessary that the ac¬ tion of a centripetal power should make it immediately approach the centre from which it would otherwise have receded ; the centripetal force is not without ef¬ fect if it cause the body to recede more slowly from that centre than otherwise it would have done. Thus, the smallest centripetal power, if it act on the body, will force it out of the line BC, and cause it to pass in a bent line between BC and the point A, as has been already explained. When the body, for instance, has advanced to the line AD, the effect of the centri¬ petal force discovers itself by having removed the body out of the line BC, and brought it to cross the line AD somewhere between A and D, suppose at F. Now, AD being longer than AB, AF may also be longer than AB. The centripetal power may indeed be so strong, that AF shall be shorter than AB 5 or it may be so evenly balanced with the progressive motion of the body that AF and AB shall be just equal 5 in which case the body would describe a circle about the centre A : this centre of the force being also the centre of the circle. If now the body, instead of setting out in the line BC perpendicular to AB, had set out in another line BG more inclined towards the line AB, moving in the curve line BH j then, as the body, if it were to continue its motion in the line BG, would for some time approach the centre A, the centripetal force would cause it to make greater advances towards that centre : But if the body were to set out in the line BI, reclined the other way from the perpendicular BC, and were to be drawn by the centripetal force into the curve line BK; the body, notwithstanding any centripetal force, would for some time recede from the centre ; since some part at least of the curve line BK lies between the line BI and the perpendicular BC. Let us next suppose a centripetal power directed to¬ ward the point A (fig. 109.), to act on a body in B, which is moving in the direction of the straight line BC, the line BC reclining off from AB. If from A the straight lines AD, AE, AF, are drawn to the line CB, prolonged beyond B to G, it appears that AD is inclined to the line GC more obliquely than AB, AE more obliquely than AD, and AF than AE •, or, to speak more correctly, the angle under ADG is less than that under ABG, that under AEG is less than ADG, and AFG less than AEG. Now sup¬ pose the body to move in the curve line BHIK, it is likewise evident that the line BHIK being concave t is towards A. and convex towards BC, it is more and Theory of more turned off from that line : so that in the point H, Universal the line AK will be more obliquely inclined to the ^,l^V:ta- curve line BHIK than the same line AHD is inclined , to BC at the point D j at the point I the inclination of the line AI to the curve line will be more differ¬ ent from the inclination of the same line AIE to the line BC at the point IE ; and in the points K and F the difference of inclination will be still greater ; and in both, the inclination at the curve will be less ob¬ lique than at the straight line BC. But the straight line AB is less obliquely inclined to BG than AD is inclined towards DG : therefore, although the line AH be less obliquely inclined towards the curve HB than the same line AHD is inclined towards DG, yet it is possible, that the inclination at H may be more oblique than the inclination at B. The incli¬ nation at H may indeed be less oblique than the other, or they may be both the same. This depends upon the degree of strength wherewith the centripetal force exerts itself during the passage of the body from B to H : and in like manner the inclinations at I and K depend entirely on the degree of strength wherewith the centripetal force acts on the body in its passage from H to K: if the centripetal force be tveak enough, the lines AH and AI drawn from the centre A to the body at H and at I, shall be more obliquely inclined to the curve than the line AB is inclined towards BG. The centripetal force may be of such a strength as to render all these inclinations equal ; or if stronger, the inclination at I and K will be less oblique than at B ; and Sir Isaac Newton has particularly shown, that if the centripetal power decreases after a certain manner without the increase of distance, a body may describe such a curve line, that all the lines drawn from the centre to the body shall be equally inclined to that curve line. We must further remark, that if the centripetal Revolutioti power, while the body increases its distance from the°falj0<*? round a centre efc« centre, retain sufficient strength to make the lines^ ^ drawn from the centre to the body to become at plained!^ length less oblique to the curve : then, if this diminu¬ tion of the obliquity continue, till at last the line drawn from the centre to the body shall cease to be obliquely inclined to the curve, and become perpendi¬ cular thereto ; from this instant the body shall no longer recede from the centre, but in its following mo¬ tion shall again descend, and describe a curve in all respects like that which it has described already, pro¬ vided the centripetal power, everywhere at the same distance from the body, acts with the same strength. This return of the body may be proved by the follow¬ ing proposition : That if the body in any place, sup¬ pose at I, were to be stopped, and thrown directly backward with the velocity wherewith it was moving forward in that point I, then the body, by the action of the centripetal force upon it, would move back again over the path IHB, in which it had before advanced forward, and would arrive again at the point B in the same space of time as was taken up in its passage from B to I 5 the velocity of the body at its return from the point B being the same as that wherewith it first set out from that point. The truth of this proposition may be illustrated in the following manner. Suppose, in fig. no. that a F 2 body u6 ASTRONOMY. Theory of were carried after the following manner through passed through it undisturbed. tion. Universal the bent figure ABCDEF, composed of the straight Gravita- lines AB, BC, CD, DE, EE : let the body then first be supposed to receive an impulse to some point within the concavity of the figure, as G. Now, as this body, when once moving in the straight line AB, will conti¬ nue to move on in this line as long as it shall be left to itself; but being disturbed at the point B by the im¬ pulse given it, it will be turned out of this line AB into some other straight line, -wherein it will afterwards con¬ tinue to move as long as it shall be left to itself; there¬ fore, let this impulse have strength sufficient to turn the body into the line BC j then let the body move on un¬ disturbed from B to C: but at C let it receive another impulse pointed also towards G, and of sufficient strength to turn the body into the line CD ; at D let a third im¬ pulse turn it into the line DE} and at E let another turn it into EF. Now, if the body, while moving on m the line EF, be stopped and turned hack again with the same velocity with which it was moving forward, then by the repetition of the former impulse at E, the body will be turned into the line ED, and move in it from E to D with the same velocity as that wherewith it was moving forwai’d in this line : then by a repeti¬ tion of the impulse at D, when the body shall have re¬ turned to that point, it will be turned into the line DC } and by the repetition of the former impulses at C and at B, the body will be brought back again into the line BA, with the velocity wherewith it first moved in that line. To illustrate this still farther, let DE and EE he con¬ tinued beyond E. In DE thus continued, take at plea¬ sure the length EH, and let HI be so drawn as to be equidistant from the line GE ; then, from the second law of motion, it follows, that after the impulse on the body on E, it will move through the space El in the same time it would have employed in moving from E to II with the velocity it had in the line DE. In FE prolonged, take EKi equal to El, and draw KL equidistant from GE. Then because the body is thrown back in the line FE, with the same velocity with which it went forward in that line, if, when the body was turned to E, it were permitted to go straight on, it would pass through EK in the same time as it took up in passing through El, when it went forward in the line EF. But if, at the body’s return to the point E, such an impulse directed toward the point D were to be given it as was sufficient to turn it into the line DE, it is plain that this impulse must be equal to that which originally turned the body out of the line DE into EF j and that the velocity with which the body will return into the line ED is the same as that wherewith it moved before through this line from D to E. Because EK is equal to El, and KL and HI being each equidistant from GE, are by consequence equidistant from each other ; it follows, that the two triangular figures IEH and KEL, are altogether like and equal to each other. EK there¬ fore being equal to El, and EL equal to KH, and KL equal to HL, it is plain, that the body, after its return to E, being turned out of the line FE into ED by an impulse acting upon it in E after the manner above mentioned, it will receive such a velocity by this impulse as will carry it through EL in the same time it would have taken to go through EK, if it had 2 Part IV, It has already been Theor,< observed, that the time in which the body would pass Universal over EK, with the velocity wherewith it returns, is Gravita- equal to the time it took up in going forward from E ^on to I; that is, to the time in which it would have gone v"' through EH with the velocity wherewith it moved from D to E j therefore the time in which the body will pass from E to L, after its return into the line ED, is the same as would have been taken up by the body in passing through the line EH with the velocity wherewith it first moved in the line DE. Since, there¬ fore, EL and EH are equal, the body returns into the line DE -with the velocity which it had before in that line—Again, we may affirm, that the second impulse in E is equal to the first 5 for, as the impulse in E, whereby the body was turned out of the line DE into the line EF, is of such strength, that if the body had been at rest when this impulse had acted up¬ on it, it would have communicated as much motion to it, as would have been sufficient to carry it through a length equal to FII, in the time wherein the body would have passed from E to H, or in the time wherein it passed from E to I. In the same manner, on the"return of the body, the impulse in E, whereby it is turned out of the line FE into ED, is of such strength, that if it had acted on the body at rest, it would have caused it move through a length equal to KL in the same time as the body would employ in passing through EK with the velocity wherewith it re¬ turns in the line FE: therefore the second impulse, had it acted on the body at rest, would have caused it to move through a length equal to KL, in the same space of time as would have been taken up by the body- in passing through a length equal to HI were the first impulse to act on the body while at rest j that is, the effects of the first and second impulse on the body when at rest would be the same 5 for KL and HI are equal: Consequently the second impulse is equal to the first. Thus, if the body be returned through EE with the velocity wherewith it moved forward, it has been shown how, by the repetition of the impulse which acted on it in E, the body will return again into the line DE with the velocity which it had before in that line. By the same method of reasoning it may be proved, that when the body is returned back to D, the impulse which before acted on that point will throw the body into the line DC with the velocity which it first had in that line j and the other impulses being successively repeated, the body will at length be brought back again into the line BA with the velocity wherewith it set out in that line.—Thus these impul¬ ses, by acting over again in an inverted order all their operations on the body, bring it back again through the path in which it had proceeded forward j and this obtains equally whatever be the number of straight lines whereof this curve figure is composed. Now, by a method of reasoning of which Sir Isaac Newton made much use, and which he introduced into geo¬ metry, thereby greatly enriching that science, we might make a transition from this figure, composed of a number of straight lines, to a figure of one continued curvature, and from a number of separate impulses re¬ peated at distinct intervals to a continued centripetal force, and show that because what has been here ad¬ vanced holds universally true whatever be the num¬ ber I'lPft IV. Ion. ASTRO Ttyryof her °f straight lines whereof the curve figure ACF is t%ersal composed, and however frequently the impulses at the CJivita- angles of this figure are repeated j therefore the same t will still remain true although this figure should be converted into one of a continued curvature; and these distinct impulses should be changed into a conti¬ nual centripetal force. This being allowed, suppose the body in K to have the line AK no longer obliquely inclined to its mo¬ tion. In this case, if the body be turned back in the manner we have been considering, it must be directed back perpendicularly to AK : but if it had proceeded forward, it would likewise have moved in a direction perpendicular to AK: consequently, whether it move from this point K backward or forward, it must de¬ scribe the same kind of course. Therefore, since by being turned back it will go over again the line KIHB, if it be permitted to go forward, the line KL, which it shall describe, will be altogether similar to the line KHB. In like manner we may determine the nature of the motion, if the line wherein the body sets out be in¬ clined, as in fig. 127. down toward the line BA drawn between the body and the centre. If the centripetal power so much increases in strength as the body ap¬ proaches, that it can bend the path in which the body moves to that degree as to cause all the lines, AH, AI, AK, to remain no less oblique to the motion of the body than AB is oblique to BC, the body shall continually more and more approach the centre. But if the centripetal power increases in so much less a degree as to permit the line drawn from the centre to the body, as it accompanies the body in its motion, at length to become more and more erect to the curve wherein the body moves, and in the end, suppose at K, to become perpendicular to it $ from that time the bo¬ dy shall rise again. This is evident from what has been said above j because, for the very same reason, here also, the body will proceed from the point K to describe a line altogether similar to that in which it has moved from B to K. Thus it happens as in the pendulum, whichj all the time it approaches a perpendicular posi¬ tion towards the horizon, descends more and more j but as soon as it is come into that situation, it imme¬ diately rises again by the same degrees as it descended before : so here the body more and more approaches the centre all the time it is moving from B to K ; but thenceforward it rises from the centre again by the same degrees as it approached before. If, as in fig. 127. the line BC be perpendicular to N O M Y. AB j then, as has already been observed, the centri¬ petal power may be so balanced with the progressive motion of the body, that it may keep moving round the centre A constantly at the same distance 5 as the body does when whirled about any point to which it is tied by a string. If the centripetal power be too weak to produce this effect, the motion of the body will presently become oblique to the line drawn from itself to the centre ; but if it be stronger, the body must constantly keep moving in a curve to which a line drawn from it to the body is perpendicular. If the centripetal power change with the change of distance, in such a manner that the body, after its mo¬ tion has become oblique to the line drawn from itself to the centre, shall again become perpendicular there¬ to ; then the body shall, id its subsequent motion, re¬ turn again to the distance of AB, and from that di¬ stance take a course similar to the former : and thus, if the body move in a space void of all resistance, which has been all along supposed, it will continue in a per¬ petual motion about the centre, descending and ascend¬ ing from it alternately.. If the body, setting out from B (fig. 126.) in the line BC perpendicular to AB, describe the line BDE, which in X) shall be ob¬ lique to the line AD, but in E shall again become erect to AE, drawn from the body in E to the centre A $ then from this point E the body shall describe the line EFG entirely similar to BDE, and at G shall be at the same distance as it was at B y and the line AG shall be erect to the body’s motion. Therefore the body shall proceed to describe from G the line GHI altogether similar to the line GFE, and at I it will have the same distance from the centre as it had at E 3 and also have the line AI erect to its motion : so that its subsequent motion must be in the line IKL similar to IKG, and the distance AL equal to AG. Thus the body will go on in a perpetual round without cea¬ sing, alternately enlarging and contracting its distance from the centre. If it so happen that the point E fall upon the line BA, continued beyond A 3 then the point G will fall upon B, I on E, and L also on B; so that the body will in this case describe a simple curve line round the centre A, like the line BDEF in fig. 126. in which it will revolve from P to E, and from E to B, with¬ out end. If AE in fig 126. should happen to be per¬ pendicular to AB, in this case also a simple line will be described 3 for the point G will fall on the line BA prolonged beyond A 3 the point I on the line AE pro¬ longed beyond A 5 and the point L on B 3 so that the body will describe a line like the curve line BEG! in fig. 128. in which the opposite points B and G are equally distant from A3 and the opposite points E and E are also equally distant from the same point A. In other cases the body will have a course of a more com¬ plicated nature. Thus it must be apparent how a body, while it is constantly attracted towards the centre, may notwith¬ standing by its progressive motion keep itself from falling down to the centre, describing about it an end¬ less circuit, sometimes approaching and sometimes re¬ ceding from it. Hitherto, however, we have suppo¬ sed, that the centripetal power is everywhere of equal strength at the same distance from the centre : and this is indeed the case with that power which keeps the planets in their orbits 3 but a body may be kept on in a perpetual circuit round a centre, although the cen¬ tripetal power be kept moving in any curve line what¬ ever, that shall have its concavity turned everywhere towards the centre of the force. To illustrate this, v/e shall in the first place propose the case of a body moving, in the incurvated figure ABCDE (fig. 129.), which is composed of the straight lines, AB, BC, CD, DE, and AE 3 the motion being carried on in the follow¬ ing manner. Let the body first move in the line AB with any uniform velocity. When it is arrived at the point B, let it receive an impulse directed towards any point F taken within the figure 3 and let the impulse be of such a strength as to turn the body out of the line AB into the line. BC: The body after this impulse, while ~ 3 I j- Theory of Uni-versal Gravita¬ tion. — y-—i-a 340 A body may be moved in any curvili¬ near direc¬ tion by means of centripetal force. ASTRO while left to itself, will continue moving in the line BC. At C let the body receive another impulse directed to¬ wards the same point F, of such strength as to turn it from the line CB into CD. At D, let the body, by another impulse, directed likewise towards the point F, be turned out of the line CD into DE. At E, let ano¬ ther impulse, directed likewise towards the point F, turn the body from the line DE into EA : and thus the body will, by means of these impulses, be carried through the whole figure ABCDE. Again, when the body is come to the point A, if it there receive another impulse directed like the rest to the point F, and of such a degree of strength as to turn it into the line AB, wherein it first moved ; the body will then return into this line with the same velo¬ city it had originally. To understand this, let AB be prolonged beyond B at pleasure, suppose to G ; and from G let GH be d rawn ; which, if produced, should always continue equidistant from BF, i. e. let GH be drawn parallel to BF, in the time, then, in which the body would have moved from B to G, had it not re¬ ceived a new impulse in B ; by the means of that im¬ pulse it will have acquired a velocity which will carry it from B to H. After the same manner, if Cl be taken equal to BH, and IK be drawn parallel to CF, the body will have moved from C to K, with the ve¬ locity which it has in the line CD, in the same time it would* have employed in moving from C to I with the velocity it had in the line BC. Therefore, since Cl and BH are equal, the body will move through CK in the same time as it would have taken up in moving from B to G with the velocity wherewith it moved through the line AB. Again, DL being taken equal to CK, and LM drawn parallel to DE'1, the body will for the same reason as before, move through DM with the velocity which it has in the line DE, in the same time it would employ in moving through BG with its original velocity. Lastly, if EN be taken equal to DM, and NO he drawn parallel to EF j like¬ wise, if AP be taken equal to EO, and PQ be drawn parallel to Ah' ; then the body, with the velocity wherewith it runs into the line AB, will pass through AQ in the time it would have employed in passing through BG with its original velocity. Now as all this follows directly from what has been delivered concern¬ ing oblique impulses impressed upon bodies in motion 5 so we must here observe farther, that it can he proved by geometry, that AQ will always be equal to BG ; which, being granted, it follows, that the body has Re¬ turned into the line AB with the swme velocity which it had when it first moved in that line ; for the velocity with which it returns into the line AB will carry it over the line AQ in the same time as would have beeti taken up in its passing over an equal line BG with the original velocity. The conclusion naturally deduced from the above reasoning is, that by means of a centripetal and pro¬ jectile force, a body may be carried round any fixed point as a curve figure which shall be concave towards it, as that marked ABC, fig. 130. and when it is re¬ turned to that point from whence it set out, it shall re¬ cover again the velocity with which it departed from that point. It is not indeed always necessary that it should return again into its first course, for the curve line may have some such figure as ABCDBE in N O M Y. ir 34» laid down the following proposition as a foundation forjyrryal1' in anj discovering this, viz. that if a line be drawn from some curye liw fixed point to the body, and remaining by one ex¬ treme united to that point, it be carried round along with the body 5 then if the power whereby the body is kept in its course be always pointed to this fixed point as a centre, this line will move over equal spaces in equal portions of time. Suppose a body were moving through the curve line ABCD (fig. 132.), and passed over the arches AB, BC, CD in equal portions of time ; then if a point, as E, can be found, from whence the line EA being drawn to the body in ac¬ companying it in its motion, it shall make the spaces EAB, EEC, and ECD, over which it passes, equal where the times are equal *, then is the body kept in th is line by a power always pointed to E as a centre. To prove this, suppose a body set out from the point A, fig. 133, to move in a straight line AB j and after it had moved for some time in that line, it were to receive an impulse directed to some point, as C. Let it receive that impulse at D, and thereby be turned in¬ to the line DE ; and let the body after this impulse, take the same time in passing from D to E that is em¬ ployed in passing from A to D. Then the straight lines CA, CD, and CE being drawn, the triangular spaces CAD and CDE are proved to be equal in tfie following manner. Let EF be drawn parallel to CD. Then it follows, from the second law of motion, that since the body was moving in the line AB when it re¬ ceived the impulse in the direction DC, it will have mo¬ ved after that impulse through the line DEi in the same time as it would have moved through DF, provided it had received no disturbance in D. But the time of the body’s moving from D to E is supposed to be equal to the time of its moving through AD 5 therefore the time which the body would have employed in moving through DF, had it not been disturbed in D, is equal to the time wherein it moved through AD : conse¬ quently DF is equal in length to AD ; for if the body had gone on to move through the line AB without interruption, it would have moved through all the parts of it with the same velocity, and have passed over equal parts of that line in equal portions of time. Now CF be¬ ing drawn, since AD and DF are equal, the triangular space CDF is equal to the triangular space CAD. E^ur- ther, the line EF being parallel to CD, it follows from the 37th proposition of Euclid’s first book, that the tri¬ angle jive; Part IV fig. 131. In this curve line, if the body set out from Theory. B in the direction BF, and moved through the line Uiiirem BCD till it returned to B ; here the body would not Gryvita. enter again into the line BCD, because the two parts, tlon' Jl0!1 BD and BC of the curve line make an angle at the point B : so that the centripetal power, which at the point B would turn the body from the line BF into the curve, will not be able to turn it into the line BC from the direction in which it returns to the point B. A forcible impulse must be given the body in the point B to produce that effect. If, at the point B, whence the body sets out, the curve line return into itself, as in fig. 130. then the body, upon its arrival again at B, may return into its former course, and thus make an endless circuit about the centre. The force requisite to carry a body in any curve line Calculatis proposed, is to be deduced from the curvature which °f the fon the figure has in any part of it. Sir Isaac Newton hasre 34S Thus we have been led, without assuming any hypo-Hence tin thesis, by the necessary consequence of the laws of the sun’sce"tB celestial movements, to consider the centre of the sun as ^ the focus of -a force, which extends itself indefinitely through space, diminishing inversely as the squares of the distance, and which attracts all bodies within the sphere of its activity. Each of Kepler’s laws points out a pro¬ perty of this attractive force. The law of the areas pro¬ portional to the times, informs us, that the force is di¬ rected towards the sun j the elliptical figure of the pla¬ nets proves to us, that its intensity diminishes as the square of the distance augments; and the law of the squares of the times proportional to the cubes of the di¬ stance, informs us, that the tendency, or gravitation of all the planets to the sun is the same, provided the di¬ stances were the same. We may call this force solar attraction, supposing, for the sake of a distinct con¬ ception, that it is a force residing in the sun. ^ The tendency or gravitation of the satellites towards SateliitM their planets is a necessary consequence of the areas de-ten?t0. scribed by their radii vectors being proportional to thettiei*fn times; that this gravitation is inversely as the square of their distance, is indicated by the ellipticity of their or¬ bits. This ellipticity, indeed, being scarcely apparent in most of the satellites of Jupiter, Saturn,'and Herschel, would leave some uncertainty, did not the third law, namely, the squares of the times being inversely as the cubes of their distance, demonstrate, that from one sa¬ tellite to another, the tendency to the planet is inverse¬ ly as the square of the distance. This proof, indeed, is wanting with respect toourMocn’i moon; but the defect maybe supplied by the follow-tendencr ing considerations. Gravity, or the weight by which ^*2. a body tends towards the earth, extends itself to the™tion, top of the highest mountains, and the very trifling di-1* minution which it experiences at that height, cannot permit us to doubt, that it would still be sensible at a considerably I 21 Prt IV. Tlbi-y of considerably greater distance from the earth’s centre. Is it not natural to extend it as far as the moon, and to suppose that the force which retains that satellite in its orbit, is its gravitation towards the earth, just as it is the solar attraction which retains the planets in their orbits ? The forces at least seem to be of the same na¬ ture ; they both act upon every particle of bodies, and cause them to move at the same rate : for the solar at¬ traction acts equally upon all bodies placed at the same distance from the sun, just as gravitation causes all bo¬ dies to fall from the same height with the same velo¬ city. A body projected horizontally, falls upon the earth at some distance after describing a curve sensibly parabolic. It would fall at a greater distance, if the force of projection were more considerable j and, if projected with a certain velocity, it would not fall back at all, but revolve round the earth like a satellite. To make it move in the orbit of the moon, it would be necessary only to give it the same height and the same projecting force. But what demonstrates the identity ol gravitation and of the force which retains the moon in its orbit is, that if we suppose gravity to diminish in¬ versely as the square of the distance from the centre of the earth, at the distance of the moon it will be precisely equal to the moon’s tendency to the earth. Let A in fig. 134. represent the earth, B the moon, BCD the moon’s orbit j which differs little from a cir¬ cle of which A is the centre. If the moon in B were left to itself to move with the velocity it has in the point B, it would leave the orbit, and proceed straight forward in the line BE which touches the orbit in B. Suppose the moon would upon this condition move from B to E in the space of one minute of time : By the action of the earth upon the moon, whereby it is retained in its orbit, the moon will really be found at xplmed. ilie en(^ minute in the point F, from whence a straight line drawn to A shall make the space BFA in the circle equal to the triangular space BEAj so that the moon in the time wherein it would have moved from B to E, if left to itself, has been impelled to¬ wards the earth from E to F. And when the time of the moon’s passing from B to F is small, as here it is only one minute, the distance between E and F scarce diflers from the space through which the moon would descend in the same time if it were to fall directly down from B toward A without any other motion. AB, the distance of the moon from the earth, is about 60 of the semidiameters of the latter; and the moon com¬ pletes her revolution round the earth in about 27 days 7 hours and 43 minutes : therefore the space EF will here be found by computation to be about i6-j- feet. Consequently, it the power by which the moon is re¬ tained in its orbit be near the surface of the earth greater than at the distance of the moon in the dupli¬ cate proportion of that distance, the number of feet a ■»t body would descend near the surface of the earth, by (Calciiition the action of this power upon it, in one minute would elo-be equal to the number 16^ multiplied twice into the fal1'number 60 j that is, to c8oco. But how fast bodies tali near the surface of the earth may be known by the pendulum ; and by the exactest experiments, they are found to descend the space of 16^ feet in one se¬ cond ; and the spaces described by falling bodies be¬ ing in the duplicate proportion of the times of their fall, the number of feet a body would describe in its Vol. III. Part L f ASTRONOMY. fall near the surface of the earth in one minute of time Theoiy of will he equal to 16^ twice multiplied by 60 ; the same Universal as would be caused by the power which acts upon the moon. In this computation the earth is supposed to be at rest: but it would have been more exact to have sup-Earth and posed it to move, as well as the moon, about their com-moon move mon centre of gravity j as will be easily understood a*)0Ut t^e’r from what has been already said concerning the motion cemre'of of the sun and primary planets about their common gravity, centre of gravity. The action of the sun upon the moon is also here neglected ; and Sir Isaac Newton shows, if you take in both these considerations, the present computation will best agree to a somewhat greater distance of the moon and earth, viz. to 60^ semidiameters of the latter, which distance is more con¬ formable to astronomical observations : and these com¬ putations aflord an additional proof that the action of the earth observes the same proportion to the distance which is here contended for. We see then that the force which retains the moon in its orbit is gravitation, or that force w’hich causes heavy bodies to fall to the ground. This comparison between gravity and the lunar tendency to the earth shows us, that, in our calculations, we ought to measure distance from the centre of gravity of the sun and of the planets; for this is obviously the case with the earth, and its tendency to the sun is precisely the same with that of the other planets. ^ Hie sun and the planets which have satellites, pos-Planet* sessing, as we have seen, an attracting force inversely rcac* npoa as the square of the distance, one is tempted to give the**1® 8U11, same property to the other planets also. The sphericity common to all these bodies, indicates clearly, that their particles are retained round their centre of gravity, by a force which at equal distances attracts them equally to that centre. But this important point is not left to analogical reasoning. We have seen, that if the pla¬ nets and comets were placed at equal distances from the sun, their gravitation towards it would be pro¬ portional to their masses. But it may be considered as a general matter of fact, to which there is no excep¬ tion, that action and reaction are equal and contrary. 01 course all these bodies react upon the sun, and at* tract it in proportion to their mass, and consequently possess an attractive force proportional to their mass, and inversely as the square of their distance. The sa¬ tellites also, in consequence ot the same principle, at¬ tract the planets and the sun according to the same law. This attracting force is then common to all the heaven¬ ly bodies. This force does not disturb the elliptical motion of the plants round the sun, when we consider only their mutual action. For the relative movement of a system of bodies does not change by giving them a common motion. Neither is the elliptical motion of the satel¬ lites disturbed by the revolution of the planets round the sun, for the very same reason. The attractive force does not belong to these bodies only as wholes ; but it belongs to every particle of matter of which each of them is composed. If the sun acted only upon the centre of the earth, without at¬ tracting every one of the particles of which it is com¬ posed individually, there would result tides incom¬ parably greater, and very different from those that we Q observe. 122 ASTRONOMY. 355 General law of gra- ■vitation. observe. Besides, every body on the earth gravitates towards its centre, in proportion to its mass. It reacts of course upon the earth, and attracts it in the same ra¬ tio. Unless that were the case, or if any part of the earth, however small, did not attract the other part as it is attracted by it, the centre of gravity of the earth would be moved in space, in consequence of gravitation J which is impossible. All these phenomena, compared with the laws of mo¬ tion, lead us to this grand conclusion : All the'parti¬ cles of matter mutually attract each other, in propor¬ tion to their masses, and inversely as the squares of their distances. This is called universal gravitation, and was the discovery which crowned the happy indus¬ try, the consummate skill, and the unrivalled sagacity of Newton. In universal gravitation, we readily perceive a cause of the irregularities and disturbances perceptible in the planetary motions. For as the planets and comets act upon each other, they ought to deviate a little from that exact ellipticity, which they would follow if they obeyed only the action of the sun. The satellites, dis¬ turbed equally by their mutual attraction, and by that of the sun, must deviate also from these laws. We see also, that the particles of which each heavenly body is composed, provided they be at liberty to move, ought to form themselves into a sphere, and that the result of their mutual action at the surface of this sphere ought to produce all the phenomena of gravity. We see also, that the rotation of the heavenly bodies round an axis ought to alter this sphericity somewhat by flattening them at the poles, and that the result of their mutual action not passing exactly through their centres of gra¬ vity, ought to produce in their axis of rotation mo¬ tions similar to those which we perceive. We see also, that the particles of the ocean, unequally attracted by the sun and moon, ought to have an oscillation similar to the tides. But it will be necessary to consider the effects of gravitation more particularly ; in order to show that it is established in the compietest mdnner by all the phenomena. This shall be the subject of the next chapter. Chap. III. Of the Effects of Gravitation. We shall in this chapter consider, in the first place, several points which could only be ascertained by the assistance of gravitation, and afterwards examine the se¬ veral subjects hinted at towards the conclusion of the last chapter. Sect. I. Of the Masses of the Planets. 356 _ Calculation of the den¬ sities of the planets. It would appear, at first view, impossible to ascertain the respective masses of the sun and planets, and to cal¬ culate the velocity with which heavy bodies fall towards each when at a given distance from their centres 5 yet these points may be determined from the theory of gra¬ vitation without much difficulty. It follows from the theorems relative to centrifugal forces, given in the first chapter of this part, that the gravitation of a satellite towards its planet is to the gravitation of the earth towards the sun, as the mean distance of the satellite from its primary, divided by the square of the time of its sidereal revolution, or the mean distance of the earth from the sun divided by the 1066.08 Jupiter, that of tiny sun being represented by 1. It is necessary to add unity to the denominator of this frac¬ tion, because the force which retains Jupiter in his orbit is the sum of the attractions of Jupiter and the sun. The mass of Jupiter is then —T—The mass 1067.08’ of Saturn and Herschel may be calculated in the same manner. That of the earth is best determined by the following method : If we take the mean distance of the earth from the sun for unity, the arch described by the earth in a se¬ cond of time will be the ratio of the circumference to the radius divided by the number of seconds in a side¬ real year. If we divide the square of that arch by the diameter, we obtain —for its versed sine, which 104 is the deflection of the earth towards the sun in a se¬ cond. But on that parallel of the earth’s surface the square of the sine of whose latitude is a body falls in a second i6|- feet. To reduce this attraction to the mean distance of the earth from the sun, we must di¬ vide the number by the feet contained in that distance ; but the radius of the earth at the above-mentioned pa¬ rallel is 19614648 French feet. If we divide this num¬ ber by the tangent of the solar parallax, we obtain the mean radius of the earth’s orbit expressed in feet. The effect of the attraction of the earth at a di¬ stance equal to the mean radius of its orbit, is equal to i6T 19614648 b7 tbe cube °f tbe tangent of the solar parallax — Hence the masses of the sun and earth are to each other as the numbers I4795^0,5 a11^ 4*486113 ; therefore the mass of the earth is 5—, that of the sun being unity. 329809 ° M. de la Place calculated the masses of Mars and Venus from the secular diminution of the obliquity of the ecliptic, and from the mean acceleration of the moon’s motion, The mass of Mercury he obtained from its volume, supposing the densities of that planet and yV Part square of a sidereal year. To bring these gravitations Theory to the same distance irom the bodies which produce Ttniversi them, we must multiply them respectively by the squares Gravita. of the radii of the orbits which are described : and, as , at equal distances the masses are proportional to the at- tractions, the mass of the earth is to that of the sun as the cube of the mean radius of the orbit of the satel¬ lite, divided by the square of the time of its sidereal motion, is to the cube of the mean distance of the earth from the sun, divided by the square of the sidereal year. Let us apply this result to Jupiter. The mean di¬ stance of his 4th satellite subtends an angle of 1530".86 decimal seconds. Seen at the mean distance of the earth from the sun, it would appear under an angle of 7964". 75 decimal seconds. The radius of the circle contains 636619".8 decimal seconds. Therefore the mean radii of the orbit of Jupiter’s 4th satellite and of the earth’s orbit are to each other as these two num¬ bers. The time of the sidereal revolution of the 4th satellite is 16.6890 days; the sidereal year is 365.2564 days. These data give us ^ for the mass of 'ivBoiy of ant^ t^ie eartl1 reciprocally as their mean distance riltlli verbal from the sun, a rule which holds, with respect to the earth, Jupiter, and Saturn. The following table exhi- L"“*. bits the masses of the difl’erent planets, that of the sun .57 being unity : falb of IV. A S T R he lasses. )ft: 4 if9 )f Rivity ttWr ur(fcs. Mercury Venus Earth Mars Jupiter Saturn Herschel 2025810 x -3S3'31 1 329809 1 1846082 1 1067.09 1 3359-4° 1 The densities of bodies are proportional to their masses divided by their bulks j and, when bodies are nearly spherical, their bulks are as the cubes of their se¬ midiameters, of course the densities in that case are as the masses divided by the cubes of the semidiameters. For greater exactness, we must take that semidiameter of a planet w-hich corresponds to the parallel, the square of the sine of which is equal to -f, and which is equal to the third of the sum of the radius of the pole, and twice the radius of the equator. This method gives us the densities of the principal planets as follows, that of the sun being unity : Earth 3-93933 Jupiter 0.86014 Saturn 0.49512 Herschel 1.13757 To have the intensity of gravitation at the surface of the sun and planets, let us consider, that, if Jupiter and the earth were exactly spherical, and destitute of their rotatory motion, gravitation at their equators would be proportional to the masses of these bodies divided by the squares of their diameters. But at the mean di¬ stance of the sun from the earth, the diameters of the equators of Jupiter and of the earth are to each other as the numbers 626.26 and 54.5. If then we represent the weight of a body at the earth’s equator by I, the same body, if transported to the equator of Jupiter, would weigh 2.509. But the difference of the centri¬ fugal forces on the surface of the earth and J upiter ren¬ ders it necessary to diminish this last number by about f The same body at the surface of the sun would weigh 27.65. Sect. II. Of the Perturbations in the Elliptical Orbit of the Planets. If the planets were influenced only by the sun, they would describe ellipses round that luminary: but thev act upon one another, and from these various attractions there result disturbances in their elliptical motions, dis¬ coverable by observation, and which it is necessary to determine, in order to be able to construct accurate ta- O N O M Y. bles of the planetary motions. The rigorous solution of this problem is above the reach of the mathematical ana- lysis; mathematicians have been obliged to satisfy them¬ selves with approximations. The disturbances in the elliptical motions of the pla¬ nets may be divided into two classes. The first class affects the elements of the elliptical motion : they in¬ crease very slowly, and have been called secular inequa¬ lities. The other class depends upon the configuration of the planets, either with respect to each other, or with respect to their nodes and perihelions, and are renewed every time that the relative situation of the planets be¬ comes the same. They are called periodical inequali¬ ties, to distinguish them from the secular, whose periods are much longer and altogether independent of the mu¬ tual configuration of the planets. Before proceeding farther, we beg leave to introduce the following quota¬ tion from Dr Pemberton, because it will convey some notion of these disturbances in a very familiar manner to our readers. “ The only inequalities which have been observed common to all the planets are, the motion of the aphe¬ lion and the nodes. The transverse axis of each orbit does not remain always fixed, but moves about the sun with a very slow progressive motion j nor do the planets keep constantly in the same planes, but change them and the lines by which these planes intersect each other by insensible degrees. I he first of these inequalities, which is the motion of the aphelion, may be accounted for, by supposing the gravitation of the planets to¬ wards the sun to differ a little farther from the foremen- tioned reciprocal duplicate proportion of the distances ; but the second, which is the motion of the nodes, can¬ not be accounted for by any power directed towards the sun j for no such power can give it any lateral impulse to divert it from the plane of its motion into any new plane, but of necessity must be derived from some other centre. Where that power is lodged, remains to be discovered. Now it is proved, as shall afterwards be explained, that the three primary planets, Saturn, Ju- piter, and the Earth, which have satellites revolving about them, are endowed with a power of causing bo¬ dies, in particular those satellites, to gravitate towards them with a force which is reciprocally in the duplicate proportion of their distances ; and the planets are, in all respects in which they come under our considera¬ tion, so similar and alike, that there is no reason to question but they have all the same property, though it be sufficient for the present purpose to have it proved of Jupiter and Saturn only ; for these planets contain much greater quantities of matter than the rest, and proportionally exceed the others in power. But the influence of these two planets being allowed, it is evident how the planets come to shift their places continually -, for each of the planets moving in a differ¬ ent plane, the action of Jupiter and Saturn upon the rest will be oblique to the planes of their motion, and therefore will gradually draw them into new ones. fI he same action of these two planets upon the rest will likewise cause a progressive motion of the aphe¬ lion j so that there will be no necessity for having re¬ course to the other cause for this motion, which was before hinted at, viz. the gravitation of the planets toward the sun differing from the exact duplicate pro- Q 2 portion 123 360 Secular and periodical inequali¬ ties. 36 r Motion of Uie apheli¬ on account¬ ed for. Saturn influence each other’ motions. I 24 Theory of portion of their distances. And, in the last place, the Universal action of Jupiter and Saturn upon each other will pro¬ duce in their motions the same inequalities as their joint action produces upon the rest. All this is effect¬ ed in the same manner as the sun produces the same kind of inequalities and many others in the motion of the moon and other secondary planets; and there¬ fore will be best apprehended by what is said after¬ wards. Those other irregularities in the motion of the secondary planets have place likewise here, but are too minute to be observable, because they are produced and rectified alternately, for the most part in the time of a single revolution ; whereas the motion of the 362 aphelion and nodes, which increase continually, become Jupiter and sensible after a long series of years. Yet some of these other inequalities are discernible in Jupiter and Sa- sturnj in Saturn chiefly: for when Jupiter, who moves faster than Saturn, approaches to a conjunction with him, his action upon the latter will a little retard the motion of that planet; and by the reciprocal action of Saturn, he will himself be accelerated. After con¬ junction, Jupiter will again accelerate Saturn, and be likewise retarded in the same degree as before the first was retarded and the latter accelerated. Whatever inequalities besides are produced in the motion of Sa¬ turn by the action of Jupiter upon that planet, will be sufficiently rectified by placing the focus of Saturn’s ellipsis, which should otherwise he the sun, in the common centre of gravity of the sun and Jupiter. And all the inequalities of Jupiter’s motions, caused by the action of Saturn upon him, are much less considerable than the irregularities of Saturn’s motion. This one principle, therefore, of the planets having a power as well as the sun to cause bodies gravitate towards them, which is proved by the motion of the secondary planets to obtain in fact, explains all the irregularities rela¬ ting to the planetary motions ever observed by astrono¬ mers (c). “ Sir Isaac Newton after this proceeds to make an improvement in astronomy, by applying this theory to the farther correction of their motions. For as we have here observed the planets to possess a principle of gravitation as w'ell as the sun ; so it will be explained at large hereafter, that the third law of motion, which makes action and reaction equal, is to be applied in this case, and that the sun does not only attract each planet, but is also itself attracted by them 5 the force wherewith the planet is acted on, bearing to the force wherewith the sun itself is acted upon at the same time, the proportion which the quantity of matter in the sun bears to the quantity of matter in the planet. Sun moves From the action of the sun and planet being thus mu- jound the jua]> gjr lsaac Newton proves that the sun and planet centre of describe about their common centre of gravity gravity of similar ellipses 5 and then, that the transverse axis of the him and the ellipsis, which would be described about the sun at rest planets. jn t[le lSame time, the same proportion as the quantity ASTRONOMY. Method of correcting the plane- taiy mo¬ tions. 364 Part IV of solid matter in the sun and planet together hears to ’Theory the first of two mean proportionals between this quantity Univcrs and the quantity of matter in the sun only. Gravita, “ It will be asked, perhaps, how this correction can . tl01l‘ be admitted, when the cause of the motions of the ~ planets was before found, by supposing them to be the centre of the power which acted upon them ? for, ac¬ cording to the present correction, this power appears rather to be directed to the common centre of gravity. But whereas the sun was at first concluded to be the centre to which the power acting on the planets was directed, because the spaces described in equal times round the sun were found to be equal j so Sir Isaac Newton proves, that if the sun and planet move round their common centre of gravity, yet, to an eye placed planet, the spaces which will appear to be de- the tlie world scribed about the sun will have the same relation to the times of their description as the real spaces would if the sun were at rest. I further asserted, that, sup¬ posing the planets to move round the sun at rest, and to be attracted by a power which should everywhere act with degrees of strength reciprocally in the dupli¬ cate proportions of their distances) then the periods of the planets must observe the same relations to their di¬ stances as astronomers have found them to do. But here it must not be supposed, that the observations of astrono¬ mers absolutely agree without any the least difference : and the present correction will not cause a deviation from any one astronomer’s observations so much as they differ from one another) for in Jupiter, where this cor¬ rection is greatest, it hardly amounts to the 3000th part of the whole axis. A “ Upon this head, I think it not improper to men-Argument tion a reflection made by our excellent author upon against tk these small inequalities in the planets motions, which eitern'jj contains in it a very strong philosophical argument against the eternity of the world. It is this, that these inequalities must continually increase by slow degrees, till they render at length the present frame of nature unfit for the purposes it now serves. And a more con¬ vincing proof cannot be desired against the present constitution’s having existed from eternity than this, that a certain period of years will bring it to an end. I am aware, that this thought of our author has been represented even as impious, and as no less than casting a reflection upon the wisdom of the Author of nature for framing a perishable work. But I think so bold an assertion ought to have been made with singular caution : for if this remark upon the increasing irre¬ gularities in the heavenly motions be true in fact, as it really is, the imputation must return upon the asser- tor, that this does not detract from the divine wisdom. Certainly we cannot pretend to know all the omnisci¬ ent Creator’s purposes in making this world, and there¬ fore cannot pretend to determine how long he designed it should last ) and it is sufficient if it endure the time designed by the Author. The body of every animal shows uti Saturn, even before the discovery of the Georgium Sidus. M. de la Lande also has observed some unaccountable inequalities in the motion of Saturn for more than 30 years past. t IV. A S T R ory Of shows the unlimited wisdom of the Author, no less, nay, versal in many respects more, than the larger frame of nature : and yet we see they are all designed to last but a small space of time.” <3(5 Sir Isaac Newton had no sooner discovered the uni- Dehetion versality and reciprocity of the deflections of the planets of Me pin- and the sun, than he also suspected that they were con- tinually deflected towards each other. He immediately obtained a general notion of what should be the more general results of such a mutual action. They may be conceived in this way. Let S (fig. 135.) represent the sun, E the earth, and I Jupiter, describing concentric orbits round the centre of the system. Make IS : EA=EI* : SI*. Then, if „/ IS be taken to represent the deflection of the sun to- ral re-wards Jupiter, EA will represent the deflection of the wans each otftr. !®7 Gearal sujf such£arth to Jupiter. Draw EB eijual and parallel to SI, boo aC" ant^ comP^ete the parallelogram EBAD. ED will re¬ present the disturbing force of Jupiter. It may be re¬ solvent into EF perpendicular to ES, and EG in the direction of SE. By the first of these the earth’s an¬ gular motion round the sun is affected, and by the se¬ cond its deflection towards him is diminished or increa¬ sed. In consequence of this first part of the disturbing force, the angular motion is increased, while the earth ap¬ proaches from quadrature to conjunction with Jupiter (which is the case represented in the figure), and is di¬ minished from the time that Jupiter is in opposition till the earth is again in quadrature, westward of his oppo¬ sition. The earth is then accelerated till Jupiter is in conjunction with the sun; after wiiich it is retarded till the earth is again in quadrature. I he earth’s tendency to the sun is diminished while Jupiter is in the neighbourhood of his opposition or con¬ junction, and increased while he is in the neighbourhood of his stationary positions. Jupiter being about 1000 times less than the sun, and 5 times more remote, IS must be considered as representing ^T4^th of the earth’s deflection to the sun, and the forces ED and EG are to be measured on this scale. In consequence of this change in the earth’s tenden¬ cy to the sun, the aphelion sometimes advances by the diminution, and sometimes retreats by the augmenta¬ tion. It advances when Jupiter chances to be in oppo¬ sition when the earth is in its aphelion ; because this di¬ minution of its deflection towards the sun makes it later before its path is brought from forming an obtuse angle with the radius vector, to form a right angle with it. Because the earth’s tendency to the sun is, on the whole, more diminished by the disturbing force of Jupiter than it is increased, the aphelion of the earth’s orbit advan¬ ces on the whole. In like manner the aphelia of the inferior planets ad¬ vance by the disturbing forces of the superior: but the aphelion of a superior planet retreats ; for these rea¬ sons, and because Jupiter and Saturn are larger and more powerful than the inferior planets, the aphelia of them all advance while that of Saturn retreats. In consequence of the same disturbing forces, the node ol the ^disturbed planet retreats on the orbit of the disturbing planet ; therefore they all retreat on the ecliptic, except that of Jupiter, which advances by retreating on the orbit ol Saturn, from which it suf¬ fers the greatest disturbance. This is owing to the O N O M Y. J25 particular position of the nodes and the inclinations of Theory of the orbits. Universal The inclination of a planetary orbit increases while <-*rav‘ta- the planet approaches the node, and diminishes while , t‘on' f the planet retires from it. M. de la Place has completed this deduction of the A peculia- planetary inequalities, by explaining a peculiarity in therky ex¬ motions ol Jupiter and Saturn, which-has long employ-,'n ed the attention ot astronomers. The accelerations and retardations of the planetary motions depend, as has and Saturn, been shown, on their configurations, or the relative quarters of the heavens in which they are. Those of Mercury, Venus, the Earth, and Mars, arising from their mutual deflections, and their more remarkable deflections to the great planets Jupiter and Saturnr nearly compensate each other, and no traces of them remain after a few revolutions : but the positions of the aphelia of Saturn and Jupiter are such, that the retar¬ dations ol Saturn sensibly exceed the accelerations, and the anomalistic period of Saturn increases almost a day every century ; on the contrary, that of Jupiter dimi¬ nishes. M. de la Place shows, that this proceeds from the position of the aphelia, and the almost perfect com- mensurability of their revolutions ; five revolutions of Jupiter making 21,675 days, while two revolutions of Saturn make 21,538 differing only 137 days. Supposing the relation to be exact, the theory shows,, that the mutual actions of these planets must produce mutual accelerations and retardations of their mean mo¬ tions, and ascertains the periods and limits of the secu¬ lar equations thence arising. These periods include se¬ veral centuries. Again, because this relation is not precise, but the odd days nearly divide the periods al¬ ready found, there must arise an equation of this secu¬ lar equation, of which the period is immensely longer, and the maximum very minute. He shews that this retardation of Saturn is now at its maximum, and is diminishing again, and will, in the course of years, change to an acceleration. This investigation of the small inequalities is the most, intricate problem in mechanical philosophy, and has been completed only by very slow degrees, by the ar¬ duous efforts ol the greatest mathematicians, of whom M. de la Grange is the most eminent. Some of his ge¬ neral results are very remarkable. He demonstrates, that since the planets move in one direction, in orbits nearly circular, no mutual disturb¬ ances make any permanent change in the mean distan¬ ces and mean periods of the planets, and that the pe¬ riodic changes are confined within very narrow limits. The orbits can never deviate sensibly from circles. Oscillation None of them ever has been or will be a comet moving of the pla¬ in a very eccentric orbit. The ecliptic will never coin-netary sy- cide with the equator, nor change its inclination above stem* two degrees. In short, the solar planetary system os¬ cillates, as it were, round a medium state, from which it never swerves very far. This theory of the planetary inequalities, founded on the universal law of mutual deflection, has given to our tables a precision, and a coincidence with observation, that surpasses all expectation, and insures the legitimacy of the theory. The inequalities are most sensible in the motions of Jupiter and Saturn; and these present them¬ selves in such a complicated state, and their periods are so long, that ages were necessary for discovering them, 2 by lion. 370 . Authenti¬ city of the Indian a- stronomy. .371 Origin of I 26 Theory of by mere observation. In this respect, therefore, the Universal theory has outstripped the observations on which it is ,i drawing from G towards A, the other from G towards H •, therefore the moon must necessarily be impelled toward D. Again, because the sun does not act in the direction GH parallel to SA, but in the direction GS oblique to it, the sun’s action on the moon will, by reason of this obliquity, farther contribute to the moon’s acceleration. Suppose the earth, in any short space of time, would have moved from A to I, if not attracted by the sun, the point I being in the straight line CE, which touches the earth’s orbit in A. Sup¬ pose the moon in the same time would have moved in her orbit from G to K, and besides have partook of all the progressive motion of the earth. Then, if KL be drawn parallel to AI, and taken equal to it, the moon, if not attracted to the sun, would be found in E. But the earth, by the sun’s action, is removed from I. Suppose it rvere moved down to M in the line 1MN parallel to SA, and if the moon were at¬ tracted but as much, and in the same direction as the earth is here supposed to be attracted, so as to have descended during the same time in the line LO paral¬ lel also to AS, down as far as P, till LP were equal to IM, the angle under PMN would be equal to that un¬ der LIN j that is, the moon will appear advanced as much farther forward than if neither it nor the earth had been subject to the sun’s action. But this is on the supposition that the actions of the sun upon the earth and moon are equal j whereas the moon being acted upon more than the earth, did the sun’s action draw the moon in the line LO parallel to AS, it would draw it down so far as to make LP greater than IM, whereby the angle under PMN will be rendered greater than that under LIN. But, moreover, as the sun draws the earth in a direction oblique to IN, the earth will be found in its orbit somewhat short of the point M. However, the moon is attracted by the sun still more out of the line LO than the earth is out of the lint; IN ; therefore this obliquity of the sun’s action will yet farther diminish the angle under PMN. Thus the moon at the point G receives an impulse from the sun whereby her motion is accelerated ; and the sun pro¬ ducing this effect in every place between the quarter and the conjunction, the moon will move from the quarter w'ith a motion continually more and more ac¬ celerated j and therefore, by acquiring from time to time an additional degree of velocity in its orbit, the spaces which are described in equal times by the line drawn from the earth to the moon will not be every- where equal, but those toward the conjunction will be greater than those toward the quarter. But in the moon’s passage from the conjunction D to the next quarter, the sun’s action will again retard the moon, till, at the next quarter at E, it be restored to the first velocity which it had in C. When the moon moves from E to the full, or opposition to the sun in B, it is again accelerated $ the deficiency of the sun’s action on the moon from what it has upon the earth producing here the same effect as before the excess of its action. Let us now consider the moon in Q as moving from F. towards B. Here, if she were attracted by the sun in a direction parallel to AS, yet being acted on less O N O M Y. Part IV than the earth, as the latter descends towards the sun, Theoryo. the moon will in some measure be left behind. There- Univera fore, QF being drawn parallel to SB, a spectator on Gravita. the earth would see the moon move as if attracted , from the point Q in the direction QF, with a degree y*" of force equal to that whereby the sun’s action on the moon falls short of its action on the earth. But the obliquity of the sun’s action has here also an effect. In the time the earth would have moved from A to I without the influence of the sun, let the moon have moved in its orbit from Q to R. Drawing, therefore, RT parallel and equal to AI, the moon, by the mo¬ tion of its orbit, if not attracted by the sun, must be found in T : and therefore, if attracted in a direction parallel to SA, would be in the line TV parallel to AS ; suppose in W. But the moon in Q being far¬ ther off the sun than the earth, it will be less attracted ; that is TW will be less than IM; and if the line SM be prolonged towards X, the angle under XMW will be less than XIT. Thus, by the sun’s action, the moon’s passage from the quarter to the full would be accelerated, if the sun were to act on the earth and moon in a direction parallel to AS j and the obliquity of the sun’s action will still increase this acceleration : For the action of the sun on the moon is oblique to the line SA the whole time of the moon’s passage from Q to T, and will carry her out of the line TV towards the earth. Here we suppose the time of the moon’s passage from Q to T so short, that it shall not pass be¬ yond the line SA. The earth will also come a little short of the line IN, as was already mentioned j and from these causes the angle under XMW will be still farther lessened. The moon, in passing from the oppo- ‘ sition B to the next quarter, will be retarded again by the same degrees as it was accelerated before its appulse to the opposition 5 and thus the moon, by the sun’s action upon it, is twice accelerated and twice restored to its first velocity every circuit it makes round the earth ; and this inequality of the moon’s motion about the earth is called by astronomers its variation. The next effect of the sun upon the moon is, that it gives the orbits of the latter in the quarters a greater the sun’s degree of curvature than it would receive from the attractios earth alone: and, on the contrary, in the conjunction'" differ{! and opposition the orbit is less inflected. When theparts,°„!’ moon is in the conjunction with the sun at D, the lat-bit. ter attracting her more forcibly than it does the earth, the moon is by that means impelled less to the earth than otherwise it would be, and thus the orbit is less in- curvated 5 for the power by which the moon is impel¬ led towards the earth being that by which it is inflect¬ ed from a rectilinear course, the less that power is, the less it will be inflected. Again, when the moon is in the opposition in B farther removed from the sun than the earth is, it follows, then, that though the earth and moon are both continually descending toward the sun, that is, are drawn by the sun towards itself out of the place they would otherwise move into, yet the moon descends with less velocity than the earth: inso¬ much that, in any given space of time from its passing the point of opposition, it will have less approached the earth than otherwise it would have done; that is, its orbit, in respect to the earth, will approach nearer to a straight line. Lastly, when the motion is in the quar¬ ter in F, and equally distant from the sun as the earth, it -ai i' of 'fat ft; 79 Men coirs aefest pair iea. au trailed bjr il-J trt IV. A S T R leory ef it was before observed, that they would both descend liversal with equal velocity towards the sun, so as to make no hjon.1' C!mnZe in the angle. F-A-Sj ljut the length of the line 'it ■ FA must necessarily be shortened. Therefore the moon, in moving from F toward the conjunction with the sun, will be impelled more toward the earth by the sun’s action than it would have been by the earth alone, if neither the earth nor the moon had been acted upon by the sun : so that, by this additional impulse, the orbit is rendered more curve than it otherwise should bo. The same effect will also be produced in the other i'; quarter. A third effect of the sun’s action, and which fol¬ lows from that just now explained, is, that though the moon undisturbed by the sun might move in a circle, having the earth for its centre, by the sun’s action, if the earth were to be in the very middle or centre of sttlie^16 010011,3 orhit, yet the moon would be nearer the when earth at the new and full than in the quarters. This may at first appear somewhat difficult to be understood, that the moon should come nearest to the earth when it is least attracted by it ^ yet, upon a little considera¬ tion, it will evidently appear to flow from that very cause, because her orbit, in the conjunction and oppo¬ sition, is rendered less curve : for the less curve the or¬ bit is, the less will the moon have descended from the place it would move into without the action of the earth. Now, if the moon were to move from any place without further disturbance from that action, since it would proceed on the line touching the orbit in that place, it would continually recede from the earth $ and therefore, if the power of the earth upon the moon be sufficient to retain it at the same distance, this di¬ minution of that power will cause the distance to in¬ crease, though in a less degree. But, on the other hand, in the quarters, the moon being pressed in a less degree towards the earth than by the earth’s single action, will be made to approach it: so that, in passing from the conjunction or opposition to the quarters, the moon ascends from the earth j and in passing from the quarters to the opposition or conjunction, it descends again, becoming nearer in these last-mentioned places than in the other. All the inequalities we have mentioned are different in degree as the sun is more or less distant from the earth ; being greatest when the earth is in its perihe¬ lion, and smallest when it is in its aphelion: for in the quarters, the nearer the moon is to the sun, the greater is the addition to the earth’s action upon it by the power of the sun j and, in the conjunction and opposi¬ tion, the difference between the sun’s action upon the earth and upon the moon is likewise so much the great- M»eij|ata er’ difference in the distance between the earth uoJTthe and.tbe sun Produces a further effect upon the moon’s *o and become greater than when at a t4 a, IV. A S T R Vhfey of the of these cases the nodes have no motion ; in all "VjiJri’sat others, the nodes will each month have receded : and this retrograde motion will be greatest when the nodes are in the quarters, for in that case they will have no progressive motion during the whole month $ but in all other cases they at some times go forward, viz. when¬ ever the moon is between either of the quarters and the node which is less distant from that quarter than the fourth part of a circle. We have now only to explain those irregularities of sin£ the lunar motion which arise fiom her motion in an mo efi'Ps‘s* From what has been already said it appears, un that the earth acts on the moon in the reciprocal du¬ plicate proportion of the distance *, therefore the moon, if undisturbed by the sun, would move round the earth in a true ellipsis, and a line drawn from the earth to the sun would pass over equal spaces in equal times. We have, however, already shown, that this equality is disturbed by the sun, and likewise how the figure of the orbit is changed each month j that the moon is nearer the earth at the new and full, and more re¬ mote in the quarters than it would be without the sun. We must, however, pass by those monthly changes, and consider the effect which the sun will have in the diffe¬ rent situations of the axis of the orbit in respect of that luminary. This action varies the force wherewith the moon is drawn towards the earth. In the quarters the force of the earth is directly increased by the sun, but diminished at the new and full j and in the inter¬ mediate places the influence of the earth is sometimes lessened, sometimes assisted, by the action of that lumi¬ nary. In these intermediate places, however, between the quarters and the conjunction or opposition, the sun’s action is so oblique to that of the earth on the moon, as to produce that alternate acceleration and re- tai’dation of her motion so often mentioned. But be¬ sides this effect, the power by which the moon attracts the earth towards itself, will not be at full liberty to act with the same force as if the sun acted not at all on the moon $ and this effect of the sun’s action, whereby it coj-roborates or weakens the action of the eai'th, is here only to be considered ; and by means of this influence it comes to pass, that the power by which the moon is impelled towards the earth is not perfectly in the reciprocal duplicate proportion of the distance, and of consequence the moon will not describe a per¬ fect ellipsis. One particular in which the lunar orbit will differ from a perfect elliptic figure, consists in the places where the motion of the moon is perpendicular to the line drawn from itself to the earth. In an ellip¬ sis, after the moon should have set out in the direction perpendicular to this line, drawn from itself to the earth, and at its greatest distance from the earth, its motion would again become perpendicular to this line drawn between itself and the earth, and the moon be at its nearest distance from the earth, when it should have performed half its period : after having performed the other half period of its motion, it would again be¬ come perpendicular to the forementioned line, and the moon return to the place when it set out, and have recovered again its greatest distance. But the moon in its real motion, after setting out as before, some¬ times makes more than half a revolution before its mo¬ tion comes again to be perpendicular to the line drawn from itself to the earth, and the moon is at its nearest tioa. 3S6 O N O M Y. 133 distance, and then performs moi’e than another half of Tlieory of an entire revolution befoi’e its motion can a second time Universal recover its perpendicular direction to the line drawn from Gravila¬ the moon to the earth, and the former arrive again at its greatest distance from the earth. At other times the moon will descend to her nearest distance before she has made half a revolution, and recover again its greatest distance before she has made an entire revolution. The place where the moon is at its greatest distance is called the moori's apogeon, and the place of her greatest di-^p0geon stance herperigeon; and this change of place, where the and peri- moon comes successively to its greatest distance from the gecm tbs earth, is called the motion of the apogeon. The manner mocn* in which this motion of the apogeon is caused by the sun, comes now to be explained. Sir Isaac Newton has shown, that if the moon were attracted towards the earth by a composition of two powers, one of which was reciprocally in the dupli¬ cate proportion of the distance from the earth, and the other x’eciprocally in the triplicate proportion of the same distance j then, though the line described by the moon would not be in reality an ellipsis, yet the moon’s motion might be pexffectly explained by an ellipsis whose „ axis should be made to move round the earth: this Motion in motion being in consequence, as astronomers express antece- themselves, that is, the same way as the moon itselfdence and moves, if the moon be attx-acted by the sum of the twoconse* powers ; but the axis must move in antecedence, or plaint, the contrary way, if the moon be acted upon by the difterence of these forces. We have already explained what is meant by duplicate proportion, namely, that if three magnitudes, as A, B, and C, are so related that the second B bears the same proportion to the third C as the first A bears to the second B ; then the propor¬ tion of the fix’st A to the third C is the duplicate of the ^sg proportion of the first A to the second B. Now if a Triplicate fourth magnitude as D be assumed, to which D shall proportion bear the same proportion as A bear’s to B, and B to C ; explained, then the proportion of A to D is the triplicate of the proportion of A to B. Let now T (fig. 147, 148.) denote the earth, and Motion of suppose the moon in the point A its apogeon or die moon’s greatest distance from the earth, moving in the ^^rec- tion AF perpendicular to AB, and acted upon from aec} the earth by two such forces as already mentioned. By that power alone, which is reciprocally in tlxe duplicate proportion of the distance, if the moon set out with a proper degree of velocity, the ellipsis AMB may be described : but if the moon be acted upon by the sum of the forementioned powers, and her velocity in the point A be augmented in a certain proportion.j or if that velocity be diminished in a certain proportion See .Mw. and the moon be acted upon by the difference of those bora’s Prm- powers; in both these cases the line AE, which shall be described by the moon, shall thus be determined. Let the point M be that into which the. moon would have arrived in any given point of time, had it moved in the ellipsis AMB ; di’aw MT and likewise CTD in such a manner that the angle ATM" shall bear the same proportion to the angle under ATC, as the velo¬ city with which the ellipsis must have been desci’ibed y bears to the difference between this velocity and that with which the moon must set out from the point A, in order to describe the path AE. Let the angle ATC be taken towards the moon, as in fig. 133. if/ 390 Inequality in the mo¬ tion of the apogeon. A S T R if the nloon he attracted by the sum of the powers ; but the contrary way (as in fig. 134.) if by their differ¬ ence. Then let the line AB be moved into the posi¬ tion CD, and the ellipsis AMB into the situation CND, so that the point M be translated to L j then the point L shall fall upon the path of the moon AE. Now the angular motion of the line AT, whereby it is removed into the situation CT, represents the motion of the apogeon 5 by the means of which the motion of the moon might be fully explained by the ellipsis AMB, if the action of the sun upon it W'as directed to the centre of the earth, and reciprocally in the triplicate proportion of the moon’s distance from it; hut that not being so, the motion of the apogeon will not pro¬ ceed in the regular manner now described. It is, however, to be observed here, that in the first of the two preceding cases, where the apogeon moves for¬ ward, the whole centripetal power increases faster, with the decrease of distance, than if the entire power were reciprocally in the duplicate proportion of the di¬ stance $ because one part only is already in that pro¬ portion, and the other part, which is added to this to make up the whole power, increases faster with the decrease of distance. On the other hand, when the centripetal power is the difi’erence between these two bodies, it increases less with the decrease of the di¬ stance, than if it were simply in the reciprocal duplicate proportion of the distance. Therefore, if we choose to explain the moon’s motion by an ellipsis, which may be done without any sensible error, we may collect in general, that when the power by which the moon is attracted to the earth, by varying the distance, in¬ creases in a greater than the duplicate proportion of the distance diminished, a motion in consequence must be ascribed to the apogeon j but that when the attrac¬ tion increases in a smaller proportion than that just mentioned, the apogeon must have given to it a mo¬ tion in antecedence. It is then observed by Sir Isaac Newton, that the former of these cases obtains when the moon is in the conjunction and opposition, and the latter when she is' in the quarters; so that in the for¬ mer the apogeon moves according to the order of the signs $ in the other, the contrary way. But, as has been already mentioned, the disturbance given to the action of the earth by the sun in the conjunction and opposition, being near twice as great as in the quarters, the apogeon will advance with a greater velocity than recede, and in the compass of a whole revolution of the moon wdll be carried in consequence. Sir Isaac shows, in the next place, that when the line AB coincides with the line that joins the sun and earth, the progressive motion of the apogeon, when the moon is in conjunction or opposition, exceeds the retrograde, in the quadratures, more than in any other situation of the line AB. On the contrary, when the line AB makes right angles with that which joins the earth and sun, the retrograde motion will be more con¬ siderable, nay, is found so great as to exceed the pro¬ gressive 5 so that in this case the apogeon, in the com¬ pass of an entire revolution of the moon, is carried in antecedence. Yet from the considerations already men¬ tioned, the progressive motion exceeds the other 5 so that, on the whole, the motion of the apogeon is in consequence. The line AB also changes its situation tvith that which joins the earth and sun by such slow O N O M Y. Part It degrees, that the inequalities of the motion of the apo- Theory geon, arising from this last consideration, are much Uimers greater than what arise from the other. Gwita. This unsteady motion of the apogeon gives rise to tlon another inequality in the motion of the moon herself, ^ so that it cannot at all times be explained by the same Occasioi ellipsis. For whenever the apogeon moves in conse-au°tlier quence, the motion of the luminary must be referred to an orbit more eccentric than what the moon would tncity describe, if the whole power by which the moon was the mow acted upon in its passing from the apogeon -changedorbit, according to the reciprocal duplicate proportion of its distance from the earth, and by that means the moon did describe an immoveable ellipsis: and when the apo¬ geon moves in antecedence, the moon’s motion must be referred to an orbit less eccentric. In the former of the two figures last referred to, the true place of the moon L falls without the orbit AMB, to which its motion is referred : whence the orbit ALE truly de¬ scribed by the moon, is less incurvated in the point A than is the orbit AMB : therefore this orbit is more oblong, and differs fai'ther from a circle than the ellip¬ sis would, whose curvature in A were equal to that of the line ALB : that is, the proportion of the distance of the earth T from the centre of the ellipsis to its axis, will be greater in AMB than in the other j but that other is the ellipsis which the moon would describe, if the power acting upon it in the point A were alter¬ ed in the recipi-ocal duplicate proportion of the di¬ stance ; and consequently the moon being drawn more forcibly toward the earth, it will descend nearer to it. On the other hand, when the apogeon recedes, the power acting on the moon increases with the decrease of distance, in less than the duplicate proportion of the distance $ and therefore the moon is less impelled to¬ wards the earth, and will not descend so low. Now, suppose, in the former of these figures, that the apo¬ geon A is in the situation where it is approaching to- Wards the conjunction or opposition of the sun ; in this case its progressive motion will be more and more ac¬ celerated. Here suppose the moon, after having de¬ scended from A through the orbit AE as far as F, where it is come to its nearest distance from the earth, ascends again up the line FG. As the motion of the apogeon is here more and more accelerated, it is plain that the cause of its motion must also be on the in¬ crease : that is, the power by which the moon is drawn to the earth, will decrease with the increase of the moon’s distance in her ascent from F, in a greater pro¬ portion than that wherewith it is increased with the decrease of distance in the moon’s distance to it. Con¬ sequently the moon will ascend to a greater distance than AT from whence it is descended $ therefore the proportion of the greatest distance of the moon to the least is increased. But farther, when the moon again descends, the power will increase yet farther with the decrease of distance than in the last ascent itinci*eased with the augmentation of distance. The moon there¬ fore must descend nearer to the earth than it did before, and the proportion of the greatest distance to the least be yet more increased. Thus, as long as the apogeon is advancing to the conjunction or opposition, the pro¬ portion of the greatest distance of the moon from the earth to the least will continually increase ; and the el¬ liptical orbit to which the moon’s motion is referred will 5ft ;t. 3* ompa ion! unarie- tialfts. P* IV. ASTRONOMY. tii:. The y of will become more and more eccentric. As soon, bow- Uwn'sal ever, as the apogeon is past the conjunction or oppo- Gmita- sjQ0n vvith the sun, its progressive motion abates, and with it the proportion of the greatest distance of the moon from the earth to the least will also diminish : and when the apogeon becomes retrograde, the diminution of this proportion will he still farther continued, until the apogeon comes into the quarter; from thence this proportion, and the eccentricity of the orbit, will in¬ crease again. Thus the orbit of the moon is most eccentric when the apogeon is in conjunction with the sun, or in opposition to it, and least of all when the apogeon is in the quarters. These changes in the nodes, the inclination of the orbit to the plane of the earth’s motion, in the apogeon and in the eccentricity, are varied like the other inequalities in the motion of the moon,'by the different distance of the earth from the sun being greatest when their cause is greatest : that is, when the earth is nearest the sun. Sir Isaac Newton has computed the very quantity of many of the mr»rm*c i npn n a 1111 TTiaf a pr'/Rpru frinn nf t!n^ 135 moon s inequalities. That acceleration of the moon’s motion which is called the variation, when greatest, removes the luminary out of the place in which it would otherwise be found, somewhat more than half a degree. If the moon, without disturbance from the sun, would have described a circle concentri- cal to the earth, his action will cause her approach nearer in the conjunction and opposition than in the quarters, nearly in the proportion of 69 to 70. It has already been mentioned, that the nodes perform their period in almost 19 years. This has been found by observation ; and the computations of Sir Isaac assigned to them the same period. The inclination of the moon’s orbit, when least, is an angle about one- eighteenth of that which constitutes a right angle ; and the difference between the greatest and least inclina¬ tion, is about one-eighteenth of the least inclination, according to our author’s computation : which is also agreeable to the general observations of astronomers. There is one empirical equation of the moon’s mo¬ tion which the comparison of ancient and modern eclip¬ ses obliges the astronomers to employ, without being able to deduce it, like the rest, a priori, from the theory of an universal force inversely proportional to the square of the distance. It has therefore been considered as a stumbling block in the Newtonian philosophy. This is what is called the secular equation of the moon's mean 011 gi-he motion. The mean motion is deduced from a compari- rin/i son ^'s*;an*; observations. The time between them, anoe being divided by the number of intervening revolutions, gives the average time of one revolution, or the mean lunar period. When the ancient Chaldean observations are compai’ed with those of Hipparchus, we obtain a certain period ; when those of Hipparchus are compa¬ red with some in the 9th century, we obtain a period somewhat shorter ; when the last are compared with those of Tycho Brahe, we obtain one still shorter ; and when Brahe’s are compared with those of our day, we obtain the shortest period of all—and thus the moon’s mean motion appears to accelerate continually ; and the accelerations appear to be in the duplicate ratio of the times. The acceleration for the century which ended in 1700 is about 9 seconds of a degree; that is to say, the whole motion of the moon during the 17th centu- he »;u- r eqn ry must be increased 9 seconds, in order to obtain its Theory of motion during the 18th ; and as much must be taken Universal from it, or added to the computed longitude, to obtain Cravita- its motion during the x6th : and the double of this must. ti^"‘ . be taken from the motion during the 16th, to obtain its motion during the 15th, &e. Or it will be sufficient to calculate the moon’s mean longitude for any time past or to come by the secular motion which obtains in the present century, and then to add to this longitude the product of 9 seconds, multiplied by the square of the number of centuries which intervene. Thus having found the mean longitude for the year 1200, add 9 se¬ conds, multiplied by 36, for six centuries. By this me¬ thod we shall make our calculation agree with the most ancient and all intermediate observations. If we ne¬ glect this correction, we shall differ more than a degree from the Chaldean observation of the moon’s place in the heavens. The mathematicians having succeeded so completely in deducing all the observed inequalities of the plane¬ tary motions, from the single principle, that the deflect¬ ing forces diminished in the inverse duplicate ratio of the distances, were fretted by this exception, the reality of which they could not contest. Many opinions were formed about its cause. Some have attempted to deduce it from the action of the planets on the moon ; others have deduced it from the oblate form of the earth, and the translation of the ocean by the tides ; others have supposed it owing to the resistance of the ether in the celestial spaces; and others have imagined that the action of the deflecting force requires time for its pro¬ pagation to a distance : But their deductions have been proved unsatisfactory, and have by no means the preci¬ sion and evidence that have been attained in the other questions of physical astronomy. At last M. de la Place, of the Royal Academy of Sciences at Paris, has happily succeeded, and deduced the secular equation of the moon from the Newtonian law of planetary deflection. It is produced in the following manner. Suppose the moon revolving round the earth, undi-Deduced sturbed by any deflection toward the sun, and that the from the time of her revolution is exactly ascertained. Now let Newtonian the influence of the sun be added. This diminishes her^a°f tendency to the earth in opposition and conjunction,flectj011i and increases it in the quadratures : but the diminutions exceed the augmentations both in quantity and dura¬ tion ; and the excess is equivalent to T-^th of her ten¬ dency to the earth. Therefore this diminished tendency cannot retain the moon in the same orbit: she must re¬ tire farther from the earth, and describe an orbit which is less incurvated by T^th part; and she must employ a longer time in a revolution. The period therefore which we observe, is not that which would have obtain¬ ed had the moon been influenced by the earth alone. We should not have known that her natural period was increased, had the disturbing influence of the sun re¬ mained unchanged ; but this varies in the inverse tri¬ plicate ratio of the earth’s distance from the sun, and is therefore greater in our winter, when the earth is nearer to the sun. This is the source of the annual equation, by which the lunar period in January is made to exceed that in July nearly 24 minutes. The angular velocity of the moon is diminished in general and this nu¬ merical coefficient varies in the inverse-ratio of the cube of.. 136 ASTRONOMY. Theory of of the earth’s distance from the sun. If vve expand this Universal inverse cube of the earth’s distance into a series arran¬ ged according to the sines and cosines of the earth’s mean motion, making the earth’s mean distance unity, we shall find that the series contains a term equal to y of the square of the eccentricity of the earth’s orbit. Therefore the expression of the diminution of the moon’s angular velocity contains a term equal to j^g-ofthis ve¬ locity multiplied by y of the squai'e of the earth’s ec¬ centricity ; or equal to the product of the square of the eccentricity, multiplied by the moon’s angular velocity, and divided by 119,33 (y of 179). Did this eccentri¬ city remain constant, this product would also be con¬ stant, and would still be confounded with the general* diminution, making a constant part of it: but the ec¬ centricity of the earth’s orbit is known to diminish, and its diminution is the result of the universality of the Newtonian law of the planetary deflections. Although this diminution is exceedingly small, its effect on the lu¬ nar motion becomes sensible by accumulation in the course of ages. The eccentricity diminishing, the dimi¬ nution of the moon’s angular motion must also diminish, that is, the angular motion must increase. During the 18th century, the square of the earth’s eccentricity has diminished 0,0000015325, the mean distance from the sun being m. This has increased the angular motion of the moon in that time 0,00000001285. As this augmentation is gradual, we must multiply the angular motion during the century by the half of this quantity, in order to obtain its accumulated effect. This will be found to be 9" very nearly, which exceeds that ded uced from a most careful comparison of the motion of the last two centuries, only by a fraction of a se¬ cond. As long as the diminution of the square of the eccen¬ tricity of the earth’s orbit can be supposed proportion¬ al to the time, this effect will be as the squares of the times. When this theory is compared with observa¬ tions, the coincidence is wonderful indeed. The effect on the moon’s motion is periodical, as the change of the solar eccentricity is, and its period includes millions of years. Its effect on the moon’s longitude will amount to several degrees before the secular acceleration change to a retardation. Those who are not familiar with the disquisitions of modern analysis, may conceive this question in the fol¬ lowing manner. Let the lepgth of a lunar period be computed for the earth’s distance from the sun for every day of the year. Add them into one sum, and divide this by their num¬ ber, the quotient will be the mean lunar period. This will be found to be greater than the arithmetical me¬ dium between tire greatest and the least. Then suppose the eccentricity of the earth’s orbit to be greater, and make the same computation. The average period will be found still greater, while the medium between the greatest and least periods will hardly differ from the former. Something very like this may be observed without any calculation, in a case very similar. The angular velocity of the sun is inversely as the square of bis distance. Look into the solar tables, and the great¬ est diurnal motion will be found 3673", and the least 3433". The mean of these is 3553", but the medium of the whole is 3548". Now make a similar observation in tables of the motion of the planet Mars, whose ec» Part 1\ centricity is much greater. We shall find that the me- dium between the greatest and least exceeds the true UniveiSl medium of all in a much greater proportion. It has been supposed by some philosophers that the ( moon was originally a comet, which passing very near the earth, had been made to revolve round her by the force of attraction. But if we calculate ever so far backwards, we still find the moon revolving round the earth as the planets round the sun, which could not be the case if this opinion were true. Hence it follows, that neither the moon nor any of the satellites have ever been comets. Sect. V. 0/' Irregularities in the Satellites of Jupiter. The subserviency of the eclipses of Jupiter’s satel¬ lites to geography and navigation had occasioned their motions to be very carefully observed, ever since these uses of them were first suggested by Galileo j and their theory is as far advanced as that of the primary pla¬ nets. It has peculiar difficulties. Being very near to Jupiter, the great deviation of his figure from perfect sphericity makes the relation between their distances from his centre and their gravitations toward it vastly complicated. But this only excited the mathematici¬ ans so much the more to improve their analysis j and they saw, in this little system of Jupiter and his attend¬ ants, an epitome of the solar system, where the great rapidity of the motions must bring about in a short time every variety of configuration or relative position, and thus give us an example of those mutual disturbances of the primary planets, which require thousands of years for the discovery of their periods and limits. We have derived some very remarkable and useful pieces of information from this investigation ; and have been led to the discovery of the eternal durability of the solar system, a thing which Newton greatly doubt¬ ed of. Mr Pound had observed long ago, that the irregu¬ larities of the three interior satellites were repeated in a period of 437 days j and this observation is found to be just to this day. 247 revolutions of the first occupy 123 second 6r third 26 fourth Days. 437 437 437 435 H. M. 3 3 3 44 42 16 This naturally led mathematicians to examine their mo¬ tions, and see in what manner their relative positions or configurations, as they are called, corresponded to this period : and it is found, that the mean longitude of the first satellite, minus thrice the mean longitude of the second, plus twice the mean longitude of the third, always made 180 degrees. This requires that the mean motion of the first, added to twice that of the third, shall be equal to thrice the mean motion of the second. This correspondence of the mean motions is of itself a singular thing, and the odds against its probability seems infinitely great j and when we add to this the particular positions of the satellites in any one moment, which is necessary for the above constant relation of their longitudes, the improbability of the coincidence, as a thing quite fortuitous, becomes infi¬ nitely greater. JDoubts were first entertained of the coincidence, P4i IV. ASTRO Tljc-y of coincidence, because It was not incleed accurate to a Uwi'isal second. 'I'he result of the investigation is curious. Cfcita- When we follow out the consequences of mutual gra- , fr' vitation, we find, that although neither the primitive motions of projection, nor the points of the orbit from which the satellites were projected, were precisely such as suited these observed relations of their revolutions and their contemporaneous longitudes ; yet if they dif¬ fered from them only by very minute quantities, the mutual gravitations of the satellites would in time bring them into those positions, and those states of mean motion, that would induce the observed relations 5 and when they are once induced they will he continued for ever. There will indeed be a small equation, depending on the degree of unsuitableness of the first motions and positions ; and this causes the whole system to oscillate, as it were, a little, and hut a very little way on each side of this exact and permanent state. The permanency of these relations will not be destroyed by any secular equations arising from external causes 5 such as the ac¬ tion of the fourth satellite, or of the sun, or of a resist¬ ing medium j because their mutual actions will distri¬ bute this equation as it did the original error. For a full discussion of this curious but difficult subject, we refer the reader to the dissertations of La Grange and La Place, and to the tables lately pub¬ lished by Delambre. These mathematicians have shown, that if the mass of Jupiter be represented by unity, that of his satellites will be represented by the following numbers. First satellite O.OOOO172OH Second satellite 0.0000237103 Third satellite 0.0000872128 Fourth satellite 0.0000544681 N it uric Sect. VI. Of Saturn's Ring. 45 ;eo]r*y Dr E! r iel r»- to|i. The most important addition (in a philosophical view) which has been made to astronomical science since the discovery of the aberration of light and the nutation of the earth’s axis, is that of the rotation of Saturn’s ring. Ihe ring itself is an object quite peculiar*, and when it was discovered that all the bodies which had any im¬ mediate connexion with a planet gravitated toward that planet, it became an interesting question to ascertain what was the nature of this ring ? What supports this immense arch of heavy matter without its resting on the planet ? What maintains it in perpetual concentricity with the body of Saturn, and keeps its surface in one invariable position ? The theory of universal gravitation tells us what things are possible in the solar system j and our conjec¬ tures about the nature of this ring must always be re¬ gulated by the circumstance of its gravitation to the planet. Philosophers had at first supposed it to be a luminous atmosphere, thrown out into that form by the great centrifugal force arising from a rotation : but its well-defined edge, and, in particular, its being two very narrow rings, extremely near each other, yet perfectly separate, rendered this opinion of its constitution more improbable. Dr Herschel’s discovery of brighter spots on its sur¬ face, and that those spots were permanent during the whole time of his observation, seem to make it "more probable that the parts of the ring have a solid con- Vol. III. Part I. j- O M Y. I ^ nexion. Mr Herschel has discovered, by the help of Theory of these spots, that the ring turns round its axis, and that Universal this axis is also the axis of Saturn’s rotation. The time Gravita- of rotation is loh. 32^:,• But the other circumstances, ^on* are not narrated with the precision sufficient for an ac- ^ curate comparison with the theory of gravity. He in¬ forms us, that the radii of the four edges of the ring are 59°» 75L 774> %30> °f a certain scale, and that the angle subtended by the ring at the mean distance from the earth is 46^". Therefore its elongation is 23y". I lie elongation of the second Cassinian satellite is 56", and its revolution is 2d. 17b. 44'. This should give, by the third law of Lepler, 17I1. ic/ for the revolution of the outer edge of the ring, or rather of an atom of that edge, in order that it may maintain itself in equili- brio. Ihe same calculation applied to the outer edge of the inner ring gives about 13b. 36'; and we obtain 1 ih. 16' for the inner edge of this ring. Such varie¬ ties are inconsistent with the permanent appearance of a spot. We may suppose the ring to be a luminous fluid or vapour, each particle of which maintains its situation by the law of planetary revolution. In such a state, it would consist of concentric strata, revolving more slowly as they were more remote from the planet,°1 ike the con- centi ic strata of a vortex, and therefore having a relative motion incompatible with the permanency of any spot. Besides, the rotation observed by Flerschel is too rapid even for the innermost part of the ring. We think there¬ fore that it consists of cohering matter, and of consider¬ able tenacity, at least equal to that of a very clammy fluid, such as melted glass. We can tell the figure which a fluid ring must have, so that it may maintain its form by the mutual gravita¬ tion of its particles to each other, and their gravitation to the planet. Suppose it cut by a meridian. It may he in equilibrio if the section is an ellipse, of which the longer axis is directed to the centre of the planet, and very small in comparison with its distance from the centre of the planet, and having the revolution of its middle round Saturn, such as agree with the Keplerean law. These circumstances are not very consistent with the dimensions of Saturn’s inner ring. The distance between the middle of its breadth and the centre of Sa¬ turn is 670, and its breadth is 161', nearly one-fourth of the distance from the centre of Saturn. De la Place says, that the revolution of the inner ring observed by Herschel is very nearly that required by Kepler’s law': but we cannot see the grounds of this assertion. The above comparison with the second Cassinian satellite shows the contrary. The elongation of that satellite is taken from Bradley’s observations, as is also its pe¬ riodic time. A ring of detached particles revolving in xoh. 324 must be of much smaller diameter than even the inner edge of Saturn’s ring. Indeed the quau- tity of matter in it might be such as to increase the gra¬ vitation considerably j but this would be seen by its disturbing the seventh and sixth satellites, which are exceedingly near it. We cannot help thinking, there- Its proba- fore, that it consists of matter which has very consider- ble consis. able tenacity. An equatorial zone of matter, tenacioustency* like melted glass, and whirled briskly round, might be thrown off, and, retaining its great velocity, would stretch out while whirling, enlarging in diameter and diminishing in thickness or breadth, or both, till the centrifugal force was balanced by the united force of B gravity rsB ASTRONOMY. Part IV, Theory of gravity and tenacity. We find the equilibrium will Universal Hot be sensibly disturbed by considerable deviations, such as equal breadth, or even want of flatness. Such i , ^ ’ , inequalities appear on the ring at that time of its dis- parition, when its edge is turned to the sun or to us. The appearances of its different sides are then consider¬ ably different. Such a ring or rings must have an oscillatory motion round the centre of Saturn, in consequence of their mutual action, and the action of the sun, and their own irregularities : but there will be a certain po¬ sition which they have a tendency to maintain, and to which they will be brought back, after deviating from it, by the ellipricity of Saturn, which is very great. The sun will occasion a nutation of Saturn’s axis and a precession of his equinoxes, and this will drag along with it both the rings and the neighbouring satellites. The atmosphere which surrounds a whirling planet cannot have all its parts circulating according to the third law of Kepler. The mutual attrition of the pla¬ net, and of the different strata, arising from their diffe¬ rent velocities, must accelerate the slowly moving strata, and retard the rapid, till all acquire a velocity propor¬ tional to their distance from the axis of rotation j and this will be such that the momentum of rotation of the planet and its atmosphere remains always the same. It will swell out at the equator, and sink at the poles, till the centrifugal force at the equator balances the height of a superficial particle. The greatest ratio which the equatorial diameter can acquire to the polar axis is that of four to three, unless a cohesive force keeps the par¬ ticles united, so that it constitutes a liquid, and not an elastic fluid like air j and an elastic fluid cannot form an atmosphere bounded in its dimensions, unless there be a certain rarity which takes away all elasticity. If the equator swells beyond the dimension which makes the gravitation balance the centrifugal force, it must imme¬ diately dissipate. If we suppose that the atmosphere has extended to this limit, and then condenses by cold, or any chemical or other cause different from gravity, its rotation ne¬ cessarily augments, preferring its former momentum, 398 and the limit will approach the axis ; because a greater and origin, velocity produces a greater centrifugal force, and re¬ quires a greater gravitation to balance it. Such an at¬ mosphere may therefore desert, in succession, zones of its own matter in the plane of its equator, and leave them revolving in the form of rings. It is not unlikely that the rings of Saturn may have been furnished in this very way 5 and the zones, having acquired a common velocity in their different strata, will preserve it ; and they are susceptible of irregularities arising from local causes at the time of their separation, which may afford permanent spots. Sect. VII. Of the Atmospheres of the Planets. By atmosphere is meant a rare, transparent, compres¬ sible, and elastic fluid surrounding a body. It is sup¬ posed that all the heavenly bodies possess atmospheres. The atmosphere of the earth is familiar to all its inha¬ bitants. Observation points out the atmospheres of the sun and of Jupiter ; but that of the other planets is scarcely perceptible. The atmosphere becomes rarer in proportion to its 3. distance from the body to which it belongs, in conse- Theory quence of its elasticity, which causes it to dilate the Univeria! more the less it is compressed. If its most remote parts ^wha. were still possessed of elasticity, they would separate , tl011' indefinitely, and the whole would be scattered through space. To prevent this effect, it is necessary that the elasticity should diminish at a greater rate than the compressing force, and that when it reaches a certain degree of rarity its elasticity should vanish altogether. All the atmospheric strata must gradually acquire the same rotatory motion with the bodies to which they belong in consequence of the continual friction to which their different parts must be subjected, which will gradually accelerate or retard the different parts till a common motion is produced. In all these changes, and indeed in all those which the atmosphere undergoes, the sum of the products of the particles of the body and of its atmosphere multiplied by the areas described round their common centres of gravity by their radii vectors projected in the plane of the equa¬ tor continue always the same, the times being the same. If we suppose then, by any cause whatever, the height of the atmosphere is diminished, and a portion of it condenses on the surface of the planet ; the conse¬ quence will be, that the rotatory motion of the planet and of its atmosphere will be accelerated. For the radii vectors of the areas described by the particles of the primitive atmosphere becoming shorter, the sum of the products of all these particles by the corresponding areas cannot remain the same unless the rotatory mo¬ tion augment. At the upper surface of the atmosphere the fluid is retained only by its weight. Its figure is such that the direction resulting from the combination of the centri¬ fugal forces and the attracting forces is perpendicular to it. It is flattened at the poles, and more convex at the equator. But this flattening has its limits. When a maximum the axis of the poles is to that at the equa¬ tor as 2 to 3. At the equator the atmosphere can only extend to the place where the centrifugal force and gravitation exactly balance each other j for if it pass that limit, it will be dissipated altogether. Hence it follows that the solar atmosphere does not extend as far as Mercury; con¬ sequently it is not the cause of the zodiacal light which appears to extend beyond even the earth’s orbit. The place where the centrifugal force and gravita¬ tion balance each other is so much the nearer a body the more rapid its rotatory motion is. If we suppose the atmosphere to extend to that limit, and then to con¬ dense by cooling, &c. at the surface of the planet, the rotatory motion will increase in rapidity in proportion to this condensation, and the limit of the height of the atmosphere will constantly approach the planet. The atmosphere would of course abandon successively zones of fluid in the plane of the equator, which would con¬ tinue to circulate round the body. We have shown in the last section that Saturn’s ring may owe its origin to this cause. We may add also, that the action of another bo- Probate dy may considerably change the constitution of thisreason* atmosphere. Thus, supposing that the moon had .^mosple originally an atmosphere, the limit will be that di-about tit stance from the moon where the centrifugal force, ari- luoon. sing from the moon’s rotation, added to the gravita¬ tion Hr 9. Pit IV. ASTRONOMY; Thry of tion to the earth, balances the gravitation to the moon. Uoi rsal If the moon be ^th of the earth, this limit will be Gwita- about l-tli of the moon’s distance from the earth. If at ; . this distance the elasticity of the atmosphere is not anni¬ hilated by its rarefaction, it will be all taken off’ by the earth, and accumulate round it. This may be the rea¬ son why we see no atmosphere about the moon. >39 Theory of Universal Gravita¬ tion. Sect. VIT. Of the Tides. V auttof be | es •£• HP The cause of the tides was discovered by Kepler, who, in his Introduction to the Phi/sicsof the Heavensy liscjrcrcd thus explains it: “ The orb of the attracting power >y Sfrler. vv|,icj5 ;s jn t|ie moonj is extended as far as the earth ; and draws the waters under the torrid zone, acting upon places where it is vertical, insensibly on confined seas and bays, but sensibly on the ocean, whose beds are large, and where the waters have the liberty of recipro¬ cation, that is, of rising and falling.” And in the 70th page of his Lunar Astronomy—“ But the cause of the tides of the sea appears to be the bodies of the sun and moon drawing the waters of the sea.” This hint being given, the immortal Sir Isaac Newton improved it, and wrote so amply on the subject, as to make the theory of the tides in a manner quite his own, by discovering the cause of their rising on the side of the earth opposite to the moon. For Kepler believed that the presence of the moon occasioned an impulse which caused another in her absence. It has been already observed, that the power ofgra- vity diminishes as the square of the distance increases ; and therefore the waters at Z on the side of the earth ABCDEFGH next the moon M, are more attracted than the central parts of the earth O by the moon, and the central parts are more attracted by her than the wa¬ ters on the opposite side of the earth at n : and therefore the distance between the earth’s centre and the waters on its surface under and opposite to the moon will be increased. For, let there be three bodies at H, O, and D : if they are all equally attracted by the body M, they will all move equally fast towards it, their mutual distances from each other continuing the same. If the attraction of M is unequal, then that body which is most strongly attracted will move fastest, and this will increase its distance from the other body. Therefore, by the law of gravitation, M will attract H more strongly than it does O, by which the distance between H and O will be increased ; and a spectator on O will perceive II rising higher toward Z. In like manner, O being more strongly attracted than D, it will move farther towards M than D does : consequently, the di¬ stance between O and D will be increased $ and a spec¬ tator on O, not perceiving his Own motion, will see D receding farther from him towards n ; all effects and appearances being the same, whether D recedes from O, or O from D. Suppose now there is a number of bodies, as A, B, C, D, E, F, G, II, placed round O, so as to form a flex¬ ible or fluid ring: then, as the whole is attracted to¬ wards M, the parts at H and D will have their di¬ stance from O increased ; whilst the parts at B and F being nearly at the same distance from M as O is, these parts will not recede from one another ; but rather, by the oblique attraction of M, they will approach nearer to O. Hence the fluid ring will form itself into an ellipse ZIBL n KFNZ, whose longer axis n OZ pro¬ duced will pass through M, and its shorter axis EOF will terminate in B and F. Let the ring be filled with fluid particles, so as to form a sphere round O ; then, as the whole moves towards M, the fluid sphere being lengthened at Z and n, will assume an oblong or oval form. If M is the moon, O the earth’s centre, ABC DEFGH the sea covering the earth’s surface, it is evi¬ dent, by the above reasoning, that whilst the earth by its gravity falls towards the moon, the water directly below her at B will swell and rise gradually towards her $ also the water at D will recede from the centre [strictly speaking, the centre recedes from D], and rise on the opposite side of the earth; whilst the water at B and F is depressed, and falls below the former le¬ vel. Hence, as the earth turns round its axis from the moon to the moon again in 24^ hours, there will be two tides of flood and two of ebb in that time, as we find by experience. cf As this explanation of the ebbing and flowing of the why the sea is deduced from the earth’s constantly falling to tides are wards the moon by the power of gravity, some mav at fud find a difficulty in conceiving how this is possible, when"10011, the moon is full, or in opposition to the sun ; since the earth revolves about the sun, and must continually fall towards it, and therefore cannot fall contrary ways at the same time: or if the earth is constantly falling to¬ wards the moon, they must come together at last. To remove this difficulty, let it be considered, that it is not the centre of the earth that describes the annual orbit round the sun, but the (e) common centre of gravity of the earth and moon together; and that whilst the earth is moving round the sun, it also describes a circle round that centre of gravity ; going as many times round it in one revolution about the sun as there are lunations or courses of the moon round the earth in a year: and therefore the earth is constantly falling to¬ wards the moon from a tangent to the circle it describes round the said common centre of gravity. Let M be Fi the moon, TW part of the moon’s orbit, and C the centre of gravity of the earth and moon ; whilst the moon goes round her orbit, the centre of the earth de¬ scribes the circle dg e round C, to which circle gak is a tangent; and therefore when the moon has gone from M to a little past W, the earth has moved from g to e; and in that time has fallen towards the moon, from the tangent at a to e: and so on, round the whole circle. The sun’s influence in raising the tides is but small S 2 in 153. (e) I his centre is as much nearer the earth’s centre than the moon’s as the earth is heavier, or contains a great- ei quantity of matter than the moon, namely, about 40 times; If both bodies were suspended on it, they would lang in equilibria. So that dividing 240,000 miles, the moon’s distance from the earth’s centre, by 40, the ex¬ cess ot the earth’s weight above the moon’s, the quotient will be 6000 miles, which is the distance of the commoUt centre ol gravity ol the earth and moon from the earth’s centre. 140 ASTRONOMY. Part Theory of in comparison of the moon’s ; for though the earth’s T.’niveml diameter bears a considerable proportion to its distance tionta" ^rom ro0011* it is next to nothing when compared i . to its distance from the sun. And therefore the differ¬ ence of the sun’s attraction on the sides of the earth 402 Influence of under and opposite to him, is much less than the differ- Uie sun in ence 0f t|je moon’8 attraction on the sides of the earth raising tides. 403 Why they are not highest when the chan. under and opposite to her ; and therefore the moon must raise the tides much higher than they can be raised by the sun. On this theory, the tides ought to be highest direct¬ ly under and opposite to the moon •, that is, when the moon is due north and south. But we find, that in moon is in open seas, where the water flows freely, the moon M the men- is generally past the north and south meridian, as aty>, when it is high water at Z and at n. The reason is obvious: for though the moon’s attraction was to cease altogether when she was past the meridian, yet the mo¬ tion ol ascent communicated to the water before that time would make it continue to rise for some time af¬ ter j much more must it do so when the attraction is only diminished ; as a little impulse given to a moving ball will cause it still to move farther than otherwise it could have done j and as experience shows that the day is hotter about three in the afternoon, than when the sun is on the meridian, because of the increase made to the heat already imparted. 1 he tides answer not always to the same distance of the moon from the meridian at the same places $ but are variously affected by the action of the sun, which brings them on sooner when the moon is in her first and third quarters, and keeps them back later when she is in her second and fourth : because, in the former case, the tide raised by the sun alone would be earlier than.the tide raised by the moon : and, in the latter ease later. The moon goes round the earth in an elliptic ox-bit; and therefore, in evex-y lunar month, she approaches nearer to the earth than her mean distance, and recedes farther from it. When she is nearest, she attracts strongest, and so raises the tides most: the conti-ary happens when she is farthest, because of her weaker at¬ traction. When both luminaries ax-e in the equator, and the moon in perigee, or at her least distance from the earth, she raises the tides highest of all, especially at her conjunction and opposition 5 both because the equatorial parts have the greatest centrifugal force from their describing the largest circle, and from the concur¬ ring actions of the sun and moon. At the change, the attractive forces of the sun and moon being united, they diminish the gravity of the waters under the moon, and their gravity on the opposite side is diminished by means of a greater centrifugal force. At the full, whilst the moon raises the tide under and opposite to her, the sun, acting in the same line, raises the tide un¬ der and opposite to him ; whence their conjoint effect is the same as at the change ; and, in both cases, occasion what we call the Spring Tides. But at the quarters the sun’s action on the waters at O and H diminishes the effect of the moon’s action on the waters at Z and N j so that they rise a little under and opposite to the sun at O and H, and fall as much under and opposite to the moon at Z and N j making what we call the Neap Tides, because the sun and moon then act cross-wise to each other. But these tides happen not till some lime 2 after $ because in this, as in other cases, the actions do not produce the greatest effect when they are at the strongest, but some time afterward. The sun being nearer the earth in winter than in summer, is of course nearer to it in February and Oc¬ tober than in March and September; and therefore the greatest tides happen not till some time after the autumnal equinox, and return a little before the ver¬ nal. Theory Universal Gravita tion The sea, being thus put in motion, would continue to ebb and flow several times, even though the sun and moon were annihilated, or their influence should cease 5 as, if a bason of water were agitated, the wa¬ ter would continue to move for some time after the bason was left to stand still j or, like a pendulum, which, having been put in motion by the hand, con¬ tinues to make several vibrations without any new im¬ pulse. When the moon is in the equator, the tides are equally high in both pax-ts of the lunar day, or time of the moon’s x-evolving from the meridian to the meridian again, which is 24 hours 50 minutes. But as the moon declines from the equator towards either pole, the tides are alternately higher and lower at places hav¬ ing north or south latitude. For one of the highest elevations, which is that under the moon, follows her towards the pole to which she is neaiest, and the other declines towards the opposite pole ; each elevation de¬ scribing parallels as far distant from the equator, on opposite sides, as the moon declines from it to either side j and consequently the parallels described by these elevations of the water are twice as many degrees from one another as the moon is from the equator; increa¬ sing their distance as the moon increases her declina¬ tion, till it be at the greatest, when the said parallels are, at a mean state, 47 degrees from one another : and on that day, the tides are most unequal in their heights. As the moon returns towards the equator, the parallels described by the opposite elevations approach towards each other, until the moon comes to the equator, and then they coincide. As the moon declines towards the opposite pole, at equal distances, each elevation de¬ scribes the same parallel in the other part of the lunar day, which its opposite elevation described before. Whilst the moon has north declination, the greatest tides in the northern hemisphei'e ai’e when she is above the horizon ; and the reverse whilst her declination is south. Let NESQ be the earth, NSC its axis, EQ fjg, I;-i the equator, T 22 the tropic of Cancel-, t vy the tro-152,153' pic of Capricorn, a b the arctic circle, cd the antarctic, N the north pole, S the south pole, M the moon, F and G the two eminences of water, whose lowest parts are at a and d, at N and S, and at b and c, always 90 degrees from the highest. Now, when the moon is in he r greatest north declination at M, the highest eleva¬ tion G under her is on the tropic of Cancer T 22, and the opposite elevation F on the tropic of Capri¬ corn ^ Vy j and these two elevations describe the tropics by the earth’s diurnal rotation. All places in the northern hemisphere ENQ have the highest tides when they come into the position £ 25 Q, under the moon ; and the lowes't tides when the earth’s diurnal rotation carries them into the position a TE, on the side oppo¬ site the moon 3 the reverse happens at the same time in the southern hemisphere ESQ, as is evident to sight. The i-it iv. ASTRONOMY. Th ry of The axis of the tides aCd had now its poles a and d Uhic-rsal (being always 90 degrees from the highest elevations) .i- ita- jn j|ie arctJc antj antarctic circles j and therefore it is t ’ ' . plain, that at these circles there is but one tide of flood, and one of ebb, in the lunar day. For, when the point a revolves half round to & in T2 lunar hours, it has a tide of flood ; but when it comes to the same point a again in 12 hours more, it has the lowest ebb. In seven days afterward, the moon M comes to the equinoctial circle, and is over the equator EQ, when both elevations describe the equator j and in both hemispheres, at equal distances from the equator, the tides are equally high in both parts of the lunar day. The whole phenomena being reversed, when the moon has south declination, to what they were when her declination was north, require no farther description. In the three last-mentioned figures, the earth is or- thographically projected on the plane of the meridian j but in order to describe a particular phenomenon, we now project it on the plane of the ecliptic. Let HZON be the earth and sea, FED the equator, T the tropic of Cancer, C the arctic circle, P the north pole, and the curves, 1, 2, 3, &c. 24 meridians or hour circles, intersecting each other in the poles : AGM is the moon’s orbit, S the sun, M the moon, Z the water elevated under the moon, and N the opposite equal elevation. As the lowest parts of the water are always 90 degrees from the highest, when the moon is in either of the tropics (as at M), the elevation Z is on the tropic of Capricorn, and the opposite elevation N on the tropic of Cancer; the low-water circle HCO touches the polar circles at C; and the high-water cir¬ cle ETP 6 goes over the poles at P, and divides every parallel of latitude into two equal segments. In this case, the tides upon every parallel are alternately higher and lower ; but they return in equal times : the point T, for example, on the tropic of Cancer, (where the depth of the tide is represented by the breadth of the dark shade) has the shallower tide of flood at T than when it revolves half round from thence to 6, according to the order of the numeral figures ; but it revolves as soon from 6 to T as it did from T to 6. When the moon is in the equinoctial, the elevations Z and N are transferred to the equator at O and H, and the high and low-water circles are got into each other’s former places j in which case the tides return in unequal times, but are equally high in both parts of the lunar dayj for a place at 1 (under D) revolving as formerly, goes sooner from I to x 1 (under F) than from II to 1, be¬ cause the parallel it describes is cut into unequal seg¬ ments by the high-water circle HCO : but the points 1 and 11 being equidistant from the pole of the tides at C, which is directly under the pole of the moon’s or¬ bit MG A, the elevations are equally high in both parts of the day. And thus it appears, that as the tides are governed by the moon, they must turn on the axis of the moon’s orbit, which is inclined 234 degrees to the earth’s axis it. II at a mean state: and therefore the poles of the tides must be so many degrees from the poles of the earth, or in opposite points of the polar circles, going round these circles in every lunar day. It is true, that ac¬ cording to fig. 153’ when the moon is vertical to the equator ECQ, the poles of the tides seem to fall in with the poles of the world N and S: but when we 4 • ’I'ifttuirn 11 thluds niJ loop 1 or consider that FGH is under the moon’s orbit, it will appear, that when the moon is over H, in the tropic of Capricorn, the north pole of the tides (which can be no more than 90 degrees from under the moon) must be at C in the arctic circle, not at P the north pole of the earth j and as the moon ascends from H to G in her or¬ bit, the north pole of the tides must shift from c to a in the arctic circle, and the south poles as much in the antarctic. It is not to be doubted, but that the earth’s quick rotation brings the poles of the tides nearer to the poles of the world than they would be if the earth were at rest, and the moon revolved about it only once a month ; tor otherwise the tides would be more unequal in their height and times of their returns, than we find they are. But how near the earth’s rotation may bring the poles of its axis and those of the tides to¬ gether, or how far the preceding tides may affect those which follow, so as to make them keep up nearly to the same heights and times of ebbing and flowing, is a problem more fit to he solved by observation than by theory. Those who have opportunity to make observations, and choose to satisfy themselves whether the tides are really affected in the above manner by the different po¬ sitions of the moon, especially as to the unequal times of their return, may take this general rule for know¬ ing when they ought to be so affected. When the earth’s axis inclines to the moon, the northern tides, if not retarded in their passage through shoals and chan¬ nels, nor affected by the winds, ought to be greatest when the moon is above the horizon, least when she is below it, and quite the reverse when the earth’s axis declines from her; but in both cases, at equal inter¬ vals of time. When the earth’s axis inclines sidewise to the moon, both tides are equally high, but they happen at unequal intervals of time. In every lunation the earth’s axis inclines once to the moon, once from her, and twice sidewise to her, as it does to the sun every year $ because the moon goes round the ecliptic every month, and the sun but once in a year. In sum¬ mer, the earth’s axis inclines towards the moon when new; and therefore the day-tides in the north ought to be highest, and night-tides lowest, about the change : at the full, the reverse. At the quarters, they ought to be equally high, but unequal in their returns : be¬ cause the earth’s axis then inclines sidewise to the moon. In winter, the phenomena are the same at full moon as in summer at new. In autumn the earth’s axis inclines sidewise to the moon when new and full j. therefore the tides ought to be equally high and uneven in their returns at these times. At the first quarter, the tides of flood should be least when the moon is above the horizon, greatest when she is below it •, and the reverse at her third quarter. In spring, the phenomena of the first quarter answer to those of the third quarter in au¬ tumn j and v/ce versa. The nearer any tide is to either of the seasons, the more the tides partake of the pheno¬ mena of these seasons j and in the middle between any two of them the tides are at a mean state between those of botli. In open seas, the tides rise but to very small heights in proportion to what they do in wide-mouthed rivers, opening in the direction of the stream of tide. For in channels growing narrower gradually,,, the water is ac¬ cumulated I4T Theory of Universal Gravita¬ tion. for. 142 ASTRO Theory of cumulated by the opposition of the contracting bank j Universal like a gentle wind, little felt on an open plain, but Gravita. strong ami brisk in a streetespecially if the wider end . t11^11' of the street be next the plain, and in the way of the 405 wind. Irregularis The tides are so retarded in their passage through ties of tides diflfcrent shoals and channels, and otherwise so various- accounted a{yecte(l by striking against capes and headlands, that to different places they happen at all distances of the moon from the meridian, consequently at all hours of the lunar day. The tide propagated by the moon in the German ocean, when she is three hours past the meridian, takes 12 hours to come from thence to London bridge, where it arrives by the time that a new tide is raised in the ocean. And therefore, when the moon has north declination, and we should expect the tide at London to be greatest when the moon is above the horizon, we find it is least; and the contra¬ ry when she has south declination. At several places it is high water three hours before the moon comes to the meridian ; but that tide which the moon pushes as it were before her, is only the tide opposite to that which was raised by her when she was nine hours past the op¬ posite meridian. There are no tides in lakes, because they are gene¬ rally so small, that when the moon is vertical she at¬ tracts every part of them alike, and therefore by ren¬ dering all the water equally light, no part of it can be raised higher than another. The Mediterranean and Baltic seas have very small elevations, because the inlets by which they communicate with the ocean are so nar¬ row, that they cannot, in so short a time, receive or dis¬ charge enough to raise or sink their surfaces sensibly. For a more complete discussion of this important sub¬ ject, we refer the reader to the article Tide. Sect. IX. Of the Precession of the Equinoxes, and the Nutation of the Eartfi’s Axis. 406 Precession of the equi¬ noctial points, Sec. 407 Observa¬ tions of Newton and others on this sub ject. It now remains to consider the precession of the equi¬ noctial points, with its equations, arising from the nuta¬ tion of the earth’s axis as a physical phenomenon, and to endeavour to account for it upon those mechanical principles which have so happily explained all the other phenomena of the celestial motions. This did not escape the penetrating eye of Sir Isaac Newton ; and he quickly found it to be a consequence, and the most beautiful proof, of the universal gravitation of all matter to all matter j and there is no part of his immortal work where his sagacity and fertility of re¬ source shine more conspicuously than in this investiga¬ tion. It must be acknowledged, however, that New¬ ton’s investigation is only a shrewd guess, founded on assumptions, of which it would be extremely difficult to demonstrate either the truth or falsity, and which requir¬ ed the genius of a Newton to pick out in such a com¬ plication of abstruse circumstances, fhe subject has occupied the attention of the first mathematicians of Europe since his time j and is still considered as the inost curious and difficult of all mechanical problems. The most elaborate and accurate dissertations on the precession of the equinoxes are those of Sylvabella and Walmesly, in the Philosophical Transactions, published about the year 17545 that of Thomas Simpson, publish¬ ed in his Miscellaneous Tracts 5 that of Father Frisius, titm. 40$ N O M Y. Part IV, in the Memoirs of the Berlin Academy, and afterwards, Theory of with great improvements, in his Cosmographia 5 that of 'Universal Euler in the Memoirs of Berlin 5 that of D’Alembert in G™yju' a separate dissertation 5 and that of De la Grange on the Libration of the Moon, which obtained the prize in the Academy of Paris in 1769. We think the disserta¬ tion of Father Frisius the most perspicuous of them all, being conducted in the method of geometrical analysis ; whereas most of the others proceed in the fluxionary and symbolic method, which is frequently deficient in distinct notions of the quantities under consideration, and therefore does not give us the same perspicuous conviction of the truth of the results. In a work like ours, it is impossible to do justice to the problem, with¬ out entering into a detail which would be thought ex¬ tremely disproportioned to the subject by the genera¬ lity of our readers. Yet those who have the necessary preparation of mathematical knowledge, and wish to un¬ derstand the subject fully, will find enough here to give them a very distinct notion of it; and in the article Ro¬ tation, they will find the fundamental theorems, which will enable them to carry on the investigation. We shall first give a short sketch of Newton’s investigation, which is of the most palpable and popular kind, and is highly valuable, not only for its ingenuity, but also because it will give our unlearned readers distinct and satisfactory conceptions of the chief circumstances of the whole phe¬ nomena. Let S (fig. 154.) be the sun, E the earth, and M theSketchol moon, moving in the orbit NMCD «, which cuts theNewtom plane of the ecliptic in the line of the nodes N n, and™™8^ has one half raised above it, as represented in the figure, the other half being hid below the ecliptic. Sup¬ pose this orbit folded down 5 it will coincide with the ecliptic in the circle IN m e dn. Let EX represent the axis of this orbit, perpendicular to its plane, and there¬ fore inclined to the ecliptic. Since the moon gravitates to the sun in the direction MS which is all above the ecliptic, it is plain that this gravitation has a tendency to draw the moon towards the ecliptic. Suppose this force to be such that it would draw the moon down from M to i in the time that she would have moved from M to t, in the tangent to her orbit. By the com¬ bination of these motions, the moon will desert her or¬ bit, and describe the line M r, which makes the diagonal of the parallelogram 5 and if no farther action of the sun be supposed, she will describe another orbit M § n', lying between the orbit MCD n and the ecliptic, and she wilt come to the ecliptic, and pass through it in a point n', nearer to M than n is, which was the former place of her descending node. By this change of orbit, the line EX will no longer be perpendicular to it; but there will be another line E x, which will now be perpendicular to the new orbit. Also the moon, moving from M to r, does not move as if she had come from the ascending node N, but from a point N lying beyond it; and the line of the nodes of the orbit in this new position is N'ra. Also the angle MN'm is less than the angle MN m. Thus the nodes shift their places in a direction op¬ posite to that of her motion, or move to the westward 5 the axis of the orbit changes its position, and the orbit itself changes its inclination to the ecliptic. These momentary changes are different in different parts of the orbit, according to the position of the line of the nodes. Pit IV. ASTRONOM Y. 143 Thr7 of nodes. Sometimes the inclination of the orbit is in- Uifprsal creased, and sometimes the nodes move to the eastward. Gw'ta- But, in general, the inclination increases from the time j*n' „ that the nodes are in the line of syzigee, till they get in¬ to quadrature, after which it diminishes till the nodes are again in syzigee. The nodes advance only while they are in the octants after the quadratures, and while the moon passes from quadrature to the node, and they recede in all other situations. Therefore the recess ex¬ ceeds the advance in every revolution of the moon round the earth, and, on the whole, they recede. What has been said of one moon, would be true of each of a continued ring of moons surrounding the earth, and they would thus compose a flexible ring, which would never be flat, but rvaved, according to the difference (both in kind and degree) of the disturbing forces acting on its different parts. But suppose these moons to cohere, and to form a rigid and flat ring, no¬ thing would remain in this ring but the excess of the con¬ trary tendencies of its different parts. Its axis would be perpendicular to its plane, and its position in any moment will be the mean position of all the axes of the orbits of each part of the flexible ring ; therefore the nodes of this rigid ring will continually recede, except when the plane of the ring passes through the sun, that is, when the nodes are in syzigee; and (says Newton) the mo¬ tion of these nodes will be the same with the mean mo¬ tion of the nodes of the orbit of one moon. The in¬ clination of this ring to the ecliptic will be equal to the mean inclination of the moon’s orbit during any one revolution which has the same situation of the nodes. It will therefore be least of all when the nodes are in quadrature, and will increase till they are in syzigee, and then diminish till they are again in quadrature. Suppose this ring to contract in dimensions, the dis¬ turbing forces will diminish in the same proportion, and in this proportion will all their effects diminish. Sup¬ pose its motion of revolution to accelerate, or the time of a revolution to diminish ; the linear effects of the dis¬ turbing forces being as the squares of the times of their action, and their angular effects as the times, those er¬ rors must diminish also on this account ; and we can compute what those errors will be for any diameter of the ring, and for any period of its revolution. We can tell, therefore, what would be the motion of the nodes, the change of inclination, and deviation of the axis, of a ring which would touch the surface of the earth, and jj revolved in 24 hours j nay, we can tell what these mo¬ tions would he, should this ring adhere to the earth. I| They must he much less than if the ring were detached j for the disturbing forces of the ring must drag along with it the whole globe of the earth. Tire quantity of motion which the disturbing forces would have produced in the ring alone, will now (says Newton) be produced in the whole mass ; and therefore the velocity must be as much less as the quantity of matter is greater : But still this can he computed. Now there is such a ring on the earth: for the earth is not a sphere, but an elliptical spheroid. Sir Isaac New¬ ton therefore engaged in a computation of the effects of the disturbing force, and has exhibited a most beautiful example of mathematical investigation. He first asserts, that the earth be an elliptical spheroid, whose po¬ lar axis is to its equatorial diameter as 229 to 230. Then lie demonstrates, that if the sine of the inclina¬ tion of the equator be called w, and if t be the num¬ ber of days (sidereal) in a year, the annual motion of a detached ring will be 360° X 3s/1 4 * He then shows that the effect of the disturbing force on this ring is to its effect on the matter of the same ring, dis¬ tributed in the form of an elliptical stratum (but still detached) as 5 to 2 •, therefore the motion of the nodes will be 360° X ,or 16'i6"24,/,annually. He then proceeds to show, that the quantity of motion in the sphere is to that in an equatorial ring revolving in the same time, as the matter in the sphere to the mat¬ ter in the ring, and as three times the square of a qua- drantal arch to two squares of a diameter, jointly : Then he shows, that the quantity of matter in the ter¬ restrial sphere is to that in the protuberant matter of the spheroid, as 52900 to 461 (supposing all homoge¬ neous). From these premises it follows, that the mo¬ tion of 16' 16" 24"', must be diminished in the ratio of 10717 to 100, which reduces it to 9" 07"' annually. And this (he says) is the precession of the equinoxes, occasioned by the action of the sun ; and the rest of the 50^, which is the observed precession, is owing to the action of the moon, nearly live times greater than that of the sun. This appeared a great difficulty : for the phenomena of the tides show that cannot much exceed twice the sun’s force. ,r^ Nothing can exceed the ingenuity of this process. His deter- Justly does his celebrated and candid commentator, Da-mination niel Bernoulli, say (in his Dissertation on the Tides,of t^e.lorm which shared the prize of the French Academy with M‘Laurin and Euler), that Newton saw through a veil garth ,]e_ what others could hardly discover with a microscope monstrated in the light of the meridian sun. His determination ofby M‘JLau» the form and dimensions of the earth, which is thenn* foundation of the whole process, is not offered as any thing better than a probable guess, in re difflcillima ; and it has been since demonstrated with geometrical rigour by M‘Laurin. His next principle, that the motion of the nodes of the rigid ring is equal to the mean motion of the nodes of the moon, has been most critically discussed by the first mathematicians, as a thing which could neither he proved nor refuted. Frisius has at least shown it to he a mistake, and that the motion of the nodes of the ring is double the mean motion of the nodes of a single moon ; and that Newton’s own principles should have produced a precession of i 8^ seconds annually, which removes the difficulty formerly mentioned. H is third assumption, that the quantity of motion of the ring must be shared with the included sphere, was acquiesced in by all his commentators, till D’Alem¬ bert and Fuler, in 1749, showed that it was not the quantity of motion round an axis of rotation which re¬ mained the same, but the quantity of momentum or ro¬ tatory effort. The quantity of motion is the product of every particle by its velocity 5 that is, by its distance from the axis ; while its momentum, or power of pro¬ ducing rotation, is as the square of that distance, and is to be had by taking the sum of each particle multiplied by the square of its distance from the axis. Since the earth 14-1- 4io Examina¬ tion of the phenome¬ non of pre¬ cession on mechanical principles. ASTRONOMY. eaTtli diners so little from a perfect sphere, this makes the sun no sensible difference in the result. It will increase New¬ ton’s precession about three-fourths of a second. We proceed now to the examination of this pheno¬ menon upon the fundamental principles of mechanics. Because the mutual gravitation of the particles of matter in the solar system is in'the inverse ratio of the squares of the distance, it follows, that the gravitations of the different parts of the earth to the sun or to the moon are unequal. The nearer particles gravitate more than those that are more remote. Let PQy? E (fig. i J5-), be a meridional section of the terrestrial sphere, and PO pq the section of the in¬ scribed sphere. Let CS be a line in the plane of the ecliptic passing through the sun, so that the angle ECS is the sun’s declination. Let NCM be a plane passing through the centre of the earth at right angles to the plane of the meridian PQ p E j NCM will therefore be the plane of illumination. In consequence of the unequal gravitation of the mat¬ ter of the earth to the sun, every particle, such as B, is acted on by a disturbing force parallel to CS, and pro¬ portional to BD, the distance of the particle from the plane of illumination 5 and this force is to the gravi¬ tation of the central particle to the sun, as three times BD is to CS, the distance of the earth from the sun. Let AB a be a plane passing through the particle B, parallel to the plane EQ of the equator. This section of the earth will be a circle, of which A a is a diameter, and Q q will be the diameter of its section with the in¬ scribed sphere. These will be two concentric circles, and the ring by which the section of the spheroid ex¬ ceeds the section of the sphere will have AQ for its breadth j P is the axis of figure. Let EC be presented by the symbol OC or PC - EO their difference rr 7- a-\-v CL - QL - - - - The periphery of a circle to radius I The disturbing force at the distance from the plane NCM The sine of declination ECS The cosine of ECS s/ d1—x* n S It is evident, that with respect to the inscribed sphere, the disturbing forces are completely compensated, for every particle has a corresponding particle in the ad¬ joining quadrant, which is acted on by an equal and opposite force. But this is not the case with the pro¬ tuberant matter which makes up the spheroid. The segments NS s n and MT t m are more acted on than the segments NT t n and MS s m; and thus there is produced a tendency to a conversion of the whole earth, round an axis passing through the centre C, perpendicular to the plane PQyj E. We shall distin¬ guish this motion from all others to which the spheroid may be subject, by the name LlBRATlON. The axis of this libration is always perpendicular to that diameter of the equator over which the sun is, or to that meridian in which he is. Pros. I. To determine the momentum of lihration corresponding to any position of the earth respecting Part IV that is, to determine the accumulated energy Theory of the disturbing forces on all the protuberant matter of Univensl the spheroid. Let B and b be two particles in the ring formed by the revolution of AQ, and so situated, that they are at equal distances from the plane NM ; but on opposite sides of it. Draw BD, b d, perpendicular to NM, and FLG perpendicular to LT. Then, because the momentum, or power of produ* cing rotation, is as the force and as the distance of its line of direction from the axis of rotation, jointly, tl»e combined momentum of the particles B and b, will be f.X$Y).Y)C—f.bd.d c, (for the particles B and b are urged in contrary directions). But the momentum of B isyiBF.DC-f-yiFD.DC, and that of ^ is f.b.G.dC— f.dG.dC 5 and the combined momentum is yiBF.D f/—— /.FD.DC+rfC7= 2/.BF.LF—2/.LT.TC. Because m and n are the sine and cosine of the angle ECS or LCT, we have LT=:ot.CL, and CT = n. CL, and LF^ot.BL, and BF=«.BL. This gives the mo¬ mentum =: 2/mn BL2—CL2’ The breadth AQ of the protuberant ring being very small, we may suppose, without any sensible error, that all the matter of the line AQ is collected in the point Q $ and, in like manner, that the matter of the whole ring is collected in the circumference of its inner circle, and that B and b now represent, not single particles, but the collected matter of lines such as AQ, which terminate at B and b. The combined momentum of two such lines will therefore he 2 mnyiAQ.BL*—CLa. Let the circumference of each parallel of latitude be divided into a great number of indefinitely small and equal parts. The number of such parts in the circum¬ ference, of which Q y is the diameter, will be irQL. To each pair of these there belongs a momentum 2m nj •AQ’BTi —-CL*. The sum of all the squares of BL, which can be taken round the circle, is one half of as many squares of the radius CL : for BL is the sine of an arch, and the sum of its square and the square of its corresponding cosine is equal to the square of the radius. Therefore the sum of all the squares of tire sines, together with the sum of all the squares of the cosines, is equal to the sum of the same number of squares of the radius $ and the sum of the squares of the sines is equal to the sum of the squares of the cor¬ responding cosines j therefore the sum of the squares of the radius is double of either sum. Therefore / Il'QL •EL*=4n-QL*QL2. In like manner the sum of the number II-QL of CL2^ will be = irQL'CL2. These sums, taken for the semicircle, are ^irQL'QL*, and in QL-CL2, or II-QL^QL2, and n-QL.^CL2 : there¬ fore the momentum of the whole ring will he 2 m n f •AQ'QL*ir(5QL—|CL2) : for the momentum of tire ring is the combined momenta of a number of pairs, and this number is 4n*QL. By the ellipse we have OC : QL rr EO : AQ, and EO d AQ=QL , =QL - ; therefore the momentum of the ring is 2 m (|QL*—4CL*), — mnj~b Q (tQ E*—C L2) : but Q L*:=£2—j therefore i QL* Th TJn trsal ^ ‘Gr IV. Ill = U2—l ASTRONOMY. b*—3,v2 145 ta- ^~~sxly therefore the momentum of the ring is mnf - IT {]?—a?2) rd [b*—4^2^2+3^4\ C rd -.mni -n\ L-2—= mnf—rU 2 / J b \ 2 /’ J 2b (b*—4/>iz«2-}-3^4). If we now suppose another paral¬ lel extremely near to A a, as represented by the dotted line, the distance L l between them being at, we shall have the fluxion of the momentum of the spheroid lii nf—~U (J^x—4&V!#-j-3tf4#), of which the fluent is m nf -An '\b*x—j. This expresses the mo¬ mentum of the zone EA a Q, contained between the equator and the parallel of latitude A a. Now let x become and we shall obtain the momentum of the hemispheroid — mnf ~T\ {b$—an(^ ^iat °f the spheroid = m n(b* —■ 4 + b's')—-Lm nfd b 15 rib*. This formula does not express any motion, but only a pressure tending to produce motion, and particularly tending to produce a libration by its action on the co¬ hering matter of the earth, which is affected as a num¬ ber of levers. It is similar to the common mechanical formula w. d, where w means a weight, and d its di¬ stance from the fulcrum of the lever. It is worthy of remark, that the momentum of this protuberant matter is just 4 of what it would be if it were all collected at the point O of the equator : for the matter in the spheroid is to that in the inscribed sphere as «2 to 62, and the contents of the inscribed sphere is 4 n b*. Therefore «* : a2—b3 : 4nZ>J o*—b* . . ———, which is the quantity of protuberant mat¬ ter. We may, without sensible error, suppose — Cl — 2d; then the protuberant matter will be ^Tlfrd. If all this were placed at O, the momentum would be 4 H ^^/0,H*HC,=4 m nf d b*, because OH'llQ—ninb*; now 4 is 5 times T4-. Also, because the sum of all the rectangles OH’HC round the equator is half of as many squares of OC, it follows that the momentum of the protuberant matter placed in a ring round the equator of the sphere, or spheroid, is one half of what it would be if collected in the point G or E ; whence it follows that the momen¬ tum of the protuberant matter in its natural place is two-fifths of what it would he if it were disposed in an equatorial ring. It was in this manner, that Sir Isaac Newton was enabled to compare the effect of the sun’s action on the protuberant matter of the earth, with his effect on a rigid ring of moons. The preceding in¬ vestigation of the momentum is nearly the same with his, and appears to us greatly preferable in point of perspicuity to the fluxionary solutions given by later authors. These indeed have the appearance of greater accuracy, because they do not suppose all the protube¬ rant matter to he condensed on the surface of the in¬ scribed sphere: nor were we under the necessity of do¬ ing this ; only it would have led to very complicated Yol. III. Part I. t 411 axis. Effects of expressions, had we supposed the matter in each line AQ collected in its centre of oscillation or gyration. W e made a compensation for the error introduced by this which may amount to X4x of the whole, and should not be neglected, by taking d as equal to a2—b* . a2— — instead ot —. ine consequence is, that our 2a a + b ^ ’ formula is the same with that of the later authors. Thus far Sir Isaac Newton proceeded with mathema¬ tical rigour; but in the application he made two assump¬ tions, or, as he calls them hypotheses, which have been found to be unwarranted. The first was, that when the ring of protuberant matter is connected with the in¬ scribed sphere, and subjected to the action of the di¬ sturbing force, the same quantity of motion is produced in the whole mass as in the ring alone. The second was, that the motion of the nodes of a rigid ring of moons is the same with the mean motion of the nodes of a solitary moon. But we are now able to demon¬ strate, that it is not the quantity of motion, but of mo¬ mentum, which remains the same, and that the nodes of a rigid ring move twice as fast as those of a single particle. We proceed therefore to, ProB. II. To determine the deviation of the and the retrograde motion of the nodes which result the lihrato- from this libratory momentum of the earth’s protube-ry inoir!e,u' ,, turn 01 the rant matter. earth s pro- But here we must refer our readers to some funda-tuberant mental propositions of rotatory motions which are de- matter, monstrated in the article Rotation. If a rigid body is turning round an axis A, passing through its centre of gravity with the angular velocity a, and receives an impulse which alone would cause it to turn round an axis B, also passing through its centre of gravity, with the angular velocity b, the body will now turn round a third axis C, passing through its cen¬ tre of gravity, and lying in the plane of the axis A and B, and the sine of the inclination of this third axis to the axis A will be to the sine of the inclination to the axis B as the velocity b to the velocity a. When a rigid body is made to turn round any axis by the action of an external force, the quantity of mo¬ mentum produced (that is, the sum of the products of every particle by its velocity and by its distance from the axis) is equal to the momentum or similar product of the moving force or forces. If an oblate spheroid, whose equatorial diameter is a, and polar diameter b, be made to librate round an equa¬ torial diameter, and the velocity of that point of the equator which is farthest from the axis of libration be t\ the momentum of the spheroid is ~n azb2v. I5 The two last are to be found in every elementary book of mechanics. Let AN an (fig. 156.) be the plane of the earth’s equa¬ tor, cutting the ecliptic CNKw in the line of the nodes or equinoctial points N a. Let OAS he the section of the earth by a meridian passing through the sun, so that the line OCS is in the ecliptic, and CA is an arch of an hour-circle or meridian, measuring the sun’s de¬ clination. The sun not being in the plane of the equa¬ tor, there is, by prop. I. a force tending to produce a libration round an axis ZO2; at right angles to the dia¬ meter A a of that meridian in which the sun is situated, T and 146 ASTRONOMY Theory of an^ momentum of all the disturbing forces is Universal nf dU b*. The product of any force by the mo¬ ment t of its action expresses the momentary increment of velocity; therefore the momentary velocity, or the Part IV, ing in the equator of libration), as a r to mnf dt*, Theory and completing the parallelogram kr me, km will Universal be the compound motion of A, and a r : m n df l* ^tion^ velocity of libration granted in the time t \% ^mnfd Tlb*t. This is the absolute velocity of a point at the distance 1 from the axis, or it is the space which would be uniformly described in the moment t, with the velo¬ city which the point has acquired at the end of that moment. It is double the space actually described by the libration during that moment $ because this has been an uniformly accelerated motion, in consequence of the continued and uniform action of the momentum during this time. This must be carefully attended to, and the neglect of it has occasioned very faulty solu¬ tions of this problem. Let v be the velocity produced in the point A, the most remote from the axis of libration. The momen¬ tum excited or produced in the spheroid is b*v (as above), and this must be equal to the momentum of the moving force, or to m nf dll b^t; therefore we . -^mnfdU bAt . r obtain V— -r^-— , that is, v~m n f dt — or H o26 ’ J a* b* very nearly m nf d t, because —1 very nearly. Al¬ so, because the product of the velocity and time gives the space uniformly described in that time, the space de¬ scribed by A in its libration round Z2; is mnf dt*, and , . , . . m n f dt the angular velocity is ^ . Let r be the momentary angle of diurnal rotation. The arch kr, described by the point A of the equa¬ tor in this moment t will therefore be ar, that is, ay^r, • • CIV and the velocity of the point A is —, and the angular r velocity of rotation is —. t Here then is a body (fig. 157.) turning round an axis OP, perpendicular to the plane of the equator « 0 », and therefore situated in the plane ZPss; and it turns round v this axis with the angular velocity —. It has received t an impulse, by which alone it would librate round the m n f d t axis Ziz, with the angular velocity It will therefore turn round neither axis, but round a third axis OP', passing through O, and lying in the plane ZP 2;, in which the other two are situated, and the sine P'lT of its inclination to the axis of libration Z2; will be to the sine Vp of its inclination to the axis OP r m n f dt of rotation as — to ; . t a Now A, in fig. 156. is the summit of the equator both of libration and rotation : m nf dt* is the space described by its libration in the time t; and a r is the space or arch Ar (fig. 156.) described in the same time by its rotation : therefore, taking A r to A e (perpen¬ dicular to the plane of the equator of rotation, and ly- 3 77171 t Cl t* ~ I ’• , which will be the tangent of the angle ar 7n A r, or of the change of position of the equator. But the axes of rotation are perpendicular to their equator; and therefore the angle of deviation w is equal to this angle r A m. This appears from fig. c. : for n P' : Y’p—O'p : P'p,:=OP : tan. POP j and it is evident that ar \ mnfdt*— —m nf d—, as is requi- t a red by the composition of rotations. In consequence of this change of position, the plane of the equator no longer cuts the plane of the ecliptic in the line N n. The plane of the new equator cuts the former equator in the line AO, and the part AN of the former equator lies between the ecliptic and the new equator AN', while the part Aw of the former equator is above the new one Aw'j therefore the new node N', from which the point A was moving, is removed to the westward, or farther from A j and the new node to which A is approaching, is also moved westward, or near¬ er to A j and this happens in every position of A. The nodes therefore, or equinoctial points, continually shift to the westward, or in a contrary direction to the rotation of the earth ; and the axis of rotation always deviates to the east side of the meridian which passes through the sun. This account of the motions is extremely different from what a person should naturally expect. If the earth were placed in the summer solstice, with respect to us who inhabit its northern hemisphere, and had no rotation round its axis, the equator would begin to ap¬ proach the ecliptic, and the axis would become more upright; and this would go on with a motion conti¬ nually accelerating, till the equator coincided with the ecliptic. It would not stop here, but go as far on the other side, till its motion were extinguished by the op¬ posing forces j and it would return to its former position, and again begin to approach the ecliptic, playing up and down like the arm of a balance. On this account this motion is very properly termed libixition : but this very slow libration, compounded with the incomparably swifter motion of diurnal rotation, produces a third mo¬ tion extremely different from both. At first the north pole of the earth inclines forward toward the sun j after a long course of years it will incline to the left hand, as viewed from the sun, and be much more inclined to the ecliptic, and the plane of the equator will pass through the sun. The south pole will come into view, and the north pole will begin to decline from the sun j and this will go on (the inclination of the equator dimi¬ nishing all the while) till, after a course of years, the north pole will be turned quite away from the sun, and the inclination of the equator will be restored to its original quantity. After this the phenomena will have another period similar to the former, but the axis will now deviate to the right hand. And thus, although both the earth and sun should not move from their places, the inhabitants of the earth would have a com¬ plete succession of the seasons accomplished in a period of many centuries. This would be prettily illustrated by an iron ring poised very nicely on a cap like the card of Pitt IV. A S T R Tlfary »f a mariner’s compass, having its centre of gravity co- tlnii-rsal inciding with the point of the cap, so that it may whirl Gfta- ronnd in any position. As this is extremely difficult to ■ .l' . execute, the cap may be pierced a little deeper, which will cause the ring to maintain a horizontal position with a very small force. When the ring is whirling very steadily, and pretty briskly, in the direction of the hours of a watch-dial, hold a strong magnet above the middle of the nearer semicircle (above the 6 hour point) at the distance of three or four inches. We shall imme¬ diately observe the ring rise from the 9 hour point, and sink at the 3 hour point, and gradually acquire a mo¬ tion of precession and nutation, such as has been de¬ scribed. If the earth be now put in motion round the sun, or the sun round the earth, motions of libration and devia¬ tion will still obtain, and tbe succession of their different phases, if we may so call them, will be perfectly analo¬ gous to the above statement. But the quantity of devi¬ ation, and change of inclination, will now be prodigi¬ ously diminished, because the rapid change of the sun’s position quickly diminishes the disturbing forces, annihi¬ lates them by bringing the sun into the plane of the equator, and brings opposite forces into action. We see in general that the deviation of the axis is al¬ ways at right angles to the plane passing through the sun, and that the axis, instead of being raised from the eclip¬ tic, or brought nearer to it, as the libration would occa¬ sion, deviates sidewise ; and the equator, instead of be¬ ing raised or depressed round its east and west points, is !, twisted sidewise round the north and south points ; or at least things have this appearance : but we must now at¬ tend to this circumstance more minutely. The composition of rotation shows us that this change of the axis of diurnal rotation is by no means a translation of the former axis (which we may suppose to be the axis of figure) into a new position, in which it again becomes the axis of diurnal motion ; nor does j the equator of figure, that is, the most prominent sec¬ tion of the terrestrial spheroid* change its position, and ; in this new position continue to be the equator of ro¬ tation. This was indeed supposed by Sir Isaac New¬ ton 5 and this supposition naturally resulted from the train of reasoning which he adopted. It was strictly true of a single moon, or of the imaginary orbit attach¬ ed to it *, and therefore Newton supposed that the whole earth did in this manner deviate from its former posi¬ tion, still, however, turning round its axis of figure. In this he has been followed by Walmesly, Simpson, and most of his commentators. D’Alembert was tbe first who entertained any suspicion that this might not be certain ; and both he and Euler at last showed that the new axis of rotation vyas really a new line in the body of the earth, and that its axis and equator of figure did not remain the axis and equator of rotation. They as¬ certained the position of the real axis by means of a most intricate analysis, which obscured the connexion of the different positions of the axis with each other, and gave us only a kind of momentary information. Father Fri- sius turned bis thoughts to this problem, and fortunately discovered the composition of rotations as a general principle of mechanical philosophy. Few things of this kind have escaped the penetrating eyes of Sir Isaac Newton. Even this principle had been glanced at by himi He affirms it in express terms with respect to , O N O M V. , a body that is perfectly spherical (cor. 22. prop. 66. Theory of book i.). But it was reserved for Frisius to demonstrate Universal it to be true of bodies of any figure, and thus to enrich Uravita- mechanical science with a principle which gives simple tU)11' and elegant solutions of the most difficult problems. -y- But here a very formidable objection naturally offers itself. If the axis of the diurnal motion of the heavens is not the axis of the earth’s spheroidal figure, but an imaginary line in it, round which even the axis of figure must revolve * and if this axis of diurnal rotation has so greatly changed its position, that it now points at a star at least 12 degrees distant from the pole observed by I imochares, how comes it that the equator has the very same situation on the surface of the earth that it had m ancient times ? No sensible change has been observed in the latitudes of places. The answer is very simple and satisfactory : Suppose that in 12 hours the axis of rotation has changed from the position PR (fig. 158.) to pr, so that the north pole, instead of being at P, which we may suppose to be a par¬ ticular mountain, is now at p. In this 12 hours the mountain P, by its rotation round p r, has acquired the position Jr. At the end of the next 12 hours, the axis of rotation has got the position «■£, and the axis of figure has got the position p r, and the mountain P is now at p. Ihus, on the noon of the following day, the axis of figure PR is in the situation which the real axis of rota¬ tion occupied at the intervening midnight. This goes on continually, and the axis of figure follows the posi¬ tion of the axis of rotation, and is never further remo¬ ved from it than the deviation of 12 hours, which does not exceed 7~^th part of one second, a quantity altoge¬ ther imperceptible. Therefore the axis of figure will always sensibly coincide with the axis of rotation, and no change can be produced in the latitudes of places on the surface of the earth. We have hitherto considered this problem in the most Applica- general manner; let us now apply the knowledge we ti°n °f this have gotten of the deviation of the axis or of the mo- reasoning mentary action of the disturbing force to the explanation of the phenomena; that is, let us see what precession sJon.^ and what nutation will be accumulated after any given time of action. For this purpose we must ascertain the precise devia¬ tion which the disturbing forces are competent to pro¬ duce. I his we can do by comparing the momentum of libration with the gravitation of the earth to the sun, and this with the force which would retain a body on the equator while the earth turns round its axis. The gravitation of the earth to the sun is in the pro¬ portion of tbe sun’s quantity of matter M directly, and to the square of the distance A inversely, and may there- M fore be expressed by the symbol —. The disturbing force at the distance 1 from the place of illumination is to the gravitation of the earth’s centre to the sun as 3 to A, (A being measured on the same scale which measures the distance from the plane of illumination). 3M Therefore will be the disturbing force f of our for¬ mula. Let p be the centrifugal force of a particle at the distance 1 from the axis of rotation ; and let t and T be the time of rotation and of annual revolution, viz. T 2 sidereal 148 Theory of Universal Gravita¬ tion. A sidereal day and year. Then P : S T R O _A : .p Hence • O r * we derive But since r was the angu- ' A3 J l1 jar velocity of rotation, and conseq,uently lX?‘the space described, and —7— the velocity ; and since the centrifugal force is as the square of the velocity divided by the radius, (this being the measure of the generated velocity, which is the proper measure of any accele¬ rating force), we haveyr tx 1 X y,‘ — —, and/: 3 r t1 X Now the formula/m n d— expressed the sine of the angle. This being extremely small, the sine may be considered as equal to the arc which measures the angle. Now, substitute for it the value now found, viz. 3— x —, and we obtain the angle of deviation w—r i1 T* and this is the simplest form in which it T1 a can appear. But it is convenient, for other reasons, to a*—bx express it a little differently: d is nearly equal to 2 or O ft (ft . . 5 mn —and this is the form therefore w—r X — 2 1 a in which we shall now employ it. 2 ft eft — • • The small anale r Ak™> n™ is the angle in which a 211 a* the new equator cuts the former one. It is different at different times, as appears from the variable part m n, the product of the sine and cosine of the sun’s declina¬ tion. It will be a maximum when the declination is in the solstice, for mn increases all the way to 450, and the declination never exceeds It increases, therefore, from the equinox to the solstice, and then diminishes. Let ESL (fig. 159.) be the ecliptic, EAC the equa¬ tor, BAD the new position which it acquires by the momentary action of the sun, cutting the former in the • 3 a*—b* angle BAE=r •mn Let S be the sun’s place in the ecliptic, and AS the sun’s declination, the meridian AS being perpendicular to the equator. Let 2/2 *2 ft ^ — be k. The angle BAE is then ~r —rrr^kmn. a* 2 In N O M Y. Part IV, non. BE is indefinitely small, CD may be taken for the dif- Theory ference of LD and l c, they being ultimately in the Universal ratio of equality. Therefore CD measures the change Gl;/ta' of the obliquity of the ecliptic, or the nutation of the axis with respect to the ecliptic. The real deviation of the axis is the same with the change in the position of the equator, Pp being the measure of the angle EAB. But this not being al¬ ways made in a plane perpendicular to the ecliptic, the change of obliquity generally differs from the change in the position of the axis. Thus, when the sun is in the solstice, the momentary change of the position of the equator is the greatest possible 5 but being made at right angles to the plane in which the obliquity of the ecliptic is computed, it makes no change whatever in the obliquity, but the greatest possible change in the precession. In order to find CD the change of obliquity, observe that in the triangle CAD, B : sin. AC, or H : cos. AE=sin. A : sin. CD, =A : CD (because A and CD are exceedingly small). Therefore the change of obli¬ quity (which is the thing commonly meant by nutation) CD=A X cos. AE, =r -pjra k m n, cos. AE' =r A— kx sin. declin. X cos. declin. Xcos. E. ascens. But it is more convenient for the purposes of astro¬ nomical computation to make use of the sun’s longitude SE. Therefore make The sun’s longitude ES — 25 = x the spherical triangle BAE we have sin. B : sin. AE— sin. A : sin. BE, “or = A : BE, because very small angles and arches are as their sines. Therefore BE, which is the momentary precession of the equinoctial . ^ . . -r, . , . a sin. AE _ 3 P the momentary nutation will be r—y^kp ley. In this point E, is equal to A ^ , — r X nmn 2 1 Sine of the sun’s long. - - — Cosine I—**= y Sine obliq. eclipt. - - 23^= p Cosine obliq. - - - — (J In the spherical triangle EAS, right-angled at A (because AS is the sun’s declination perpendicular to the equator), we have K : sin. ESrrsin. E : sin. AS, and sin. AS=ry;«. Also K : cos. ASrrcos. AE : cos. ES, and cos. ES or y=cos. AS X cos. AE. There¬ fore pxy— sin. AS cos. AS X cos. AE, =?» n x cos. AE. * 3 ft Therefore the momentary nutation CD=r We must recollect that this angle is a certain frac¬ tion of the momentary diurnal rotation. It is more convenient to consider it as a fraction of the sun’s an¬ nual motion, that so we may directly compare his mo¬ tion on the ecliptic with the precession and nutation corresponding to his situation in the heavens. This change is easily made, by augmenting the fraction in the ratio of the sun’s angular motion to the motion of T rotation, or multiplying the fraction by — ; therefore 4i3 Various modes of application, . B sin. E. ascens. sin. obi. eel. The equator EAC, by taking the position BAD, recedes from the ecliptic in the colure of the solstices CL, and CD is the change of obliquity or the nu¬ tation. For let CL be the solstitial colure of BAD, and cl the solstitial colure of EAC. Then we have sin. B : sin. E = sin. LD : sin. Ic; and therefore the difference of the arches LD and Ic will be the measure of the difference of the angles B and E. But when 2 va{ue j t ^P is a constant quantity, and the momentary 2 i nutation is proportional to xy, or to the product of the sine and cosine of the sun’s longitude, or to the sine of twice the sun’s longitude j for xy is equal to half the sine of twice 2. If therefore we multiply this fraction by the sun’s momentary angular motion, which we may suppose, with abundant accuracy, proportional to 2;, we obtain the fluxion of the nutation, th.e fluent of which will ex¬ press ?* IV. q.jJL 0f press the whole nutation while the sun describes the UiJjrsaJ acch 2 of the ecliptic, beginning at the vernal equr- G*t.a- nox> Therefore, in place of y put I—and in place tation for the moment when the sun’s longitude is $s, and the fluent will be the whole nutation. The fluxion resulting from this process is xx, of which the fluent is a?*. This is the whole change produ- A ced on the obliquity of the ecliptic while the sun moves along the arch 25 ecliptic, reckoned from the vernal equinox. When this arch is 90°, # is 1, and there¬ fore - Vi" ^ the nutation produced while the sun moves 4 # . 44 from the equinox to the solstice. 'lie cil The momentary change of the axis and plane of the ml n>- equator (which is the measure of the changing force) rf .3^ laIl 18 n' re at.it at 2 1 he sdii- The momentary change of the obliquity of the eelip- er* at ntkn he ejii- tic is -— loxdfiiO- 2 I hin| ASTRONOMY. 149 the equinoxes while the sun moves from the vernal Tlieory of equinox along the arch z of the ecliptic. 3tkq of 25 put \T' and we have the fluxion of the nu- In this expression, which consists of two parts, Universal Gravita¬ tion. The whole change of obliquity is StkP 4 1 nne. CD = -^L=: V l—X q x cos. long. ~ 1—A?* and CD =r EB Therefore EB sin. obliq. eclip. tan. long. © H t k T) • lue found in N° 40, viz. x x, o ^ k(jx*x X—y— , the fluxion of the precession of the 2 L ^/i—.r- equinoxes occasioned by the action of the sun. The xx If we now substitute for CD its va- we obtain EB zr fluent of the variable part — xy, of which the fluent is evidently a segment of a circle whose arch is 2! and sine a\ that is, zr ——_ . .1 and the 2 rvliole precession, while the sun describes the arch 2;, is -^Tjr; X —( 2—XfJ i—This is the precession of CtJ 1—the first is incomparably 3, and 4 ^ ^ greater than the second, which never exceeds i", and is always compensated in the succeeding quadrant. The Q, t k q 'w 25, and precession occasioned by the sun will be from this expression we see that the precession increases uniformly, or at least increases at the same rate with the sun’s longitude ss. , . . 3 tkq . because the quantity - is constant. 416 In order to make use of these formulae, which are Mode of now reduced to very great simplicity, it is necessary t0 determine the 3 tkp 3 tkq values of the two constant quantities which we shall call N and P, as factors 4t ’ 4T , of the nutation and precession. Now t is one sidereal day, and T is 3665. k is —^—, which according to Sir Isaac Newton is 2312—230* •jpandy Hence we see that the force and the real momentary change of position are greatest at the solstices, and di¬ minish to nothing at the equinoxes. The momentary change of obliquity is greatest at the octants, being proportional to x x or to x y. The whole accumulated change of obliquity is greatest at the solstices, the obliquity itself being then smallest. tuanty of We must in like manner find the accumulated quan- iree« ion tity of the precession after a given time, that is, the 1 Pen arch BE for a finite time. We have ER : CD ~ sin. EA : sin. CA (or cos. EA) = tan. EA : i,andEB : ERm : sin.B. There¬ fore EB : CD=tan. EA : sin. B. But tan. EA= . -no t-. sin. long, cos. Ex tan. ES, = cos. Ex 231 . Hi are the sine and cosine of 230 28', viz. 0,39822 and 0,91729. These data give Nz= ^ and Pro , of 0 141030 61224 which the logarithms are 4.85069 and 5.21308, viz. the arithmetical complements of 5.14931 and 4.78692. 417 Let us, for an example of the use of this investiga-Example of tion, compute the precession of the equinoxes when the^®^1*1^ sun has moved from the vernal equinox to the summer solstice, so that z is 90°, or 324000". Log. 324ooo"=25 - - - 5:51055 Log. P - - - - - 5-21308 Log. 5",292 - . - . 0.72363 The precession therefore in a quarter of a year is 5,292 seconds *, and, since it increases uniformly, it is 2l", 168 annually. 418 We must now recollect the assumptions on whichAsramp- tbis computation proceeds. The earth is supposed t°he be homogeneous, and the ratio of its equatorial diame”conipUla. ter to its polar axis is supposed to be that of 231 to tion pro- 230. If the earth be more or less protuberant attheeeeds. equator, the precession will be greater or less in the ra¬ tio of this protuberance. The measures which have been taken of the degrees of the meridian are very in¬ consistent among themselves j and although a compari¬ son of them all indicates a smaller protuberance, nearly instead of their differences are too great to leave much confidence in this method. But if this figure be thought more probable, the precession will be reduced to about ly" annually. But even though the figure of the earth were accurately determined, we have no authority to say that it is homogeneous. If it be denser towards the centre, the momentum of the protu¬ berant matter will not be so great as if it were equally dense with the inferior parts, and the precession will be diminished on this account. Did we know the propor¬ tion of the matter in the moon to that in the sun, we could 4 I jd Theory of Universal Gravita* tion. 419 ICfl’ect of the moon’s action on the protu¬ berant mat¬ ter of the earth. ASTRO could easily determine the proportion of the whole ob¬ served annual precession of 50-y" which is produced by the sun’s action. But we have no unexceptionable data for determining this j and we are rather obliged to in¬ fer it from the effect which she produces in disturbing the regularity of the precession, as will be considered immediately. So far, therefore, as we have yet pro¬ ceeded in this investigation, the result is very uncertain. We have only ascertained unquestionably the law which is observed in the solar precession. It is probable, how¬ ever, that this precession is not very different from 20" annually j for the phenomena of the tides show the di¬ sturbing force of the sun to be very nearly of the di¬ sturbing force of the moon. Now 20" is -y- of §o". But let us now proceed to consider the effect of the moon’s action on the protuberant matter of the earth ; and as we are ignorant of her quantity of matter, and consequently of her influence in similar circumstances with the sun, we shall suppose that the disturbing force of the moon is to that of the sun as m to i. Then (ccetems paribus') the precession will be to the solar pre¬ cession n in the ratio of the force and of the time of its action jointly. Let t and T therefore represent a pe¬ riodical month and year, and the lunar precession will mM . be ^1,s precession must he reckoned on the plane of the lunar orbit, in the same manner as the so¬ lar precession is reckoned on the ecliptic. We must also observe, that represents the lunar precession only on the supposition that the earth’s equator is in¬ clined to the lunar orbit in an angle of 23^ degrees. This is indeed the mean inclination j but it is sometimes increased to above 28°, and sometimes reduced to 180. . Now in the value of the solar precession the cosine of the obliquity was employed. Therefore whatever is the angle E contained between the equator and the lu- ... . ... ( rnict Cos. E nar orbit* the precession will be = -rrr— 7^ To> I Cos. 23^ and it must he reckoned on the lunar orbit. Now let T1 B (fig. 160.) be the immoveable plane of the ecliptic, HP EDrCiF the equator in its first situation, before it has been deranged by the action of the moon, AGRDBH the equator in its new position, after the momentary action of the moon. Let EGNFH be the moon’s orbit, of which N is the ascending node, and the angle Nrr5° 8' 46". 4*0 Lunar pre¬ cession in & month re¬ duced to the eclip¬ tic. Let N ‘Y’ the long, of the node be - - Sine N ■ . 1 Cos. ‘V But we must exterminate the angleE, because it changes by the change of the position of N. Now, in the tri- ahgle'V’EN we have cos. E=cos.HpN • sin. N • sin. ^— cos. N • cos. HP, —yea—db. And because the angle E is necessarily obtuse, the perpendicular will fall without the triangle, the cosine of E will be negative, and we shall have cos. Y.—bd—acy. Therefore the nutation the node being supposed all the while in N. These two expressions of the monthly precession andma/be ttutation may be considered as momentary parts of thecomidert! moon’s action, corresponding to a certain position of theasmonie‘ node and inclination of the equator, or as the fluxions^hr*1 of the whole variable precession and nutation, while theraocm’sK node continually changes its place, and in the space of tion. 18 years makes a complete tour of the heavens. ^ We must, therefore, take the motion of the nodes as the Preceii® fluent of comparison, or we must compare the fluxions and n”1'' of the node’s motion with the fluxions of the precession tion,c0ir and nutation ; therefore, let the longitude of the nodepare be and its monthly change — vs; we shall then have t: e , mn-t cx(bd— tor one month will be X—-—v 1 0 PI ' Ti P li * 0 IV. ASTRONOMY. • ,722; nx *al t ; n—x : <*, and i——, —— ,—==•. LetTbe=r, in order that n may be 18,6, and substitute for t its value iu the fluxion of the nutation, by putting \—x* in place of y. By this substitution we obtain m tt n -^-y e o ( * X.'—22ca:«ay The fluent of this is m * n— W!—** J eb ^—dbsj I—a:2—'~~2~~y {Vide Simpson’s Fluxions, § 77.) But when x 13=0, the nutation must be =r n, because it is from the position in the equinoctial points that all our deviations are reckoned, and it is from this point that the periods of the lunar action recommence. But if we make x=o in this expression, the term — a c*!. vanishes, and the term—db 1 —a?* becomes =—db; therefore our fluent has a constant part-j-f/£ ; and the complete fluent is mien ^-^db—dbyj 1—-x* — (l C X* \ c ). Now this is equal to m urn ^ ( d b X versed 2 / eb sine, %—J acX versed sine 22;) : For the versed sine of ss is equal to (1—cos. 2;) ; and the square of the sine of an arch is 4 the versed sine of twice that arch. This, then, is the whole nutation while the moon’s ascending node moves from the vernal equinox to the longitude qp It is the expression of a certain number of seconds, because one of its factors, is the solar precession in seconds ; and all the other factors are numbers, or fractions of the radius 1; even e is ex¬ pressed in terms of the radius 1. The fluxion of the precession, or the monthly preces¬ sion, is to that of the nutation as the cotangent of E is to the sine of qr. This also appears by considering fig. 159. measures the angle A, or change of position of the equator j but the precession itself, reckoned on the ecliptic, is measured by Po, and the nutation by po; and the fluxion of the precession is equal to the fluxion of . cot. op E , a _ ad+bey , nutation X —; , but cot. qp E= — £ . there- sine qp cx fore co** E ad+hcsj 1—x* sine *Y> cx the fluxion of the nutation, gives b abe \Jt~M ^ : This, multiplied into a b da . . {b*—au)dc—abc'.^i—xxj x for the monthly pre¬ cession. The fluent of this —^ d* £ z -}- {b* «*) dex—^abe'z—lab&x*/ 1—x^j, 0r it is equal m nr nf t0 ~ab~e\ c*) ab* + {b'—a') d c z—£ a b c* sine 2z^. Let us now express this in numbers: When the node J51 has made a half revolution, we have z—180°, whose Theory of versed sine is 2, and the versed sine of 2 z, or 360°, is Universal =0 j therefore, after half a revolution of the node, mirnc , , T„ . , . ;— 2 b a. It, in this expres- the nutation becomes : 1 44": we shall find sion, we supposed 772=24, and it: the nutation to be ipf". Now the observed nutation is about 18". This re¬ quires 772 to be 2tIo-, and ir=z 164". But it is evident, that no astronomer can pretend to w'arrant the accuracy of his observations of the nutation within 1". To find the lunar precession during half a revolution and the and the 2 -c* m nr n of the node, observe, that then z becomes r sine of z and of 2z vanish, J2 becomes i- precession becomes (J*—ic2),= (1—4-c*), and the precession in 18 years \s m ic n i—\c%. We see, by comparing the nutation and precession learly for nine years, that they are as ^ C ^ to 1—| as x to I7f. This gives 313" of precession, correspond¬ ing to 18", the observed nutation, which is about 35" of precession annually produced by the moon. And thus we see that the inequality produced by Gives the the moon in the precession of the equinoxes, and, morediltobing particularly, the nutation occasioned by the variable ob-force and liquity of her orbit, enables us to judge of her share inmatter of the whole phenomenon ; and therefore informs us of her^ie moon* disturbing force, and therefore of her quantity of mat¬ ter. This phenomenon, and those of the tides, are the only facts which enable us to judge of this matter : and this is one of the circumstances which has caused this problem to occupy so much attention. Dr Bradley, by a nice comparison of his observations with the ma¬ thematical theory, as it is called, furnished him by Mr Machin, found that the equation of precession comput¬ ed by that theory was too great, and that the theory would agree better with the observations, if an ellipse were substituted for Mr Machin’s little circle. He thought that the shorter axis of this ellipse, lying in the colure of the solstices, should not exceed l6w. Nothing can more clearly show the astonishing accuracy of Bradley’s observations than this remark: for it results fi om the theory, that the pole must really describe an ellipse, having its shorter axis in the solstitial colure, and the ratio of the axes must he that of 18 to 16,8 ; for the mean precession during half a revolution of the . . mienf ca\ node is— — ) } and therefore for the longi¬ tude z, it will be y when this is taken from the true precession for that longitude, it leaves the equation of precession ( ba a* j d c' abe V sine z—\abc sine 2z J ; therefore when the node is in the solstice, and the equation greatest, we have it= miened ~~a"i,e —a > We ,iere neglect the second term as insignificant* This. I52 ASTRONOMY. Part IV, Theory of Universal Gravita¬ tion. Greatest equation of precession. . . . imrrncd This greatest equation ot precession is to , the nutation of 18", as 6*—to lab; that is, as ra¬ dius to the tangent of twice the obliquity of the eclip¬ tic. This gives the greatest equation of precession 16",8, not differing half a second from Bradley’s obser¬ vations. Thus have we attempted to give some account of this curious and important phenomenon. It is curious, be¬ cause it affects the whole celestial motions in a very in¬ tricate manner, and received no explanation from the more obvious application of mechanical principles, which so happily accounted for all the other appearances. It is one of the most illustrious proofs of Sir Isaac New¬ ton’s sagacity and penetration, which catched at a very remote analogy between this phenomenon and the li- bration of the moon’s orbit.—It is highly important to the progress of practical and useful astronomy, because it has enabled us to compute tables of such accuracy, that they can be used with confidence for determining the longitude of a ship at sea. This alone fixes its im¬ portance : but it is still more important to the philoso¬ pher, affording the most incontestable proof of the uni¬ versal and mutual gravitation of all matter to all mat¬ ter. It left nothing in the solar system unexplained from the theory of gravity but the acceleration of the moon’s mean motion j and this has at last been added to the list of our acquisitions by M. de la Place. Qjice toties animos veterum torsere Sophorum, Quceque scholasfrustra raaco certamine vexanl, Obvia conspicimus, nube pellente Mathesi. Ja?n dubios nulla caligine prcegravat error Qaeis superum penetrare domos, atque ardua cedi Scandere sublimis genii concessit acumen. Idee fas est propius mortali attingere divos. Halley. Sect. X. Of the Libration of the Moon. The only phenomena which still remain to be ex¬ plained are the libration of the moon and the motion of the nodes of her equator. The moon, in conse¬ quence of her rotation round her axis, is a little flat¬ tened towards the poles-, but the attraction of the earth must have lengthened the axis of the moon directed to¬ wards that planet. If the moon were homogeneous and fluid, she would assume the form of an ellipsoid, whose shorter axis would pass through her poles of ro¬ tation } the longer axis would be directed towards the earth, and in the plane of the moon’s equator j and the mean axis, situated in the same plane, would be per¬ pendicular to the two others. The excess of the longer over the shorter would be quadruple the excess of the mean axis over the shorter, and would amount to about—-—, the shorter axis being represented by 29711 It is easy to see, that if the longer axis of the moon Theom: deviate a little from the direction of the radius vector, Universs; which joins together the centres or the earth and moon, Gravita, the attraction of the earth will tend to bring it towards , tlon' that radius just as gravity tends to bring a pendu- ^ lum towards the vertical position. If the rotation of the satellite had been at first sufficiently rapid to over¬ come this tendency, the time of a rotation would not have been equal to that of a revolution round the earth, and their difference would have discovered to us suc¬ cessively all the points of the moon’s surface. But the angular motions of rotation and revolution having been at first but very little different, the force with which the longer axis separated from the radius vec¬ tor was not sufficient to overcome the tendency toward the radius vector occasioned by the attraction of the earth. This last tendency, therefore, has rendered the two motions rigidly equal. And, as a pendulum dri¬ ven from the vertical direction by a very small force constantly returns to it, making small oscillations on each side, in like manner the longer axis of the moon ought to oscillate on each side of the radius vector of her orbit. The libration of the moon then depends up¬ on the small difference which originally subsisted be¬ tween the angular motions of the moon’s rotation and • revolution. Thus we see, that the theory of gravitation explains the equality which subsists between the mean rotation and revolution of the moon. It is only necessary to suppose, that the original difference between them was small. In that case the attraction of the earth would soon reduce them to a state of equality. The singular coincidence of the nodes of the moon’s equator, with those of its orbit, is also owing to the attraction of the earth. This was first demonstrated by La Grange. The planes of the equator and of the orbit of the moon, and the plane which passes through its centre, parallel to the ecliptic, have always nearly the same intersection. The secular movements of the ecliptic neither alter the coincidence of the nodes of these three planes, nor their mean inclination, which the attraction of the earth keeps always the same. We have now examined all the phenomena of the heavenly bodies, and have found that they are all ex¬ plicable on the theory of gravitation, and indeed neces¬ sary consequences of that theory. The exact coinci¬ dence of all the phenomena must be considered as a complete demonstration of the truth of the theory ; and indeed places it beyond the reach of every possible ob¬ jection. With respect to the nature of this force call¬ ed gravitation, nothing whatever is known, nor is it likely that any thing ever will be known. The discus¬ sion being evidently above the reach of the human fa¬ culties, all the different theories which have been pub¬ lished, explaining it by ethers, &c. have only served to show the weakness of human reason, when it attempts to leave the plain path of experience, and indulge in fancy and conjecture. unity. APPENDIX. iiiendix. ASTRONOMY. )f Ci‘ ula- in^lslip- APPENDIX. In tlie preceding article xve have endeavoured to give as full a view as possible of astronomy j avoiding, at the same time, the introduction of minute details up¬ on those subjects which are not essential, that the read¬ ers attention might not be distracted and diverted from objects of primary importance. But for the sake of those persons who may wish to indulge their taste for practical astronomy, we have thought proper to subjoin an appen¬ dix ; in which we shall give, in the first place, the rules for calculating eclipses, and in the second, a description of the most important astronomical instruments. I. Method of Calculating Eclipses. The method of constructing tables for the calculation of eclipses will be understood from the following obser¬ vations. 'Ihe motions of the sun and moon are observed to be continually accelerated from the apogee to.the perigee, aud as gradually retarded from the perigee to the apo¬ gee ; being slowest of all when the mean anomaly is no- ! thing, and swiftest of all when it is six signs. When the luminary is in its apogee or perigee, its place is the same as it would be if its motion were equable in all parts of its orbit. The supposed equable ;| motions are called mean i the unequable are justly call¬ ed the true. Hie mean place of the sun or moon is always for¬ warder than the true place, whilst the luminary is mov¬ ing from its apogee to its perigee: and the true place is always forwarder than the mean, whilst the lu¬ minary is moving from its perigee to its apogee. In the former case, the anomaly is always less than six signs 5 and in the latter case, more. It has been found, by a long series of observations, | that the sun goes through the ecliptic, from the vernal equinox to the same equinox again, in 365 days 5 hours 48 minutes 55 seconds ; from the first star of Aries to the same star again, in 365 days 6 hours 9 minutes 24 seconds ; and from his apogee to the same again, in 365 days 6 hours 14 minutes o seconds. Ihe first of these is called the solar year ; the second the sidereal year; and the third the anomalistic year. So that the solar year is 20 minutes 29 seconds shorter I than the sidereal ; and the sidereal year is four minutes 36 seconds shorter than the anomalistic. Hence it ap- pears, that.the equinoctial point, or intersection of the I ecliptic and equator at the beginning of Aries, goes f backward with respect to the fixed stars, and that the l| sun’s apogee goes forward. It is also observed, that the moon goes through her I orbit from any given fixed star to the same star again, i 27 days 7 hours 43 minutes 4 seconds at a mean rate ; s from her apogee to her apogee again, in 27 days 13 hours 18 minutes 43 seconds; and from the sun to the sun again, in 29 days 12 hours 44 minutes 3XL- seconds. Ibis shows that the moon’s apogee moves forward in the ecliptic, and that at a much quicker rate than the !: sun’s apogee does: since the moon is 5 hours .55 mi¬ nutes 39 seconds longer in revolving from her apogee to her apogee again, than from any star to the same star again. The moon’s orbit crosses the ecliptic in two oimo- Vol. III. Part I. 11 4 site points, which are called her nodes: and it is ob¬ served, that she revolves sooner from any node to the node again, than from any star to the star again, by 2 hours 38 minutes 22 seconds; which shows that her nodes move backward, or contrary to the order of signs in the ecliptic. The time in which the moon revolves from the sun to the sun again (or from change to change) is called a lunation; which, according to X)r Pound’s mean measures, would always consist of 29 days 12 hours 44 minutes 3 seconds 2 thirds 38 fourths, if the mo¬ tions of the sun and moon were always equable. Hence 12 mean lunations contain 354 days 8 hours 48 mi¬ nutes 36 seconds 35 thirds 40 fourths, which is 10 days 21 hours 11 minutes 23 seconds 24 thirds 20 fourths less than the length of a common Julian year, consist- ing of 363 days 6 hours ; and 13 mean lunations con- tain 383 days 21 hours 32 minutes 39 seconds 38 thirds 38 fourths, which exceeds the length of a com¬ mon Julian year, by 18 days 13 hours 32 minutes 39 seconds 38 thirds 38 fourths. . The mean time of a new moon being found for any given year and month, as suppose for March 1700 old style, if this mean new moon falls later than the nth day of March, then 12 mean lunations added to the time of tins mean new moon will give the time of the mean newr moon in March 1701, after having thrown 011363 days. But when the mean new moon happens to be. before the nth of March, we must add 13 mean lunations, in order to have the time of mean new moon in March the year following; always taking care to subtract 363 days in common years, and 366 days in leap years, from the sum of this addition. I bus, A. I). 1700, old style, the time of mean new moon in March was the 8th day, at 16 hours 11 minutes 23 seconds after the noon of that day (viz. at 11 minutes 23 seconds past four in the morning of the 9th day), according to common reckoning. To this wre must add 13 mean lunations, or 383 days 21 hours 32 minutes 39 seconds 38 thirds 38 fourths, and the sum will be 392 days 13 hours 44 minutes 4 seconds 38 thirds 38 fourths : from which subtract 363 days, because the year 1701 is a common year, and there will remain 27 days 13 hours 44 minutes 4 seconds 38 thirds 38 fourths for the time of mean new moon in March, A. D. 1701. Carrying on this addition and subtraction till A. D. I73>3> we bnd the time of mean new moon in March that year.to be on the 6th day, at 7 hours 21 minutes, 1 7 seconds 49 thirds 46 fourths past noon ; to which add 13 mean lunations, and the sum will be 390 days 4 hours 33 minutes 37 seconds 28 thirds 20 fourths ; from which subtract 366 days, because the year 1704 is a leap-year, and there will remain 24 days 4 hours 33 minutes 37 seconds 28 thirds 20 fourths, for the time of mean new moon in March A. X). 1704. In this manner w'as the first of the following tables constructed to seconds, thirds, and fourths; and then wrote out to the nearest seconds. The reason why we chose to begin the year with March, was to avoid - the inconvenience of adding a day to the tabular time in leap-years after February, or subtracting a day there- from 154 ASTRO Of Calcula- from in January and February in those years ; to which ting h'clipfc all tables of this kind are subject, which begin the year »es,&c. wJth January, in calculating the times of new or full v moons. The mean anomalies of the sun and moon, and the sun’s mean motion from the ascending node of the moon’s orbit, are set down in Table III. from I to 13 mean lunations. These numbers, for 13 lunations, be¬ ing added to the radical anomalies of the sun and moon, and to the sun’s mean distance from the ascend¬ ing node, at the time of mean new moon in March 1700 (Table I.) will give their mean anomalies, and the sun’s mean distance from the node, at the time of mean new moon in March 1701 J and being added for 12 lunations to those for 1701, give them for the time of mean new moon in March 1702. And so on as far as you please to continue the table (which is here car¬ ried on to the year 1800), always throwing off 12 signs when their sum exceeds 12, and setting down the remainder as the proper quantity. If the number belonging to A. D. 17CO (in Table I.) be subtracted from those belonging to 1800, we shall have their whole differences in 100 complete Julian years •, which accordingly we find to be 4 days 8 hours 10 minutes 52 seconds 15 thirds 40 fourths, with re¬ spect to the time of mean new moon. These being ad¬ ded together 60 times (always taking care to throw off a whole lunation when the days exceed 29^) make up 60 centuries or 6000 years, as in Table VI. which was carried on to seconds, thirds, and fourths : and then wrote out to the nearest seconds. In the same manner were the respective anomalies and the sun’s distance from the node found, for these centurial years j and then (for want of room) wrote out only to the nearest minutes, which is sufficient in whole centuries. By means of these two tables, we may find the time of any mean new moon in March, together with the ano¬ malies of the sun and moon, and the sun’s distance from the node at these times, within the limits of 6000 years either before or after any given year in the 18th cen¬ tury ; and the mean time of any new or full moon in any given month after March, by means of the third and fourth tables, within the same limits, as shown in the precepts for calculation. Thus it would be a very easy matter to calculate the time of any new or full moon, if the sun and moon moved equably in all parts of their orbits. But we have already shown, that their places are never the same as they would be by equable motions, except when they are in apogee or perigee ; which is when their mean anomalies are either nothing or six signs : and that their mean places are always forwarder than their true places, whilst the anomaly is less than six signs ; and their true places are forwarder than the mean, whilst the anomaly is more. Hence it is evident, that whilst the sun’s anomaly is less than six signs, the muon will overtake him, or be opposite to him, sooner than she could if his motion were equable j and later whilst his anomaly is more than six signs. The greatest difference that can pos¬ sibly happen between the mean and true time of new or full moon, on account of the inequality of the sun’s motion, is 3 hours 48 minutes 28 seconds : and that is, when the sun’s anomaly is either 3 signs 1 degree, or 8 signs 29 degrees ; sooner in the first case, and later in the last.—In all other signs and degrees of N O M Y. Appent anomaly, the difference is gradually less, and vanishes of Cal when the anomaly is either nothing or six signs. ting E The sun is in his apogee on the 3Cth of June, and in ses’ ^ his perigee on the 30th of December, in the present age : so that he is nearer the earth in our winter than in our summer.—The proportional difference of di¬ stance, deduced from the difference of the sun’s appa¬ rent diameter at these times, is as 983 to 1017. The moon’s orbit is dilated in winter, and contract¬ ed in summer j therefore the lunations are longer in winter than in summer. The greatest difterence is found to be 22 minutes 29 seconds j the lunations in¬ creasing gradually in length whilst the sun is moving from his apogee to his perigee, and decreasing in length whilst he is moving from his perigee to his apogee.—On this account the moon will be later every time in co¬ ming to her conjunction with the sun, or being in op¬ position to him, from December till June, and sooner from June till December, than if her orbit had conti¬ nued of the same size all the year round. As both these differences depend on the sun’s ano¬ maly, they may be fitly put together into one table, and called The annual or first equation of the mean to the true sy%igy, (See Table VII.). This equational dif¬ ference is to be subtracted from the time of the mean syzigy when the sun’s anomaly is less than six signs, and added when the anomaly is more.—At the greatest it is 4 hours 10 minutes 57 seconds, viz. 3 hours 48 minutes 28 seconds, on account of the sun’s unequal motion, and 22 minutes 29 seconds, on account of the dilatation of the moon’s orbit. This compound equation would be sufficient for re¬ ducing the mean time of new or full moon to the true time thereof, if the moon's orbit were of a circular form, and her motion quite equable in it. But the moon’s orbit is more elliptical than the sun’s, and her motion in it is so much the more unequal. The diffe¬ rence is so great, that she is sometimes in conjunction with the sun, or in opposition to him, sooner by 9 hours 47 minutes 54 seconds, than she would be if her mo¬ tion were equable j and at other times as much later. The former happens when her mean anomaly is 9 signs 4 degrees, and the latter when it is 2 signs 26 de¬ grees. See Table IX. At difl’erent distances of the sun from the moon’s apogee, the figure of the moon’s orbit becomes diffe¬ rent. It is longest of all, or most eccentric, when the sun is in the same sign and degree either with the moon’s apogee or perigee j shortest of all, or least eccentric, when the sun’s distance from the moon’s apogee is ei¬ ther three signs or nine signs ; and at a mean state when the distance is either 1 sign 15 degrees, 4 signs 15 degrees, 7 signs 15 degrees, or 10 signs 15 degrees. When the moon’s orbit is at its greatest eccentricity, her apogeal distance from the earth’s centre is to her perigeal distance therefrom, as 1067 ’s 933 5 wlien least eccentric, as 1043 is to 957 ; and when at the mean state, as 1055 is to 943. But the sun’s distance from the moon’s apogee is equal to the quantity of the moon’s mean anomaly at the time of new moon, and by the addition of 6 signs it becomes equal in quantity to the moon’s mean ano¬ maly at the time of full moon. Therefore, a table may be constructed so as to answer to all the various inequalities depending on the different eccentricities of the moon’s orbit, in the syzigies, and called The se¬ cond t es. ippendk. A S ]cu,{u cond equation of the mean to the true syxigy. t / Eclip- ble lA.) : and the moon’s anomaly, when equated by s, Sec. Table VIII. may be made the proper argument for taking out this second equation of time ; which must be added to the former equated time, when the moon’s anomaly is less than six signs, and subtracted when the anomaly is more. There are several other inequalities in the moon’s motion, which sometimes bring on the true syzigy a little sooner, and at other times keep it back a little later, than it would otherwise be; but they are so small, that they may be all omitted except two; the former of which (see Table X.) depends on the difference be¬ tween the anomalies of the sun and moon in the syzi- gies, and the latter (see Table XL) depends on the sun’s distance from the moon’s nodes at these times. The greatest difference arising from the former is 4 minutes 58 seconds $ and from the latter, I minute 34 seconds. The tables here inserted being calculated by Mr Ferguson according to the methods already given, he gives the following directions for their use. To calculate the True Time of New or Full Moon, I Actions PRECEPT I. If the required time be within the li- \ ;he use mits of the 18th century, write out the mean time of P hose new moon in March, for the proposed year, from Table I. in the old style, or from Table II. in the new $ to¬ gether with the mean anomalies of the sun and moon, and the sun’s mean distance from the moon’s ascending node. If you want the time of full moon in March, add the half lunation at the foot of Table III. with its anomalies, &c. to the former numbers, if the new moon falls before the 15th of March; but if it falls af¬ ter, subtract the half lunation, with the anomalies, &c. belonging to it, from the former numbers, and write down the respective sums or remainders. II. In these additions or subtractions, observe, that 60 seconds make a minute, 60 minutes make a degree, 30 degrees make a sign, and 12 signs make a circle. When you exceed 12 signs in addition, reject 12, and set down the remainder. When the number of signs to be subtracted is greater than the number you sub¬ tract from, add 12 signs to the lesser number, and then you will have a remainder to set down. In the tables signs are marked thus8, degrees thus0, minutes thus', and seconds thus". III. When the required new or full moon is in any given month after March, write out as many lunations with their anomalies, and the sun’s distance from the node from Table III. as the given month is after March, setting them in order below the number taken out for March. IV. Add all these together, and they will give the mean time of the required new or full moon, with the mean anomalies and sun’s mean distance from the ascending node, which are the arguments for finding the proper equations. "V. With the number of days added together, enter Table IV. under the given month ; and against that number you have the day of mean new or full moon in the left-hand column, which set before the hours, minutes, and seconds, already found. But (as it will sometimes happen) if the said num¬ ber of days fall short of any in the column under the given month, add one lunation and its anomalies, &c. (from Table III.) to the foresaid sums, and then you T R O N O M Y. '' 155 (SeeTa- will have a new sum of days wherewith to enter of Calcula- under the given month, where you are sure ting t'.ciip. Table IV. to find it the second time, if the first falls short. VI. W7ith the signs and degrees of the sun’s ano¬ maly, enter Table VII. and therewith take out the annual or first equation for reducing the mean syzigy to the true $ taking care to make proportions in the table for the odd minutes and seconds of anomaly, as the table gives the equation only to whole degrees. Observe, in this and every other case of finding equa¬ tions, that if the signs are at the head of the table, their degrees are at the left hand, and are reckoned downwards 5 but if the signs are at the foot of the table, their degrees are at the right hand, and are counted upward j the equation being in the body of the table, under or over the signs, in a collateral line with the degrees. The titles Add or Subtract at the head or foot of the tables where the signs are found, show whe¬ ther the equation is to be added to the mean time of new or full moon, or to be subtracted from it. In this table, the equation is to be subtracted, if the signs of the sun’s anomaly are found at the head of the table ; but it is to be added, if the signs are at the foot. VII. With the signs and degrees of the sun’s mean anomaly, enter Table VIII. and take out the equation of the moon’s mean anomaly $ subtract this equation from her mean anomaly, if the signs of the sun’s anoma¬ ly be at the head of the table, but add it if they are at the foot ; the result will be the moon’s equated ano¬ maly, with which enter Table IX. and take out the second equation for reducing the mean to the true time of new or full moon j adding this equation, if the signs of the moon’s anomaly are at the head of the table, but subtracting it if they are at the foot $ and the re¬ sult will give you the mean time of the required new or full moon twice equated, which will be sufficiently near for common almanacs.—But when you want to calculate an eclipse, the following equations must be used : thus, VIII. Subtract the moon’s equated anomaly from the sun’s mean anomaly, and with the remainder in signs and degrees enter Table X. and take out the third equation, applying it to the former equated time, as the titles Add or Subtract do direct. IX. With the sun’s mean distance from the ascend¬ ing node enter Table XI. and take out the equation answering to that argument, adding it to, or subtract¬ ing it from, the former equated time, as the titles di¬ rect, and the result will give the time of new or full moon, agreeing with well regulated clocks or watches very near the truth. But to make it agree with the solar or apparent time, you must apply the equation of natural days, taken from an equation-table, as it is leap-year, or the first, second, or third after. This, however, unless in very nice calculations, needs not be regarded, as the difference between true and apparent time is never very considerable. The method of calculating the time of any new or full moon without the limits of the 18th century will be shown further on. Anti a few examples compared with the precepts will make the whole work plain. N. B. The tables begin the day at noon, and reckon forward from thence to the noon following.—-Thus, March the 31st, at 22 h. 30 m. 25 sec. of tabular time is April 1st (in common reckoning) at 30 m. 25 sec. after 10 o’clock in the morning. U 2 ses, 6ce. EXAMPLE 156 Of Calcnlar ting Eclip¬ ses, &c. ASTRONOMY. EXAMPLE I. Required the true'time of New Moon in April 1764, New Style ? Appendix .by the tTecepts. March 1764, Add x Lunation, Mean New Moon, First Equation, Time once equated, Second Equation, Time twice equated, Third Equation, Time thrice equated, Fourth Equation, True New Moon, Equation of days, Apparent time. JSew Moon. D. H. M. S. 2 8 55 36 29 12 44 3 31 21 39 39 + 4 10 40 32 1 50 19 — 3 24 49 31 22 25p + 4 37 31 22 30 7 -f- 18 31 22 30 25 ~ 3 48 31 22 26 37 Sun’s Anomaly, 8 2 2C O o 29 6 19 9 1 26 19 11 10 59 18 9 20 27 1 Are;. 3d equation. Moon’s Anomaly. a O IV io 13 35 21 o 25 49 o 11 + 9 24 21 1 34 57 11 10 59 18 Arg. 2d equation. Sun from Node. II 4 54 48 i o 40 14 5 35 Sun from Node, and Arg. 4th e- quation. So the true time is 22 h. 30 min. 25 sec. after the noon of the 31st March ; that is, April 1st, at 30 min. 25 sec. after ten in the morning. But the apparent time is 26 min. 37 sec. after ten in the morning. EXAMPLE II. Qu. The true time of Full Moon in May 1762, New Style ? by the brecepts. March 1762, Add 2 lunations, New Moon, May, Subt. Lunation, Full Moon, May, First Equation, Time once equated, Second Equation, Time twice equated, Third Equation, Time thrice equated, Fourth Equation, The Full Moon, New Moon. D. H. M. S. 24 15 18 24 59 1 28 6 22 16 46 30 14 18 22 2 7 22 24 28 + 3 36 8 1 41 4 — 9 47 53. 7 15 53 11 — 2 36 7 15 50 35 ~r 15 71550 50 Sun’s Anomaly. Moon’s Anomaly. 8 23 48 16 I 28 12 39 I 23 59 II I 21 38 I 10 22 O 55 o 14 33 IQ IO 7 27 45 3 57 18 1 3 30 27 Arg. 3d equation. 3 15 37 12 6 12 54 30 9 2 42 42 + I 14 36 9 3 57 .18 Arg. 2d equation. Sun from Node. IO 18 49 14 2 I 20 28 O 20 0 15 9 42 20 7 4 49 35 Sun from Node, and Arg. 4th e- q nation. Ans. May 7th at 15 h. 50 min. 50 sec. past noon, viz. May 8th at 3 h. 50 sec. in the morning. Of Calculi! ting tlclip, scs, &Ci P lies, &e. belonging to the said centuries, and set them below those taken out for March in the 18th century. III. Subtract the numbers belonging to these centu¬ ries from those of the 18th century, and the remainders will be the mean time and anomalies, &c. of new moon To calculate the time of New and Fidl Moon in a o-iven year and month of any particular century bet ween the Christian era and the 1 %th century. Precept I. Find a year of the same number in the 18th century with that of the year in the century pro- in March, in the given year of the'cen7u~ry"proposed"— posed, and take out the mean time of new moon in Then, work in all respects for the true time of new or March, old style, for that year, with the mean ano- ■ malies and sun’s mean distance from the node at that time, as already taught. II. Take as many complete centuries of years from Table VI. as, when subtracted from the above-said year in the 18th century, rvill answer to the given year j and take out the first mean new moon and its anoma- 2 / ~ Clue liiuc; Ul UCYT VL lull moon, as shown in the above precepts and examples. IV • If the days annexed to these centuries exceed the number of days from the beginning of March taken out in the 18th century, add a lunation and its anomalies, &c. from I able III. to the time and anomalies of new moon in March, and then proceed in all respects as above. I his circumstance happens in Example V. EXAMPLE Wpendix. f ( cula- iglcHp- S'gS-.-.C. ASTRONOMY. EXAMPLE III. Required the trice time of Full Moon in April, Old Style, A. D. 30 ? From 1730 substract 1700 (or 17 centuries) and there remains 30. 157 Of Calcula¬ ting Eclip¬ ses, &c. By the Precepts. March 1730, Add ^ Lunation. Full Moon, 1700 years suhtr. Full 5 March A. D. 30. Add 1 Lunation, Full Moon, April First Equation, Time once equated, Second Equation, Time twice equated, Third Equation, Time thrice equated, Fourth Equation, True Full Moon, April, New Moon. D. H. M. 7 12 34 l6 14 l8 22 2 22 6 56 l8 14 17 36 42 7 13 19 36 29 12 44 3 6 2 3 39 -f- 3 28 4 6 5 31 43 *f 2 57 48 6 8 29 31 — 2 54 8 26 37 - 1 33 8 25 4 Sun’s Anomaly. 8 18 4 31 o 14 33 10 9 2 37 41 I X 28 46 o 9 3 51 4i o 29 6 19 10 2 58 o 5 10 58 4° Moon’s Anomaly. 9 o 32 17 6 12 54 30 3 13 26 47 10 29 36 o 4 J3 5° 47 o 25 49 o 5 + 9 39 47 1 18 53 4 21 59 20 Arg. 3d equation. 4 10 58 _ 40 Arg. 2d equation. Sun from Node. I 23 17 l6 O 15 20 7 2 8 37 23 4 29 23 O 9 I4 23 o 40 14 10 9 54 37 Sun from Node, and Arg. fourth equation. Hence it appears, that the true time of Full Moon in April A. D. 30, old style, was on the 6th day, at 25 no, 4 s. past eight in the evening. To Calculate the true time of New or Full Moon in any given year and month before the Christian era. Precept I. Find a year in the 18th century, which being added to the given number of years before Christ diminished by one, shall make a number of complete centuries. II. Find this number of centuries in Table VI. and subtract the time and anomalies belonging to it from those of the mean new moon in March, the above found year of the 18th century ; and the remainder will de¬ note the time and anomalies, &c. of mean new moon in March, the given year before Christ.—Then, for the true time thereof in any month of that year, proceed as above taught. EXAMPLE IV. Required the true time of New Moon in May, Old Style, the year before Christ 385 ? The years 584 added to 1716, make 2300, or 23 centuries. By the Precepts. March 1716, 2300 years subtract, March before Christ 585, Add 3 Lunations, May before Christ 585, First Equation, Time once equated, Second equation, Time twice equated, Third Equation, Time thrice equated, Fourth equation. True New Moon, New Moon, D. II. M. S. II 17 33 29 11 5 57 53 0 n 35 36 88 14 12 9 28 1 47 45 — 1 37 28 + 1 46 2 15 28 4 + 28 2 18 + 12 28 3° Sun’s Anomaly. 8 22 50 39 ii 19 47 o 9 3 3 39 2 27 18 58 o o 22 37 5 15 41 11 6 14 41 20 Arg. 3d. equation. Moon’s Anomaly. 4 I4 5 59 2 28 15 2 2 17 27 1 5 *5 42 3 — 46 5 J9 41 f7 Arg. 2d equation. Sun from Node. 4 27 17 5 7 25 27 o 1 50 5 2042 2 3 5° 47 Sun from Node, and Arg. fourth equation. So the true time was May 28th, at 2 minutes 30 seconds past four in the afternoon. These Tables are calculated for the meridian of Lo- don ; but they will serve for any other place, by sub¬ tracting four minutes from the tabular time, for every degree that the meridian of the given place is westward of London, or adding four minutes for every degree that the meridian of the given place is eastward : as in EXAMPLE 153 Of Calcula¬ ting Eclip¬ ses, See. ASTRONOMY. EXAMPLE V. Required the true time of Full Moon at Alexandria in Egypt in September, Old Style, the year before Christ The years 200 added to 1800, make 2000 or 20 centuries. By the Precepts March 1800, Add 1 Lunation, From the sum, Subtract 2000 years, N. M. bef. Chr. 201, .11^6 Lunations, t \ half Lunations, Full moon, September, First Equation, Time once equated, Second Equation, Time twice equated, Third Equation, Time thrice equated, Fourth Equation, True time at London, Add for Alexandria, True time there, xNew Moon. D. H. M. S. 13 o 22 17 29 12 44 3 42 13 6 20 27 18 9 19 44 18 57 1 177 4 24 18 14 18 22 2 22 17 43 21 — 3 52 6 22 13 51 15 — 8 25 4 22 5 26 11 - 58 22 5 25 13 — 12 22 5 25 1 2 1 27 22 7 26 28 Sun’s Anomaly. 8 23 I9 55 o 29 6 19 9 22 26 14 o 8 50 o o 13 36 14 5 24 37 56 o 14 33 10 3 22 47 20 10 4 19 55 5 18 27 25 Arg. 3d equation. Moon’s Anomal). IO 7 52 36 0 25 48 o II 3 41 36 o 15 42 o 10 17 59 36 5 4 54 3 6 12 54 30 10 5 48 9 — 1 28 14 10 4 19 55 Arg. 2d equation. Sun from Node. II 3 58 24 i o 40 14 o 4 38 38 6 27 45 o 5 6 53 38 6 4 1 24 o 15 20 7 11 26 15 9 Sun from Node, and Argument 4th equation. Thus it appears, that the true time of Full Moon, at Alexandria, in September, old style, the year before Christ 201, was the 22d day, at 26 minutes 28 seconds after seven in the evening. EXAMPLE VI. Required the true time of Full Moon at Babylon in October, Old Style, the year 4008 before the first year of Christ, or 4007 before the year of his birth? The years 4007 added to 1793, make 5800, or 58 centuries. By the Precepts. March 1793, Subtract 5800 years, N. M. bef. Chr. 4007, 4 jj y? Lunations, \ half Lunations, Full Moon, October, First Equation, Time once equated, Second Equation, Time twice equated, Third Equation, Time thrice equated, Fourth Equation, Full Moon at London, Add for Babylon, True time there, New Moon. D. H. M. S. 30 9 J3 55 15 12 38 7 14 20 35 48 206 17 8 21 14 18 22 2 22 8 6 11 — 13 26 22 7 52 45 + 8 29 21 22 16 22 4 6 10 22 16 J7 56 — 51 Sun’s Anomaly. 9 10 16 10 21 35 11 o 10 18 41 11 6 23 44 15 o 14 33 10 5 26 58 36 1 26 27 26 4 o 31 10 Arg. 3d equation. Moon’s Anomaly. 8 7 37 58 6 24 43 o 1 12 54 58 6 0 43 3 6 12 54 30 1 26 32 31 — 5 5 1 26 27 26 Arg. 2d equation. bun from Node. 7 6 18 26 9 13 1 o 9 23 17 26 7 4 41 38 o 15 20 7 5 r3 J9 11 Sun from Node, and Argument 4th equation. 22 16 17 5 2 25 41 22 18 42 46 So that, on the meridian of London, the true time was October 23d, at 17 minutes 5 seconds past four in the morning j but at Babylon, the true time was October 23d, at 42 minutes 46 seconds past six in the morning.—This is supposed by some to have been the year of the creation. To mmmmm ^)pendix. ASTRONOMY. tiniEclip- Ib, &C. ' •( alcula- To calculate the true time of New or Full Moon in any given year and month after the I ^ih century. Precept I. Find a year of the same number in the 18th century with that of the year proposed, and take out the mean time and anomalies, &c. of new moon in March, old style, for that year, in Table I. II. Take so many years from Table VI. as when added to the above-mentioned year in the 18th century 159 will answer to the given year in which the new or full Qf Calcula. moon is required j and take out the first new moon, ting Edip. with its anomalies for these complete centuries. ses> III. Add all these together, and then work in all respects as above shown, only remember to subtract a lunation and its anomalies, when the above-said addition carries the new moon beyond the 31st of March ; as in the following example. EXAMPLE VII. Required the true time of New Moon in July, Old Style, A. D. 2180 ? Four centuries or (400 years) added to A. D. 1780, make 2100. By the Precepts. March 1780, Add 400 years, From the sum Subtract 1 Lunation New Moon March 2180, Add 4 Lunations, New Moon July 2180, First Equation, Time one equated, Second Equation, Time twice equated, Third Equation, Time thrice equated, Fourth Equation, True time, July, New Moon. D. H. M. S. 23 23 17 8 1 34 43 29 41 7 29 12 45 l3 44 3 11 19 118 2 1 10 56 12 21 1 57 22 3 39 7 20 + 9 53 43 24 8 8 6 + J7 51 3 56 8 6 + 21 47 1 8 8 6 22 55 Sun’s Anomaly. 9 4 18 *3 o 13 24 o 9 17 42 13 o 29 6 19 8 18 35 54 3 26 25 17 o 15 1 11 3 9 38 37 10 5 22 34 Arg. 3d equation. Moon’s Anomaly. 1 21 7 47 IO I 28 C 11 22 35 47 o 25 49 O IO 26 46 47 3 13 i6 2 10 2 49 24 12 2 9 38 .37 Arg. 2d equation. Sun from Node. IO 18 21 I 6 17 49 O 6 10 o 40 14 4 5 29 47 4 2 4° 56 8 8 16 43 Sun fromNode and Argument fourth equation. True time, July 8th, at 22 minutes 55 seconds past six in the evening. In keeping by the old style, we are always sure to be right, by adding or subtracting whole hundreds of years to or from any given year in the 18th century. But in the new style we may be very apt to make mis¬ takes, on account of the leap year’s not coming in re¬ gularly every fourth year : and therefore, when we go without the limits of the 18th century, we had be*t keep to the old style, and at the end of the calculation reduce the time to the new. Thus, in the 2id century there will be fourteen days ddlerence between the styles ; and therefore the true time of new moon in this last example being reduced to the new style will be the 22d of July, at 22 minutes 55 seconds past six in the evening. To calculate the true place of the Sun for any given mo* ment of time. Precept I. In 1 able XII. find the next lesser year in number to that in which the sun’s place is sought, and write out his mean longitude and anomaly an¬ swering thereto : to which add his mean motion and anomaly for the complete residue of years, months, days, hours, minutes, and seconds, down to the given time, and this will be the sun’s mean place and ano¬ maly at that time, in the old style, provided the said time be in any year after the Christian era. See the first following example. II. Enter Table XIII. with the sun’s mean anoma¬ ly, and making proportions for the odd minutes and se¬ conds thereof, take out the equation of the sun’s centre: which, being applied to his mean place as the title Add or Subtract directs, will give his true place or longitude from the vernal equinox, at the time for which it was required. III. To calculate the sun’s place for any time in a given year before the Christian era, take out his mean longitude and anomaly for the first year thereof, and from these numbers subtract the mean motions and ano¬ malies for the complete hundreds or thousands next above the given year; and to the remainders, add those for the residue of years, months, &c. and then work in all respects as above. See the second example following. EXAMPLE, ASTRONOMY. 160 Appenu Calcula¬ ting Eclip¬ ses, See. EXAMPLE I. Of Ci) lip Required the Sun's true place, March 10th, Old Style, 1764, at 22 hours 30 minutes 25 seconds past Noon ? In common reckoning, March 21 st, at 10 hours 30 minutes in the Forenoon. ses, To the radical year after Christ Add complete years { 1701 60 3 March Bissextile Days Honrs Minutes Seconds 20 22 30 25 Sun’s mean place at the given time Equation of the Sun’s centre, add Sun’s true place at the same time Sun’s Longitude. 9 o 11 1 20 43 o 50 29 28 27 12 17 O 9 II 20 41 55 54 J3 1 14 o 10 14 36 1 55 3^ Sun’s Anomaly. 6 13 1 11 29 26 11 29 14 I 28 Q C o o o 20 41 55 54 13 1 14 1 9 1 27 23 Mean Anomaly. o 12 10 12 or 'Y1 12 10 12 4 EXAMPLE II. Required the Sun's true place, Oct. 23c?, Old Style, at 16 hours 57 minutes past Noon, in the 4008^ year before the year of Christ 1; which was the 4007^ before the year of his birth, and the year of the Julian period 706. By the Precepts. From the radical numbers after Christ Subtract those for 5000 complete years Bemains for a new radix To which add, to bring it to < the given time complete years {900 80 , T 2 October Days 23 Hours 16 Minutes 57 Sun’s mean place at the given time Equation of the Sun’s centre subtract Sun’s true place at the same time Sun’s Longitude. s o 7 53 10 7 46 40 6 48 3° o 36 16 8 29 26 54 22 40 12 39 26 2 20 Sun’s Anomaly. 6 28 48 10 13 25 8 11 11 11 J5 23 21 37 29 J5 29 53 8 29 4 22 40 12 39 26 2 20 5 28 33 58 Sun’s Anomaly. o or =0= o So that in the meridian of London, the sun was then just entering the sign ^ Libra, and consequently was upon the point of the autumnal equinox. If to the above time of the autumnal equinox at London, we add 2 h. 25 m. 41 sec. for the longitude of Babylon, we shall have for the time of the same equinox, at that place, October 23d, at 19 h. 22 m. 41 sec. ; which, in the common way of reckoning, is October 24th, at 22 m. 41 sec. past seven in the morn- the day of full moon.—The dominical letter for that year was G, and consequently the 24th of October was on a Wednesday. To find the Sun's distance from the Moon's ascending node, at the time of any given new or full moon : and consequently, to know whether there is an eclipse at that time or not. mg And it appears by Example VI. that in the same year the true time of full moon at Babylon was Octo¬ ber 23d, at 42 m. 46 sec. after six in the morning ; so that the autumnal equinox was on the day next after The sun’s distance from the moon’s ascending node is the argument for finding the moon’s fourth equation in the syzigies; and, therefore, it is taken into all the foregoing examples in finding the times thereof. Thus, at the time of mean new moon in April 1764, the sun’s mean t: ippendix. A S T R ^‘OCalcula-meiin distance from the ascending node is o* 50 35' 2". "St* Eclip- See Example I. , ^ s, Sec. The clescending node is opposite to the ascending one, (.-y—and they are just six signs distant from each other. When the sun is within 17 degrees of either of the nodes at the time of new moon, he will be eclipsed at that time ; and when he is within 12 degrees of either of the nodes at the time of full moon, the moon will be then eclipsed. Thus we find, that there will be an e- clipse of the sun at the time of new moon in April 1764. But the true time of that new moon comes out by the equations to be 50 minutes 46 seconds later than the mean time thereof, by comparing these times in the above example : and therefore we must add the sun’s motion from the node during that interval to the above mean distance os 5® 35' 2", which motion is found in Table XII. for 50 minutes 46 seconds, to be 2' 12". And to this we must apply the equation of the sun’s mean distance from the node in Table XV. found by the sun’s anomaly, which, at the mean time of new moon in Example I. is 9s i° 26' 19" 5 and then we shall have the sun’s true distance from the node, at the true time of new moon, as follows: O N O M Y. 161 Sun from Node. At the mean time of new moon in April 1764 Sun’s motion from the T 50 minutes node for (_ 46 seconds } s 35 2 10 2 Sun’s mean distance from node at true new moon ^ Equation of mean distance from! node, add J } ° 37 5 Sun’s true distance from the ascend-1 ing node ^ 0 7 42 I4 Which being far within the above limit of 17 degrees, shows that the sun must then be eclipsed. And now we shall show how to project this, or any other eclipse, either of the sun or moon. To project an Eclipse of the Sun. In order to this, we must find the 10 following ele¬ ments by means of the tables. 1. The true time of conjunction of the sun and moon ; and at that time, 2. The semidiameter of the earth’s disk, as seen from the moon, which is equal to the moon’s horizontal parallax. 3. The sun’s distance from the solstitial colure to which he is then nearest. 4. The sun’s declination. 3. The angle of the moon’s visible path with the ecliptic. 6. The moon’s latitude. 7. The moon’s true horary motion from the sun. 8. The sun’s semidiameter. 9. The moon’s. 10. The semidiameter of the penumbra. We shall now proceed to find these elements for the sun’s eclipse in April 1764. 20 find the true time of new moon. This, by Ex¬ ample I. is found to be on the first day of the said month, at 30 minutes 25 seconds after ten in the morn¬ ing. 2. To find the moon's horizontal parallax, or semi dia¬ meter of the earth's dish, as seen from the moon. Enter Table X\ II. with the signs and degrees of the moon’s Vol. III. Part I. f anomaly (making proportions, because the anomaly is Of Calcula- in the table only to every 6th degree), and thereby ting Eclip- take out the moon’s horizontal parallax j which for the, ses> _ above time, answering to the anomaly 11s 90 24' 2l", v is 54' 43". 3. To find the sun's distance from the nearest solstice, viz. the beginning of Cancer, which is 3s or go° from the beginning of Aries. It appears by Example I. (where the sun’s place is calculated to the above time of new moon), that the sun’s longitude from the beginning of Aries is then os 120 10' 12" : that is, the sun’s place at that time is qp Aries, 120 10' 12". Therefore from - " 3 0 Subtract the sun’s longitude or place o 12 O 10 o 12 Remains the sun’s distance from 7 0 the solstice C5 j 2 17 49 48 Or 770 49' 48" $ each sign containing 30 degrees. 4. To find the sun's declination. Enter Table XIV. with the signs and degrees of the sun’s true place, viz. 0s 120, and making proportions for the io' 12", take out the sun’s declination answering to his true place, and it will be found to be 40 49’ north. 5. To find the moon's latitude. This depends on her distance from her ascending node, which is the same as the sun’s distance from it at the time of new moon j and is thereby found in Table XVI. But we have already found that the sun’s equated distance from the ascending node, at the time of new moon in April 1764, is os 7® 42' 14". See above. Therefore, enter Table XVI. with o signs at the top, and 7 and 8 degrees at the left hand, and take out 36' and 39", the latitude for 70; and 41' 51", the lati¬ tude for 8°: and by making proportions between these latitudes for the 42' 14", by which the moon’s distance from the node exceeds 7 degrees, her true latitude will be found to be 40' iS" north ascending. 6. To find the moon's true horary motionfrom the sun. With the moon’s anomaly, viz. IIs 90 24’ 21", enter Table XVII. and take out the moon’s horary motion 4 which, by making proportions in that Table, will be found to be 30' 22w. Then, with the sun’s anomaly, 9s i° 26' 19", take out his horary motion 2' 28" from the same table j and subtracting the latter from the former, there will remain 27' 54" for the moon’s true horary motion from the sun. 7. To find the angle of the moon's visible path with the ecliptic. This, in the projection of eclipses, may be always rated at 50 35', without any sensible error. 8. 9. To find the semidiameters of the sun and moon. These are found in the same table, and by the same ar¬ guments, as their horary motions. In the present case, the sun’s anomaly gives his semidiameter 16' 6", and the moon’s anomaly gives her semidiameter 14' 57"* 10. To find the semidiameter of the penumbra. Add the moon’s semidiameter to the sun’s, and their sum will be the semidiameter of the penumbra, viz. 31’ S"- Now collect these elements, that they may be found the more readily when they are wanted in the construc¬ tion of this eclipse. X 1. True 162 A S T R Ol Calcula¬ ting i;dp- «es, &c. I. True time of new moon in April 1764 - - 1 10 30 25 2. Semidiameter of the earth’s disk 3. Sun’s distance from the nearest solst. 4. Sun’s declination, north 5. Moon’s latitude, north ascending 6. Moon’s horary motion from the sun 7. Angle of the moon’s visible path 1 with the ecliptic j 8. Sun’s semidiameter 9. Moon’s semidiameter 3 0. Semidiameter of the penumbra O 54 53 77 49 48 4 49 0 o 40 18 o 27 54 5 35 0 16 6 , H 57 31 3 To project ati Eclipse of the Sun geometrically. i'jg. i^S. a. Make a scale of any convenient length, as AC, and divide it into as many equal parts as the earth’s semi¬ disk contains minutes of a degree ; which, at the time of the eclipse in April 1764, is 54' 53". Then, with the whole length of the scale as a radius, describe the semicircle AMB upon the centre C j which semicircle shall represent the northern half of the earth’s enlight¬ ened disk as seen from the sun. Upon the centre C raise the straight line CH, per¬ pendicular to the diameter ACB; so ACB shall be a part of the ecliptic, and CH its axis. Being provided with a good sector, open it to the radius CA in the line of chords ; and taking from thence the chord of 23^ degrees in your compasses, set it off both ways from H, to g and to A, in the peri¬ phery of the semidisk j and draw the straight line g \h, in which the north pole of the disk will be always found. When the sun is in Aries, Taurus, Gemini, Can¬ cer-, Leo, and Virgo, the north pole of the earth is en¬ lightened by the sun : but whilst the sun is in the other six signs, the south pole is enlightened, and the north pole is in the dark. And when the sun is in Capricorn, Aquarius, Pisces, Aries, Taurus, and Gemini, the northern half of the earth’s axis C XII P lies to the right hand of the axis of the ecliptic, as seen from the sun j and to the left hand, whilst the sun is in the other six signs. Open the sector till the radius (or distance of the two 90’s) of the sines be equal to the length of V h, and take the sine of the sun’s distance from the sol- tice (77° 49' 48^) as nearly as yon can guess, in your compasses, from the line of the sines, and set off that distance from V to P in the line g V h, because the earth’s axis lies to the right hand of the axis of the ecliptic in this case, the sun being in Aries; and draw the straight line C XII P for the earth’s axis, of which P is the north pole. If the earth’s axis had lain to the left hand from the axis of the ecliptic, the distance VP would have been set off from V to¬ wards g. To draw the parallel of latitude of any given place, as suppose London, or the path of that place on the earth’s enlightened disk as seen from the sun, from sun¬ rise till sunset, take the following method. Subtract the latitude of London, 5i°4, from 90°, and the remainder 38°4 will be the colatitude, which take in your compasses from the line of chords, making 3 O N O M Y. Appendij CA or CB the radius, and set it from h (where the or Cal^ earth’s axis meets the periphery of the disk) to VI and ting £* VI, and draw the occult or dotted line VI K VI. scsAc Then, from the points where this line meets the earth’s disk, set off the chord of the sun’s declination 40 49' to D and F, and to E and G, and connect these points by the two occult lines F XII G and DLE. Bisect LK XII in K, and through the point K draw the black line VI K VI. Then make CB the radius of a line of sines on the sector, take the colati¬ tude of London 38°4 from the sines in your compasses, and set it both ways from K to VI and VI. These hours will be just in the edge of the disk at the equi¬ noxes, but at no other time in the whole year. With the extent K VI taken into your compasses, set one foot in K (in the black line below the occult one) as a centre, and with the other foot describe the semicircle VI 789 10, &c. and divide it into 12 equal parts. Then from these points of division draw the occult lines 77?, 80, qn, &c. parallel to the earth’s axis C XII P. With the small extent K XII as a radius, describe the quadrantal arc XIIf and divide it into six equal parts, as XII, a, ab, be, cd, de, and ef; and through the division points c, b, c, d, e, draw the occult lines VII * V, VIII d IV, IX c III, X b II, and XI o I, all parallel to VI K. VI, and meeting the former occult lines 7/?, 80, &c. in the points Vll VIII IX X XI, V IV HI II and I: which points shall mark the se¬ veral situations of London on the earth’s disk, at these hours x-espectively, as seen from the sun j and the ellip¬ tic curve VI VII VIII, &c. being drawn through these points, shall represent the parallel of latitude, or path of London on the disk, as seen from the sun, from its rising to its setting. N. B. If the sun’s declination had been south, the diurnal path of London would have been on the upper side of the line VI K VI, and would have touched the line DLE in L. It is requisite to divide the horary spaces into quarters (as some are in the figure), and, if possible, into minutes also. Make CB the radius of a line of chords on the sec¬ tor, and take therefrom the chord of f 33', the angle of the moon’s visible path with the ecliptic, set it off from II to M on the left hand of CH, the axis of the ecliptic, because the moon’s latitude is north ascending. Then draw CM for the axis of the moon’s orbit, and bisect the angle MCH by the right line Cz. If the moon’s latitude had been north descending, the axis of her orbit would have been on the right hand from the axis of the ecliptic. N. B. The axis of the moon’s orbit lies the same way when her latitude is south ascending as when it is north ascending j and the same way when south descending as when north descending. Take the moon’s latitude 40' 18" from the scale CA in your compasses, and set it from i to x in the bisecting line Css, making ix parallel to Cy: and through x, at right angles to the axis of the moon’s orbit CM, draw the straight line N wxy S for the path of the pe¬ numbra’s centre over the earth’s disk.—The point u>, in the axis of the moon’s orbit, is that where the pe¬ numbra’s centre approaches nearest to the centre of the earth’s disk, and consequently in the middle of the ge¬ neral eclipses; the point a? is that where the conjunction of rn< l i Lppiclix. Calila-of the sun and moon falls, according to equal time by ng Hip- the tables; and the point y is the ecliptical conjunction ics, ic. 0f sun and moon. Take the moon’s true horary motion from the sun, 27/ 54,,» in your compasses, from the scale CA (every division of which is a minute of a degree), and with that extent make marks along the path of the penum¬ bra’s centre; and divide each space from mark to mark into 60 equal parts or horary minutes, by dots ; and set the hours to every 6oth minute, in such a manner, that the dot signifying the instant of new moon by the tables may fall into the point X, half way between the axis of the moon’s orbit and the axis of the eclip¬ tic ; and then the rest of the dots will show the points of the earth’s disk, where the penumbra’s centre is at the instants denoted by them, in its transit over the earth. Apply one side of a square to the line of the penum¬ bra’s path, and move the square backwards and for¬ wards until the other side of it cuts the same hour and minute (as at tn and wi) both in the path of London and in the path of the penumbra’s centre; and the particular minute or instant which the square cuts at the same time on both paths shall be the instant of the visible conjunction of the sun and moon, or greatest obscuration of the sun, at the place for which the con¬ struction is made, namely London, in the present ex¬ ample ; and this instant is at 37^ minutes past ten o’clock in the morning; which is 17 minutes five se¬ conds later than the tabular time of true conjunction. Take the sun’s semidiameter, l6' 6", in your com¬ passes, from the scale CA, and setting one foot on the path of London, at m, namely at 47^ minutes past ten, with the other foot describe the circle UY, which shall represent the sun’s disk as seen from London at the greatest obscuration.—Then take the moon’s semidia¬ meter, 14' 57", in your compasses from the same scale, and setting one foot on the path of the penumbra’s centre at m, in the 47^ minutes after ten, with the other foot describe the circle TY for the moon’s disk, as seen from London, at the time when the eclipse is at the greatest, and the portion of the sun’s disk which is hid or cut off by the moon’s will show the quantity of the eclipse at that time ; which quantity may be mea¬ sured on a line equal to the sun’s diameter, and divided into 12 equal parts for digits. Lastly, take the semidiameter of the penumbra, 3i'3", from the scale Cx4 in your compasses; and setting one foot in the line of the penumbra’s centre path, on the left hand from the axis of the ecliptic, direct the other foot toward the path of London ; and carry that extent backwards and forwards till both the points of the com¬ passes fall into the same instants in both the paths : ami these instants will denote the time when the eclipse be¬ gins at London.—Then do the like on the right hand of the axis of the ecliptic ; and where the points of the compasses fall into the same instants in both the paths, they will show at what time the eclipse ends at London. These trials give 20 minutes after nine in the morning for the beginning of the eclipse at London, at the points N and O ; 474- minutes after ten, at the points m and n, for the time of greatest obscuration ; and 18 minutes after twelve, at R and S, for the time when the eclipse ends; according to mean or equal time. From these times we must subtract the equation of natural days, viz. 3 minutes, 48 seconds, in leap- year April r. and we shall have the apparen t times; 163 namely, 9 hours 16 minutes 12 seconds for the begin-or Calcula- ning of the eclipse, 10 hours 43 minutes 42 seconds for tingKclip- the time of greatest obscuration, and 12 hours 14 minutes ^ M , 12 seconds for the time when the eclipse ends. But the best way is to apply this equation to the true equal time of new moon, before the projection be begun ; as is done in Example I. For the motion or position of places on the earth’s disk answers to apparent or solar time. In this construction it is supposed, that the angle under which the moon’s disk is seen, during the whole time of the eclipse, continues invariably the same ; and that the moon’s motion is uniform and rectilineal du¬ ring that time. But these suppositions do not exactly agree with the truth; and therefore, supposing the elements given by the tables to be accurate, yet the times and phases of the eclipse, deduced from its con¬ struction, will not answer exactly to what passeth in the heavens; but may be at least two or three minutes wrong, though done with the greatest care. More¬ over, the paths of all places of considerable latitudes are nearer the centre of the earth’s disk as seen from the sun than those constructions make them ; because the disk is projected as if the earth were a perfect sphere, although it is known to be a spheroid. Consequently^ the moon’s shadow will go farther northward in all places of northern latitude, and farther southward in all places of southern latitude, than it is shown to do in these projections.——According to Meyer’s I ables, this eclipse was about a quarter of an hour sooner than either these tables, or Mr Flamstead’s, or Dr Halley’s, make it; and was not annular at London. But M. de la Caille’s make it almost central. The Projection of Lunar Eclipses. When the moon is within 12 degrees of either of her nodes at the time when she is full, she will be eclipsed; otherwise not. We find by Example II. that at the time of mean full moon in May 1762, the sun’s distance from the ascending node was only 40 49' SS" '■> an^ tlm moon being then opposite to the sun, must have been just as near her descending node, and was therefore eclipsed. The elements for constructing an eclipse of the moon are eight in number, as follows : 1. The true time of full moon ; and at that time, 2. The moon’s horizontal parallax. 3. The sun’s se¬ midiameter. 4. The moon’s. 5. The semidiameter of the earth’s shadow at the moon. 6. The moon’s lati¬ tude. 7. The angle of the moon’s visible path with the ecliptic. 8. The moon’s true horary motion from the sun.—Therefore, 1. To find the true time of new orfull moon. Work as already taught in the precepts.—Thus we have the true time of full moon in May 1762 (see Example II. page 562) on the 8th day, at 50 minutes 50 seconds past three o’clock in the morning. 2. To find the moon's horizontal parallax. Enter Table XVII. with the moon’s mean anomaly (at the above full) 9s 2° 42' 42", and thereby take out her horizontal parallax ; which, by making the requisite proportions, will be found to be 57' 23"* 3. 4. To find the semidiameters of the sun and moon. Enter Table XVII. with their respective anomalies, the sun’s being 10s 70 27' 45" (by the above example), and the moon’s 9s 2® 42' 42"; and thereby take out their respective semidiameters ; the sun’s if 56", and the moon’s 15' 38". ASTRONOMY. 164 A S T R Of Calcula- 5. To find the semidiameter of the earth"1 s shadow at ting Eclip the moon. Add the sun’s horizontal parallax, which is , ses’ Stc- _ always io', to the moon’s, which in the present case is y" 37' 23//, the sun will he 57' 33", from which subtract the sun’s semidiameter 15' 56", and there will remain 41' 37" for the semidiameter of that part of the earth’s shadow which the moon then passes through. 6. To find the mooli’s latitude. Find the sun’s true distance from the ascending node (as already taught at the true time of full moon) j and this distance increased by six signs will be the moon’s true distance from the same node j and consequently the argument for finding her true latitude. Thus, in Example II. the sun’s mean distance from the ascending node was o* 40° 49' 35", at the time of mean full moon ; but it appears by the example, that the true time thereof was six hours 33 minutes 38 seconds sooner than the mean time ; and therefore we must subtract the sun’s motion from the node (found in Table XII.) du¬ ring this interval from the above mean distance of 0s 40 49' 35'', in order to have his mean distance from it at the true time of full moon. Then to this apply the equation of his mean distance from the node, found in Table XV. by his mean anomaly 10s 70 27' 45" : and lastly add six signs : so shall the moon’s true distance from the ascending node be found as follows: s » ' « O 4 40 ^ *5 35 1 26 3 [I 3 o 4 32 32 1 38 o o 6 jo 32 Sun from node at mean full moon {6 hours • 33 minutes 38 seconds Sum, subtract from the uppermost line Remains his mean distance at true full moon Equation of his mean distance, add Sun’s true distance from the node » To which add u u U O And the sum will be - _ . T~ 10 Which is the moon’s true distance from her ascending node at the true time of her being full j and consequently the argument for finding her true latitude at that time.—. Therefore, with this argument enter Table XVI. mak¬ ing proportions between the latitudes belonging to the 6th and 7th degree of the argument at the left hand (the signs being at top) for the 10'32", and it will give 1 i0f ?e mT’,S trUe !atkude’ vvhich aPPeArs by the table to be south descending. } 7. To find the angle of the moon’s visible path with the ecliptic. This may be stated at 5° 35', without any error of consequence in the projection of the eclipse. ^. lo find the moon's true horary motion from the sun With their respecti ve anomalies take out their horary mol tions from Table XVII. and the sun’s horary motion sub¬ tracted fi om the moon s, leaves remaining the moon’s true horary motion from the sun : in the present case qo' 22" JNow collect these elements together for use. ° ^ 1. True time of full moon in May 1762 *. Moon’s horizontal parallax 3. Sun’s semidiameter 4. Moon’s semidiameter 5- Semidiameter of the earth’s shadow at the'moon 6. Moon s true latitude, south descending . 7- Angle of her visible path with the ediptic - 8. Her true horary motion from the sun . r>. H. M. s. 8 3 5C 50 o 57 23 © 15 0 *5 3s 0 37 o 32 21 5 35 G tl J!re ?IemintS b.ein& fou"d for the construction of the moon s eclipse in May 1762, proceed as follows: O N O M 1. Appendix, Make a scale of any convenient length, as WX (fig. Of Calcs],. 159. 0), and divide it into 60 equal parts, each part ting IC|]p. standing for a minute of a degree. , ses,&c, Draw the right line ACB (fig. 160. a.) for part of the ecliptic, and CD perpendicular thereto for the south¬ ern part of its axis ; the moon having south latitude. Add the semidiameters of the moon and earth’s sha¬ dow together, which in this eclipse will make 57' 15"; and take this from the scale in your compasses, and set¬ ting one foot on the point C as a centre, with the other foot describe the semicircle ADB ; in one point of which the moon’s centre will he at the beginning of the eclipse, and in another at the end thereof. Take the semidiameter of the earth’s shadow, 41' 37", in your compasses from the scale, and setting one foot in the centre C, with the other foot describe the semicircle KLM for the southern half of the earth’s shadow, because the moon’s latitude is south in this eclipse. IVIake CD equal to the radius of a line of chords on the sector, and set off the angle of the moon’s visible path with the ecliptic 50 35' from D to E, and draw the right line CEE for the southern half of the axis of the moon’s orbit lying to the right hand from the axis of the eclipw tic CD, because the moon’s latitude is south descend- ing.—It would have been the same way (on the other side of the ecliptic) if her latitude had been north de¬ scending, but contrary in both cases, if her latitude had1 * 3 4 * 6 * 8 been either north ascending or south ascending. Bisect the angle DCE by the right line Cg-, in which line the true equal time of opposition of the sun and moon falls as given by the table. Take the moon’s latitude 32' 21", from the scale with your compasses, and set it from C to G in the and through the point G, at right angles to CEE, draw the right line PHGEN for the path of the moon’s centre. Then F shall be the point in the earth’s shadow, where the moon’s centre is at the middle of the eclipse j G, the point where her centre is at the tabular time of her being full; and H, the point where her centre is at the instant of her ecliptica! opposition. r . 1alce moon’s horary motion from the sun 30' 52" in your compasses from the scale j and with that extent make marks along the line of the moon’s path PGN : then divide each space from mark to mark into 60 equal parts, or horary minutes, and set the hours to the proper dots m such a manner, that the dot signifying the instant of full moon (viz. 50 minutes 50 seconds fi r r, 6 morning) may be in the point G, where the line of the moon’s path cuts the line that bisects the angle DCE. lake the moon’s semidiameter, 15' 38", in your com¬ passes from the scale, and with that extent, as a radius, upon the points N, F, and P, as centres, describe the circle Q for the moon at the beginning of the eclipse, when she touches the earth’s shadow at Vj the circle R for the moon at the middle of the eclipse; and the circles for the moon at the end of the eclipse, just leaving the earth’s shadow at W. r > J The pomt N denotes the instant when the eclipse he- gan, namely, at I j minutes 10 seconds after II in the morning; the point F the middle of the eclipse at 4T minutes 44 seconds past III; and the point F the eid of the eclipse at 18 minutes after V.-At the greatest obscuration the moon was iq digits eclipsed. TABLE 1. ASTRONOMICAL TABLES for calculating ECLIPSES. 2Vic mean time of New Moon in March, Old Style ; with the mean Anomalies of tlie Sun and Moon, and the Sun's mean distance from the Mooli's ascending Node, from A.D. xyoo to A. if. icoo inclusive. table 1. !700 'yoi .702 7°3 704 7°5 706 7°7 708 7°9 1710 711 71 225 713 714 71 716 5 23 717 71 ll9 720 8 19 721 722 723 724 725 726 727 728 729 73° 731 73 733 734 735 : 736 737 fr- 738 739 74° 741 742 743 744 745 646 747 .WeanNewMoon in March. D. H. M. S. 258 8 16 11 27 T3 44 5 16 22 32 41 6 7 21 18 24 4 53 57 34 8 13 l3 42 2 22 31 11 21 20 3 50 10 4 52 27 8 43 8 9 2 25 8 11 13 7 20 2 20 17 34 5 79 99 x5 2 4 11 8 11 17 36 8 23 12 1 44 52 33 3 8 29 8 1 2 22 5812 632 9 o 28 44 8 19 44 37 9 8 6 49 23 9 8 27 6 54 45 43 22 16 16 15 4 38 5 23 53 1 24 2i 25 54 13 6 14 31 2 I5 3 21 12 35 47 10 21 24 23 28 18 57 18 3 45 4° 7 i2 34 *6 26 10 6 56 r4 18 55 33 3 44 1 16 49 10 5 25 18 54 16 26 42 1 15 188 22 47 c8 7 3^ 34 16 25 11 l3 57 52 48 13 22 46 278 2 7 35 21 5 7 44 10 13 56 20 29 11 29 i 748 749 75° 751 752 Sun’s Mean Anomaly. 19 58 48 8 2° 59 8 27 36 51 52 43 5 J4 54 24 3° 47 *3 4^ 39 2 8 50 21 24 43 9 46 54 29 2 47 8 18 18 39 6 40 51 25 56 43 15 12 35 9 3 34 47 22 50 39 4 8 8 27 22 41 16 38 33 9 5 ° 45 8 24 16 37 7 8 39 13 32 29 9 1 54 41 8 21 10 34 9 52 46 8 28 48 39 8 18 4 31 9 6 26 42 8 25 42 34 9 8 9 28 9 14 58 26 3 20 39 22 36 30 11 52 22 ° M 34 19 30 26 7 52 38 27 8 3° 16 24 22 4 46 34 2 27 18 20 24 *3 1 40 32 20 56 24 09 9 18 36 Moon’s Mean Anomaly. 3° 37 7 42 22 28 7 55 47 J7 43 52 20 57 23 Sun’s meauDist from tlie Node M 31 7 23 14 8 1 16 55 9 J9 42 18 2 43 7 3 9 2 5 12 57 7 4 18 34 J3 2 28 22 18 2 3 59 24 o 13 47 30 10 23 35 36 9 29 12 42 8 9 o 47 6 18 48 52 5 24 25 57 4 4 14 2 2 14 2 1 '9 39 !3 11 29 27 18 11 5 4 24 9 r4 52 29 7 24 4° 34 7 o 17 40 5 5 45 3 19 53 5° 2 25 30 56 1 5 J9 o 10 56 10 20 44 12 9 o 32 17 8 ^ 9 23 6 15 57 28 25 45 1 11 33 22 30 10 44 20 c8 49 26 35 55 10 6 24 o 9 12 1 6 7 21 49 11 6 1 37 16 5 7 I4 22 17 2 27 26 50 32 2 27 38 12 15 43 10 17 52 49 368 26 3 8 17 20 17 7 5 6 2 38 53 L5 11 27 29 3 20 16 6 28 34 28 17 50 20 9 6 12 32 8 25 28 24 8 14 44 16 8 27 40 54 7 7 28 59 613 6 4 22 54 10 3 2 42 15 9 26 5 30 10 4 8 17 11 12 51 18 11 20 54 o 29 37 1 7 39 54 1 15 42 41 2 14 25 43 2 28 30 10 31 17 19 14 18 27 J7 5 !9 52 14 2 54 22 5 41 o 48 45 8 8 51 29 8 16 54 16 9 25 37 18 10 3 40 10 11 42 52 11 20 25 54 11 28 28 41 1 7 11 42 1 15 14 29 1 23 17 16 3 2 o 17 3 10 3 3 18 5 51 4 26 48 53 5 4 51 4 5 12 54 27 6 21 37 29 6 29 40 16 8 8 23 18 8 16 26 5 8 24 28 52 ° 3 11 54 10 1 14 41 10 19 17 28 11 28 o 30 o 6 3 17 1 14 46 19 22 49 5 ° 51 52 9 34 53 17 37 4c 25 40 27 I Mean New Moon in March. x753 1754 1755 '756 I757 D. H. M. S. 22 17 48 45 12 2 37 22 1 11 25 19 8 58 389 8 17 47 1 59 8 1758 1759 1760 1761 1762 1763 1764 n6s 1766 1767 1768 1769 1770 ,77I 1772 T773 i774 x775 !776 1777 1778 :779 1780 1781 1782 j783 1784 1785 1786 1787 1788 1789 179° I79I 1792 1793 1794 1795 1796 !797 1798 1799 1 Sea 58 27 !5 !9 54 17 o 8 31 8 57 6 29 47 15 18 24 3 ° 7 20 21 39 40 10 6 29 4 Sun’s mean Anomaly. Moon’s mean Anomaly. Sun’r mean Dist. from the Node. 9 3 6 28 8 22 22 20 11 38 12 o o 24 19 16 16 9 7 38 28 8 26 54 20 16 10 12 88 9 4 S2 24 8 23 48 16 13 4 1 26 20 28 178 20 42 13 ° 569 9 4 20 338 18 12 49 6 21 38 10 25 19 10 40 A5 3 59 26 4 12 48 2 22 IO 20 43 II 19 9 19 1 3 57 55 20 1 30 35 8 10 19 12 27 7 51 51 16 16 40 28 6 1 29 4 23 23 1 44 13 7 50 21 9 23 38 57 14 11 37 o 13 28 20 32 53 18 5 21 30 14 10 6 11 42 46 14 20 31 23 A 5 I9 59 23 2 52 39 lS 11 11 41 3° 9 I3 55 19 18 2 32 9 2 51 27 23 48 16 9 12 24 5 18 1 1 24 51 33 4l 13 o 22 17 28 20 17 8 17 36 9 5 58 21 8 25 14 13 8 14 3° 9 2 52 17 8 22 8 8 11 24 1 8 29 46 13 8192 9 7 24 17 8 26 40 8 15 56 4 18 13 8 23 34 5 12 49 58 1 12 10 20 28 8 5° !5 ~ 6 8 28 8 9 5 8 25 17 21 59 44 11 o !4 1S 55 9 2 38 7 8 21 53 59 9 1016 11 8 29 32 8 18 47 45 9 7 10 8 26 25 39 8 J5 45 51 9 4 4 8 23 19 55 2 8 19 21 o 18 7 26 27 55 31 1° 3 S2 37 8 13 20 42 18 57 48 28 45 54 8 34 14 11 6 23 59 11 o 3 47 16 1 9 24 21 9 19 12 26 8 24 49 32 4 37 37 14 25 42 20 2 48 29 5° 53 9 38 58 o 15 16 10 25 4 9 4 9 52 14 8 10 29 20 6 20 17 25 25 54 31 5 42 36 !5 3° 41 21 7 47 ° 55 52 10 43 57 16 21 26 9 46 14 11 34 19 21 22 24 26 59 30 6 47 35 35 4° 10 22 12 46 2 7 17 26 52 37 58 4 23 28 12 26 1 20 29 29 12 3 7 J4 5 8 lS 57 52 8 24 o 39 9 2 3 26 10 10 46 17 10 18 49 14 10 26 52 ° 5 35 ° J3 37 49 1 22 20 51 2 o 23 38 2 8 26 25 3 17 9 27 3 25 12 14 4 3 *5 11 20 28 6 58 3 o 50 3 37 46 38 14 49 25 8 23. 32 26 9 1 35 13 9 9 38 o 10 18 21 1 10 26 23 48 11 4 26 35 o 13 9 36 0. 21 12 23 1 29 55 25 2 7 58 12 16 o 59 24 44 1 2 46 48 49 35 J9 S2 37 27 M 9 2 51, 14 2 12 39 19 o 22 27 25 11 28 4 31 10 7 52 36 5 27 35 24 7 6~ 18 26 7 14, 21 13 7 22 24 o ,9171 9 9 9 48 9 i7 12 35 25 55 37 11 3 58 24 166 ASTRONOMICAL TABLES for calculating ECLIPSES. 11S2 *753 i754 23 2 37 22 r755 175630 8 58 389 *757 ^758 »759 1760 1761 TABLE II. Mean New Moot}, &fc. in March, New Style, from A. D. 1752 to A. D. 1800. XleanNewMoon in March D. H. M. S. 14 20 16 6 4 5 4 42 f2 II 25 598 I9 17 47 I 9 2 35 51 ,8 o 8 31 6 8 57 8 5 J7 45 1762 1763 1764 ^65 1766 24 1; 18 14 o 7 8 55 6 28 1 c 16 1767 1768 1769 I77° 1771 1772 T773 1774 r775 1776 1777 1778 !779 1780 1781 1782 r783 1784 1785 1786 1787 1788 1789 l79° I79I 1792 1793 1794 J795 i796 1797 1798 1799 1800 58 44 8 24 8 368 29 12 49 33 17 21 38 Sim’s mean Anomaly. 14 44 l6 408 22 22 20 II 38 o o 12 24 19 l6 l6 8 32 8 8 26 54 20 8 16 10 12 5 26 4 23 48 16 13 4 8 2 20 o 178 20 42 13 53 8 9 58 5 Moon’s mean Anomaly. 2 42 15 12 30 20 7 26 l8 27 55 31 10 o 32 37 3 *4 5 5 6 8 13 20 42 6 23 8 47 5 28 45 54 4 8 34 o 2 18 22 5 1 23 59 11 o 3 47 16 10 13 35 21 9 19 12 26 7 29 o 31 Sun’s mean Dist from the Node. 25 40 27 3 43 J4 12 26 15 20 29 2 29 12 3 7 7 J4 5° 7 *5 !7 S8 10 18 49 14 10 26 52 1 11 4 54 48 0 l3 37 49 21 40 37 8 28 20 17 8 17 36 9 7 6 26 468 6 52 1 26 3 59 268 25 14 13 15 12 48 2 [98 3 21 36 398 22 19 9 12 3 57 1 12 46 31 19 10 19 12 55 8 8 19 7 48 27 16 40 28 J7 29 48 5 10 J7 40 24 7 50 21 3 20 23 16 38 578 1 27 33 1 5 10 7 48 508 5 29 21 308 H 4° 5 3 22 11 o 8 19 54 57 8 9 24 1 39 53 2 8 8 17 57 8 26 40 *5 56 8 5 II 8 23 24 53 12 49 58 5° 2 5 20 28 43 55 6 18 14 10 6 6 22 58 42 25 20 31 5 x9 x4 8 35 38 59 8 22 11 41 15 11 20 29 51 17 21 59 6 37 51 25 o 14 x5 55 3 3r 47 8 21 53 59 8 11 95 30 18 2 3218 29 32 20 2 51 8|8 18 47 55 8 11 39 4418 8347 27 9 12 24 16 18 1 1 6 2 49 37 2; o 22 17 8 26 25 59 8 15 41 51 8 4 57 43 8 23 19 55 4 37 37 14 2; 42 24 13 47 29 5° 53 9 38 58 11 19 27 !0 25 4 9 4 52 T4 7 14 40 16 6 20 17 25 0 5 3° 5 42 36 x5 3° 41 25 18 46 o 55 52 10 10 43 57 8 20 32 9 26 9 6 5 57 x3 5 11 34 x9 2 12 39 19 o 22 27 25 n 2 15 30 10 7 56 36 o 23 38 8 26 25 16 29 13 25 12 14 3 15 11 17 48 20 o 50 28 3 37 6 6 24 14 49 25 22 52 12 2 35 x3 9 S8 7 9 9 9 x7 40 47 10 26 23 48 11 4 26 35 11 12 29 22 o 21 12 23 o 29 15 10 2 7 58 12 16 o 59 24 3 46 2 46 48 49 35 18 52 22 5 27 35 24 6 5 S8 11 7 *4 21 13 7 22 24 o 8 o 26 47 9 9 9 48 9 r7 12 35 9 25 15 22 11 3 58 24 TABLE III. Mean Anomalies, and Sun's mean Distance from the Node, for 3 mean Lunations. N. 10 11 Mean Lunations. D. H. M. S 29 12 44 39 1 28 88 14 12 9 118 2 56 12 147 15 40 15 x77 7 209 24 18 8 21 4 17 5 52 24 18 36 27 295 7 20 30 8 236 9265 324 20 4 33 2 354 8 48 36 21 32 49 3 383 14 18 22 2 Sun’s mean Anomaly. o 29 6 19 1 28 12 39 2 27 l8 58 3 26 25 17 4 25 31 37 24 37 56 23 44 15 22 50 35 21 56 54 21 3 14 10 20 9 33 11 19 15 55 o 18 22 12 o 14 33 10 Moon’s mean Anomaly. Sun’s mean Disi from the Node, o 25 49 1 21 38 2 17 27 1 2 2 3 J3 16 4 9 5 4 54 ° 43 26 32 22 21 9 13 59 10 9 48 “ 5 37 6 12 54 30 o 15 20 1 o 40 1 2 1 20 2 3204 4 2 40 5 5 3 21 1 6412 7 4 4i 3 8 5 21 j 962 8 18 10 4 10 6 42 1 7 22 8 -2 8 43 TABLE IV. The Days of the Year, reckoned from th beginning of March. Inna L 921 [Ok (on: ASTRONOMICAL TABLES for calculating ECLIPSES. TABLE V. Mean Lunations from I to 100000. ,unat. Days. Decimal Parts. 400)( joo b[9 cf: | k-j u 700 800 900 1000 2000 3000 4000 500° 6000 7000 8000 9000 |0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 29-53059o85io8° cp.odi 181702160 88.59177255324° 118.122363404320 I47-^52954255401 i77«l83545Io6481 206.714135957561 236.244726808641 265-7753i7659722 295-3059o85io8° 590.61181702160 885,9i 77255324° 1181.22363404320 I47^'52954255401 i77i-835451o6481 2067.14135957561 2362 44726808641 26i7-753l7659722 2953,059o85io8° 5906.1181702160 8859-i77255324° 11812.2363404320 I47^5-2954255401 i77l8-3545i°648i 20671.4135957561 23624.4726808641 2^577,53I7^59722 29530*59o85io8c 59061.181702160 8859i,77255324° 118122.363404320 I47^52-954255401 i77i83-545i°6481 206714.135957561 236244.726808641 265775-3I7659722 295305-9o85io8° 590611.81702160 8859i7-7255324° 1181223.63404320 i476529-54255401 177i835-45io6481 2067141.35957561 2362447.26808641 2^57753-17^59722 2953059 o85io8° Days. H. M. S. Th. Ko. = 29 59 88 118 I47 J77 206 236 26? 295 590 885 1181 1476 1771 2067 2362 2657 2953 5906 8859 11812 M765 17718 20671 23624 26577 2953° 59061 8859! 118122 i47652 i77i83 206714 236244 265775 2953°5 590611 885917 1181223 1476529 i77i835 2067141 2362447 2657753 2953059 12 44 1 28 4 *7 5 1412 9 2 56 12 !5 40 I5 24 18 8 21 52 24 18 36 27 7 20 30 14 41 o 22 1 31 5 22 1 12 42 32 20 3 2 3 23 33 10 44 3 i8 4 34 1 25 4 50 9 7 57 x5 J4 40 19 5 24 8 30 29 9 55 34 11 20 39 12 45 44 14 10 49 4 21 39 18 32 28 8 43 18 22 54 J3 4 3 J5 46 17 26 36 7 37 25 21 48 15 19 36 30 17 24 46 !5 !3 1 13 I 16 10 49 32 8 37 47 6 25 2 4 14 18 2 2 33 2 58 5 57 8 55 11 53 J4 52 !7 5° 20 48 23 47 26 45 29 43 59 26 29 10 58 53 28 36 58 !9 28 2 57 46 27 29 57 12 54 24 51 36 48 48 46 o 43 12 40 24 37 S6 34 48 32 0 4 36 8 40 12 44 16 48 20 40 o 20 40 o 20 40 o 20 BLE VI. The first mean New Moon, with the mean Anomalies of the Sun and Moon, and the Sun’s mean Distance from the Ascending Node, next after complete Centuries of Julian Years. first New Moon. D. H. M. S 4 8 10 52 8 16 21 44 r3 ° 32 37 17 8 43 29 21 16 54 21 26 1 5 14 o 20 32 3 5 4 42 55 Sun’s mean Anomaly. o 321 O 64 o 10 3 o 13 24 o 16 46 O 20 7 II 24 22 I! 27 43 M’s mean Anomaly. Sun from Node. S 8 15 22 5 o 44 1 16 6 10 1 28 6 16 50 2212 10 21 45 111 4 19 27 9 8 55 1 28 22 6 17 49 n 716 3 26 44 7 IS 31 o 4 58 Luna¬ tions. 11132 12369 13606 i4843 900 1000 1100 1200 16080 il3i6 i8553 I979° 21072 22264 23 5°1 2473 8 25974 27211 28448 29685 30922 32159 33396 34632 35869 37106 38343 3 290c 300c 100 395803200 4081 42054 4329° 44527 7 3300 3400 35oo 3600 45764 47001 4823" 49475 50711 5T948 53185 i4422 55659 56896 58i33 59369 60606 6i843 63080 5 64317 65554 66791 68028 69265 70502 7I739 72976 74212 1300 1400 1500 1600 1700 1800 1900 2000 First New Moon. D. II. M. S. 9 12 53 47 13 21 4 40 18 5 J5 32 22 13 26 24 Sun smean Anomalv. 26 21 37 16 I 17 4 ' 6 i 14 58 1o 9 25 50 2100 2200 2300 2400 2500 2600 2700 2800 3700 38oo 83900 4000 4100 4200 4300 440c 4500 4600 4700 4800 4900 5000 100 5200 5300 5400 55oo 5600 57oo 58oo 59°° 6000 14 17 36 42 x9 1 47 35 23 9 58 27 27 18 9 19 2 13 36 6 21 47 11 5 57 53 15 14 8 45 19 22 19 38 24 6 30 30 28 14 41 22 3 10 8 7 18 I9 3 12 2 29 56 16 10 40 48 20 18 51 40 25 3 2 33 29 11 J3 25 4 6 40 14 8 14 51 6 12 23 1 59 17 7 12 51 21 15 23 43 25 23 34 35 o 19 5. 3 25 12 1 9 11 23 9 l3 !9 34 1 18 3 44 54 22 11 55 46 26 20 6 38 1 !5 33 27 5 23 44 20 10 7 55 12 14 16 6 4 19 o 16 56 1 4 4 25 7 46 11 7 M’s mean Anomaly o 14 28 II 18 43 II 22 4 11 25 25 II 28 46 O 2 O 5 29 8 50 11 13 11 16 26 11 19 47 11 23 8 11 26 29 11 29 50 o 3 11 11 7 26 11 10 47 11 14 11 17 30 11 20 51 11 24 12 n 27 33 11 1 48 11 5 9 11 8 30 11 11 51 11 15 12 11 18 33 io 22 48 10 26 9 10 29 31 11 2 52 11 613 11 9 34 11 12 55 17 9 10 10 20 31 10 23 52 10 27 13 11 o 34 23 8 27 49 11 27 16 38 41 2 12 5 30 6 20 16 22 3 55 11 7 16 10 11 31 10 14 52 4 27 15 i5 12 38 7 19 20 48 eo 24 4 59 52 10 18 14 10 21 35 10 24 56 10 28 17 3 22 29 o 7 51 8 23 53 5 8 35 1 23 57 9 13 30 5 28 52 2 14 14 10 29 36 7 14 58 4 o 20 o 15 42 8 5 15 4 20 37 1 5 59 9 21 21 6 6 43 2224 11 7 26 6 26 59 3 12 21 11 27 43 8 13 5 4 28 27 1 13 49 9 29 11 5 18 44 246 10 19 28 7 4 50 3 20 12 0 5 34 Sun from Node. 4 24 25 9 13 53 2 3 20 6 22 47 11 12 15 3 1 7 20 29 o 9 56 4 29 23 9 I8 51 2 8 18 6 27 45 10 16 32 360 7 25 27 o 14 54 5 4 22 9 23 49 2 13 16 623 10 21 30 3 10 58 8 o 25 o 19 52 5 9 20 9 28 47 1 i7 34 6 7 1 7 25 7 4 10 29 o 25 51 9 11 13 5 26 35 2 11 57 10 27 19 6 16 52 3 2 14 n 17 36 8 2 58 4 18 20 1 3 42 919 4 5 8 37 1 23 59 10 9 21 6 24 43 3 !o 5 11 25 27 10 26 27 2 15 56 8 5 23 o 24 50 4 13 37 9 3 5 1 22 32 6 1159 11 1 27 3 20 54 8 10 21 11 29 8 18 36 8 5 4 9 1 27 30 6 16 57 ii 6 25 2 25 52 7 1 4 39 046 4 23 34 9 13 1 2 2 28 6 21 57 t5S ASTRONOMICAL TABLES for calculating ECLIPSES. TABLE VII. The annual or first Equation of the mean to the true Si%ygy. Argument. Sun’s mean Anomaly. Subtract. O Signs. H. M. S 26 o 4 18 0 8 35 o 12 51 017 8 o 21 24 25 28 34 38 42 46 52 51 4 55 59 27 3 36 1 7 45 1 11 53 116 o 1 20 1 24 10 1 28 12 1 32 12 I 36 IC I 40 i 44 1 47 51 55 59 o 1 S‘gn H. M. S 2 Signs H. M. S 12 6 55 10 36 J4 1S J7 52 21 27 2 25 2 28 2 31 2 35 38 44 2 42 2 45 2 48 3° 2 51 40 2 54 48 57 53 o 54 6 3 3 9 36 6 3 12 24 r5 9 !7 51 20 30 23 12 11 Si?ns 25 28 36 30 26 32 45 35 10 Signs 3 35 37 10 39 1 31 23 43 26 45 25 3 Signs H. M.S. 4 10 53 84 ^ 57 ^ 55 10 49 10 39 10 24 3 47 J9 3 49 7 3 3 3 54 4 5° 5° 52 29 3 55 35 3 57 2 3 58 27 3 59 49 3 1 7 2 18 3 23 4 22 18 10 6 58 7 4l 8 21 8 57 9 29 9 10 33 10 45 10 53 9 Signs 10 4 9 39 9 10 8 37 7 59 16 29 37 41 40 2 35 1 26 o 12 58 52 57 27 4 Signs H. M. S. H. M.S. 3 39 3° 37 19 35 6 32 50 3° 3° 28 5 25 35 23 ° 20 20 r7 35 14 49 11 59 9 6 6 10 3 10 o 7 2 57 0 2 53 49 2 5° 36 2 47 18 2 43 57 .5 Signs 7 45 2 3 55 201 1 56 1 52 527 48 4 41 39 56 35 49 31 41 27 31 23 !9 l9 14 49 10 32 6 15 3° r9 5 18 l5 1 56 57 36 53 J5 48 52 44 28 55 59 54 26 52 49 51 9 49 26 6 3 3 47 38 45 44 3 43 45 3 41 40 3 39 3° 8 Signs 40 33 37 6 33 35 30 2 26 26 2 22 47 2 19 5 2 15 20 2 11 35 2 7 45 7 Signs o 40 2 ° 35 36 o 31 10 o 26 44 O 22 17 O I' 7 5° o 13 23 o 8 56 o 4 29 000 6 Signs Add TABLE VIII. Equation of the Moon's mean Anomaly. Argument. Sun’s mean Anomaly. Subtract. O Siems 1 Sign o o|o 46 45 37 0 13 0 52! o JO 48 49 34 50 53 281 o 52 19 6 0 53 40 2 Sitrns 1 21 32 I 22 21 i 23 ro I 23 57 1 24 41 1 25 24 Signs 4 Signs .5 Sicrns n o 35 i| 1 23 4 0 I93° 1 35 1 35 1 1 35 ° 1 34 57 1 34 50 2 1 1 1 22 14 21 24 20 32 0 46 51 o 45 23 . o 43 54 19 380 42 24 18 42 o 40 53 25 10 o Signs l Sign 2 Signs o 942 o 11 20 o 12 56 O 14 33 o 16 10 16 o 17 47 o 19 23 O 20 59 O 22 35 o 24 10 ° 25 45 o 27 19 o 28 52 o 30 25 ° 31 57 o 33 29 ° 35 o 36 32 o 38 1 o 39 29 o 40 59 o 42 26 ^ 43 54 o 45 T9 46 45 o 55 0 o 56 21 O 57 38 o 58 56 1 o 13 1 29 2 43 3 56 5 8 6 18 7 27 8 36 9 42 10 49 11 54 1 12 58 1 14 1 1 15 1 1 16 o 1 16 59 1 i7 57 1 18 52 1 19 47 1 20 40 1 21 32 11 Signs 10 Signs 1 26 6 1 26 48 1 27 28 6 1 28 1 28 43 .3 Signs i 34 43 1 34 33 1 34 22 1 34 9 1 33 53 1 29 17 1 29 51 1 30 22 1 3° 5° 1 31 19 31 45 S2 12 32 34 32 57 33 i7 33 36 33 52 34 6 34 18 34 3° 34 4° 34 48 34 54 34 58 35 1 9 Signs 1 33 37 1 33 20 1 33 ° 1 32 38 1 32 14 4 Signs .5 Signs 17 45 16 48 15 47 14 44 13 41 12 37 “ 33 10 26 9 »7 8 8 1 3i 5° 1 31 23 1 30 55 1 3° 25 1 29 54 1 29 20 1 28 45 1 28 9 1 27 30 1 26 50 26 27 25 5 24 39 23 52 23 4 8 Signs 1 ° 45 o 59 26 o 58 7 o 56 45 ° 55 23 o 54 o 52 37 o 51 12 O 49 45 o 48 19 o 39 21 0 37 49 o 36 15 0 34 40 0 33 5 3i 31 29 54) 28 18 26 40 25 23 23 21 45 20 18 28 16 48 15 13 28 11 48 10 7 8 20 3 _ o 6 44 ° 5 3 o 3 21 o 1 40 000 7 Signs 6 Signs Add CABLE IX. The second Equation of the mean to the true Sizy^ Argument. Moon’s equated Anomaly. Add Sigr H.M.S. o 10 58 o 21 56 O 32 54 ° 43 52 0 54 5° 5 48 Sign H. M. S. H. M. S. 5 !2 48 5 21 56 30 57 39 51 48 37 57 x7 16 46 27 44 38 40 49 33 2 o 23 2 11 10 2 21 54 2 32 34 2 43 9 5 5i 14 1 22 41 3° 57 39 6 47 6 54 46 7 2 24 7 9 52 7 17 Signs 47 8 5i 45 8 56 ic 9 0 9 4 9 8 25 3 Signs H. M. S. 9 46 44 9 45 9 45 9 44 9 42 59 9 41 36 4 Signs H. M. S. 8 8 59 4 34 3 H. M. S 12 9 9 i5 43 19 5 22 14 25 12 9 9 27 54 3° 32 32 58 35 J4 37 12 9 40 3 9 38 19 9 36 24 9 34 i8 9 S2 9 29 33 9 26 54 9 24 9 21 3 9 !7 5i 3 12 57 23 5i 33 45 46 39 46 33 36 27 22 21 14 3° 7 5° 46 54 47 40 32 56 2 57 4i j 2 48 3|( 2 21 i I i: I i 41 jfSTR GNOMICAL TABLES for calculating ECLIPSES. 163 TABLE IX. Concluded. [3° I|2 53 387 24 199 31 3« 44 51 51 73 4 3 7 33 14 24 7 i?3 24 42 7 33 34 587 ^ a: 72 6 Add. 7 Add M. S.M. S Signs hTMTs, 5 12 488 47 89 46 44 13 45 11 7 23 55 4 a 54 5 268 44 15 268 14 25 208 5435 68 74 44 428 ?5 54 IIn )5 3 338 >5 12 488 11 Signs 189 99 57 4 3 9 J5 21 569 579 469 £49 53 9 26 32 11 37 42 47 10 Signs 2 Siens H.M.S H.M. S.H. M.S 39 89 14 286 40 519 10 546 42 219 7 96 9 43 429 3 136 249 44 53 8 59 65 59 45 528 54 5°5 46 388 50 245 3 Signs 4 Signs 47 I38 45 483 47 36 8 41 2 c 47 498 65 47 548 31 05 9 47 468 25 44 5 T99 47 33 8 20 184 189 47 148 14 334 89 46 448 8 594 9 Signs 8 8 59 5 Signs H. M. S 10 3 55 38 4 2 c 40 2 18 182 1 1 1 1 1 1 o o o o o 34 33 47 40 32 24 16 8 Signs 7 49 51 43 34 56 42 T5 2 33P .7 Signs 12 8 2 53 53 36 44 34 54 25 31 16 7 6 41 57 43 47 44 38 13 28 41 J9 9 o 6 Signs ABLE X. The third equation the mean to the true Syzygy Argument. Sun’s Anomaly— Moon’s Anomalv. 0 Sub. 4 ;- Signs 1 Sub. 0 5 0 10 0 15 0 20 0 25 0 30 0 35 0 40 0 45 0 50 0 55 1 0 1 5 I TO 1 T5 I 20 1 25 1 30 1 35 1 40 Signs 22 26 30 2 2 2 34 2 38 2 42 Signs 2 Sub. 8 Add M. S I 2 46 50 2 2 2 54 2 58 3 3 3 M 3 I8 3 22 I I 1 52 1 56 2 2 2 2 13 2 18 2 22 Signs 5 Sub. n Add 3 3 3 3 3 42 34 38 45 48 3 3 3 51 3 54 3 57 Signs 3 Sub. 4 Sub. 10 Add 9 Add ^irirp^n: J5 18 28 21 30 32 34 36 38 4° 42 44 46 48 50 51 52 53 4 54 55 56 57 57 57 4 58 4 58 4 58 4 58 4 58 30 29 TAB.XI. The fourth equation of the mean to the true Syzygy. Argument. Sun’s mean diftance from the Node. 17 15 Sigr Uo 10 Add }sig. M. S 4 7j 10 L3 16 M. S.M. S 22 *3 6 r4 Crq 20 23 26 29 32 35 38 o o o 41 o 44 o 47 5° i2 54 57 10 12 *4 16 18 20 22 23 24 25 26 27 28 29 3° 31 32 33 33 34 34 34 34 34 34 33 33 32 3i 30 29 28 27 26 25 24 22 l! 22 1 21 1 20 1 18 27 1 1 !6 !4 12 24 10 23 8 22 621 3 20 I O ° 57 o 54J7 0 5i o 49 0 45 o 41 ° 37 0 34 o 31 28 25 o o O 22 0 19 O 16 !3 IO 6 3 3° Sig 3 J2 Subtract. l!£ TABLE XII. The Sun's mean Longitude, Motion, and Anoma/y, Old Style. °2 K Sun’s mean Longitude. 301 301 401 501 1001 IIOl 1*01 1301 1401 1501 1601 1701 1801 3 7 53 9 10 9 10 54 15 39 15 26 16 ir 16 57 17 42 18 37 19 13 19 58 30 43 31 39 IO 50 IO 30 50 30 50 IO 30 50 10 3° 50 xo Sun’s mean Anomaly. Sun’s mean Motion. III 2 II 3 11 o 6 7 ii o 11 n 11 o II 9 10 11 13 13 I4II 15 16 I7|H 18 II 29 45 29 31 39 17 O I 29 47 29 33 39 18 o 3 29 49 29 34 39 30 O 5 29 51 39 36 39 23 o 7 39 53 39 38 4011 49II 39 9 49 38 48 26 57 36 25 5 24 9 19 32 18 36 17 40 16 44 15 49 14 53 13 57 13 13 Sun’s mean Anomaly. 11 II II 11 11 11 II II 11 11 11 11 11 3511 29 45 29 29 29 14 29 58 29 42 29 37 29 11 29 55 29 40 29 24 29 29 53 29 37 39 22 29 7 29 50 29 35 29 30 3 K 19 20 40 60 80 100 200 300 400 500 600 700 800 900 1000 2000 3000 4000I 5000 6000 Sun’s mean Motion. 39 24 o 9 18 27 36 45 3° 16 1 3 46 4 32 5 6 6 7 15 17 2 48 33 6 22 40 o 13 7 46 15 30 16 4 8 12 16 20 40 o 3d 40 o 20 40 o 30 4° o Sun’s mean Anomaly. 11 11 11 II 11 II II II 11 II 11 11 11 11 11 II 11 2010 Sun?s mean Motion. Jan. Feb. Mar. Apr. May Tune 'uly Aug. Sept. O&. Nov. Dec. ° 33 28 9 28 42 28 16 38 49 28 24 28 57 29 3° 29 4 29 38 29 13 O 18 11 30 40 50 ,8 36 44 54 12 22 29 4 29 48 29 37 29 26 29 15 29 4 28 8 27 12 36 16 25 21 24 25 23 29 22 33 21 37 20 41 II 23 2 3 22 44 13 25 4 6 Sun’s mean Anomaly. o 33 28 38 42 28 17 28 50 28 34 28 57 29 30 29 29 37 39 11 Sun’s mean Motion and Anomaly. 59 58 57 56 55 54 53 53 8 53 9 5i 10 50 11 49 13 48 13 47 14 47 15 46 16 45 17 44 18 43 19 42 20 41 21 41 22 40 23 39 24 38 25 37 26 36 27 35 28 35 29 34 o 33 8 27 25 33 42 5o| 58 7 25 23 32 4011I0 3 4 50 60 70 80 90 100 3017 38 47 55 3 12 20 38 45 37 53 3 1029 Sun’s mean Motion and Anomaly. ///!/ //// 3 380 4 56° 7 240 9 5io 12 190 14 470 17 150 19 43 0 23 IIO 24 380 27 60 29 340 32 20 34 300 36 580 39 260 4i 53° 44 21 o 46 490 49 170 51 45 0 54 130 56 400 59 81 1 361 4 41 6 331 9 01 11 281 Sun’s mean dist. from the Node. 2 3631 5 12 7 48 10 12 59 15 35 18 11 20 47 23 23 25 58 28 34 31 10 33 45 36 31 38 57 4i 33 44 Sun’s mean Motion and Anomaly. n 32 33 934 35 3 6 7 38 39 40 41 46 46 4448 47i 55 49 20 49 5i 5650 54 32 5i 57 • 852 53 54 59 43 3 19 4 55j55 16 18 31 23 26 28 31 33 36 38 41 421 43 45 48 45i 5° 53 58 o 3 5 8 10 13 15 7 31563 17 10 7572 20 13 43 583 23 15 J9593 25 1830I1 13 551 *7 45|6o 3 27 23 51 19 57 15 42 10 38 6 34 2 30 57 25 53 21 49 17 44 12 40 8 36 4 32 59 27 55 23 51 Sun’s mean dist. from the Node. 20 30 23 6 25 42 28 18 30 54 33 29 36 5 38 40 41 16 43 52 46 28 49 4 51 39 54 15 55 5i 59 27 2 3 39 13 50 12 25 15 2 17 38 20 14 23 50 25 26 38 3 30 38 33 14 35 50 In Leap years, after February, add one day, and one day’s motion. ASTRONOMICAL TABLES for calculating ECLIPSES, TABLE XIII. Equation of the Sun’s centre, or the dif¬ ference between his mean and true place. Argument. Sun’s mean Anomaly. Subtract 56 47 55 37 .o 58 30 1 012 561 1 53 o 21 37 ! 3 23 33 Io 25 29 [0 27 25 150 29 2C l60 31 Ij 33 !8o 35 19° 36 55 38 47 20 4° 39 2 3 d 42 30 o 44 20 240 46 47 57 55 39 55 38 55 36 55 31 55 24 1 53 57 1 53 36 1 53 12 1 52 46 1 52 18 28 41 29 57 1 31 u 1 32 25 1 33 35 53 54 54 28 54 44 54 58 48 46 48 47 !9 46 12 1 45 44 34 45 35 53 36 59 38 3 39 6 37 1 34 43: 33 32 47 57 46 32 190 44 11 31 40 42 1 29 470 41 38 25 90 36 28 oo 3° 33*5 1 21 340 28 60 26 33 24 33 50 22 32 20 30 49 1 41 120 58 530 Add TABLE XIV. The Sun's Declination. Argument. Sun’s true place. Signs Sgns 00 ojn 30 20 II I3 34 14 58;i4 5*6 Signs Signs Signs 30 9 22 21 !5 Sg n s 16 Signs o o 11 30 318 2 23 IO 21 IO 47 3C Signs Signs 18 Sign" 20 TABLE XV. Equation of the Suns mean Distance from the Node. Argument. Sun’s mean Anomaly. Subtract > Sign a I .3 SignsjSigns! 23 33 23 48 23 3 23 23 o 23 120 25 I3'o 28 21 47 a 5 48 2 5°1 4 481 2 471 o 460 58 450 5626 440 5425 30 27 I4!o 301 262 lijo 321 27 II Signs 43° 5^ 41 o 50 400 48 41 390 46 41 37 ° 44 3ji 360 42 31 34|° 4018 3 1 33|° 37 21 SL0 35 21 3°° 33 i9 Signs 18,0 38 i9'o 40 200 42 Signs o 34 o 36 o 44 o 46 230 48 24 0 50 aj|o 52 260 54 270 56 280 58 1 o 1 2 2 iV.j U 8 S.f 2610 419 1723 25 23 27 23 28 23 29 23 29 l9 3l l9 45 19 58 20 11 Add 11 Sign 28 1 47 2 2 O Signs Signs Signs 41 41 59 50 1 21 1 J3t 0 311 0 29 ij 0 27 u 0 2411 0 221; 0 20 5 190 181 0 16 0 13 0 11 11 Signs Signs TABLE XVI. The Moon's Latitude in E- clipses. Arg. Moon’s equated Di¬ stance from the Node. TABLE XVII. The Moon's hori%ontal Parallax, the Semidiameters and true Horary Motions of the Su and Moon, to every sixth degree of their mean Anoint lies, the quantities for the intermediate degrees bm\ easily proportioned by sight. ■-i 2.0 5L n 2 b 3. Signs. North Ascend. 6 Signs. South Descend. Z B ¥ J5 31 J5 Signs Signs t 5 Signs North Descend. r854 54 1 054 56 214 59 6 55 c2 55 [855 55 4: 656 15 58 *5 59 1856 11 Signs. South Ascend. 859 This Table shows the Moon’s Lati¬ tude a little beyond the ut¬ most Limits of Eclipses. 21 543 630 430 831 1231 31 4° 31 * 56 13 2632 17 15 3032 39 15 3633 11 l5 463 583 33 23 3 47 34 11 _4 34 34 58 4 16 935 22 16 1435 45 16 1936 16 24 3 6 20 460 16 2836 40 2. 8 » 28 II 10 irrety ;h 060 II 660 21 1260 30 i8j6o 38 2460 45 383' 60 4516 2316 3937 40 2 33 6 A S T R lln° II* description of Astronomical Instruments serving to lU' illustrate the Motions of the Heavenly Bodies. iyi struments. The machine represented hy fig. 161. is the Grand Orrery, first made in this kingdom by Mr Ilowley for King George I. The frame of it, which contains the wheel-work, &c. and regulates the whole machine, is made of ebony, and about four feet in diameter; the outside thereof is adorned with 12 pilasters. Between these the 12 signs of the zodiac are neatly painted with gilded frames. Above the frame is a broad ring sup¬ ported with 12 pillars. This ring represents the plane of the ecliptic; upon which ye two circles of degrees, and between these the names and characters of the 12 signs. Near the outside is a circle of months and days, exactly corresponding to the sun’s place at noon each day throughout the year. Above the ecliptic stand some of the principal circles of the sphere, agreeable to their respective situations in the heavens : viz. N° 10. are the two colures, divided into degrees and half degrees; N° 11. is one-half the equinoctial circle, making an angle of 2^\ degrees. The tropic of Can¬ cer and the arctic circle are each fixed parallel at their proper distance from the equinoctial. On the north¬ ern half of the ecliptic is a brass semicircle, moveable upon two points fixed in ‘Y> and sQ:. This semicircle serves as a moveable horizon to be put to any degree of latitude upon the north part of the meridian, and the whole machine may be set to any latitude without disturbing any of the internal motions, by two strong hinges (N° 13.) fixed to the bottom-frame upon which the instrument moves, and a strong brass arch, having holes at every degree, through which a strong pin is put at every elevation. This arch and the two hinges support the whole machine when it is lifted up accord¬ ing to any latitude : and the arch at other times lies conveniently under the bottom-frame. When the ma¬ chine is to be set to any latitude (which is easily done by two men, each taking hold of two handles convenient¬ ly fixed for the purpose), set the moveable horizon to the same degree upon the meridian, and hence you may form an idea of the respective altitude or depres¬ sion of the planets both primary and secondary. The sun (N° 1.) stands in the middle of the whole system upon a wire, making an angle with the ecliptic of about 82 degrees. Next the sun is a small ball (2.), re¬ presenting Mercury. Next to Mercury is Venus (3.), represented by a larger balk The earth is represent¬ ed (N° 4.) by an ivory ball, having some circles and a map sketched upon it. The wire which supports the earth makes an angle with the ecliptic of 66^ degrees, the inclination of the earth’s axis to the ecliptic. Near the bottom of the earth’s axis is a dial-plate (N° 9.), having an index pointing to the hours of the day as the earth turns round its axis. Round the earth is a ring supported by two small pillars, representing the orbit of the moon ; and the divisions upon it answer to the moon’s latitude. The motion of this ring represents the motion of the moon’s orbit according to that of the nodes. Within this ring is the moon (N° 5.), having a black cap or case, by which its motion represents the phases of the moon according to her age. Without the orbits of the earth and moon is Mars (N° 6.). The next in order to Mars is Jupiter and his four moons o isr o M y. (N° <7.). Each of these tiioohs is supported by a wire Dcscriptioa fixed in a socket which turns about the pillar support- of Astiono- ing Jupiter. These satellites may be turned by the ,,uca' bi¬ hand to any position, and yet when the machine is put into motion, they will all move in their proper times. The outermost of all is Saturn, his five moons and his ring (N° 8.). These moons are supported and con¬ trived similar to those of Jupiter. The machine is put into motion by turning a small winch (N° 14.) ; and the whole system is also moved by this winch, and by pulling out and pushing in a small cylindrical pin above the handle. When it is pushed in, all the planets, both primary and secondary, will move according to their respective periods by turning the handle. When it is drawn out, the motions of the satellites of Jupiter and Saturn will be stopped, while all the rest move without interruption. There is also a brass lamp, ha- -ving two convex glasses to be put in room of the sun ; and also a smaller earth and moon, made somewhat in proportion to their distance from each other, which may be put on at pleasure. The lamp turns round at the same time with the earth, and tlie glasses of it cast a strong light upon her ; and when the smaller earth and moon are placed on, it will be easy to show when either of them will be eclipsed. When this machine is intended to be used, the planets must be duly placed by means of an ephemeris hereafter described; ami you may place a small black patch or bit of wafer upon the middle of the sun. Right against the first degree of T1, you may also place patches upon Venus, Mars, and Jupiter, right against some noted point in the ecliptic. Put in the handle, and push in the pin which is above it. One turn of this handle answers to a re¬ volution of the ball which represents the earth about its axis ; and consequently to 24 hours of time, as shown by the hour index (9.), which is marked and placed at the foot of the wire on which the ball of the earth is fixed. Again, when the index has moved the space of ten hours, Jupiter makes one revolution round its axis, and so of the rest. By these means the revo¬ lutions of the planets, and their motions round their own axes, will be represented to the eye. By observ¬ ing the motions of the spots upon the surface of the £un and of the planets in the heavens, their diurnal rotation was first discovered, after the same manner as we in this machine observe the motions of their representatives by that of the marks placed upon them. The Orrery (fig. 162.) is a machine contrived by the late ingenious Mr James Ferguson. It shows the motions of the sun, Mercury, Venus, earth, and moon ; and occasionally the superior planets, Mars, Jupiter, and Saturn, may be put on. Jupiter’s four satellites are moved round him in their proper times by a small winch ; and Saturn has his five satellites, and his ring which keeps its parallelism round the sun ; and by a lamp put in the sun’s place, the ring shows all its va¬ rious phases already described. In the centre, N° 1. represents the sun, supported by its axis, inclining almost 8 degrees from the axis of the ecliptic, and turning round in 25^ days on its axis, of which the north pole inclines toward the eighth de¬ gree of Pisces in the great ecliptic (N° II.), where¬ on the months and days are engraven over the signs and degrees in which the sun appears, as seen from the earth, on the different days of the year. Y 2 The 172 ASTRO Description The nearest planet (N° 2.) to the sun is Mercury, of 4strc>no- which goes round him in 87 days, 23 hours, or 87!^ mica! In- rotations,of the earth j but has no motion round . ^ “ its axis in the machine, because the time of its diurnal motion in the heavens is not known to us. The next planet in order is Venus (N° 3.), which performs her annual course in 224 days 17 hours, and turns round her axis in 24 days 8 hours, or in 24^ diurnal rotations of the earth. Her axis inclines 75 degrees from the axis of the ecliptic, and her north pole inclines towards the 20lh degree of Aquarius, according to the observations of Bianchini. She shows all the phenomena described in Part II. Next, without the orbit of Venus, is the earth (N0 4.) which turns round its axis, to any fixed point at a great distance, in 23 hours 56 minutes 4 seconds of mean solar time ; but from the sun to the sun again, in 24 hours of the same time. N° 6. is a sidereal dial- plate under the earth, and N° 7. a solar dial-plate on the cover of the machine. The index of the former shows sidereal, and of the latter, solar time ; and hence the former index gains one entire revolution on the lat¬ ter every year, as 365 solar or natural days contain 366 sidereal days, or apparent revolutions of the stars. In the time that the earth makes 365!: diurnal rota¬ tions on its axis, it goes once round the sun in the plane of the ecliptic ; and always keeps opposite to a moving index (N° 10.) which shows the sun’s daily change of place, and also the days of the months. The earth is half covered with a black cap, for di¬ viding the apparently enlightened half next the sun from the other half, which, when turned away from him, is in the dark. The edge of the cap represents the circle bounding light and darkness, and shows at what time the sun rises and sets to all places throughout the year. The earth’s axis inclines 23! degrees from - the axis of the ecliptic; the north pole inclines to¬ wards the beginning of Cancer, and keeps its parallel¬ ism throughout its annual course j so that in summer the northern parts of the earth incline towards the sun, and in winter from him : by which means, the differ¬ ent lengths of days and nights, and the cause of the va¬ rious seasons, are demonstrated to sight. There is a broad horizon, to the upper side of which is fixed a meridian semicircle in the north and south points, graduated on both sides from the horizon to 900 in the zenith or vertical point. The edge of the horizon is graduated from the east and west to the south and north points, and within these divisions are the points of the compass. From the lower side of this thin horizontal plate stand out four small wires, to which is fixed a twilight circle 18 degrees from the graduated side of the horizon all round. This horizon may be put upon the earth (when the cap is taken away), and rectified to the latitude of any place j and then by a small wire, called the solar ray, which may be put on so as to proceed directly from the sun’s cen¬ tre towards the earth’s, but to come no farther than almost to touch the horizon, the beginning of twi¬ light, time of sunrising, with his amplitude, meridian „ altitude, time of setting, amplitude then, and end of twilight, are shown for every day of the year, at that place to which the horizon is rectified. The moon (N° 5.) goes round the earth, from be- N O M Y. Appendii Ai tween it and any fixed point at a great distance, in 27 Descripi days 7 hours 43 minutes, or through all the signs and of Astrom J}j degrees of her orbit, which is called her periodical re- “deal in, volution ; but she goes round from the sun to the sun ,Ululllcnli again, or from change to change, in 29 days 12 hours 35 minutes, which is her synodical revolution ; and in that time she exhibits all the phases already described. When the above-mentioned horizon is rectified to the latitude of any given place, the times of the moon’s rising and setting, together with her amplitude, are shown to that place as w'ell as the sun’s j and all the various phenomena of the harvest-moon are made ob¬ vious to sight. The moon’s orbit (N° 9.) is inclined to the ecliptic (N° 11.) one half being above, and the other below it. The nodes, or points at o and o, lie in the plane of the ecliptic, as before described, and shift backward through all its sines and degrees in 18-} years. The de¬ grees of the moon’s latitude to the highest at NL (north latitude) and lowest at SL (south latitude), are engraven both ways from her nodes at o and o, and as the moon rises and falls in her orbit according to its inclination, her latitude and distance from hep nodes are shown for every day, having first rectified her orbit so as to set the nodes to their proper places in the ecliptic j and then as they come about at differ¬ ent and almost opposite times of the year, and then point towards the sun, all the eclipses may be shown for hundreds of years (without any new rectification) by turning the machinery backward for time past, or forward for time to come. At 17 degrees distance from each node, on both sides, is engraved a small sun ; and at 12 degrees distance, a small moon which show the limits of solar and lunar eclipses •, and when, at any change, the moon falls between either of these suns and the node, the sun will be eclipsed on the day pointed to by the annual index (N°io)j and as the moon has then north or south latitude, one may easily judge whether that eclipse will be visible in the north¬ ern or southern hemisphere : especially as the earth’s axis inclines toward the sun or from him at that time. And when at any full the moon falls between either of the little moons and node, she will be eclipsed, and the annual index shows the day of that eclipse. There is a circle of 2p|- equal parts (N* 8.) on the cover of the machine, on which an index shows the days of the moon’s age. There are two semicircles (fig. 163.) fixed to an el¬ liptical ring, which being put like a cap upon the earth, and the forked part F upon the moon, shows the tides as the earth turns round within them, and they are led round it by the moon. When the difi’er- ent places come to the semicircle A a E & B, they have tides of flood ; and when they come to the semi¬ circle CED, they have tides of ebb 5 the index on the hour-circle (fig. 162.) showing the times of these phe¬ nomena. There is a jointed wire, of which one end being put into a hole in the upright stem that holds the earth’s cap, and the wire laid into a small forked piece which may be occasionally put upon A enus or Mercury, shows the direct and retrograde motions of these two planets, with their stationary times and places as seen from the earth. The endix. A S T R The whole machinery is turned by a winch or handle >no. (N° 12.) *, and is so easily moved, that a clock might nio In- turn it without any danger of stopping. To give a plate of the wheel-work of this machine would answer no purpose, because many of the wheels lie so behind others as to hide them from sight in any view whatever. The Planetarium (fig. 164.) is an instrument contrived by Mr William Jones of Holborn, London, mathematical instrument maker, who has paid consi¬ derable attention to those sort of machines, in order to reduce them to their greatest degree of simplicity and perfection. It represents in a general manner, by va¬ rious parts of its machinery, all the motions and phe¬ nomena of the planetary system. This machine con¬ sists of, the Sun (in the centre), with the planets, Mercury, Venus, the Earth and Moon, Mars, Jupiter and his four moons, Saturn and his five moons ; and to it is occasionally applied an extra long arm for the Georgian planet and his two moons. To the earth and moon is applied a frame CD, containing only four wheels and two pinions, which serve to preserve the earth’s axis in its proper parallelism in its motion round the sun, and to give the moon her due revolution about the earth at the same time. These wheels are con¬ nected with the wheel-work in the round box below, and the wheel is set in motion by the winch H. The arm M that carries round the moon, points out on the plate C her age and phases for any situation in her or¬ bit, and which accordingly are engraved thereon. In the same manner the arm points out her place in the ecliptic B, in signs and degrees, called her geocentric place ; that is, as seen from the earth. The moon’s orbit is represented by the flat rim A 5 the two joints of which, and upon which it turns, denoting her nodes. This orbit is made to incline to any desired angle. The earth of this instrument is usually made of a three inch or l|- globe, papered, &c. for the pur¬ pose -, and by means of the terminating wire that goes over it, points out the changes of the seasons, and the different lengths of days and nights more conspicuously. This machine is also made to represent the Ptolemaic System, or such as is vulgarly received 1 which places the earth in the centre, and the planets and sun revol¬ ving about it. (It is done by an auxiliary small sun and an earth, which change their places in the instru¬ ment). At the same time, it affords a most manifest confutation of it: for it is plainly observed in this construction, (1.) That the planets Mercury and Ve¬ nus, being both within the orbit of the sun, cannot at any time be seen to go behind it $ whereas in nature we observe them as often to go behind as before the sun in the heavens. (2.) It shows, that as the planets move in circular orbits about the central earth, they ought at all times to be of the same apparent magni¬ tudes j whereas, on the contrary, we observe their ap¬ parent magnitude in the heavens to be very variable, and so far different, that, for instance, Mars will some¬ times appear as big as Jupiter nearly, and at other times you will scarcely know him from a fixed star. (3.) It shows that any of the planets might be seen at all distances from the sun in the heavens ; or, in other words, that when the sun is setting, Mercury or Ve¬ nus may be seen not only in the south but even in the eastj which circumstances were never yet observed. O N O M Y. 173 (4.) You see by this planetarium that the motions of Description the planets should always be regular and uniformly the of Astrono- same j whereas, on the contrary, we observe them al- ways to move with a variable velocity, sometimes faster, , then slower, and sometimes not at all, as will be pre¬ sently shown. (5.) By the machine you see the planets move all the same way, viz. from west to east continual- Iv: but in the heavens we see them move sometimes direct from west to east, sometimes retrograde from east to west, and at other times to be stationary. All which phenomena plainly prove this system to be a false and absurd hypothesis. The truth of the Copernican or Solar System of the world is hereby most clearly represented. For taking the earth from the centre, and placing thereon the usual large brass ball for the sun, and restoring tire earth to its proper situation among the planets, then every thing will be right, and agree exactly with celes¬ tial observations. For turning the winch H, (1.) You will see the planets Mercury and Venus go both before and behind the sun, or have two conjunctions. (2.) You will observe Mercury never to be more than a cer¬ tain angular distance, 2i°, and Venus 47*, from the sun. (3.) That the planets, especially Mars, will be sometimes much nearer to the earth than at others, and therefore must appear larger at one time than at an¬ other. (4.) You will see that the planets cannot ap¬ pear at the earth to move with an uniform velocity ; for when nearest they appear to move faster, and slower when most remote. (5.) You will observe the planets will appear at the earth to move sometimes directly from west to east, and then to become retrograde from east to west, and between both to be stationary or with¬ out any apparent motion at all. Which particulars all correspond exactly with observations, and fully prove the truth of this excellent system. Fig. 165. represents an apparatus to show these latter particulars more evi¬ dently. An hollow wire, with a slit at top, is placed over the arm of the planet Mercury or Venus at E. The arm DG represents a ray of light coming from the planet at D to the earth, and is put over the centre which carries the earth at F. The planets being then put in motion, the planet D, as seen in the heavens from the earth at F, will undergo the several changes of position as above described. The wire prop that is over Mercury at E, may be placed over the other superior planets, Mars, See. and the same phenomena be exhi¬ bited. By this machine you at once see all the planets in mo¬ tion about the sun, with the same respective velocities and periods of revolution which they have in the hea¬ vens j the wheel-work being calculated to a minute of time, from the latest discoveries.. You will see here a demonstration of the earth’s motion about the sun, as well as those of the rest of the planets : for if the earth were to be at rest in the heavens, then the time between any two conjunctions of the same kind, or oppositions, would be the same with the periodical time of the planets, viz. 88 days in Mercury, 225 in Venus, &c.; whereas you here observe this time, instead of being 225 days, is no less than 583 days in Venus, occasioned by the earth’s moving in the mean time about the sun the same way with the planet. And this space of 583 days always passes between two like conjunctions of Venus in the heavens*-. 174 Description heavens. Hence the most important point of astrenomy of Astrono- is satisfactorily demonstrated, mica! In- The diurnal rotation of the earth'about its axis, and ttruments, ^ demonstration of the cause of the different seasons of the year, and the different lengths of days and nights, are here answered completely : for as the earth is placed on an axis inclining to that of the ecliptic in an angle of 2^ degrees, and is set in motion by the wheel-work, there will be evidently seen the different inclination of the sun’s rays on the earth, the different quantity there¬ of which falls on a given space, the different quantity of the atmosphere they pass through, and the different continuance of the sun above the horizon at the same place in different times of the year; which particulars constitute the difference betwixt heat and cold in the summer and winter seasons. As the globe of the earth is moveable about its in¬ clined axis, so by having the horizon of London drawn upon the surface of it, and by means of the termina¬ ting wire going over it, by which is denoted, that on that side of the wire next the sun is the enlightened half of the earth, and the opposite side the darkened half, you will here see very naturally represented the cause of the different lengths of day and night, by ob¬ serving the unequal portions of the circle which the island of Great Britain, or the city of London, or any other place, describes in the light and dark hemispheres at different times of the year, by turning the earth on its axis with the hand. But in some of the better or¬ reries on this principle, the earth revolves about its axis by wheel-work. As to the eclipses of the sun and moon, the true causes of them are here very clearly seen ; for by placing the lamp (fig. 166.) upon the centre, in room of the brass ball denoting the sun, and turning the winch until the moon comes into a right line between the centres of the lamp (or sun) and earth, the shadow of the moon will fall upon the earth, and all who live on that part over which the shadow passes, will see the sun eclipsed more or less. On the other side, the moon passes (in the aforesaid case) through the shadow of the earth, and is by that means eclipsed. And the orbit A (fig. 164.) is so moveable on the two joints called nodes that any per¬ son may easily represent the due position of the nodes and intermediate spaces of the moon’s orbit; and thence show when there will or will not be an eclipse of either luminary, and what the quantity of each will be. While the moon is continuing to move round the earth, the lamp on the centre will so illumine the moon, that you will easily see all her phases, as new, dichoto¬ mized, gibbous, full, waning, &c. just as they appear in the heavens. You will moreover observe all the same phases of the earth as they appear at the moon. •Append,1 ji The satellites of Jupiter and Saturn are moveable Descripti | only by the hand ; yet may all their phenomena be ea-of Astrom j j sily represented, excepting the true relative motions and micalln - distances. Thus, if that gilt globe which before re- ,slrumtl1'1 itf® presented the sun be made now to denote Jupiter, and ^ four of the primary planets only be retained, then will the Jovian system he represented j and, by candle light only, you will see (the machine being in motion) the immersions and emersions of the satellites into and out of Jupiter’s shadow. You will see plainly the manner in which they transit his body, and their occultations behind it. You will observe the various ways in which one or more of these moons may at times disappear. And if the machine be set by a white wall, &c. then by the projection of their shadows will be seen the rea¬ sons why those moons always appear on each side of Ju¬ piter in a right line, why those which are most remote may appear nearest, and e co?itrario. And the same may be done for Saturn’s five moons and his ring. The Method of Rectifijivg the Orrery, and the proper Manner of placing the Planets in their true Situa¬ tions. Having dwelt thus much on the description of orre¬ ries, it may be useful to young readers, to point out the method by which the orrery should be first recti¬ fied, previous to the exhibition or using of it: and the following is extracted from Mr William Jones’s descrip¬ tion of his new Portable Orrery. “ The method of showing the places, and relative aspects of the planets on any day of the year in the planetarium, must be done by the assistance of an ephemeris or almanack, which among other almanacks is published annually by the Stationers Company. “ The ephemeris contains a diary or daily account of the planets places in the heavens, in signs, degrees, and minutes, both as they appear to theVeye supposed to be at the sun, and at the earth, throughout the year. The first of these positions is called the helio¬ centric place, and the latter, the geocentric place. The heliocentric place is that made use of in orreries j the geocentric place, that in globes. As an example for finding their places, and setting them right in the or¬ rery, we will suppose the ephemeris (by White, which for this purpose is considered the best) at hand, where¬ in lat the bottom of the left-hand page for every month is the heliocentric longitudes (or places) of all the pla¬ nets to every six days of the month $ which is near enough for common use : A copy of one of these ta¬ bles for March 1784 is here inserted for the informa¬ tion of the tyro. ASTRONOMY. Day 11 35 59 23 47 Helioc. long. 12 16 56 16 56 ty 7 17 17 17 28 Helioc. long. % 17 17 18 18 *9 II 43 J5 47 J9 Helioc. long. $ 05 30 23 1S 6 55 Helioc. long. © 11 iijt 37 n 23 29 5 £b 37 36 33 3° Helioc. long. $ o / 10 r9 29 8 38 35 7 38 8 Helioc. long. $ 7 m 58 25 II / 28 33 l5 V? 49 “ Now ^plndix. A S T II escAion “ Now as an example, we will suppose, that in order Astfio- to set the planets of the orrery, we want their heliocen- 1 fiicaljn- t,.;c places for the 21 st of this month. Looking into rU!iyts‘, the table, Ave take the 19th clay, which is the nearest to the day wanted : then, accordingly, we find the place of Saturn ( ), is in 170 17', or 17 degrees (rejecting the minutes, being in this case useless) of Capricor- nus j of Jupiter (It ) in 180 of Aquarius ( CS") ; Mars ( 5 ) in 10° of Cancer (25) ; the earth (©) in 290 of Virgo (irg) ; Venus ( d ) in 290 of Sagittarius, ( / ); Mercury ( ^ ) in 28 degrees of tlie same sign; and in the same manner for any other day therein specified. Upon even this circumstance depends a very pleasing astronomical praxis, by which the young tyro may at any time be able to entertain himself in a most rational and agreeable manner, viz. he may in a minute or two represent the true appearance of the planetary sy¬ stem just as it really is in the heavens, and for any day he pleases, by assigning to each planet its proper place in its orbit; as in the following manner: For the 19th of March, as before, the place of Saturn is in 170 of Capricornus (v^) ; now laying hold of the arm of Saturn in the orrery, you place it over or against the 170 of Capricorn on the ecliptic circle, constantly placed on or surrounding the instrument; thus doing the same for the other planets, they will have the pro¬ per heliocentric places for that day. “ Now, in this situation of the planets, we observe, that if a person was placed on the earth, he would see Venus and Jupiter in the same line and place of the ecliptic, consequently in the heavens they would ap¬ pear together or in conjunction ; Mercury a little to the left or eastward of them, and nearer to the sun ; Saturn to the right, or rvestward, farther from the sun ; Mars directly opposite to Saturn ; so that when Saturn appears in the west, Mars appears in the east, and vice versa. Several other curious and entertaining particulars, as depending on the above, may be easily represented and shown by the learner; particularly the foregoing when the winch is turned, and all the planets set into their respective motions.” We cannot close this detail on orreries more agree¬ ably than by the following account of an instrument of that sort invented by Mr James Ferguson, to which he gives the name of a Mechanical Paradox, and which is actuated by means of what many, as he ob¬ serves, even good mechanics, Avould be ready to pro¬ nounce impossible, viz. That the teeth of one wheel, taking equally deep into the teeth of three others, should aftect them in such a manner, that in turning it any Avay round its axi-, it should turn one of them the same way, another the contrary way, and the third no way at all. The solution of the paradox is given under the arti¬ cle Mechanics ; after which our author proceeds to give the following account of its uses. “ This ma¬ chine is so much of an orrery, as is sufficient to show the different lengths of days and nights, the vicissitudes of the seasons, the retrograde motion of the nodes of the moon’s orbit, the direct motion of the apogeal point of her orbit, and the months in which the sun and moon must be eclipsed. “ On the great immoveable plate A (see fig. 167.) are the months and days of the year, and the signs and degrees of the zodiac so placed, that tvken the annual O N O M Y. 175 index h is brought to any given day of the year, it tvill Description point to the degree of the sign in which the sun is onAstrono- that day. The index is fixed to the moveable frame BC, and is carried round the immoveable plate, with , ^■... . it, by means of the knob n. The carrying this frame and index round the immoveable plate, answers to the earth’s annual motion round the sun, and to the sun’s apparent motion round the ecliptic in a year. “ The central wheel D (being fixed on the axis a, which is fixed in the centre of the immoveable plate) turns the thick wheel E round its own axis by the motion of the frame ; and the teeth of the wheel E take into the teeth of the three wheels F, G, H, whose axes turn with one another, like the axes of the hour, minute, and second hands of a clock or watch, where the seconds are shown from the centre of the dial-plate. “ On the upper ends of these axes, are the round plates I, K, L ; the plate I being on the axis of the wheel F, K on the axis of G, and L on the axis of H. So that whichever way these wheels are aflected, their respective plates, and what they support, must be af¬ fected in the same manner ; each Avheel and plate be¬ ing independent of the others. “ The two upright wires M and N are fixed into the plate I; and they support the small ecliptic OP, on which, in the machine, the signs and degrees of the ecliptic are marked. This plate also supports the small terrestrial globe e, on its inclining axis/’, which is fixed into the plate near the foot of the wire N. This axis inclines 23I- degrees from a right line, supposed to be perpendicular to the surface of the plate I, and also to the plane of the small ecliptic OP, which is parallel to that plate. “ On the earth e is the crescent g, which goes more than half way round the earth, and stands perpendi¬ cular to the plane of the small ecliptic OP, directly facing the sun Z: Its use is to divide the enlightened half of the earth next the sun from the other half which is then in the dark ; so that it represents the boundary of light and darkness, and therefore ought to go quite round the earth ; but cannot in a machine, because in some positions the earth’s axis would fall upon it. The earth may be freely turned round on its axis by hand, within the crescent, which is supported by the crooked ivire w, fixed to it, and into the upper plate of the moveable frame BC. “ In the plate K are fixed the Iavo upright Avires Q and R: they support the moon’s inclined orbits ST in its nodes, which are the two opposite points of the moon’s orbit Avhere it intersects the ecliptic OP. The ascending node is marked to which the descending node is opposite below e, but hid from vieAV by the globe e. The half £b T of this orbit is on the north side of the ecliptic OP, and the other half e S £b is on the south side of the ecliptic. The moon is not in this machine; but when she is in either of the nodes of her orbit in the heavens, she is then in the plane of the ecliptic : Avhen she is at T in her orbit, she is in her greatest north latitude; and when she is at S, she is in her greatest south latitude. “ In the plate L is fixed the crooked wire UP, Avhich points doAvmvard to the small ecliptic OP, and shows the motion of the moon’s apogee therein, and its place at any given time. “ The Iy6 ASTRONOMY. Appenjix, Description u The ball Z represents the sun, which is supported ot Astrouo-by the crooked wire XY, fixed into the upper plate of struments" ^ie ^rame at X. A straight wire W proceeds from the sun Z, and points always towards the centre of the earth e ; but toward different points of its surface at different times of the year, on account of the obliquity of its axis, which keeps its parallelism during the earth’s annual course round the sun Z ; and therefore must in¬ cline sometimes toward the sun, at other times from him, and twice in the year neither toward nor from the sun, but sidewise to him. The wire W is called the solar ray. “ As the annual-index h shows the sun’s place in the ecliptic for every day of the year, by turning the frame round the axis of the immoveable plate A, ac¬ cording to the order of the months and signs, the solar ray does the same in the small ecliptic OP: for as this ecliptic has no motion on its axis, its signs and degrees still keep parallel to those on the immoveable plate. At the same time, the nodes of the moon’s orbit ST (or points where it intersects the ecliptic OP) are moved backward, or contrary to the order of signs, at the rate of 19-f degrees every Julian year $ and the moon’s apogeal w'ire UU is moved forward, or accord¬ ing to the order of the signs of the ecliptic, nearly at the rate of 41 degrees every Julian year j the year be¬ ing denoted by a revolution of the earth e round the sun Z ; in which time the annual index h goes round the circles of months and signs on the immoveable plate A. “ Take hold of the knob w, and turn the frame round thereby ; and in doing this, you will perceive that the north pole of the earth e is constantly before the cres¬ cent g, in the enlightened part of the earth toward the sun, from the 20th of March to the 23d of Sep¬ tember 5 and the south pole all that time behind the crescent in the dark j and from the 23d of September to the 20th of March, the north pole as constantly in the dark behind the crescent, and the south pole in the light before it j which shows, that there is but one day and one night at each pole, in the whole year j and that when it is day at either pole, it is night at the' other. “ From the 20th of March to the 23d of September, the days are longer than the nights in all those places of the northern hemisphere of the earth which revolve through the light and dark, and shorter in those of the southern hemisphere. From the 23d of September to the 20th of March, the reverse. “ There are 24 meridian semicircles drawn on the globe, all meeting in its poles : and as one rotation or turn of the earth on its axis is performed in 24 hours, each of these meridians is an hour distant from the other, in every parallel of latitude. Therefore, if you bring the annual index h to any given day of the year, on the immoveable plate, you may see how long the day then is at any place of the earth, by counting how many of these meridians are in the light, or before the crescent, in the parallel of latitude of that place j and this number being subtracted from 24 hours, will leave remaining the length of the night. And if you turn the earth round its axis, all those places will pass di¬ rectly under the point of the solar ray, which the sun passes vertically over on that day, because they are just as many degrees north or south of the equator as the sun’s declination is then from the equinoctial. “ At the two equinoxes, viz. on the 20th of March and 23d of September, the sun is in the equinoctial, and consequently has no declination. On these dajs, the solar ray points directly toward the equator, the earth’s poles lie under the inner edge of the crescent, or boundary of light and darkness ; and in every pa¬ rallel of latitude there are 12 of the meridians or hour- circles before the crescent, and 12 behind it, which shows that the days and nights then are each 12 hours long at all places of the earth. And if the earth be turned round its axis, you will see that all places on it go equally through the light and the dark hemi¬ spheres. “ On the 21st of June, the whole space within the north polar circle is enlightened, which is 23^ de¬ grees from the pole, all around ; because the earth’s axis then inclines 23^ degrees toward the sun : but the whole space within the south polar circle is in the dark j and the solar ray points toward the tropic of Cancer on the earth, which is 23^ degrees north from the equator. On the 2Cth of December the reverse hap¬ pens, and the solar ray points toward the tropic of Capricorn, which is 24-5- degrees south from the equa¬ tor. “ If you bring the annual-index h to the beginning of January, and turn the moon’s orbit ST by its support¬ ing wires Q and R till the ascending node (marked £t) comes to its place in the ecliptic OP, as found by an ephemeris, or by astronomical tables, for the beginning of any given year j and then move the annual index by means of the knob n, till the index comes to any given day of the year afterward, the nodes will stand against their places in the ecliptic on that day 5 and if you move on the index till either of the nodes comes di¬ rectly against the point of the solar ray, the index will then be at the day of the year on which the sun is in conjunction with that node. At the times of those new moons, which happen within seventeen days of the conjunction of the sun with either of the nodes, the sun will be eclipsed; and at the times of those full moons, which happen within twelve days of either of these conjunctions, the moon will be eclipsed. Without these limits there can be no eclipses either of the sun or moon ; because, in nature, the moon’s latitude or de¬ clination from the ecliptic is too great for the moon’s shadow to fall on any part of the earth, or for the earth’s shadow to touch the moon. “ Bring the annual-index to the beginning of Janu¬ ary, and set the moon’s apogeal wire UU to its place in the ecliptic for that time, as found by astronomical tables ; then move the index forward to any given day of the year, and the wire will point on the small ecliptic to the place of the moon’s apogee for that time. “ The earth’s axis ^inclines always toward the be¬ ginning of the sign Cancer on the small ecliptic OP. And if you set either of the moon’s nodes, and her apogeal wire to the beginning of that sign, and turn the plate A about, until the earth’s axis inclines to¬ ward any side of the room (suppose the north side), and then move the annual-index round and round the immoveable plate A, according to the order of the months Desc of As- tnies strun 111 ppendix. 1 »crii)t!on months an«! signs upon it, you will see that the earth’s Astrono-axis and beginning of Cancel’ will still keep towards the ical In- same side of the room, without the least deviation from U!li£nt‘" it but the nodes Of the moon’s orbit ST will turn progressively towards all the sides of the room, con» trary to the order of signs in the small ecliptic OP, or from east, by south, to west, and so on j and the apogeal wire UU will turn the contrary way to the motion of the nodes, or according to the order of the signs in the small ecliptic, from west, by south, to east, and so on quite round. A clear proof that the wheel F, which governs the earth’s axis and the small eclip¬ tic, does not turn any way round its own centre j that the wheel G, which governs the moon’s orbit OP, turns round its own centre backward, or contrary both to the motion of the frame BC and thick wheel E ; and that the wheel H, which governs the moon’s apo- geal wire UU, turns round its own centre forward, or in direction both of the motion of the frame and of the thick wheel E, by which the three wheels F, G, and H, are affected. “ The wheels D, E, and F, have each 39 teeth in the machine j the wheel G has 37, and H 44. “ The parallelism of the earth’s axis is perfect in this machine j the motion of the apogee very nearly so ; the motion of the nodes not quite so near the truth, though they will not vary sensibly therefrom in one year. But they cannot be brought nearer, unless larger wheels, with higher numbers of teeth, are used. “ In nature, the moon’s apogee goes quite round the ecliptic in 8 years and 312 days, in the direction of the earth’s annual motion j and the nodes go round the ecliptic, in a contrary direction, in 18 years and 225 days. In the machine, the apogee goes round the ecliptic OP in eight years and four-fifths of a year, and the nodes in 18 years and a half.” The Cometarium, (fig. 168.). This curious ma¬ chine shows the motion of a comet or eccentric body moving round the sun, describing equal areas in equal times, and may be so contrived as to show such a mo¬ tion for any degrees of eccentricity. It was invented by the late Dr Desaguliers. The dark elliptical groove round the letters abed tfghiklm is the orbit of the comet Y $ this comet is carried round in the groove according to the order of letters, by the wire W fixed in the sun S, and slides on the wire as it approaches nearer to or recedes far¬ ther from the sun, being nearest of all in the perihe¬ lion a, and farthest in the aphelion g. The areas, o*SZ>, £Sc, c S J, &c. or contents of these several triangles, are all equal •, and in every turn of the winch Y, the comet Y is carried over one of these areas ; consequently, in as much time as it moves from f to gi or from g to //, it moves from m to a, or from a to b ; and so of the rest, being quickest of all at a, and slowest at g. Thus the comet’s velocity in its orbit continually decreases from the perihelion a to the aphe¬ lion g j and increases in the same proportion from g to a. The ecliptic orbit is divided into 12 equal parts or signs, with their respective degrees, and so is the circle nopqrstu, which represents a great circle in the heavens, and to which the comet’s motion is re¬ ferred by a small knob on the point of the wire W. Whilst the comet moves from Z' to in its orbit, it Vot. III. Part I. f ASTRONOMY. 177 appears to move only about five degrees in this circle, Description as is shown by the small knob on the end of the wire of Astiouo- W j but in as short time as the comet moves from m to ,"‘ca* ll'' «, or from a to b, it appears to describe the large space l'uull^:ilU', tn or no in the heavens, either of which spaces con¬ tains 120 degrees, or four signs. Were the eccentricity of its orbit greater, the greater still would be the differ¬ ence of its motion, and vice versa. ABCDEFGH1KLM is a circular orbit for showing the equable motion of a body round the sun S, describ¬ ing equal areas ASB, BSC, &c. in equal times with those of the body Y in its elliptical orbit above men¬ tioned $ but with this difference, that the circular mo¬ tion describes the equal arcs AB, BC, &c. in the same equal times that the elliptical motion describes the un¬ equal arcs ab, be, &c. Now suppose the two bodies Y and 1 to start from the points a and A at the same moment of time, and, each having gone round its respective orbit, to arrive at these points again at the same instant, the body Y will be forwarder in its orbit than the body I all the way from a to g, and from A to G: but I will be forwarder than Y through all the other half of the or¬ bit j and the difference is equal to the equation of the body Y in its orbit. At the points o A, and gG, that is, in the perihelion and aphelion, they will be equal $ and then the equation vanishes. This shows why the equation of a body moving in an elliptic orbit is added to the mean or supposed circular motion from the perihelion to the aphelion, and subtracted from the aphelion to the perihelion, in bodies moving round the sun, or from the perigee to the apogee, and from the apogee to the perigee in the moon’s motion round the earth. This motion is performed in the following manner by the machine, fig. 169. ABC is a wooden bar (in the box containing the wheel-work), above which are the wheels D and E, and below it the elliptic plates FF and GG; each plate being fixed on an axis in one of its focuses, at E and K; and the wheel E is fixed on the same axis with the plate FF. These plates have grooves round their edges precisely of equal diameters to one another, and in these grooves is the cat-gut string gg,gg crossing between the plates at b. On H, the axis of the handle or winch N in fig, 216, is an endless screw- in fig. 217. working in the wheels D and E, whose numbers of teeth being equal, and should be equal to the number of lines, «S, 6 S, c S, &c. in fig. 168. they turn round their axis in equal times to one an¬ other, and to the motion of the elliptic plates. For, the wheels D and E having equal numbers of teeth, the plate FF being fixed on the same axis with the wheel E, and turning the equally big plate GG by a cat-gut string round them both, they must all go round their axis in as many turns of the handle N as either of the wheels has teeth. It is easy to see, that the end b of the elliptical plate FF being farther from its axis E than the oppo¬ site end I is, must describe a circle so much the larger in proportion, and therefore move through so much more space in the same time ; and for that reason the end b moves so much faster than the end I, although it goes no sooner round the centre E. But then the quick-moving end A of the plate FF leads about the shoit end b K of the plate GG with the same velocity ; ■Z and 373 Description of Aotrono- inical In¬ struments. 429 Celestial globe. ASTRO and the slow-moving end I of the plate FF coming half round as to B, must then lead the long end k of the plate GG as slowly about: so that the elliptical plate FF and its axis E move uniformly and equally quick in every part of its revolution : but the elliptical plate GG, together with its axis K, must move very unequally in different parts of its revolution j the diffe¬ rence being always inversely as the distance of any point of the circumference of GG from its axis at K : or in other words, to instance in two points, if the di¬ stance K & be four, five, or six times as great as the distance K h, the point h will move in that position, four, five, or six times as fast as the point k does, when the plate GG has gone half round ; and so on for any other eccentricity or diflerence of the distances K k and K/z. I he tooth I on the plate FF falls in between the two teeth at k on the plate GG; by which means the revolution of the latter is so adjusted to that of the former, that they can never vary from one another-. On the top of the axis of the equally-moving wheel D in fig. 169. is the sun S in fig. 168.: which sun, by the wire fixed to it, carries the ball I round the circle ABC1), &c. with an equable motion, accord¬ ing to the order of the letters : and on the top of the axis K of the unequally-moving ellipses GG, in fig. 169. is the sun S in fig. 168. carrying the ball Y unequally round in the elliptical groove abed, &c. N. B. This elliptical groove must be precisely equal and similar to the verge of the plate GG, which is also equal to that of FF. In this manner machines may be made to show the true motion of the moon about the earth, or of any planet above the sun, by making the elliptical plates of the same eccentricities, in proportion to the radius, as the orbits of the planets are, whose motions they re¬ present ; and so their different equations in different parts of their orbits may be made plain to sight, and cleai-er ideas of these motions and equations acquired in half an hour, than could be gained from reading half a day about such motions and equations. The Improved Celestial Globe, fig. 170. On the north pole of the axis, above the hour-circle, is fixed an arch MKH of 23^ degrees; and at the end FI is fixed an upright pin HG, which stands directly over the north pole of the ecliptic, and perpendicular to that part of the surface of the globe. On this pin are two moveable collets at E and FI, to which are fixed the quadrantile wires 1M and O, having two little balls on their ends for the sun and moon, as in the figure. The collet D is fixed to the circular plate F, whereon the 29J days of the moon’s age are engra¬ ven, beginning just under the sun’s wire N; and as this wire is moved round the globe, the plate F turns round with it. These wires are easily turned, if the screw G be slackened ; and when they are set to their proper places, the screw serves to fix them there, so as in turning the ball of the globe, the wires with the sun and moon go round with it; and these two little balls rise and set at the same times, and on the same points of the horizon, for the day to which they are rectified, as the sun and moon do in the hea¬ vens. Because the moon keeps not her course in the eclip¬ tic (as the sun appears to do) but has a declination of 5t degrees on each side from it in every lunation, her 2 N O M Y. Appefcj ball may be screwed as many degrees to either side of])e the ecliptic as her latitude or declination from the eclip. of r, tic amounts to at any given time. m In. The horizon is supported by two semicircular arches, because pillars would stop the progress of the balls when they go below the horizon in an oblique sphere. To rectify this globe. Elevate the pole to the lati¬ tude of the place ; then bring the sun’s place in the ecliptic for the given day to the brazen meridian, and set the hour index at 12 at noon, that is, to the upper 12 on the hour circle ; keeping the globe in that situa¬ tion, slacken the screw G, and set the sun directly over his place on the meridian ; which done, set the moon’s wire under the number that expresses her age for that day on the plate F, and she will then stand over her place in the ecliptic, and show what constellation she Lastly, fasten the screw G, and adjust the moon is in. to her latitude, and the globe will be rectified. Having thus rectified the globe, turn it round, and observe on what point of the horizon the sun and moon balls rise and set, for these agree with the points of the compass on which the sun and moon rise and set in the heavens on the given day ; and the hour index shows the time of their rising and setting: and likewise the time of the moon’s passing over the meridian. This simple apparatus shows all the varieties that can happen in the rising and setting of the sun and moon ; and makes the forementioned phenomena of the har¬ vest moon plain to the eye. It is also very useful in reading lectures on the globes, because a large com¬ pany can see this sun and moon go round, rising above and setting below the horizon at different times, ac¬ cording to the seasons of the year: and making their appulses to different fixed stars. But in the usual way, where there is only the places of the sun and moon in the ecliptic to keep the eye upon, they are easily lost sight of, unless they be covered with patches. 1 he IRAjectorium Lunare, fig. 171, This ma-Tl'flj chine is for delineating the paths of the earth and™ moon, showing what sort of curves they make in the ethereal regions. S is the sun, and E the earth, whose centres are 95 inches distant from each other ; every inch answering to 1000,000 of miles. M is the moon, ! whose centre is parts of an inch from the earth’s in this machine, this being in just proportion to the moon s distance from the earth. AA is a bar of wood, to be moved by hand round the axis^ which is fixed in the wheel Y. The circumference of this wheel is to the circumference of the small wheel L (below the other end of the bar) as 365! days is to 29J, or as a yeai is to a lunation, i he wheels are grooved round their edges, and in the grooves is the cat-gut string GG crossing between the wheels at X. On the axis of the wheel L is the index I, in which is fixed the moon’s axis M for carrying her round the earth E (fixed on the axis of the wheel L) in the time that the index goes round a circle of 29F equal parts, which are the days of the moon’s age. Ihe wheel V has the months and days of the year all round its limb; and in the bar AA is fixed the index /, which points out the days oi the months answering the days of the moon s age, shown by the index F, in the circle of 29£ equal parts at the other end of the bar. On the Wipendk. axI's ^ie w^ee^ L *s P11^ ^ie piece D, below of i\stnmo tbe cock C, in which this axis turns round ; and in a! In- D are put tiie pencils e and ??i directly under the earth ASTRONOMY. 179 between the horizon and the zenith, as well to the Description , lit1 northward as southward. This place, called an Observatory, should contain ,1 menu £ anrf moon M j so that m is carried round , to bring them to the same distances again, though not to the same points of space \ then, as m goes round e, e will go as it were round the centre of gravity be¬ tween the earth e and moon m ; but this motion will not sensibly alter the figure of the earth’s path or the moon’s. If a pin, as p, be put through the pencil m, with its head towards that of the pin q in the pencil c-, its head will always keep thereto as m goes round e, or as the same side of the moon is still obverted to the earth. But the piny?, which may be considered as an equatorial diameter of the moon, will turn quite round the point m, making all possible angles with the line of its progress, or line of the moon’s path. This is an ocular proof of the moon’s turning round her axis. III. A Description of the principal Astronomical In¬ struments by winch Astronomers make the most ac¬ curate Observations. By practical astronomy is implied the knowledge of observing the celestial bodies with respect to their po¬ sition and time of the year, and of deducing from those observations certain conclusions useful in calculating the time when any proposed position of these bodies shall happen. For this purpose, it is necessary to have a room or place conveniently situated, suitably contrived, and fur¬ nished with proper astronomical instruments. It should have an uninterrupted view from the zenith down to (or even below) the horizon, at least towards its car¬ dinal points ; and for this purpose, that part of the roof which lies in the direction of the meridian, in par¬ ticular, should have moveable covers, which may easily be moved and put on again by which means an in¬ strument may be directed to any point of the heavens I. A Pendulum Clock, for showing equal time. This should show time in hours, minutes and seconds j and with which the observer, by hearing the beats of the pendulum, may count them by his ear, while his eye is employed on the motion of the celestial object he is observing. Just before the object arrives at the position described, the observer should look on the clock and remark the time, suppose it 9 hours 15 mi¬ nutes 25 seconds : then saying, 25, 26, 27, 28, &c. responsive to the beat of the pendulum, till he sees through the instrument the object arrived at the posi¬ tion expected j which suppose to happen when he says 38, he then writes down 9 h. 15 min. 38 sec. for the time of observation, annexing the year and the day of the month. If two persons are concerned in making the observation, one may read the time audibly while the other observes through the instrument, the observer repeating the last second read when the desired position happens. II. An Achromatic Refracting Telescope, or a REFLECTING one, of two feet at least in length, for observing particular phenomena. These instruments are particularly described under Optics. _ HI- A Micrometer, for measuring small angular distances. See Micrometer. IV. Astronomical Quadrants, both mural and Quadrants, portable, for observing meridian and other altitudes of the celestial bodies. 1. The mural quadrant is in the form of a quarter of a circle, contained under two radii at right angles to one another, and an arch equal to one fourth part of the circumference of the circle. It is the most useful and valuable of all the astronomical instruments ; and as it is sometimes fixed to the side of a stone or brick wall, and the plane of it erected exactly in the plane of the meridian, it in this case receives the name of mural quadrant or arch. Tycho Brahe was the first person who contrived this mural arch, viz. who first applied it to a wall j and Mr Flamstead, the first in England who, with indefa¬ tigable pains, fixed one up in the royal observatory at Greenwich. These instruments have usually been made from five to eight feet radius, and executed by those late cele¬ brated artists Sisson, Graham, Bird, and other eminent mathematical ^instrument makers in London. The construction of them being generally the same in all the sizes, we shall here describe one made by the late Joh. Sisson, under the direction of the late Mr Graham. Fig. 172. represents the instrument as al¬ ready fixed to the wall. It is of copper, and of about five feet radius. The frame is formed of flat bars, and strengthened by edge bars affixed underneath perpen¬ dicularly to them. The radii HB, HA, being divid¬ ed each into four equal parts, serve to find out the points D and E, by which the quadrant is freely sus¬ pended on its props or iron supports that are fastened securely in the wall. , One of the supports E is represented separately in e on one side of the quadrant. It is moveable by means of a long slender rod EF or e/, which goes into a hol- Z 2 low 180 A 8 T R DesciipJoti low screw in order to restore the instrument to its si- ^tiic ^l I i° rpl.^0n 'vuen ^ *s discovered to be a little deranged, ttruments. V**3 ma^ ^no’vn the very fine perpendicular i.—y tnread IJA, which ought always to coincide with the same point A of the limb, and carefully examined to he so by a small magnifying telescope at every observation. In order to prevent the unsteadiness of so great a machine, there should be placed behind the limb lour copper ears with double cocks, I, K, I, K. There are others along the radii HA and HB. Itach of these cocks contains two screws, into which are fastened the ears that are fixed behind the qua¬ drant. Over the wall or stone which supports the instrument, and at the same height as the centre, is placed horizon¬ tally the axis PO, which is perpendicular to the plane ol the instrument, and which would pass through the centre if it was continued. The axis turns on two pivots P. On this axis is fixed at right angles ano¬ ther branch ON, loaded at its extremity with a weight Iv capable of equipoising with its weight that of the telescope LM ; whilst the axis, by its extremity nearest the quadrant, carries the wooden frame PRM, which is fastened to the telescope in M. The counterpoise takes oil from the observer the weight of the telescope when he raises it, and hinders him from either forcing or straining the instrument. The lower extremity (V) of the telescope is fur¬ nished with two small wheels, which takes the limb of the quadrant on its two sides. The telescope hardly bears any more upon the limb than the small friction of these two wheels; which renders its motion so ex¬ tremely easy and pleasant, that by giving it with the hand only a small motion, the telescope will run of it¬ self oyer a great part of the limb, balanced by the coun¬ terpoise N. When the telescope is to be stopped at a certain po¬ sition, the copper hand T is to be made use of, which embraces the limb and springs at the bottom. It is fixed by setting a screw, which fastens it to the limb, ihen, in turning the regulating screw, the telescope will be advanced j which is continued until the star or other object whose altitude is observing be on the horizontal fine thread in the telescope. Then on the plate X supporting the telescope, and carrying a ver¬ nier or nonius, will be seen the number of degrees and minutes, and even quarters of minutes, that the angu¬ lar height of the obj'ect observed is equal to. The re- maindei is easily estimated within two or three seconds nearly. There are several methods of subdividing the divi¬ sions of a mural quadrant, which are usually from five to ten minutes each j but that winch is most common¬ ly adopted is by the vernier or nonius, the contrivance °f Peter Vernier a I renchman. This vernier consists of a piece of copper or brass CDAB (fig. 173.), which is a small portion of X (fig. 172.) represented separately. The length CD is divided into 20 equal parts, and placed contiguously on a portion of the di¬ vision of the limb of the quadrant containing 21 divi¬ sions, and thereby dividing this length into 20 equal parts, i bus the first division of the vernier piece mark- ed 15, beginning at the point D, is a little matter back¬ ward, or to the left of the first division of the limb equal to 15.. The second division of the vernier is to the left a. O N O M Y. Apper of the second division of the limb double of the first p)eS( difference, 01-30"$ and so on unto the 20th and last of a J division on the left of the vernier piece $ where the 20 ni>c 1 differences being accumulated each of the 20th part of stru 1 the division of the limb, this last division will be found lid lii to agree exactly with the 21st division on the limb of the quadrant. The index must be pushed the 20th part of a divi¬ sion, or 15", to the right $ for to make the second di¬ vision on the vernier coincide with one of the divisions of the limb, in like manner is moving two 20ths, or 30", we must look at the second division of the index, and there will be a coincidence with a division of the limb. Thus may be conceived that the beginning D of the vernier, which is always the line of reckoning, has advanced two divisions, or 30", to the right, when the second division, marked 30 on the vernier, is seen to correspond exactly with one of the lines of the qua¬ drant. By means of this vernier may be readily distin¬ guished the exactitude of 15" of the limb of a qua¬ drant five feet radius, and simply divided into 5'. By an estimation by the eye, afterwards, the accuracy of two or three seconds may be easily judged. On the side of the quadrant is placed the plate of copper which carries the telescope. This plate carries two verniers. The outer line CD divides five minutes into 20 parts, or 15" each. The interior line AB answers to the parts of another division not having 90°, but 96 parts, of the quadrant. It is usually adopted by English astronomers on account of the facility of its subdivi- sions. Each of the 96 portions of the quadrant is equivalent to 56' 15" of the usual divisions. It is di- | vided on the limb into 16 parts, and the arch of the vernier AB contains 25 of these divisions $ and being divided itself into 24, immediately gives parts, the va¬ lue of each of which is 8" 47-f"'. From this mode a table of reduction may easily be constructed, which will serve to find the value of this second mode of di¬ viding in degrees, minutes, and seconds, reckoning in the usual manner, and to have even the advantage of two different modes $ which makes an excellent verifi¬ cation of the divisions on the limb of the quadrant and observed heights by the vernier. 2. The Portabk Astfvjnomical Quadrant, is that instru¬ ment of all others which astronomers make the greatest use of, and have the most esteem for. They are gene¬ rally made from 12 to 23 inches. Fig. j 74. is a re¬ presentation of the improved modern one, as made by the late Mr Sisson and by the present mathematical instrument makers. I his is capable of being carried to any part of the world, and put up for observation in an easy and accurate manner. It is made of brass, and strongly framed together by crossed perpendicular, bars. The arch AC, and telescope EF, are divided, and constructed in a similar manner to the mural qua¬ drant, but generally without the division of 96 parts.. I he counterpoise to the telescope T is represented at P, and also another counterpoise to the quadrant itself at P.. The quadrant is fixed to a long axis, which goes into the pillar KR. Upon this axis is fixed an index, which points to and subdivides by a vernier the. divisions of the azimuth circle K. This azimuth circle is extremely useful for taking the azimuth of a cele¬ stial body at the same time its altitude is observed* The ^Appendix. ^captionThe upper end of the axis is firmly connected with the ni'pistrono-adjusting frame GH ; and the pillar is supported on the tin, )cal Ilu crossed feet at the bottom of the pillar KR with the ad- ^*iJ"ients, justing screws a, b, c, d. When this instrument is set up for use or observa¬ tion, it is necessary that two adjustments he very accu¬ rately made : One, that the plane or surface of the in¬ strument be truly perpendicular to the horizon ; the other, that the line supposed to be drawn from the centre to the first line of the limb, he truly on a level or parallel with the horizon. The first of these par¬ ticulars is done by means of the thread and plum¬ met p ; the thread of which is usually of very fine sil¬ ver wire, and it is placed opposite to a mark made up¬ on the end of the limb of the instrument. The four screws at the loot, a, b, c, d, are to be turned until a perfect coincidence is observed of the thread upon the mark, which is accurately observed by means of a small telescope T, that fits to the limb. The other adjust¬ ment is effected by means of the spirit level L, which applies on the frame GH, and the small screws turned I as before until the bubble of air in the level settles in the middle of the tube. The dotted tube EB is a kind ol prover to the instrument: for by observing at what mark the centre of it appears against, or by put- ting up a mark against it, it will at any time discover if the instrument has been displaced. The screw S at the index, is the regulating or adjusting screw, to move the telescope and index, during the observation, with 1 ,2 the utmost nicety. Atonal . ^- Astronomical or Equatorial Sector. This km. is an instrument for finding the difference in right as¬ cension and declination between two objects, the di¬ stance of which is too great to be observed by the mi¬ crometer. It was the invention of the late ingenious Mr George Graham, F. R. S. and is constructed from the following particulars. Let AB (fig. 175.) repre¬ sent an arch of a circle containing 10 or 12 degrees well divided, having a strong plate CD for its radius, fixed to the middle ol the arch at D : let this radius be applied to the side of an axis HFI, and be move- able about a joint fixed to it at F, so that the plane of the sector may be always parallel to the axis HI j which being parallel to the axis of the earth, the plane of the sector will always be parallel to the plane of some hour-circle. Let a telescope CE be moveable about the centre C of the arch AB, from one end of it to the other, by turning a screw at G ; and let the line of sight be parallel to the plane of the sector. Now, by turning the whole instrument about the axis HI, till the plane ol it be successively directed, first to one of the stars and then to another, it is easy to move the sector about the joint F, into such a position, that the arch AB, when fixed, shall take in both the stars in their passage, by the plane of it, provided the differ¬ ence of their declinations does not exceed the arch AB. Then, having fixed the plane of the sector a little to the westward of both the stars, move the telescope CE by the screw G ; and observe by a clock the time of each transit over the cross hairs, and also the degrees and minutes upon the arch AB, cut by the index at each transit ; then in the difterence of the arches, the diflerence of the declinations, and by the dift’erence of the times, we have the difterejice of the right ascensions, of the stars. I 8l The dimensions of this instrument are thefce : The Description length of the telescope, or the radius of the sector, isof Astrono- 2^ feet ; the breadth of the radius, near the end C, is m'ca* *n* if inch ; and at the end D two inches. The breadth ol the limb AB is if inch ; and its length six inches, containing ten degrees divided into quarters, and num¬ bered from either end to the other. The telescope car¬ ries a nonius or subdividing plate, whose length, being equal to sixteen quarters of a degree, is divided into fif¬ teen eq*'al parts j which, in effect, divides the limb in¬ to minutes, and, by estimation, into smaller parts. The length of the square axis HIF is eighteen inches, and of the part HL twelve inches; and its thickness is about a quarter of an inch : the diameters of the circles are each five inches : the thickness of the plates, and the other measures, may be taken at the direction of a work¬ man. This instrument may be rectified, for making obser¬ vations, in this manner: By placing the intersection of the cross hairs at the same distance from the plane of the sector, as the centre of the object-glass, the plane described by the line of sight, during the circular mo¬ tion ol the telescope upon the limb, will be sufficiently true, or free from conical curvity ; which may he exa¬ mined by suspending a long plumb-line at a convenient distance from the instrument; and by fixing the plane of the sector in a vertical position, and then by observ¬ ing, while the telescope is moved by the screw along the limb, whether the cross hairs appear to move along the plumb-line. Ihe axis bfo may be elevated nearly parallel to the axis of the earth, by means of a small common qua¬ drant ; and its error may be corrected, by making the line of sight follow the circular motion of any of the circumpolar stars, while the whole instrument is moved about its axis h fo^ the telescope being fixed to the limb ; for this purpose, let the telescope A: / be direct¬ ed to the star a, when it passes over the highest point of its diurnal circle, and let the division cut by the nonius be then noted ; then, after twelve hours, when the star comes to the lowest point of its circle, having turned the instrument half round its axis, to bring the telescope into the position m n; if the cross hairs cover the same star supposed at b, the elevation of the axis hfo is exactly right; hut if it be necessary to move the telescope into the position u v, in order to point to this star at c, the arch in u, which measures the angle mfu or b fc, will be known; and then the axis hf o must be depressed half the quantity of this given angle if the star passed below b, or must be raised so much higher it above it; and then the trial must he repeat¬ ed till the true elevation of the axis be obtained. Bv making the like observations upon the same star on each side the pole, in the six-o’clock hour circle, the error of the axis, toward the east or west, may also be found and corrected, till the cross hairs follow the star, qui te round the pole ; for supposing a 0p b c to be an arch of the meridian (or in the second practice of the, six-o’clock hour circle), make the angle afp equal to half the angle a fc, and the line f p will point to the. pole ; and the angle 0f p, which is the error of the axis, will be equal to half the angle bfc, or mfu, found by the observation ; because the difference of the two angles afb, afc, is double the difference of. their halves cifo and afp. Unless the star ba very y ASTRONOM Y. 102 ASTRO struments. 4.33 tJcsciiption very near the pole, allowance must be made for refrac- of Astiono- tlons. n)Ical Ill‘ VI. Transit and Equal Altitude Instruments. I. The Transit Instrument Is used for observing ob- t.io jects as they pass over the meridian. It consists of a Transit In-telescope fixed at right angles to a horizontal axis; strumeuts. vvliich axis must be so supported that what is called the line of collimation, or line of sight of the telescope, may move in the plane of the meridian. This instru¬ ment was first made by the celebrated Mr Ro*mer in the year 1689, and has since received great improve¬ ments. It is made of various sizes, and of large dimen¬ sions in our great observatories ; but the following is one of a size sufficiently large and accurate for all the useful purposes. I he axis AB (fig. 176.)} to which the middle of the telescope is fixed, is about feet long, tapering gradually towards its ends, which terminate in cylin¬ ders well turned and smoothed. The telescope CD, which is about four feet long, and 14 inch diameter, is connected with the axis by means of a strong cube or die G, and in which the two cones MQ, forming the axis, are fixed. This cube or stock G serves as the principal part of the whole machine. It not only keeps together the two cones, but holds the two sockets KH, of 15 inches length, for the two tele¬ scopic tubes. Each of these sockets has a square base, and is fixed to the cube by four screws. These sockets are cut down in the sides about eight inches, to admit more easily the tube of the telescope ; hut when the tube is inserted, it is kept in firm by screwing up the tightening screws at the end of the sockets at K and H. These two sockets are very useful in keeping the telescope in its greatest possible degree of steadiness. They also afford a better opportunity of balancing the telescope and rectifying its vertical thread, than by any other means. In order to direct the telescope to the given height that a star would be observed at, there is fixed a semi¬ circle AN on one of the supporters, of about 84 inches diameter, and divided into degrees. The index is fixed on the axis, at the end of which is a vernier, which subdivides the degrees into 12 parts, or five mi¬ nutes. This index is moveable on the axis, and may be closely applied to the divisions by means of a tight¬ ening screw. Two upright posts of wood or stone YY, firmly fixed at a proper distance, are to sustain the support¬ ers of this instrument. These supporters are two thick brass plates HR, having well smoothed angular notches in their upper ends, to receive the cylindrical arms of the axis. Each of these notched plates is contrived to he moveable by a screw, which slides them upon the surfaces of two other plates immoveably fix¬ ed upon the two upright pillars ; one plate moving in a horizontal, and the other in a vertical direction ; or, which is more simple, these two modes are some¬ times applied only on one side, as at V and P, the ho¬ rizontal motion by the screw P, and the vertical by the screw V. These two motions serve to adjust the telescope to the planes of the horizon and meridian : to the plane of the horizon by the spirit-level EF, hung by DC on the axis MQ, in a parallel direction : and to the plane of the meridian in the following man¬ ner : N O M Y. Appen |t 1, Observe by the clock when a circumpolar star seen j)esc through this instrument transits both above and below of As the pole; arid if the times of describing the eastern and Wk« . , western parts of its circuit are equal, the telescope is strui ts, ^ then in the plane of the meridian : otherwise the screw P must he gently turned that it may move the tele¬ scope so much that the time of the star’s revolution he bisected by both the upper and lower transits, taking care at the same time that the axis remains perfectly horizontal. When the telescope is thus adjusted, a mark must be set at a considerable distance (the greater the better) in the horizontal direction of the intersection of the cross wires, and in a place where it can be illumi¬ nated in the night-time by a lanthorn hanging near it ; which mark being on a fixed object, will serve at all times afterwards to examine the position of the tele¬ scope by, the axis of the instrument being first adjust¬ ed by means of the level. lo adjust the Clock hy the Sun’s Transit over the Meridian. Note the times by the clock when the pre¬ ceding and following edges of the sun’s limb touch the cross wire. The difference between the middle time and 12 hours, shows how much the mean, or time hy the clock, is faster or slower than the apparent or so¬ lar time for that day : to which the equation of time being applied, will show the time of mean noon for that day, by which the clock may be adjusted. 1. The Equal Altitude Instrument, is an instrument that is used to observe a celestial object when it has the same altitude on both the east and west sides of the meridian, or in the morning and afternoon. It principally consists of a telescope about 30 inches long, fixed to a sextantal or semicircular divided arch ; the centre of which is fixed to a long vertical axis : but the particulars of this instrument the reader will see explained in Optics. 3. Compound Transit Instrument. Some instruments have been contrived to answer both kinds of observa¬ tions, viz. either a transit or equal altitudes. Fig. 178. represents such an instrument, made first of all for Mr le Monnier, the French astronomer, by the late Mr Sisson, under the direction of Mr Graham, mounted and fixed up ready for observation. AB is a telescope, which may be 3, 4, 5, or 6 feet long, whose cylindrical tube fits exactly into another hollow cylinder a b, perpendicular to the axis : these several pieces are of the best hammered plate brass. The cylindrical extremity of this axis MN are of so¬ lid bell metal, and wrought exquisitely true, and ex¬ actly the same size, in a lathe ; and it is on the per¬ fection to which the cylinders or trunnions are turned that the justness of the instrument depends. In the common locus of the object-glass and eye-glass is pla¬ ced a reticle (fig. iqqi), consisting of three horizontal and parallel fine-stretched silver wires, fixed by pins or screws to a brass circle, the middle one passing through its centre, with a fourth vertical wire likewise passing through the centre, exactly perpendicular to the for¬ mer three. The horizontal axis MN (fig. 178.) is placed on a strong brass frame, into the middle of which a steel cy¬ linder GH is fixed perpendicularly, being turned truly round, and terminating in a conical point at its lower extremity; where it is let into a small hole drilled in the middle of the dove-tail slider \ which slider is supported appendix. ASTRO W;>cri|>tion supported by a hollow tube fixed to the supporting piece UttAstrono-IK, consisting of two strong plates of brass joined toge- it; h eal In- ther at right angles, to which are fixed two iron cramps -}pU imcnts.^ j- ^ ^ fg fastened to the stone wall of a r '' south window. The upper part G of the steel spindle is embraced by a collar def being in contact with the blunt extre¬ mity of three screws, whose particular use will be ex¬ plained by and by. O is another cylindrical collar closely embracing the steel spindle at about a third part of its length from the top j by the means of a small screw it may be loosened or pinched close as occasion requires. From the bottom of this collar proceeds an arm or lever acted on by the two screws g h, where¬ by the whole instrument, excepting the supporting piece, may be moved laterally, so that the telescope may be made to point at a distant mark fixed in the vertical of the meridian, ik is a graduated semicircle of thin brass screwed to the telescope, whereby it may be elevated so as to point to a known celestial object in the day-time. Im is a spirit-level parallel to the axis of rotation on the telescope, on which two trun¬ nions hang by two hooks at M and N. Along the upper side of the glass tube of the level slides a pointer to be set to the end of the air-bubble $ and when the position of the axis of rotation is so adjusted by the screws that the air-bubble keeps to the pointer for a whole revolution of the instrument, the spindle GH is certainly perpendicular to the horizon, and then the line of collimation of the telescope describes a circle of equal altitude in the heavens. When the level is suspended on the axis, raise or depress the tube of the level by twisting the neb of the screw n till you bring either the end of the air-bubble to rest at any point to¬ wards the middle of the tube, to which slide the in¬ dex : then lift off the level, and, turning the ends of it contrary ways, hang it again on the trunnions ; and if the air-bubble rests exactly again, the index as be¬ fore, the axis of rotation is truly horizontal: If not, depress that end of the axis which lies on the same side of the pointer as the bubble does, by turning the neb of the screw at N, till the bubble returns about half¬ way towards the pointer; then having moved the pointer to the place where it now rests, invert the ends ot the level again, and repeat the same practice till the bubble rests exactly at the pointer in both positions of the level. If, after the telescope is turned upside down, that is, after the trunnions are inverted end for end, you perceive that the same point of a remote fixed object is covered by the vertical wire in the focus ot the telescope, that was covered by it before the in¬ version, it is certain that the line of sight or collima¬ tion is perpendicular to the transverse axis; but if the said vertical wire covers any other point, the brass circle that carries the hairs must be moved by a screw- key introduced through the perforation in the side of the tube at X, till it appears to bisect the line joining these two points as near as you can judge ; then, by reverting the axis to its former position, you will find whether the wires be exactly adjusted. N. B. Tire ball o is a counterpoise to the centre of gravity of the semi¬ circle ik, without which the telescope would not rest in an oblique elevation without being fixed by a screw or some other contrivance. N O M Y. 183 The several before-mentioned verifications being Description accomplished, if the telescope be elevated to any angle of Astrono- witb the horizon, and there stopped, all fixed stars miCfd ,n- which pass over the three horizontal wires of the re- tide on the eastern side of the meridian in ascending, will have precisely the same altitudes when in descend¬ ing they again cross the same respective wires on the west side, and the middle between the times of each respective equal altitude will be the exact moment of the star’s culminating or passing the meridian. By the help of a good pendulum-clock, the hour of their true meridional transits will be known, and consequently the difference of right ascension of different stars. Now, since it will be sufficient to observe a star which has north declination two or three hours before and after its passing the meridian, in order to deduce the times of its arrival at that circle ; it follows, that having once found the difference of right ascension of two stars about 60 degrees asunder, and you again observe the first of these stand at the same altitude both in the east and west side, you infer with certainty the moment by the clock at which the second star will be on the meridian that same night, and by this means the transit instrument may be fixed in the true plane of the meridian till the next day; when, by depressing it to some distant land objects, a mark may be discovered whereby it may ever after be rectified very readily, so as to take the transits of any of the heavenly bodies to great exactness, whether by night or day. When such a mark is thus found, the telescope be¬ ing directed carefully to it, must be fixed in that posi¬ tion by pinching fast the end of the arm or lever be¬ tween the two opposite screws g h; and if at any fu¬ ture time, whether from the effect of heat or cold on the wall to which the instrument is fixed, or by any settling of the wall itself, the mark appears no longer well bisected by the vertical wire, the telescope may easily be made to bisect it again, by giving a small motion to the pinching screws. The transit instrument is now considered as one of the most essential particulars of the apparatus of an astronomical observatory. Besides the above, may be mentioned, Equatorial, or Portable Observatory ; Portable an instrument designed to answer a number of useful pur- obseum- poses in practical astronomy, independent of any parti- toiy* cular observatory. It may be made use of in any steady room or place, and performs most of the useful problems in the science. The following is a description of one lately invented by Mr Ramsden, from whom it has re¬ ceived the name of the Universal Equatorial. The principal parts of this instrument (fig. 179.) are, 1. The azimuth or horizontal circle A, which repre¬ sents the horizon of the place, and moves on a long axis B, called the vertical axis. 2. The equatorial or hour circle C, representing the equator, placed at right angles to the polar axis D, or the axis of the earth, upon which it moves. 3. The semicircle of declination E, on which the telescope is placed, and moving on the axis of declination, or the axis of motion of the line of collimation F. These circles are measured and divided as in the following table ; Measures 1B4 Description of Astrono¬ mical In¬ struments. astronomy. Measures of the several circles and divisions on them. Azimuth or hori- 1 zontal circle J Equatorial or hour 1 circle j Vertical semicircle T for declination > or latitude. J Radius indec. 5 1 5 1 5 5 Limb divided to ij' l' in time * 5' Nonius of 30 gives seconds. 30" 30' 2 3° Divided on limb into parts ofinc. 45th 45th 42d Divided by Nonius into part* of ino. 1350th 1350th 1260th Append,, Descripm of Astn,. mical strumei 4. The telescope, which is an achromatic refractor with a triple object-glass, whose focal distance is 17 inches, and aperture 2.45 inches, and furnished with six difterent eye-tubes : so that its magnifying powers extend from 44 to 168. The telescope in this equa¬ torial may be brought parallel to the polar axis, as in the figure, so as to point to the pole star in any part of its diurnal revolution ; and thus it has been observed near noon, when the sun has shone very bright. 5. The apparatus for cori’ecting the error in altitude occasioned by refraction, which is applied to the eye-end of the telescope, and consists of a slide G moving in a groove or dove-tail, and carrying the several eye-tubes of the telescope, on which slide there is an index correspond¬ ing to five small divisions engraved on the dove-tail j a very small circle, called the refraction circle H, move¬ able by a finger-screw at the extremity of the eye-end of the telescope 5 which circle is divided into half mi¬ nutes, one entire revolution of it being equal to 3' 18", and by its motion raises the centre of the cross hairs on a circle of altitude ; and likewise a quadrant I of inch radius, with divisions on each side, one expressing the degree of altitude of the object viewed, and the other expressing the minutes and seconds of error occa¬ sioned by refraction, corresponding to that degree of al¬ titude : to this quadrant is joined a small round level K, which is adjusted partly by the pinion that turns the whole of this apparatus, and partly by the index of the quadrant; for which purpose the refraction circle is set to the same minute, &c. which the index points to on the limb of the quadrant; and if the minute, &c. given , by the quadrant exceed the 3' 18" contained in one en¬ tire revolution of the refraction circle, this must be set to the excess above one or more of its entire revolutions; then the centre of the cross hairs will appear to be rais¬ ed on a circle of altitude to the additional height which the error of refraction will occasion at that altitude. This instrument stands on three feet L distant from each other 14.4 inches: and when all the parts are ho¬ rizontal is about 29 inches high : the weight of the equa¬ torial and apparatus is only 59 lb. avoirdupois, which are contained in a mahogany case weighing 581b. The principal adjustment in this instrument is that of making the line of collimation to descr ibe a portion of an hour circle in the heavens ; in order to which, the azimuth circle must be truly level ; the line of col¬ limation, or some corresponding line represented by the small brass rod M parallel to it, must be perpendi¬ cular to the axis of its own proper motion ; and this last axis must be perpendicular to the polar axis : on the brass rod M there is occasionally placed a hanging level N, the use of which will appear in the following ad¬ justments : The azimuth circle may be made level by turning the instrument till one of the levels is parallel to an imaginary line joining two of the feet screws ; then ad¬ just that level with these two feet screws; turn the cir¬ cle half round, i. e. 180°; and if the bubble be not then right, correct half the error by the screw belonging to the level, and the other half error by the two foot screws; repeat this till the bubble comes right; then turn the circle 90° from the two former positions, and set the bubble right, if it be wrong, by the foot screw at the end of the level ; when this is done, adjust the other level by its own screw, and the azimuth circle will be truly level. The hanging level must then be fixed to the brass rod by two hooks of equal length, and made truly parallel to it : for this purpose make the polar axis perpendicular or nearly perpendicular to the horizon ; then adjust the level by the pinic n of the declination-semicircle ; reverse the level, and if it be wrongs correct half the error by a small steel screw that lies under one end of the level, and the other half-error by the pinion of the declination-semicircle ; repeat this till the bubble be right in both positions. In order to make the brass rod on which the level is suspended at right angles to the axis of motion of the telescope or line of collimation, make the polar axis horizontal, or nearly so : set the declination-semicircle to o°, turn the hour-circle till the bubble comes right ; then turn the declination circle to 90°; adjust the bub¬ ble by raising or depressing the polar axis (first by hand till it be nearly right, afterwards tighten with an ivory key the socket which runs on the arch with the polar axis, and then apply the same ivory key to the adjusting screw at the end of the said arch till the bubble comes quite right) ; then turn the declination- circle to the opposite 90°; if the level he not then right, correct half the error by the aforesaid adjusting screw at the end of the arch, and the other half error by the two screws which raise or depress the end of the brass rod. rIhe polar axis remaining nearly hori¬ zontal as before, and the declination-semicircle at o°, adjust the bubble by the hour-circle ; then turn the declination-semicircle to 90°, and adjust the bubble by- raising or depressing the polar axis ; then turn the hour-circle 12 hours; and if the bubble be wrong, correct halt the error by the polar axis, and the other halt error by the twTo pair of capstan screws at the feet of the two supports on one side of the axis of mo¬ tion ANTKOXOM \: pj,. in>: jj\. /o i / 1 A rn Rut}? Si-ulp*. 2(1 ^ //>/•. ft/ Srnt i-fsr ASTliONOMY 3 ’Life l.XJ Ay. 21 ■ Fig. 22. Fry. 23. Fig. 2J. Fig. 2 '■ Fig. 2F. Sond. Fuj. 27. A PJjATfc LXIL i A ST RO XOM Y: j 7 AS TROJN OM\: PLATE, LTTTT. Fit/. 3(>. Fit/. .37. Fig. 3(3. Fit/. 3.9. Fit/. fi3. Fig. 61. Fit/.37. Fig. IT- Fit/ . -IF- Fig. 33. Fig.. ~>6. Fuz.4.9. Fig. 34. Fig. 33. Fig .31. Fig ■ 36. Fig-4S. Fig. 44. Fig. 43. Fig.46. Fig. 63. Step Sculpt t'ft/. Oil. Ffr/. Oy VSTROXOM Y. FLU E LXI\ : SATTRX X- ///.<• Safrffifas EARTH MOOX (J ■ o J)ishnhy of f/ioJ/ofw fi-o/rt t/ioA’/irt/i /'/lpl. "ITJ* ASTRONOMY PLATE LXXL n , In/fiMif Fu). 106. MO, /,.-// VS T IIO .X C) \I \ r],ATE LXXfll M.Jj'cJ-tikalci yen /• astronomy; PLATE /A VI /. JfirfFe Sculp * Eflu t V AST RON O M V. PL. HE LXXVIir Fh/.JJJ. Tig.IX Tig. IT.9. Ft(j. IT!), a. On ">o 40 Vo ao to o 10 tTTT-;l M I I ll II ' I I II 1 I I I W X W.Aivhiittld Sntlp ! ! VN’TROXOMV. PLATKLXXIX. Fill. /AS. . i • ASTRONOMY Plate LXXXIU F^J/4. Fig.iyff. Forfai/c sisb'oivonucal Qruu/ranf . Transit In stramerit. Fif.jys. Cvinpomir/ Transit Instrument. , ppendix. A S T R Iscriptiontion of the telescope; and thus this axis will be at C Astrono-right angles to the polar axis. The next adjustment ical In- is to make the centre of cross hairs remain on the same ; uii‘eiits ; object, while you turn the eye-tube quite round by the pinion of the refraction apparatus : for this adjustment, set the index on the slide to the first division on the dove-tail ; and set the division marked 18" on the re¬ fraction circle to its index ; then look through the te¬ lescope, and with the pinion turn the eye-tube quite round; and if the centre of the hairs does not remain on the same spot during that revolution, it must be corrected by the four small screws, two and two at a time (which you will find upon unscrewing the nearest end of the eye-tube that contains the first eye-glass) ; repeat this correction till the centre of the hairs i-e- mains on the spot you are looking at during an entire revolution. In order to make the line of collimation parallel to the brass rod on which the level hangs, set the polar axis horizontal, and the declination circle to 90°, adjust the level by the polar axis ; look through the telescope, on some distant horizontal object, covered by the centre of the cross hairs; then invert the tele¬ scope, which is done by turning the hour-circle half round; and if the centre of the cross hairs does not cover the same object as before, correct half the error by the uppermost and lowermost of the four small screws at the eye-end of the large tube of the tele¬ scope ; this correction will give a second object now covered by the centre of the hairs, which must be adopted instead of the first object: then invert the te¬ lescope as before; and if the second object be not co¬ vered by the centre of the hairs, correct half the error by the same two screws which were used before : this correction will give a third object, now covered by the centre of the hairs, which must be adopted instead of the second object; repeat this operation till no error remains; then set the hour-circle exactly to 12 hours (the declination-circle remaining at 90° as before) : and it the centre of the cross hairs does not cover the last object fixed on, set it to that object by the two re¬ maining small screws at the eye-end of the large tube, and then the line of collimation will be parallel to the brass rod. For rectifying the nonius of the declina¬ tion and equatorial circles, lower the telescope as many degrees, minutes, and seconds, below o* or iE on the declination semicircle as are equal to the complement the latitude ; then elevate the polar axis till the bub- O N O M Y. 185 ble be horizontal, and thus the equatorial circle will Description be elevated to the colatitude of the place ; set this cir-of Astrono- cle to 6 hours ; adjust the level by the pinion of the ,Ti!ca^ *n~ declination-circle ; then turn the equatorial circle exT ,stlu‘”;nU,J actly twelve hours from the last position ; and if the level be not right, correct one-half of the error by the equa¬ torial circle, and the other half by the declination-cir¬ cle ; then turn the equatorial circle back again exactly 12 hours from the last position ; and if the level be still wrong, repeat the correction as before till it be right, when turned to either position ; that being done, set the nonius of the equatorial circle exactly to 6 hours, and the nonius of the declination circle exactly to o°« The principal uses of this equatorial are, 1. To find your meridian by one observation only : for this purpose, elevate the equatorial circle to the colatitude of the place, and set the declination se¬ micircle to the sun’s declination for the day and hour of the day required ; then move the azimuth and hour circles both at the same time, either in the same or contrary direction, till you bring the centre of the cross hairs in the telescope exactly to cover the centre of the sun ; when that is done, the index of the hour- circle will give the apparent or solar time at the in¬ stant of observation ; and thus the time is gained, though the sun be at a distance from the meridian ; then turn the hour-circle till the index points precisely at 12 o’clock, and lower the telescope to the horizon, in order to observe some point there in the centre of your glass, and that point is your meridian mark found by one observation only ; the best time for this opera¬ tion is three hours before or three hours after 12 at noon. 2. To point the telescope on a star, though not on the meridian, in full daylight. Having elevated the equatorial circle to the colatitude of the place, and. set the declination-semicircle to the star’s declination, move the index of the hour-circle till it shall point to the precise time at which the star is then distant from the meridian, found in tables of the right ascension of the stars, and the star will then appear in the glass. Besides these uses peculiar to this instrument, it is also applicable to all the purposes to which the principal astronomical instruments, viz. a transit, a quadrant, and an equal altitude instrument are applied. See the article Astronomy, Physical, in the Sup¬ plement. At Juration of the fixed stars, N°265 e/twy, Royal, of sciences founded, 1 n supposed to have understood astronomy, 0nso °f Castile patronizes astro¬ nomers, by whom the tables are constructed, ! ' lcans knowledge of astronomy, wean, ^ dilutions, their knowledge of a- stronomv, OL. HI. Parti, ' 30 18 5 51 INDEX. Apogee of the moon’s orbit, N° 81 of the planets, 293 Apsides, moon’s, ib. Arabians cultivate astronomy in the dark ages, 17 Archimedes determines the relative distances of the pla¬ nets, . 13 Ascension, right, 250 Attraction, laws of, act among the stars, 230 Axis of the world, N® 37 Astrological division of the heavens, 371: Atmosphere, why not seen about the moon, 399 Bailly investigates the Indian astro¬ nomy, 4 Bayer, John, fornis a celestial atlas, 26 improves the nomenclature of the stars, ib„ Benares, observatory, 3 A a BianchinL 186 Bianchini, observations of Venus, N° 146 Bissextile, ov Leap year, 63 Bodies, falling, velocity calculated, 352 weight increases towards the ■ poles, 276 Botin's opinion of comets, 301 Bradley, Dr, succeeds Dr Halley, 34 discovers the aberration of light, ib. nutation of the earth’s axis, ib. Briggs, Henry, improves logarithms, 28 Biydone observes the prodigious velo¬ city of a comet, 319 conjectures about comets with¬ out tails, 322 c Ccesar, Julius, reforms the year, 63 Caille, de la, constructs solar tables, 36 Calendar, Gregorian, 64 Cassini appointed to the observatory at Paris, 30 his observations of Venus, 141,144, J49» Ceres, planet, elements not precisely known, 183 Chaldeans cultivated astronomy early, 6 Chinese, their knowledge of astronomy, 2 give names to the zodiac, 3 Clouds, solar, two regions, 77 Cole's hypothesis of comets 3 23 Cometarium, 428 Cornets, account of, 183 atmospheres and phases, 184 appearance of one in 1618, 1680, 1744, 1759, 186, 191 tails, 187 observations on, by Hevelius and Hooke, 188 supposed by the ancient* to be planets, 298 Aristotle’s opinion of, 299 one species only exists, 300 opinion of Kepler and Bodin, 301 Bernoulli’s opinion of, 302 true doctrine revived by Ty¬ cho Brahe, 303 motion determined by New¬ ton, 304 return of one predicted by Dr Halley, 305 periodical times of different ones determined, 306 why sometimes invisible in pe¬ rihelion, 307 more seen in hemisphere to¬ wards the sun, 308 differences in eccentricities of orbits, 309 opinions of their substance, 310 distances and diameters of some computed, 311 occasion eclipses, 312 conjectures concerning their tails, 313 ASTRONOMY. Cojnets, conjectures by Appian and Tycho Brahe, N° 313 by Descartes, 314 by others, ascrib¬ ed to electrici¬ ty, ib. by Dr Hamilton, 315 velocity observed by Bry- done, 319 in 1680 subjected to great heat, 320 conjectures of their nature by Hevelius, 321 about those with¬ out tails, 322 Cole’s hypothesis, 323 periodical times, 324 Halley calculates their re¬ turn, _ 325 return at unequal intervals, why, 326 at what distance visible, 372 move in eccentric ellipses, 373 motion, how to calculate, 374 are affected by the planets, 375 consequence of meeting a planet, 376 Constellations, names of, 199 Copernicus restores the system of Py¬ thagoras, 22 his diffidence and fear of giving offence, retard the publication of his system, ib. D Day, astronomical 55 sidereal, 56 varies in length, 57 mean astronomical, 58 Declination, rules for finding, 249 Densities of planets calculated, 356 Dollond improves the telescope, 31 Dunn, Mr, his account of the solar spots, 69 E Earth, true figure discovered, 34 figure spherical, 269 dimensions ascertained, 270 different measurements, 271 anomalies in the figure, ac¬ counted for by Mr Play¬ fair, 272 latitude and longitude found, 273 motion round the sun, proved from its figure, 275 from celestial ap¬ pearances, 277 objections to, answer¬ ed, 278 demonstrated from the aberration of light, 286 diurnal motion and changes of seasons illustrated, 290 effects of motion on the ap¬ pearances of the planets, 292 Index Earth and moon move about a com¬ mon centre, N° 3^ protuberant matter, effects of, libratory momentum, applied to nuta¬ tion and pre¬ cession, 41; various modes of application, real and momentary change greatest at the solstices, 41, moon’s action, 41c Eclipses, method of calculating, 331 tables for calculating, p. 169, 170. lunar, 55 solar, 10: duration of, nc Ecliptic, 4: obliquity of, ib! Egyptians early cultivators of astrono¬ my, ( Elements of the planets, tables of, 295 Equation of the centre explained, 31 of time computed, 6c Equator, 35 Equinoctial line, points, ib( Equinoxes, precession of, discovered by Hipparchus, 25) importance of the disco¬ very, ^ 255 small irregularities, disco¬ vered by Dr Bradley, 261 F Falling bodies, velocity of, calculat¬ ed, 352 Flamstcad, Mr, appointed astronomer royal, 3c makes a catalogue of the stars, 33 Fontana improves telescopes, 31 Forces, moving, cause of motion, 331 composition of, 33^ resolution, 334 accelerating, 33^ central, 33® centripetal, effect of, 34c centrifugal compared with gra¬ vitation, 34' French philosophers cultivate astrono¬ my, 3: G Galaxy, or milky-way, 3lj seems to surround the hea¬ vens, 22: Globe, celestial, 42! Golden number, ^ Gravitation, general law of, 35. Grecian astronomy improved by Thales, i by Anaximander, it Greeks, unknown when astronomy was first cultivated among ^ them, QreenW adex. reenwich observatory built, N° 30 II .alley, Dr, appointed astronomer royal, 33 discovers the acceleration of the moon, ib. recommends the method of finding the longitude now followed, ib. account of new stars, 200 predicts the return of a co- met, _ 305 calculates their return, 3 25 wiilton's, Dr, opinion of comets, 3x3 insufficient, 317 i'avem, division of, igy method of gauging, by Her- schel, 224 interior construction, 229 Irschel, Dr, improves telescopes, 36 discovers a planet, ib. six satellites, ib. observations on the sun, 70 adopts new terms to express the appearances, 71 opinion of the construction of the universe, 217 of the via lac tea, 218 method of gauging the hea¬ vens, . 225 hypothesis of celestial ap¬ pearances, 223 method of finding the pa¬ rallax of fixed stars, 268 planet discovered by, 36 its satellites, 183 six in number, 330 hhelius, a zealous astronomer, 30 compiles his Selenographia, ib. his observatory and instru¬ ments burnt, ib. conjectures of the nature of comets, 321 ■lets taught the diurnal motion of the earth, 11 Mmrchus discovers the eccentricity of the planetary orbits, 14 makes a catalogue of the fixed stars, 13 discovers the precession of the equinoxes, 237 pyt charged with plagiarism, 260 rf5> Dr, improves telescopes, qo j^on explained, 37 a young astronomer of great talents, 29 predicted and observed the transit of Venus for the first time, ib. formed a theory of the moon, ib. numi tholr knowledge of astrono¬ my, 4 ASTBONOMY. Indians, authenticity of their astrono¬ my, > N° 370 Instruments, astronomical, first impro¬ ved in England, 31 description of^ p. 171—184. Josephus mentions the grand year known to Seth, 1 Jupiter's belts first discovered, 166 spots in them, 167 account of one, 168 no difference of seasons, 169 moons, four in number, 170 distance and perio¬ dic times, 171 eclipses, 172 appear sometimes as dark spots, 173 vary in light and magnitude, 174 shadows sometimes vi¬ sible on Jupiter’s disk, 173 three eclipsed every revolution, 176 eclipses, when visible, 177 orbits and distances, 327 irregularities in their motions, 228 K Kepler discovers the famous laws in astronomy, 26 law explained, 49 opinion of comets, 301 discovers the cause of the tides, 400 Xi Latitudes of heavenly bodies, 232 how found, 233 Libration of the moon, 133 theory, ^4 Line, meridian, method of drawing, 40 Logarithms invented by Baron Napier, improved by Ursinus and Briggs, s 28 Longitude of the heavenly bodies, 231 of places on the earth, me¬ thod of finding, 274 Long, Dr, his account of the solar spots, . 65 Louville's observations on the moon’s ring, 226 Lowe's, Mr, method of finding the longitude, 274 Lunation, or month, 61 M Mackay, Mr, method of finding the longitude, 274 Mars, spots first seen, 133 bright about the poles, 136 Dr Herschel’s account of, 137 appear and disappear, 138 white about the poles, 162 position of the poles, 139 seasons, 160 resembles the earth, 161 I87 Mars, his form spheroidical, N° i63 difference of diameter, 164 atmosphere, 163 Maskelyne, Dr, improves the lunar method of finding the longitude, 35 apparent motions, 133 diameter, J36 nature, 53 7 Meridian explained, 37 line, method of drawing, 40 Milky-way,' _ 211 Moon's motion in her orbit, 79 orbit elliptical, 80 eccentricity, 81 evection, 83 variation, 84 annual equation, 8^ revolution of her nodes, 86 parallax, method of determin- . ing, 87 distance, 89 phases, ^ is opaque, pj the earth appears a moon to it, 92 mode of measuring the year, 93 longitude found, 94 nonagesimal degree, 98 eclipses, ^9 # period, i0o why visible when eclipsed, 101 eclipses observed with difficul- ly» t 102 number in a year, 104 total and annular, 106 extent of shadow and penum- bra, 107 size, Iir %ht> 112 spots, II3 names of, ib. inequalities of surface, 114 method of measuring moun¬ tains, II3 mountains, height of, overrat¬ ed* 116 volcanoes, 1x9 substance, conjectures of, 120 atmosphere, existence of, dis¬ puted, fi¬ ring observed in eclipses, 123 lightning, 127 height of atmosphere account¬ ed for, _ I2g has no sensible atmosphere, 131 libration, j ^ ~ theory, 134 tendency the same as gravita- tion, > 330 motion explained, 33I inequalities, 377 nearest the earth when least attracted, ^79 orbit, cause of dilatation, 380 A a 2 Moon's 188 Moon's oibit changed by the action of the sun, N° 381 nodes, 382 motion explained, 384 inclination, 383 motion,irregularities from be¬ ing elliptical, 385 orbit, inequality in the eccen¬ tricity, 391 inequalities computed, 392 mean distance, secular equa¬ tion, 393 has no atmosphere, why, 399 Motion, definition of, 331 Motions of the sun, 39—51 N Nadir, 37 Napier, Baron, invents logarithms, 26 Nebula, our sidereal system, one, 236 extent, 239 how to be delineated, 241 Nebulee, in the milky-way, 219 arranged in strata, 220 assume various shapes, 221 how formed, 231 vacancies, how occasioned, 232 decay and recomposition, 242 universe composed of, 243 size and distance, 244 time of forming, 245 planetary, 247 Newton, Sir Isaac, his discoveries, 31 determines the motions of the comets, 304 his opinion of comets defend¬ ed, 316 observations on the precession of equinoxes, 407 sketch of his investigation, 408 determination of the form and dimensions of the earth, 409 examination of phenomena of precession on mechanical principles, 410 Node, ascending, 86 Nodules on the luminous clouds of the sun, 75 Number, golden, 61 Nutation, lunar, 421 compared with precession, 423 Q Observatory, portable, 434 Openings formed hy the sun’s lumi¬ nous clouds being remov¬ ed, 72 Oscillation of the planetary system, 369 P Pallas, planet, elements not precisely known, 183 Perigee of the moon’s orbit, 81 of the planets, 293 Phccnicians taught astronomy by the Egyptians, 7 apply it to navigation, ib. PJlilolaus asserts the annual motion of the earth round the sun, n ASTRONOMY. Planets, N° 37 apogee and perigee, 293 difference of apparent diame¬ ters, 294 appearances of superior, ex¬ plained, 295 orbits and laws of their mo¬ tions, ib. heliocentric circles, 296 nodes, 297 tables of elements, ib. revolve round the sun, 343 in consequence of a force in the sun, 344 the same tendency in all, 346 and same in their satellites, 347 react on the sun, 354 densities calculated, 356 masses, table of, 357 gravity at their surfaces, 359 secular and periodical inequa¬ lities, 360 motion of the aphelion, 361 motions, method of correct¬ ing . 363 Jupiter and Saturn influence each others motions, 362 deflection of, towards each other, 366 Pendulum regulated by gravitation, 337 Precession of equinoxes, 257—259 observations by Newton and others, 407 Newton’s investigation, 408 lunar, 420 greatest equation, 425 Ptolemy, his system erroneous, 16 Ptolemy Philadelphus encourages the sciences in E- gypt* 12 Purback improves astronomy, 19 Pythagoras improves astronomy, 11 correct notions of the solar system, ib. of the moon’s light, ib. of the milky-way, ib. Q Quadrants, 431 Quadratures of the moon, 90 R Revolution of a body round a centre explained, 339 Regiomontanus constructs astronomical apparatus, 20 calculates lunations and eclipses, ib. writes a theory of pla¬ nets and comets, ib. Ridges of the sun’s luminous clouds, 74 Ring of Saturn, 393 discovery concerning, by Dr Herschel, - 396 probably consistent, 397 origin, 398 Index Roemer discovers the progressive mo¬ tion of light, N° Rothman, an astronomer, S Satellites, tend to the sun, to their primaries, irregularities in Jupiter’s, Satumi, telescopic appearance of, ring discovered by Huygens, supposed to revolve round its axis, 181; diameter, ib, satellites, 18] two discovered by Herschel, 18; number, 325 Seasons, explained, ^ changes illustrated, 29c different, explained, 291 Sector, equatorial, 43; Selenographia compiled by Hevelius, 3c Shallows of the sun’s luminous clouds, 93 Shepherds, Asiatic, observe the heavens, 253 Signs of the zodiac, 52 Society, Royal, founded in London, 8c Stars, fixed, occultatious by the moon, 13c Style, old, 64 new, ib. Sun, annual motion, 39 altitude, 41 motion, method of ascertaining, 42 not uniform, 43 • diameter varies, 46 distance varies, 47 motion varies, 48 orbit, elliptical, 5°, varies, 52 distance determined, J4 spots, first discovered, 65 Long, Dr, his account, of them, ^ move from west to east, f>7 observed by different astro¬ nomers, D nnn, Mr, his account of them, 69 appearances of the luminous clouds, 72—76 two regions of clouds, theory of phenomena, eclipses, beginning and ending, account of one by Dr Halley, his place in the universe, his centre attracts all bodies, moves round the common centre of gravity, Syzigies of the moon, Stars, fixed, number increased by te¬ lescopes, difference in magnitude, telescopic, unformed, division in constellations, and uses, 196 Star Ildex. Si'rs, fixed, new, Dr Halley’s account of, N° 200 changes among, 201 accounts of variable stars, 202—208 method of discovering variations, 210 conjectures of their na¬ ture, 212 comparative brightness with the sun, 214 method of ascertaining their situation, 248 vary in right ascension and declination, 254 distance, immeasurable, 266 appear large to the eye, 267 parallax, method of ascer¬ taining, 268 Sr,emf Pythagorean, 279 suppressed by the Ptolemaic, 280 Ptolemaic, insufficient, 281 Pythagorean, revived, 282 Tychonic, 282 T T\les, Alphonsine, constructed, 18 directions for using, 356 Tihscopes invented, 27 improved by Hooke, 30 by Fontana, 31 by Huygens, ib. by Gregory, ib. by Sir Isaac New¬ ton, ib. by Dollond, ib. cautions in using, 118 T/Vy, mathematical, of the poles of the equator, 262—264 Tti?, divisions of, jj 57 equation of, computed, 60 Tt-Sf cause discovered by Kepler, 400 A S T R O N O Tides, why high at full moon, influence of the sun, not highest when the moon is in the meridian turn on the axis of the moon’s orbit, irregularities accounted for, Trajectorium lunare, Transit instruments, Tycho Brahe observes the connexion of Saturn and Jupiter, makes a more accurate quadrant, superintends the build¬ ing of Uraniburg, his observatory, revives the true doctrine of comets, M Y. N° 401 402 4°3 404 405 43° 433 24 ib. 25 301 U Ulug Beg cultivates astronomy, 17 Uraniburg, built by Tycho Brahe, and furnished with instruments, 25 Ursinus, Benjamin, calculates large ta¬ bles of logarithms, 28 Velocity, notion of, 333 apparent motions, 138 revolution round her axis, 139 doubts of the time, 147 spots first discovered, 140 seem to move from south to north, and why, 142 appearances at different times, 143 observations by Cassini, 141 by Bianchini, 146 satellites discovered by Cassini, 149 and by Mr Short, 150 Mr Mon¬ taigne, 151 difficult to be seen, 152 189 Venus, atmosphere of, observed by Mi- Hirst, N° 153 Volcanoes in the moon, 119 \V TValther cultivates astronomy, and con¬ structs instruments, 20 Weight of bodies increases towards the poles, 276 Werner, John, early attachment to astronomy, 21 observes the motion of comet, ib. proposes a method of finding the longi¬ tude at sea, xb. discovers the preces¬ sion of the equinoxes, ib. constructs a planetari- um, ib. William IV. landgrave of Hesse-Cas- sel, an astronomer, 23 World, argument against its eternity, 36 W1right, Edward, makes observations on the sun’s alti¬ tude, 26 improves the theo¬ ry of his motion, ib. computes tables of his declination, ib. Year, tropical, 59 sidereal, ib. Roman, 62 reformed by Julius Cae- sar, 63 leap, ib. lunar, ^ 93 Zenith, 3 7 Zodiac, Chinese names of the signs, 3 signs of, 52 division of, 198 AST liojyc. ASIROPE-wells, near Banbui-y in Oxfordshire, ,s are recommended as excellent in many disorders. The jjjhuc. water is a brisk, spirituous, pleasant-tasted chalybeate, j and »s also gently purgative. It should be drank from three to five quarts in the forenoon. ASTROSCOPE, a kind of astronomical instrument, composed of two cones, on whose surface the constella¬ tions, with their stars, are delineated, by means whereof the stars may be easily known. The astroscope is the invention of William Schuckhard, formerly professor of mathematics at Tubingen, who published a treatise ex¬ pressly on it in 1698. . ASfRUC, John, a celebrated physician, was born in the year 1684, at the little town of Savoy, in the province of Languedoc. His father, who was a Pro¬ testant clergyman, bestowed particular pains upon the A S T earliest part of his education. After which he went to Astruc. the university of Montpelier, where he was created 1 ■ v1*'"''1 1 master of arts in the year 1700. He then began the study of medicine; and, in two years, obtained the degree of bachelor, having upon that occasion written a dissertation on the cause of fermentation, which he defended in a very spirited manner. On the 25th of January 1703 he was created doctor of physic; after which, before arriving at extensive practice, he applied to the study of medical authors, both ancient and mo¬ dern, with uncommon assiduity. The good effects of this study soon appeared; for, in the year 1710, he published a treatise concerning muscular motion, from which he acquired very higli reputation. In the year 1717, he was appointed to teach medicine at Mont¬ pelier ; which he did with such perspicuity and elo- 3, quence, ^ AST [ 19° ] A S Y Astnic, quence, that it was universally said he had been born Asturia. to be a professor. His fame soon rose to such a height, - that the king assigned him an annual salary ; and he was, at the same time, appointed to superintend the mineral waters in the province of Languedoc. But as Montpelier did not afford sufficient scope for his aspiring genius, he went to Paris with a great stock of manuscripts, which he intended to publish, after sub¬ jecting them to the examination of the learned. Soon after, however, he left it, having in the year 1729 ac¬ cepted the office of first physician to the king of Po¬ land. In this capacity he remained only for a short time, and he again returned to Paris. Upon the death of the celebrated Geoffroy, in the year 1731, he was appointed regius professor of medicine at Paris. The duties of this office he discharged in such a manner as to answer even the most sanguine expectations. He taught the practice of physic with so great applause, as to draw from other universities to that of Paris a great concourse of medical students, foreigners as well as na¬ tives of France. At the same time he was not more celebrated as a professor than a practitioner. And even at an advanced age, he persevered with unwea¬ ried assiduity in that intense study which first raised his reputation. Hence it is that he has been enabled to transmit to posterity so many valuable monuments of his medical erudition. He died, universally regretted, on the 15th of May 1766, in the 82d year of his age. ASTURIA, an ancient kingdom of Spain, sub¬ dued by Augustus, emperor of Rome.—The inhabi¬ tants of this country, along with those of Cantabria, asserted their liberty long after the rest of Spain had received the Roman yoke. So great was their desire of liberty, that after being closely shut up by the Ro¬ man army, they endured the most terrible calamities of famine, even to the devouring of one another, rather than submit to the enemy. At length, however, the Asturians were for surrendering ; but the Cantabrians opposed this measure, maintaining that they ought all to die sword in hand like, brave men. Upon this the two nations quarrelled, notwithstanding their desperate situation $ and a battle ensuing, 10,000 of the Astu¬ rians were driven to the intrenchments of the Romans, whom they begged in the most moving manner to re¬ ceive them on any terms they pleased. But Tiberius, the emperor’s son-in-law, refusing to admit them into the camp, some of these unhappy people put an end to their lives by falling upon their own swords j others lighting great fires threw themselves into them, while some poisoned themselves by drinking the juice of a ve¬ nomous herb. The campaign being put an end to by winter, the next year the Asturians summoned all their strength and resolution against the Romans ; but notwithstand¬ ing their utmost efforts of valour and despair, they were entirely defeated in a most bloody battle, which lasted -two days, and for that time entirely subdued. A few years afterwards they rebelled, in conjunction with the Cantabrians 5 but were soon reduced by the Ro¬ mans, who massacred most of the young men that were capable of bearing arms. This did not prevent them from revolting anew in a short time afterwards ; but without success, being obliged to submit to the Ro- 2 man power, till the subversion of that empire by the Ast(li. Goths. || Asturias, anciently the kingdom of Asturia, is Asyim now a principality of modern Spain, bounded by Bis- '■"“‘V’* cay on the east, Galicia on the west, Old Castile and Leon on the south, and the sea on the north. Its greatest length is about no miles, and its breadth 54. On the south it is separated from Old Castile and Leon by high mountains covered with woods. The province is tolerably fertile, but thinly inhabited. The inhabi¬ tants value themselves much on being descended from the ancient Goths. Even the poor peasants, who are fain to go to seek work in other provinces, call them¬ selves illustrious Goths and Mountaineers, thinking it ignominious to marry even with great and rich fami¬ lies of another race. This pride is flattered by the respect paid them by the rest of the nation, and the privileges bestowed upon them by the government. The hereditary prince of Spain is styled prince of the Asturias. The Asturias contain 688 parishes, and the population is estimated at 348,000, including 2868 ec¬ clesiastics, monks and nuns. ASTYAGES, son of Cyaxares, the last king of the Medes. He dreamed, that from the womb of his daughter Mandane, married to Cambyses king of Per¬ sia, there sprung a vine that spread itself over all Asia. She being with child, he resolved to kill the infant as soon as born. Its name w'as Cyrus j and Harpagus being sent to destroy it, preserved it $ which Astyages after a long time hearing of, he caused Harpagus to eat his own son. Harpagus cajled in Cyrus, who de¬ throned his grandfather, and thereby ended the mo¬ narchy of the Medes. See Media and Persia. ASTYANAX, the only son of Hector and Andro¬ mache. After the taking of Troy, he was thrown from the top of a tower by Ulysses’s orders. ASTYNOMI, in Grecian Antiquity, magistrates in Athens, corresponding to the aediles of the Romans j they were ten in number. See ^Edile. ASYLUM, a sanctuary, or place of refuge, where criminals shelter themselves from the hands of justice. The word is compounded of the privative particle «, and s-uAatf, I hurt; because no person could be taken out of an asylum without sacrilege. The asyla of altars and temples were very ancient $ and likewise those of tombs, statues, and other monu¬ ments of considerable personages. Thus, the temple of Diana at Ephesus was a refuge for debtors, the tomb of Theseus for slaves. Among the Romans, a cele¬ brated asylum was opened by Romulus between the mounts Palatine and Capitoline, in order to people Rome, for all sorts of persons indiscriminately,'fugitive slaves, debtors, and criminals of every kind. The Jews had their asyla; the most remarkable of which were, the six cities of refuge, the temple, and the altar of burnt-offerings. It was customary among the Heathens to allow re¬ fuge and impunity even to the vilest and most flagrant offenders j some out of superstition, and others for the sake of peopling their cities : and it was by this means, and with such inhabitants, that Thebes, Athens, and Rome, were first stocked. We even read of asylums at Lyons and Vienne among the ancient Gauls j and there are some cities in Germany which still preserve A T A [ iQi ] ATE , ., the ancient right of asylum. Hence on the medals of yl lum , • ^ J *11*0* several ancient cities, particularly in byna, we meet Atjanta. with the inscription A2TAOI, to which is added EPAI. This quality of asylum was given them, according to M. Spanheim, in regard to their temples, and to the gods revered by them. The emperors Honorius and Theodosius granting the like immunities to churches, the bishops and monks laid hold of a certain tract or territory, without which they fixed the bounds of the secular jurisdiction : and so well did they manage their privileges, that convents in a little time became next akin to fortresses j where the most notorious villains were in safety, and braved the power of the magistrate. These privileges at length were extended not only to the churches and churchyards, but also to the bishops houses; whence the criminal could not be removed with¬ out a legal assurance of life, and an entire remission of the crime. The reason of the extension was, that they might not be obliged to live altogether in the churches, &c. where several of the occasions of life could not be decently performed. But at length these asyla or sanctuaries were also stripped of most of their immunities, because they ser¬ ved to make guilt and libertinage more bold and daring. In England, particularly, they were entirely abolished. See Sanctuary. ASSYMETRY, the want of proportion between the parts of any thing ; being the contrary of symmetry. Or, it is the relation of two quantities which have no common measure, as between 1 and -y/ 2, or the side and diagonal of a square. ASYMPTOTE, in Geometry, a line which conti¬ nually approaches nearer to another ; but, though con¬ tinued infinitely, will never meet with it : Of these are many kinds. In strictness, however, the term asymptotes is appropriated to right lines, which approach nearer and nearer to some curves of which they are said to be asymptotes ; but if they and their curves are inde¬ finitely continued, they will never meet. See Conic Sections. ASYNDETON, in Grammar, a figure which omits the conjunctions in a sentence. As in veni, vidi, vici, where ET is left out: or in that of Cicero concerning Catil ine, abiit, excessit, evasit, ervpit : or in that verse of Virgil, b'erte cito flammas, date vela, impellite remos. Asyndeton stands opposed to polysyndeton, where the copulatives are multiplied. ATABULUS, in Physiology, a provincial wind in Apulia, of a dry pinching quality, and very noxious in its effects. The ancient naturalists speak of the Atabu- lus in terms of horror, on account of the ravage it made among the fruits of the earth, which it scorched or wi¬ thered up. ATABYRIS, a very high mountain in the island of Rhodes, on which, according to Strabo and Diodorus Siculus, there stood a temple of Jupiter Atabyrius, whose worship a colony of Rhodians carried into Sicily, where a temple was built to the same deity at Agrigen- tum. ATALANTA, an island in the Euripus of Euboea, near the Locri Opuntii, said to have been originally a city of the Locri, but torn from the continent in the time of an earthquake, and during an eruption of Atalanta Mount iEtna. This happened in the fourth year of the || 93d Olympiad, in the reign of Artaxerxes Mnemon. Atella. ATALANTIS, Atlantica, or Atlantis. See v ' Atlantis. ATARAXY, a term used by the stoics and sceptics, to denote that calmness of mind which secures us from all emotions arising from vanity and self-conceit. ATARGATIS FANUM, the temple of a goddess worshipped by the Syrians and Parthians, having the face of a woman and tail of a fish, and called Derceto by the Greeks. Her temple stood in the city Bambyce, called afterwards Hieropolis. It was extremely rich, insomuch that Crassus, in his march against the Par¬ thians, spent several days in weighing the treasure. Vossius makes the name of this goddess Phoenician, from Addir dag, “ the great fish.” ATARNEA, an ancient town of Mysia, situated between Adrymyttium and Pitane, remarkable for the marriage of Aristotle with the sister or concubine of the tyrant Hermias; also for the dotage of that philso- pher. ATAXY, in a general sense, the want of order: With physicians, it signifies irregularity of crises and paroxysms of fevers. ATCHE, in commerce, a small silver coin used in Turkey, and worth only one-third of the English penny. ATCH1EVEMENT, in Heraldry, denotes the arms of a person or family, together with all the exterior or¬ naments of the shield ; as helmet, mantle, crest, scrolls, and motto, together with such quarterings as may have been acquired by alliances, all marshalled in or¬ der. ATCHIEVE. This term is derived from the French achever, i. e. to finish or make an end of; but signifies, in its ordinary acceptation, to perform great actions or exploits. ATE, the goddess of mischief, in the Pagan theo¬ logy. She was daughter of Jupiter, and cast down from heaven at the birth of Hercules. For Juno hav¬ ing deceived Jupiter, in causing Eurystheus to be born before Hercules, Jupiter expressed his resentment on Ate, as the author of that mischief: and threw her headlong from heaven to the earth, sivearing she should never return thither again (Homer II. xix. 123.). The name of this goddess comes from noceo, “ to hurt.” Her being the daughter of Jupiter, means, according to mythologists, that no evil happens to us but by the permission of Providence; and her banishment to earth denotes the terrible effects of divine justice among men. ATEGUA, or AttEGUA, an ancient town of Spain, placed by some in the road from Antiquara, now Antequera, to Hispalis, or Seville ; by others near Alcala Real ; which last is the more probable situation, because the Flumen Salsum, now the Salado, -was in its neighbourhood. Now Tebala Vieja, or Teivela. ATELLA, an ancient town of Campania in Italy, betxveen Capua and Neapolis. From this town the A- tellance fabidee, or Atellaniludi, took their name. Their were also called Osci, from their inventor, in whose ter¬ ritory Atella lay. They were generally a species of farce, interlarded with much ribbaldry and buffoonery; and sometimes were exordia or interludes presented between ATI! • [ 192 ] A T H Atella between the acts of other plays. The actors in these 11 farces were not reckoned among the common players, Athanasian nor deeded infamous j but retained the rights of their , C1'efcti’ , tribe, and might be listed for soldiers, the privilege only of free men. The ruins of this town are still to be seen, about n miles from the modern Aversa, which was built out of its materials. ATEMPO G1UST0, in Music, signities to sing ox- play in an equal, true, and just time. ATERGATIS, in Mythology, a goddess of the Sy¬ rians, supposed to be the mother of Semiramis. She was represented with the face and breasts of a wo¬ man, but the rest of her body resembled a fish. Vos- sius says the term signifies without fish, and con¬ jectures that the votaries of this deity abstained from fish. ATERNUM, a town of Lucania in Italy, now Aterni, (Cluverius) : Also a town in the territory of the Piceni, now Pescara, a port town of Naples, si¬ tuated on the Adriatic. E. Long. 15. 25. N. Lat. 42. 30. ATESTE, a town in Austrian Lombardy in Italy, now called Este. E. Long. 12. 6. N. Lat. 45. ATHAMADULET, the prime minister of the Persian empire, as the grand vizier is of the Turkish empire. He is great chancellor of the kingdom, presi¬ dent of the council, superintendant of the finances, and is charged with all foreign affairs. ATHAMANTA, Spignel. See Botany Itidex. ATHANASIA, Goldilocks. See Botany Im- dex. ATHANASIAN creed j a formulary, or con¬ fession of faith, long supposed to have been drawn up by Athanasius bishop of Alexandria, in the fourth century, to justify himself against the calumnies of his Arian enemies. But it is now generally allow¬ ed among the learned not to have been his. Dr Waterland ascribes it to Hilary bishop of Arles, for the following among other reasons: 1. Because Ho- noratus of Marseilles, the wi-iter of his life, tells us, that he composed an Exposition of the Creed; a pro- perer title for the Athanasian than that of Creed sim¬ ply which it now bears. 2. Hilary was a great ad¬ mirer and follower of St Austin j and the. whole com¬ position of this creed is in a manner upon St Austin’s plan, both with respect to the Trinity and incarnation. 3. It is agreeable to the style of Hilary, as far as we can judge from the little that is left of his works. Up¬ on the whole he concludes, that Hilary, bishop of Arles, about the year 430, composed the Exposition of Faith, which now bears the name of the Athana¬ sian Creed, lor the use ol the Galilean clergy, and par¬ ticularly those of the diocese of Arles : That, about the year 570, it became famous enough to be com¬ mented upon ; but that all this while, and for several years lower, it had not yet acquired the name of Atha¬ nasian, but was simply styled The Catholic Faith: That, before 670, Athanasius’s admired name came in to re¬ commend and adorn it, being in itself an excellent sys¬ tem of the Athanasian principles of the Trinity and in¬ carnation, in opposition chiefly to the Arians, Macedo¬ nians and Apollinarians. This is the hypothesis of the learned author of the Critical History of the Athanasian Creed, As to the reception of this creed in the Christian Athanas churches, we find, that it obtained in France in the creed time of Hincmar, or about 850 : that it was received 11 in Spain about 100 years later than in France, and in ^anasi. Germany much about the same time. As to our own ^ country, we have clear and positive proofs of this creed being sung alternately in our churches in the tenth century. It was in common use in some parts of Italy, particularly in the diocese of Verona, about the year 960, and was received at Rome about the year 1014. As to the Greek and oriental churches, it has been questioned whether any of them ever received this creed at all ; though some very considerable wri¬ ters are of a contrary persuasion. It appears then, that the reception of this creed has been both general and ancient ; and may vie with any, in that respect, ex¬ cept the Nicene or Constantinopolitan, the only gene¬ ral creed common to all the churches. As to the matter of this creed, it is given as a sum¬ mary of the true orthodox faith, and a condemnation of all heresies ancient and modern. Unhappily, how¬ ever, it has proved a fruitful source of unprofitable con¬ troversy and unchristian animosity even down to the present time. ATHANASIUS, St, bishop of Alexandria, and one of the greatest defenders of the faith against the Arians, was born in Egypt. He followed St Alex¬ ander to the council of Nice, in 325, where he dispu¬ ted against Arius, and the following year was made bishop of Alexandria j but, in 335, was deposed by the council of Tyre: when, having recourse to the emperor Constantine, the Arian deputies accused him of having hindered the exportation of corn from Alexan¬ dria to Constantinople ; on which the emperor, with¬ out suffering him to make his defence, banished him to Treves. The emperor, two years after, gave orders that he should be restored to his bishopric: but, on his return to Alexandria, his enemies brought fresh accu¬ sations against him, and chose Gregory of Cappadocia to his see j which obliged Athanasius to go to Rome to reclaim it of Pope Julius. He was there declared innocent, in a council held in 342, and in that of Sardica in 347’ an(l t'vo years after w7as restored to his see by order of the empei’or Constans : but after the death of that prince, he was again banished by the emperor Constantius, which obliged him to retire into the deserts. The Arians then elected one George in his room j who being killed in a popular sedition un¬ der Julian in 360, St Athanasius returned to Alexan¬ dria, but was again banished under Julian, and restored to his see under Jovian. He addressed to that emperor a letter, in which he proposed that the Nicene creed should be the standard of the orthodox faith, and con¬ demned those who denied the divinity of the Holy Ghost. He was also banished by Valens in 367, and afterwards recalled. St Athanasius died on the 2d of May.375- His works principally contain a defence of the mys¬ teries of the Trinity, and of the incarnation and divi¬ nity of the Word and Holy Spirit. There are three editions of his works which are esteemed j that of Com- melin, printed in 1600; that of Peter Nannius, in 1627 j anpg Some portions of the ancient wall may be discovered on the outside, particularly at the two extreme angles; and in many places it is patched with pieces of columns, and with marbles taken from the ruins. A considerable sum had been recently expended on the side next Hy- mettus, which was finished before we arrived. The scaffolding had been removed to the end toward Pen- tele ; but money was wanting, and the workmen were withdrawn. The garrison consists of a few Turks, who reside there with their families, and are called by the Greeks Castriani, or the soldiers of the castle. The rock is lofty, abrupt, and inaccessible, except the front, which is towards the Piraeus; and on that quarter is a moun¬ tainous ridge, within cannon-shot. It is destitute of water fit for drinking ; and supplies are daily carried up in earthen jars, on horses and asses, from one of the conduits of the town. “ The acropolis furnished a very ample field to the ancient virtuosi. It was filled with monuments of A- thenian glory, and exhibited an amazing display of beauty, of opulence, and of art ; each contending as it were for the superiority. It appeared as one entire offering to the Deity, surpassing in excellence and asto¬ nishing in richness. Heliodorus, named Periegetes, the guide, had employed on it 15 books. The curio¬ sities of various kinds, with the pictures, statues, and pieces of sculpture, were so many and so remarkable, as to supply Polemo Periegetes with matter for four volumes : and Strabo affirms, that as many would be required in treating of other portions of Athens and of Attica. In particular, the number of statues was prodigious. Tiberius Nero, who was fond of images, plundered the acropolis as well as Delphi and Olym¬ pia ; yet Athens, and each of these places, had not fewer than 3000 remaining in the time of Pliny. Even Pausanias seems here to be distressed by the mul¬ tiplicity of his subject. But this banquet, as it were, of the senses has long been withdrawn ; and is now be¬ come like the tale of a vision. The spectator views with concern the marble ruins intermixed with mean flat-roofed cottages, and extant amid rubbish ; the sad memorials of a nobler people ; which, however, as vi¬ sible from the sea, should have introduced modern Athens to more early notice. They who reported it was only a small village, must, it has been surmised, have beheld the acropolis through the wrong end of their telescopes. “ The acropolis has now, as formerly, only one entrance, which fronts the Piraeus. The ascent is by traverses and rude fortifications furnished with cannon, but without carriages, and neglected. By the second gate is the station of the guard, who sits cross-legged under cover, much at his ease, smoking his pipe, or drinking coffee, with his companions about him in like ■ attitudes. Over this gateway is an inscription in large characters on a stone turned upside down, and black from the fires made below. It records a present of a pair of gates. g “Going farther up, you come to the ruins of the Propylea, Propylea, an edifice which graced the entrance of the B b 2 citadel. A T H [i Athens, citadel. This was one of the structures of Pericles, ““-’•v——who began it when Euthymenes was archon, 435 years before Christ. It was completed in five years, at the expence of 2012 talents. It was of marble, of the Doric order, and had five doors to afford an easy pas¬ sage to the multitudes which resorted on business or de¬ votion to the acropolis. While this fabric was building, the architect Mne- sicles, whose activity equalled his skill, was hurt by a fall, and the physicians despaired of his life: but Mi¬ nerva, who was propitious to the undertaking, appeared, it was said, to Pericles, and prescribed a remedy, by which he was speedily and easily cured. It was a plant or herb growing round about the acropolis, and called ^ afterwards parthenium. Temple of “ The right wing of the Propylea was a temple of Victory. Victory. They related that iEgeus had stood there, viewing the sea, and anxious for the return of his son Theseus, who was gone to Crete with the tributary children to be delivered to the Minotaur. The vessel which carried them had black sails suiting the occasion of its voyage ; and it was agreed, that, if Theseus overcame the enemy, their colour should be changed to white. The neglect of this signal was fatal to 7Egeus, who, on seeing the sails unaltered, threw himself down headlong from the rock, and perished. The idol was named Victory without icings ; it was said, because the news of the success of Theseus did not arrive but with the conqueror. It had a pomegranate in the right hand, and a helmet in the left. As the statue was without pinions, it was hoped the goddess would remain for ever on the spot. li the left wing of the Propylea, and fronting the temple of.Victory, was a building decorated with paint¬ ings by Polygnotus, of which an account is given by Pausamas. 11ns edifice, as well as the temple, was ot the Doric order, the columns fluted, and without bases. Both contributed alike to the uniformity and grandeur of the design ; and the whole fabric, when finished, was deemed equally magnificent and orna¬ mental. The interval between Pericles and Pausanias consists of several centuries. The Propylea remained entire in the time of this topographer; and, as will be shown, continued nearly so to a much later period. It had then a roof ol white marble, which was unsur- . passed either in the size ol the stones or in the beauty of their arrangement; and before each wing was an equestrian statue. 11 H*6 Propylea have ceased to he the entrance of the acropolis. Hie passage which was between the columns in the centre, is walled up almost to their capitals, and above is a battery of cannon. The way now winds before the front of the ancient structure ; and turning to the left hand among rubbish and mean walls, you come to the back part, and to the five door-ways. Ihe soil without is risen higher than the top of the two smaller. There, under the vault and cannon, lies a heap of large stones, the ruin of the . roof. 11 temple of Victory, standing on an abrupt rock, has its back and one side encumbered with the modern ramparts. The columns in the front being walled up, you enter it by a breach in the side, within the Propylea. It was used by the Turks as a maga¬ zine lor powder, until about the year 1636, when a 96 ] A T H sudden explosion, occasioned by lightning, carried away the roof, with a house erected on it, belonging to the 1— officer who commanded in the acropolis, whose'family, ere. wrote, and the face of the country has been in that 'r~ time totally changed. Nothing perhaps would be more interesting to the curiosity of the philosopher, or con¬ duce more to the improvement of our knowledge in na¬ tural history, than a journey over Mount Atlas. The climate, though extremely cold in winter, is very heal¬ thy and pleasant5 the valleys are well cultivated, abound in fruits, and are diversified by forests and plentiful springs, the streams of which uniting at a little distance, form great rivers, and lose themselves in the ocean. According to the reports of the Moors, there are many quarries of marble, granite, and other valuable stone, in these mountains : It is probable there are also mines, but the inhabitants have no idea of these riches j they consider their liberty, which their situation enables them to defend, as the most inestimable of all treasures.” Atlas, in matters of literature, denotes a book of universal geography, containing maps of all the known parts of the world. Atlas, in Commerce, a silk-satin, manufactured in the East Indies. There are some plain, some striped, and some flowered, the flowers of which are either gold or only silk. There are atlasses of all colours, but most of them false, especially the red and the crim¬ son. The manufacture of them is admirable j the gold and silk being worked together after such a manner as no workman in Europe can imitate j yet they are very far from having that fine gloss and lustre which the French know how to give to their silk stuffs. In the Chinese manufactures of this sort, they gild paper on one side with leaf-gold) then cut it in long slips, and weave it into their silks ) which makes them with very little cost, look very rich and fine. The same long slips are twisted or turned about silk threads, so artificially, as to look finer than gold thread, though it be of no greater value. ATMOSPHERE, a word generally used to signify the whole mass of fluid, consisting of ah’, aqueous and other vapours, electric fluid, &c. surrounding the earth to a considerable height. , The composition of that part of our atmosphereAtrao- properly called air, rvas till lately very much unknown.*pherecoi In former times it was supposed to be a simple, homo-P08£j.“|r geneous and elementary fluid. The experiments whose altitude he computed to have been between 69 and 734 English miles ; its diameter 2800 yards, or upwards of a mile and a half; and its velocity about 350 miles in a minute. Others, appa¬ rently of the same kind, but whose altitude and velo¬ city were still greater, have been observed; particularly that very remarkable one, August 18th, 1783, whose distance from the earth could not be less than 90 miles, and its diameter not less than the former ; at the same time that its velocity was certainly not less than 1000 miles in a minute. Fire-balls, in appearance similar to these, though vastly inferior in size, have been some¬ times observed at the surface of the earth. Of this kind Dr Priestley mentions one seen on board the Montague, 4th November 1749, which appeared as big as a large millstone, and broke with a violent ex¬ plosion. From analogical reasoning, it seems very probable, that the meteors which appear at such great heights in the air are not essentially different from those which, like the fire ball just mentioned, are met with on the surface of the earth. The perplexing circumstances with regard to the former are, that at the great heights above mentioned, the atmosphere ought not to have any density sufficient to support flame, or to pro¬ pagate sound ; yet these meteors are commonly suc¬ ceeded by one or more explosions, nay are sometimes said to be accompanied with a hissing noise as they pass over our heads. The meteor of 1719 was not C c 3 only Atmo¬ sphere. *See Elec, tricity In¬ dex. Density of the air does not always keep pace with its gravity. ATM [ 204 ] only very bright, insomuch that for a short space it contained turned night into day, but was attended with an ex- * plosion heard over all the island of Britain, occasioning a violent concussion in the atmosphere, and seeming to shake the earth itself. That of 1783 also, though much higher than the former, was succeeded by ex¬ plosions ; and, according to the testimony of several people, a hissing noise was heard as it passed. Dr Halley acknowledged that be was unable to reconcile these circumstances with the received theory of the height of the atmosphere ; as, in the regions in which this meteor moved, the air ought to have been 300,000 times more rare than what we breathe, and the next thing to a perfect vacuum. In the meteor of 1783, the difficulty is still greater, as it appears to have been 20 miles farther up in the air. Di'IIalley offers a conjecture, indeed, that the vast magnitude of such bodies might compensate for the thinness of the medium in which they moved. Whether or not this was the case indeed cannot he ascertained, as we have so few data to go upon ; but the greatest difficulty is to account for the brightness of the light. Appearances of this kind are indeed with great probability attributed to electricity, but the dif¬ ficulty is not thus removed. Though the electrical fire pervades with great ease the vacuum of a common air-pump, yet it does not in that case appear in bright well defined sparks, as in the open air, but rather in long streams resembling the aurora borealis. From some late experiments, indeed, Mr Morgan concludes, that the electrical fluid cannot penetrate a perfect va- ■cuum*. If this is the case, it shows that the regions we speak of are not such a perfect vacuum as can be artificially made ; but whether it is or not, the ex¬ treme brightness of the light shows that a fluid was present in those regions, capable of confining and con¬ densing the electric matter as much as the air does at the surface of the ground ; for the brightness of these meteors, considering their distance, cannot be suppo¬ sed inferior to that of the brightest flashes of light¬ ning. This being the case, it appears reasonable to conclude, that what is called the density of the air does not alto¬ gether keep pace with its gravity. The latter indeed must in a great measure be affected by the vapours, but above all by the quantity of the basis of fixed or dephlogisticated air contained in it: for Mr Kirvvan has discovered that the basis of fixed air, when depri¬ ved of its elastic principle, is not greatly inferior to gold in specific gravity ; and we cannot suppose that of dephlogisticated air to be much less. It is possible, therefore, that pure air, could it be deprived of all the water it contains, might? have very little gravity ; and as there is great reason to believe that the basis of de¬ phlogisticated air is only one of the constituent parts of water, we see an evident reason why the air ought to become lighter, and likewise less fit for respiration, the higher up we go, though there is a possibility that its density, or power of supporting flame, may continue unaltered. There are not yet, however, a sufficient number of facts to enable us to determine this question ; though such as have been discovered seem rather to favour the above conjecture. Dr Boerhaave was of opinion that the gravity of the air depended entirely on the water it 2 ATM and, by the means of alkaline salts, he was enabled to extract as much water from a quantity of air as was very nearly equivalent to its weight. Bv the calcination of metals we may extract as much of the basis of dephlogisticated air from a quantity of atmo¬ spherical air as is equivalent to the weight of air lost. Were it possible, therefore, to extract the whole of this, as well as all otlmr vapours, and to preserve only the elastic principle, it is highly probable that its gra¬ vity would entirely cease. It has been found, by those who have ascended with aerostatic machines, or to the tops of high mountains, that the dephlogisticated air is found to be contained in smaller quantities in the at¬ mosphere of those elevated regions than on the lower grounds. It is also found, that in such situations the air is much drier, and parts with water with much more difficulty, than on the ordinary surface. Salt of tartar, for instance, which at the foot of a mountain will very soon run into a liquid, remains for a long time exposed to the air on the top of it, without showing the least tendency to deliquesce. Nevertheless, it hath never been observed that ftres did not burn as intensely on the tops of the highest mountains as on the plains. The matter indeed was put to the trial in the great eruption of Ve¬ suvius in I779? where, though the lava spouted up to the height of three miles above the level of the sea, the uppermost parts all the while were to appearance as much inflamed as the lowest. g The high degree of electricity, always existing inGravityof the upper regions of the atmosphere, must of necessity1^® UPPM have a very considerable influence on the gravity of anyr.csionsl)f heterogeneous particles floating in it. When we con-*w^, sider the effects of the electric fluid upon light bodies imps dirai. at the surface of the earth, it will readily be admitted, nbiiedby that in those regions where this fluid is very abundant,e*ectr‘c‘tJ*i the gravity of the atmosphere may be much diminished without affecting its density. We know that it is the nature of any electrified substance to attract light bo¬ dies; and that, by proper management, they may even be suspended in the air, without either moving up or down for a considerable time. If this is the case with light terrestrial bodies, it cannot be thought very im¬ probable that the aerial particles themselves, i. e. those which we call the basis of dephlogisticated air, and of aqueous or other vapour diffused among them, should be thus affected in the regions where electricity is so abundant. From this cause, therefore, also the gra¬ vity of the atmosphere may be affected without any al¬ teration at all being made in its density ; and hence may arise anomalies in the barometer hitherto not taken notice of. It appears, therefore, that the absolute height of the Absolute atmosphere is not yet determined. The beginning height of and ending of twilight indeed show, that the height at which the atmosphere begins to refract the sun’s light is about 44 or 45 English miles. But this mayed. not improbably be only the height to which the aque¬ ous vapours are carried : for it cannot be thought any unreasonable supposition, that light is refracted only by means of the aqueous vapour contained in the at¬ mosphere ; and that where this ceases, it is still capable of supporting the electric fire at least as bright and strong as at the surface. That it does extend much higher, is evident from the meteors already mentioned ; for all these are undoubtedly carried along with the atmosphere; A T M [ 0 Of if! pres atmosphere 5 otherwise that of 1783, which was seen for about a minute, must have been left 1000 miles to the westward, by the earth flying out below it in its annual course round the sun. It has already been mentioned, that the pressure of suraf the the atmosphere, when in its mean state, is equivalent atou to a weight of 15 pounds on every square inch. Hence splK'- j),. Cotes computed, that the pressure of the whole am¬ bient fluid upon the earth’s surface is equivalent to that of a globe of lead 60 miles in diameter. Hence also it appears, that the pressure upon a human body must be very considerable j for as every square inch of sur¬ face sustains a pressure of 15 pounds, every square foot, as containing 144 inches, must sustain a pressure of 2160; and if we suppose a man’s body to contain 15 square feet of surface, which is pretty near the truth, he must sustain a weight of 32,400 pounds, or 16 tons, for his ordinary load. By this enormous pressure we should undoubtedly be crushed in a moment, were not all parts of our bodies filled either with air or some other elastic fluid, the spring of which is just sufficient to counterbalance the weight of the atmosphere. But whatever this fluid may be, we are sure that it is just able to counteract the atmospherical gravity ami no more ; for if any considerable pressure be superadded to that of the air, as by going into deep water, or the like, it is always severely felt, let it be ever so equa¬ ble. If the pressure of the atmosphere is taken off from any part of the human body, the hand, for in¬ stance, when put in an open receiver from whence the air is afterwards extracted, the weight of the atmo¬ sphere then discovers itself, and we imagine the hand strongly sucked down into the glass. See Pneuma- t Tics. ’ Vartion In countries at some distance from the equator, the pressure of the atmosphere varies considerably, and thus itse cP. Pr°fluces consffierable changes on many terrestrial bo¬ dies. On the human body the quantity of pressure sometimes varies near a whole ton; and when it is thus so much diminished, most people find something of a listlessness and inactivity about them. It is surprising, however, that the spring of the internal fluid, already mentioned, which acts as a counterpoise to the atmo- sphex-ical gravity, should in all cases seem to keep pace with it when the pressure is naturally diminished, and even when it is artificially augmented, though not I when the pressure is artificially diminished. Thus in that kind of weather when the pressure of the air is least, we never perceive our veins to swell, or are sen¬ sible of any inward expansion in our bodies. On the contrary, the circulation is languid, and we seem ra- )fdi ul. ther to be oppressed by a weight. Even in going up ' ot ispi- to the tops of mountains, where the pressure of the at¬ mosphere is diminished more than three times wdiat it usually is on the plain, no such appearances are ob¬ served. Some travellers indeed have affirmed, that on the tops of very high mountains, the air is so light as to occasion a great difficulty of respiration, and even violent retching and vomiting of blood. It does not appear, however, that these assertions are well found¬ ed. Mr Brydone found no inconvenience of this kind on the top of Mount HLtna j nor is any such thing men¬ tioned by. Mr Houel, who also ascended this moun¬ tain. Sir William Hamilton indeed says, that he did feel a difficulty of respiration, independent of any sul- Atmo- sphere. atio ii,n tie tils of lODiiilins. 13 205 ] ATM phureons steam. But, on the top of a volcano, the respiration may be affected by so many difl’erent causes, that it is perhaps impossible to assign the true one. The French mathematicians, when on the top of a very high peak of the Andes, did not make any complaint of this kind, though they lived there for some time. On the contrary, they found the wind so extremely violent, that they were scarcely able to withstand its force 5 which seems an argument for at least equal den¬ sity of the atmosphere iu the superior as in the inferior regions. Hr Heberden, who ascended to the top of Tenerifle, a mountain higher than iEtna, makes no mention of any difficulty of respiration. M. Saussure, M. Saus- however, in his journey to the top of Mont Blanc, the sure’ssymp- highest of the Alps, felt very great uneasiness in thistoms on l^c way. His respiration was not only extremely diffi-^1’^ cult, but his pulse became quick, and he was seized Blanc ae- with all the symptoms of a fever. His strength was counted also exhausted to such a degree, that he seemed to re-for- quire four times as long a space to perform some ex¬ periments on the top of the mountain as he would have done at the foot of it. It must be observed, how¬ ever, that these symptoms did not begin to appear till he had ascended two miles and a half perpendicular above the level of the sea. The mountain is only about a quarter of a mile higher; and in this short space he was reduced to the situation just mentioned. But it is improbable that so small a difference, even at the end of his journey, should have produced such violent ef¬ fects, had not some other cause concurred. A cause of this kind he himself mentions, viz. that the atmo¬ sphere at the top of the mountain was so much im¬ pregnated with fixed air, that lime-water, exposed to it, quickly became covered with a pellicle occasioned by the absorption of that fluid. Now it is known, that fixed air is extremely pernicious to animals, and would bring on symptoms similar to those above men¬ tioned. There is no reason, therefore, to have recourse to the rarity of the atmosphere for solving a pheno¬ menon which may more naturally be accounted for otherwise. When the pressure of the atmosphere is augmented, by descending, in the diving-bell, to considerable depths in the sea, it does not appear that any inconvenience follows from its increase. Those who sit in the diving- bell are not sensible of any pressure as long as they re¬ main in the air, though they feel it very sensible in go¬ ing into the water : yet it is certain, that the pressure in both cases is the same: for the whole pressure of the atmosphere, as well as of the water, is sustained by the air iu the diving-bell, and consequently communicated to those who sit in it. But though artificial compression of the air, as well as natural rarefaction, can thus be borne, it is otherwise with artificial rarefaction. Animals in an air-pump show uneasiness from the very first, and cannot live for any time in an atmosphere rarefied artificially even as much as it appeared to be from the barometer on the top of Mont Blanc. It is not easy to assign the true reason of the varia-Variation tions of gravity in the atmosphere. Certain it is, how-of the at- ever, that they take place only in a very small degree ni0SP^er*_ within the tropics ; and seem there to depend on ^ heat of the sun, as the barometer constantly sinks near for half an inch every day, and rises again to its former station M Atmo¬ sphere. A T station in the night time. In the temperate zones the barometer ranges from 28 to near 31 inches, by its va¬ rious altitudes showing the changes that are about to take place in the weather. If we could know, there¬ fore, the latent causes by which the weather is influen¬ ced, we should likewise certainly know those by which the gravity of the atmosphere is affected. In general they may be reduced to two, viz. an emission of latent beat from the vapour contained in the atmosphere, or of electric fluid from the same, or from the earth. To one or both of these causes, therefore, may we ascribe the variations of the gravity of the atmosphere j and we see that they both tend to produce the same effect with the solar heat in the tropical climates, viz. to rarefy the air, by mixing with it or setting loose a non¬ gravitating fluid, which did not act in such large pro¬ portion in any particular place before. No doubt, the action of the latent heat and electric fluid is the same in the torrid as in the temperate zones: but in the torrid zone the solar heat and excessive eva¬ poration counteract them j so that whatever quanti¬ ties may be discharged by the excessive deluges of rain, &c. which fall in those countries, they are in¬ stantly absorbed by the abundant fluid, and are quick¬ ly ready to be discharged again ; while, in the tempe¬ rate zones, the air becomes sensibly lighter, as ryell as warmer, by them for some time before they can be ab¬ sorbed again. The variations of heat and cold to which the atmo¬ sphere is subject, have been the subject of much specu¬ lation. In general they seem to depend entirely upon the light of the sun reflected into the atmosphere from the earth ; and where this deflection is deficient, even though the light should be present ever so much, the most violent degrees of cold are found to take place. Hence, on the tops of mountains, the cold is generally excessive, though by reason of the clearness of the at¬ mosphere the light of the sun falls upon them in greater Quantity than it can do on an equal space on the plain, n long winding passages also, such as the caverns of iEtna and Vesuvius, where the air has room to circu¬ late freely, without any access of the sun, the cold is scarcely tolerable 5 whence the use of these for cooling liquors, preserving meat, &c. The coldness of the atmosphere on the tops of moun- laTcWa- taJns ’’j18 been ascribed by M. Lambert and De Luc, sons for thef° ^ie igneous fluid, or elementary fire, being more rare cold on the in those elevated situations than on the plains. M. Lam- tops of bert is of opinion that it is rarefied above by the action of the air, and that below it is condensed by its own proper weight. He considers fire as a fluid in motion, the parts of which are separable, and which is rarefied when its velocity is accelerated. He does not decide with regard to the identity of fire and light, though he seems inclined to believe it. M. de Luc compares elementary fire to a continuous fluid, whose parts are condensed by being mutually compressed. He denies that fire and light are the same ; and maintains that the latter is incapable, by itself, of setting fire to bo¬ dies, thought it does so by putting in motion the igne¬ ous fluid they contain ; and that it acts with more force near the earth than at a distance from its surface, by reason of this fluid, which he calls a heavy and elastic one, being more condensed there than at a greater height. 6 [ 206 ] ATM *5 Variation of the heat and cold of the atmo¬ sphere. 16 Xiambert and De tops mountains, M. Saussure, in treating of this subject in his ac- count of the Alps, does not consider fire as a fluid so sphere free and detached as to be able either to ascend with ra-'”~v^ pidity by its specific levity, or to condense itself sensi-M 17 bly by its proper weight. He supposes it to be unitedsu^"1' to bodies by so strict an affinity, that all its motions count.3'' are determined, or at least powerfully modified, by that affinity. As soon therefore as fire, disengaged by com¬ bustion Or by any other cause, endeavours to diffuse itself, all the bodies that come within the sphere of its activity endeavour to attract it j and they absorb such quantities of it as are in the direct ratio of their affi¬ nities with it, or in the inverse ratio of what is necessary for their equilibrium with the surrounding bodies. Now it does not appear that in this distribution the situation of places, with regard to the horizon, has any other influ¬ ence than what they receive from the different currents produced by the dilatation of the air, and by the levity which that dilatation produces. The ascent of flame, smoke, &c. or of air heated in any way, persuaded the ancients that fire is possessed of absolute levity, by which it had a tendency to mount upwards. “ But these ef¬ fects (says he) are owing either to the levity of the fluid which constitutes flame, or to that of air dilated by heat; and not to the levity of the igneous fluid. I am, how¬ ever, sufficiently convinced, that this fluid is incompa¬ rably lighter than air, though I do not believe that it possesses the power of ascending in our atmosphere by virtue of its levity alone. ,5 “ The celebrated Bouguer has demonstrated, by Mr Boo- principles the most simple, and most universally adopt-S11'1’*"1’ ed, that it is not necessary, in order to account for diminution of heat on mountains, to have recourse tot0p0ftii{ hypotheses that are at best doubtful. The following Andes, is his explanation of what was felt on the mountains of Peru. “ It was proper, in order to explain this subject, to insist on the short duration of the sun’s rays, which cannot strike the different sides of mountains but for a few hours, and even this not always. A horizontal plain, when the sun is clear, is exposed at mid-day to the perpendicular and undiminished action of these rays, while they fall but obliquely on a plain not much inclined, or on the sides of a high pile of steep rocks. But let us conceive for a moment an insulated point, half the height of the atmosphere, at a distance from all mountains, as well as from the clouds which float in the air. The more a medium is transparent, the less heat it ought to receive by the immediate action of the sun. The free passage which a very transpa¬ rent body allows to the rays of light, shows that its small particles are hardly touched by them. Indeed what impression could they make on it, when they pass through almost without obstruction ? Light, when it consists of parallel rays, does not by passing through a foot of free atmospheric air, near the earth, lose an hundred thousandth part of its force. From this we may judge how few rays are weakened, or can act on this fluid, in their passage through a stratum of the dia¬ meter not of an inch or a line, but of a particle. Yet the subtility and transparency are still greater at great heights, as was obvious on the Cordilleras, when we looked at distant objects. Lastly, the grosser air is heated below by the contact or neighbourhood of bo¬ dies of greater density than itself, which it surrounds, and ATM r 207 ] ATM A)(V anti on wiiieh It rests j and the heat may he communx- »pl(re. cated by little and little to a certain distance. The in- i————' fei-ior parts of the atmosphere by this means contract daily a vei'y considerable degree of heat, and may re¬ ceive it in proportion to its density or bulk. But it is evident that the same thing cannot happen at the di¬ stance of a league and a half or two leagues above the surface of the earth, although the light there may be something more active. The air and the wind there¬ fore must at this height be extremely cold, and colder in proportion to the elevation. “ Besides, the heat necessary to life is not merely that which we receive every instant from the sun. The momentary degree of this heat corresponds to a very small part of that which all the bodies around us have imbibed, and by which ours is chiefly regulated. The action of the sun only serves to maintain nearly in the same state the sum of the total heat, by repairing through the day the loss it sustains through the night, and at all times. If the addition be greater than the loss, the total heat will increase, as it happens in sum¬ mer, and it will continue to accumulate in a certain degree ; but for the reasons already given, this accu¬ mulation cannot be very great on the top of a moun¬ tain, where the summit, which rises high, is never of great bulk. The lowest state of the thermometer in every place is always in proportion to the heat acquired by the soil ; and that being vei-y small on the top of a mountain, the quantity added to it by the sun during the day must be comparatively greater •, and the accu¬ mulated heat will be more in a condition to receive in¬ crease in proportion to its distance from the degree which it cannot pass. “ Another particular observable on all the high places ol the Cordilleras, and which depends on the same cause, is, that when we leave the shade, and ex¬ pose ourselves to the sunshine, we feel a much greater difference than we do here in our fine days when the weather is temperate. Every thing contributes at Quito to make the sun exceedingly powerful: a single step from an exposed place to the shade gives the sen¬ sation of cold : this would not be the case if the quan¬ tity of heat acquired bv the soil were more consider¬ able. We now also see why the same thermometer, put first into the shade and then in the sun, does not undergo the same changes at all times and in all pla¬ ces. In the morning, upon Pichincha, this instrument is generally a few degrees below the freezing point, which may be reckoned the natural temperature of the place j but when during the day we expose it to the sun, it is easy to imagine that the effect must be great, and much more than double in whatever way it is mea¬ sured.” This theory is adopted by M. Saussure, who adds the following fact to prove that the action of the sun’s rays, considered abstractedly and independent of any extrinsic source of cold, is as great on mountains as on plains j viz. that the power of burning lenses and mir- umi:)L rors *s ^,e same at afi heights. To ascertain this fact, aisefe. our author procured a burning-glass so weak that at Jail) Geneva it would just set fire to tinder. This he car- J«1onried, with some of the same tinder, to the top of the mo,L R10imta‘n Saleve (a height of 3000 feet) ; where it not ins . on on,y produced the same efiect, but apparently with diu greater facility than on the plain. Being persuaded, then, that the principal source of cold on the tops of r\tnio high mountains is their being continually surrounded sphere. with an atmosphere which cannot be much heated ei- v~— ■' ther by the rays of the sun on account of its transparen¬ cy, or by the reflection of them from the earth by rea¬ son of its distance, he wished to know, whether the di¬ rect solar rays on the top of a high mountain had the same power as on the plain, while the body on which they acted was placed in such a manner as to be unaf¬ fected by the surrounding air. For this purpose he in¬ stituted a set of experiments, from which he drew the following conclusions, viz. that a difference of 777 toises in height diminishes the heat which the rays of the sun are able to communicate to a body exposed to the exter¬ nal air, 140 of the thermometer; that it diminishes the heat of a body partially exposed, only 6°; and that it augments by i° the heat of a third body completely de¬ fended from the air. Plence it appears that the atmosphere, though soAtmo- essentially necessary to the support of fire, is somehoxv sphere eve- or other the greatest antagonist of heat, and most ef- rywhere fectually counteracts the operation of the solar rays in couateractf producing it. Ibis power it seems to exert at all di-t^e sun> stances, at the surface as well as in the higher x'egions. From some experiments made by M. Pictet it appears, that even in places exposed to the rays of the sun, the Si heat, at five feet distance from the ground, is greater Is colder only by one or two degrees than at 50 feet above theverynear surface, though the ground was at that time 15 or 20°tke^®ur’acc warmer than the air immediately in contact with it. its various operations, see Meteorology. See also the at tides Atmometer, Climate, Dew, and Me¬ teorology, in the Supplement. The uses of the atmosphere are so various, that it is impossible to enumerate them. One of the most essen¬ tial is its power of giving life to vegetables, and sup¬ porting that of all animated beings. For the latter purpose, however, it is not in all places equally pro¬ per : we shall therefore conclude this article with some remarks on T/ie Salubrity of the Atmosphere.—The air on the tops of mountains is generally more salubrious than that in pits. Dense air indeed is always more proper for respiration than such as is more rare 5 yet the air on mountains, though much moremare, is more free from phlogistic vapours than that of pits. Hence it has been found, that people can live very well on the tops of mountains where the barometer sinks to 15 or 16 inches. M. de Saussure, in his journey upon the Alps, having observed the air at the foot, on the middle, and on the summits of various mountains, observes, that the air of the very low plains seems to be the least salubrious; that the air of very high mountains is neither very pure, nor, upon the whole, seems so lit for the lives of men, as that of a certain height above the level of the sea, which he estimates to be about 200 or 300 toises, that is, about 430 or 650 yards. Dr White, in the 68th volume of the Phil. Trans, giving an account of his experiments on air made at York, says, that the atmospherical air was in a very b.ad state, and indeed in the worst he had ever obser¬ ved it, the 13th of September 1777 5 when the barome¬ ter stood at 30.30, the thermometer at 69°; the wea¬ ther being calm, clear, and the air dry and sultry, no rain having fallen for above a fortnight. A slight shock of an earthquake was perceived that day. Ibe air of a bed-room at various times, viz, at night, and in the morning after sleeping in it, has been exa¬ mined by various persons ; and it has been generally found, that after sleeping in it the air is less pure than at any other time. The air of privies, even in calm weather, has not been found to be so much pblogisti- cated as might have been expected,.notwithstanding its disagreeable smell. irom this and other observations, it is thought that the exhalations of human excrements are very little if at ail injurious, except when they become putrid, or proceed from a diseased body ; in which case they in¬ fect the air very quickly. Dr Ingenhousz, soon after he left London, sent an account of his experiments made in the year 1779 up¬ on the purity of the air at sea and other parts ; which account was read at the Royal Society the 24th of A- pril 1780, and inserted in the 70th vol. of the Phil. Trans. His first observations were made on board a vessel in the month of the Thames, between Sheerness and Margate, where he found that the air was purer than any other sort of common air he had met with be¬ fore. He found that the sea-air taken farther from the land, viz. between the English coast and Ostend, was not so pure as that tried before ; yet this inferior purity seems not to take place always. The Doctor’s general observations, deduced from his numerous expe- 3 10] ATM riments, are, “ That the air at sea and close to it, is in general purer, and fitter for animal life, than the air on the land, though it seems to be subject to some inconsistency in its degree of purity with that of the land : That probably the air will be found in gene¬ ral much purer far from the land than near the shore, the former being never subject to be mixed with land air.” The Doctor in the same paper transcribes a journal of experiments, showing the degree of purity of the atmosphere in various places, and under different cir¬ cumstances ; which we shall insert here in an abridged manner. The method used in those experiments was to in¬ troduce one measure of common air into the eudiome¬ ter tube, and then one measure of nitrous air. The mo¬ ment that these two sorts of elastic fluids came into con¬ tact, he agitated the tube in the water-trough, and then measured the diminution, expressing it by hundredth parts of a measure ; thus, when he says, that such air was found to be 130, it signifies, that after mixing one measure of it with one of nitrous air, the whole mixed and d iminished quantity was 130 hundredths of a mea¬ sure, viz. one measure and 30 hundredths of a measure more. * “ The different degrees of salubrity of the atmo¬ sphere, as I found it in general in my country house at Southal-Green, ten miles from London, from June to September, lay between 103 and 109. I was surprised when, upon my return to town to my former lodgings in Pall Mall Court, I found the common air purer in general in October than I used to find it in the middle of summer in the country; for on the 22d of October, at nine o’clock in the morning, the weather being fair and frosty, I found that one measure of common air, and one of nitrous air, occupied 100 subdivisions in the glass-tube, or exactly one measure. That very day, at two o’clock in the afternoon fit being then rainy wea¬ ther), the air was somewhat altered for the worse. It gave 102. October the 23d, it being rainy weather, the air gave 102. October the 24th, the weather be¬ ing serene, the air at nine o’clock in the morning gave 100. October the 25th, the sky being cloudy at 11 o’clock in the morning, the air gave 102. At 11 o’clock at night, from live different trials, it gave toy. October the 26th, the weather being very dark and rainy, the air gave 105, as before.” The air at Ostend was found by the Doctor to be generally very good, giving between 94 and 98. At Bruges, the air taken at seven o’clock at night gave 103. November the 8th, the air at Ghent at three in the afternoon gave 103. November the 12th, the air of Brussels at seven o’clock P. M. gave loy^- The next day, the air of the low’er part of the same city gave 106 ; that of the highest appeared to be purer, as it gave 104 which agrees with the common popular observation. Novem¬ ber the 14th, both the air of the highest and that of the lowest part of the city appeared to be of the same goodness, giving 103. The weather was frosty. November the 22d, the air of Antwerp in the even¬ ing gave 109^; the weather being rainy, damp, and cold. November the 23d, the air of Breda gave 106. rIhe next day about 11 o’clock the air gave 102; the weather being fair, cold, and inclining to frost. At seven Atmo¬ sphere, r • His jourm of the pur ty of the a in differtt places. 1 I* ATM ^,0. seven o’clock it gave 103. Next day, being the 25th, I,ere. the air gave 104} the weather being cold and rainy. —'The 26th it gave 103 ; the weather being very rainy, cold, and stormy. November the 27th, the air at the Moordyke close to the water gave ioi^ j the weather being fair and cold, but not frosty. This spot is rec¬ koned very healthy. November the 28th, the air of Rotterdam gave 103; the weather being rainy and cold. November the 29th, the air of Delft gave 103; the weather being stormy and rainy. November the 30th, the air of the Hague gave 104; the weather being cold, and the wind northerly. The first of December the weather underwent a sudden change; the wind becoming southerly and stormy, and the atmosphere becoming very hot. The day after, Fahrenheit’s thermometer stood at 540 ; and the com¬ mon air being repeatedly and accurately tried gave 116; and that preserved in a glass phial from the pre¬ ceding day gave 117 ; and that gathered close to the sea gave 115. December the 4th, the air of Amsterdam gave 103 ; the weather being rainy, windy, and cold. The day after, the weather continuing nearly the same, the air gave 102. December the 10th, the air of Rotterdam gave 1015 the weather being rainy. December the 12th, being in the middle of the water between Dort and the Moordyke, the air gave 109 •, the weather be¬ ing remarkably dark, rainy, and windy. December the 13^5 a’r Breda in the morning gave 109^ the weather continuing as the day before. And in the afternoon, the air gave 1064 •, the weather having cleared up. December the 16th, the air of the lower part of the city of Antwerp gave 105, that of the higher part 1045 the weather being rainy and tempe¬ rate. December the 17th, the air of Antwerp gave 107 j the weather continuing nearly as in the preced¬ ing day. December the 10th, the air of Brussels gave 1095 the weather being rainy, windy, and rather warm. December the 2ist, the air of Brussels gave 106 5 the weather being dry and cold. The next day the air and the weather continued the same. December the 23d, the air of Mons gave 104 ; the weather being rainy and cold. December the 24th, the air near Bouchain gave 1044 5 the weather being cloudy and cold. De¬ cember the 25th, the air of Peronne gave 1024 j the weather being frosty. December the 26th, the air of j! Cuvilli gave 103 ; the weather frosty. December the 27th, the air of Senlis gave 102*; the weather frosty. December the 29th, the air of Paris gave 203 ; the 1 weather frosty. 1780, January the 8th, the air of Paris gave 100 ; the weather frosty. January the 13th, the 1 air of Paris gave 98 ; hard frost. •vitt)lrS| ^‘1US ^ar 'V'1^ ^ngen^ousz’s observations. His his <'cri. aPParatPs a very portable one, made by Mr Mar- meru were*'m’ *n reality is the eudiometer-tube and mea- aadi sure as used by Mr Montana before he made his last im¬ provement. “ The whole of this apparatus (says Dr Ingenhousz) was packed up in a box about ten inches long, five broad, and three and a half high,. The glass- tube or great measure, which was 16 inches long, and ATM divided into two separate pieces, lay in a small compass, Atmd- and could be put together by brass screws adapted to sphere, the divided extremities. Instead of a water trough, —J such as is used commonly, I made use of a small round wooden tub,” &c. ^ The abbe Fontana, who has made a great number ofFontana’s very accurate experiments upon this subject, gives his0Pinions opinion in the following words : “ I have not the least.011 tlla lsU,!' hesitation in asserting, that the experiments made to^CC’ ascertain the salubrity of the atmospherical air in vari¬ ous places in different countries and situations, men¬ tioned by several authors, are not to be depended up¬ on j because the method they used was far from being exact (a), the elements or ingredients for the experi¬ ment were unknown and uncertain, and the results very' different from one another. “ When all the errors are corrected, it will be found that the difference between the air of one country and that of another, at different times, is much less than what is commonly believed ; and that the great differ¬ ences found by various observers are owing to the fal¬ lacious effects of uncertain methods. This I advance from experience ; for I was in the same error. I found very great differences between the results of the expe¬ riments of this nature which ought to have been simi¬ lar j which diversities I attributed to myeelf, rather than to the method I then used. At Paris I examined the air of different places at the same time, and espe¬ cially of those situations where it was most probable to meet with infected air, because those places abounded with putrid substances and impure exhalationsj but the - differences I observed were very small, and much less than what could have been suspected, for they hardly arrived at one-fiftieth of the air in the tube. Having taken the air of the hill called Mount Valerian, at the height of about 500 feet above the level of Paris, and compared it with the air of Paris taken at the same time, and treated alike, I found the former to be hardly one-thirtieth better than the latter. “ In London I have observed almost the same. The air of Islington and that of London suffered an equal diminution by the mixture of nitrous air ; yet the air of Islington is esteemed to be much better. I have ex¬ amined the air of London taken at different heights (for instance, in the street, at the second floor, and at the top of the adjoining houses), and have found it to be of the same quality. Having taken the air at the iron gallery of St Paul’s cupola, at the height of 313 feet above the ground, and likewise the air of the stone gallery, which is 202 feet below the other ; and having- compared these two quantities of air with that of the street adjoining, I found that there was scarce any sen¬ sible difference between them, although taken at such different heights. “ In this experiment a circumstance is to be consi¬ dered, which must have contributed to render the above-mentioned differences more sensible : that is, the agitation of the air of the cupola j for there was felt a pretty brisk wind upon it, which I observed to be stronger and stronger the higher I ascended j whereas in experiments (a) It is plain that Dr Ingenhousz’s method is not implied in this remark j since the Doctor’s weie made long after, and the method used by him was properly that of Mr Fontana. D d 2 f 211 ] A T O [2 Atmo- in the street, and indeed in all the streets I passed sphere, through, there was no sensible wind to he felt. This Atock. experiment was made at four in the afternoon, the wea- v ther being clear. The quicksilver in the barometer at that time was 28,6 inches high, and Fahrenheit’s thermometer stood at 54e.” A few lines after, Mr Fontana proceeds thus — “ From this we clearly see, how little the experiments hitherto published about the differences of common air are to be depended upon. In general, I find that the air changes from one time to another: so that the dif¬ ferences between them are far greater than those of the airs of difl’erent countries or difl'erent heights. For instance, I have found that the air of London in the months of September, October, and November, 1778, when treated with the nitrous air, gave II, I, 1,90, and II, II, 2,25, which is a mean result of many experi¬ ments which differed very little from each other. The 26th day of November last, I found the air, for the first time, much better j for it-gave II, I, 1,8c, and II, II, 2,20; but the 14th of February 1779, the air gave II, I, 1,69 and II, II, 2,21 5 from whence it appears, that the air of this 14th of February was better than it had been six months before. There can be no doubt of the accuracy of the experiments, because I compared the air taken at different times with that which I had first used in the month of September, and which I had preserved in dry glass bottles accurately stopped.” This difference in the purity of the air at different . times, Mr Fontana farther remarks, is much greater than the difference between the air of the different places observed by him : notwithstanding this great change, as he observed, and as he was informed by va¬ rious persons, no particular change of health in the generality of people, or facility of breathing, was per¬ ceived. Mr Fontana lastly concludes with observing, that “ Nature is not so partial as we commonly believe. She has not only given us an air almost equally good everywhere at every time, but has allowed us a cer¬ tain latitude, or a power of living and being in health in qualities of air which differ to a certain degree. By this I do not mean to deny the existence of certain kinds of noxious air in some particular places ; but on¬ ly say, that in general the air is good everywhere, and that the small differences are not to be feared so much as some people would make us believe. Nor do I mean to speak here of some vapours and other bodies which are accidentally joined to the common air in particular places, but do not change its nature and intrinsical property. Bhis state of the air cannot be known by the test of nitrous air j and those vapours are to be considered in the same manner as we should consider so many particles of arsenic swimming in the atmosphere. In this case it is the arsenic, and not the degenerated air, that would kill the animals who ventured to breathe it.” ATOCK, the capital of a province of the same name in the north-western part of Hindostan. It is supposed to be the Taxila of the Greeks, and the place where Alexander, Tamerlane, and Nadir Shah crossed the Indus. Formerly nobody wTas permitted to enter the fortress without a passport from the Mogul him¬ self. E. Long. 71. 55. N. Lat. 33. 59. 2 2 ] A T O ATOM, in "Philosophy^ a particle of matter, so mi- Alom nute, as to admit of no division. Atoms are the mi- |j nima naturae, and are conceived as the first principles or component parts of all physical magnitude. ATOMICAL philosophy, or the doctrine of atoms, a system which, from the hypothesis that atoms are endued with gravity and motion, accounted for the origin and formation of things. This philosophy was first broached by Moschus, some time before the Tro¬ jan war ; but was much cultivated and improved by Epicurus ; whence it is denominated the Epicurean Philosophy. See Epicurean. ATOMIC theory, a new species of philosophy, lately introduced into chemistry, to explain the combi¬ nations of bodies. See Atomic theory, Supplement, ATONEMENT. See Expiation. ATONY, in Medicine, a defect of tone or tension, or a laxity or debility of the solids of the body. ATOOI, one of the Sandwich islands, situated in W. Long. 160. 20. N. Lat. 21. 57. Towards the north-east and north-west, the face of the country is rugged and broken j but to the southward it is more even. The hills rise from the sea-side with a gentle acclivity, and at a little distance back are covered with wood. Its produce is the same with that of the other islands of this cluster 5 but its inhabitants greatly ex¬ cel the people of all the neighbouring islands in the management of their plantations. In the low grounds, contiguous to the bay wherein our navigators * anchor-*C«L ed, these plantations were regularly divided by deepFoyag*. ditches j the fences were formed with a neatness ap¬ proaching to elegance ; and the roads through them were finished in such a manner as would have reflected credit even on an European engineer. The island is about 30 miles in length. The road, or anchoring place, which our vessels occupied, is on the south-west side of the island, about two leagues from the west end, before a village named Wymoa. This road is somewhat exposed to the trade wind 5 not¬ withstanding which defect, it is far from being a bad station, and greatly superior to those which necessity continually obliges ships to use, in countries where the Winds are not only more variable but more boisterous; as at Madeira, Teneriffe, the Azores, &c. The land¬ ing too is not so difficult as at most of those places; and, unless in very bad weather, is always practi¬ cable. The water in the neighbourhood is excellent, and may be conveyed with ease to the boats. But no wood can be cut at any convenient distance, unless the islanders could be prevailed upon to part with the few etooa trees (cordia sehestind) that grow about their vil¬ lages, or a species called dooe dooe, which grows farther up the country. The ground from the wooded part to the sea, is covered with an excellent kind of grass, about two feet in height, which sometimes grows in tufts, and appeared capable of being converted into abundant crops of fine hay. But on this extensive space not even a shrub grows naturally. Besides taro, the sweet potato, and other similar vegetables used by our crews as refreshments, among which were at least five or six varieties of plantains, the island produces bread fruit; which, however, seems to be scarce. There are also a few cocoa palms; some yams; the kappe ot the Friendly islands, or Virginian arum ; the etooa tree, and odoriferous gardenia, or cape A T O [2 10; cape jasmine. Our people also met with several trees of -- j the dooe dooe, that bear the oily nuts, which are stuck upon a kind of skewer and made use of as candles. There is a species of sida, or Indian mallow j also the morinda citrifolia, which is here called none ; a species of con¬ volvulus ; the ava or intoxicating pepper, besides great quantities of gourds. These last grow to a very large size, and are of a remarkable variety of shapes, which are perhaps the effect of art. The scarlet birds, which were brought for sale, were never met with alive ; but one small one was seen, about the size of a canary bird, of a deep crimson colour j also a large owl, two brown hawks or kites, and a wild duck. Other birds were mentioned by the natives j among which were the otoo or bluislr heron, and the torata, a sort of whimbrel. It is probable that the species of birds are numerous, if we may judge by the quantity of fine yellow, green, and small velvet-like blackish leathers, used upon the cloaks and other ornaments worn by these people. Fish, and other productions of the sea, were, to appearance, not various. The only tame or domes¬ tic animals found here were hogs, dogs, and fowls, which were all of the same kind that had been met with at the islands of the South Pacific. There were also small lizards, and some rats. The inhabitants of Atooi are of the middle size, and in general stoutly made, They are neither remarkable for a beautiful shape nor for striking features. Their visage, particularly that of the women, is sometimes round, but others have it long j nor can it justly be said, that they are distinguished as a nation by any general cast of countenance. Their complexion is nearly of a nut-brown $ but some individuals are of a darker hue. They are far from being ugly, and have to all appearance few natural deformities of any kind. Their skin is not very soft nor shining j but their eyes and teeth are, for the most part, pretty good. Their hair in general is straight; and though its natural co¬ lour is usually black, they stain it, as at the Friendly and other islands. They are active, vigorous, and most expert swimmers j leaving their canoes upon the most frivolous occasion, diving under them, and swimming to others, though at a considerable distance. Women, with infants at their breast, when the surf was so high as to prevent their landing in the canoes, frequently leaped overboard, and swam to the shore, frequently endangering their little ones. They appeared to be of a frank, cheerful disposition j and are equally free from the fickle levity which characteriz.es the inhabitants of Otaheite, and the sedate cast which is observable among many of those of Tongataboo. They seem to culti¬ vate a sociable intercourse with each other $ and ex¬ cept the propensity to thieving, which is as it were in¬ nate in most of the people in those seas, they appeared extremely friendly. It rvas pleasing to observe with what affection the women managed their infants, and with what alacrity the men contributed their assistance in such a tender office ; thus distinguishing themselves from those savages who consider a wife and child as things rather necessary than desirable or worthy of their regard and esteem. From the numbers that were seen assembled at every village in coasting along, it was conjectured that the inhabitants of this island ax-e px-etty numerous. Including the straggling houses, it was computed that there might perhaps be, in the whole island, 3 ] A T R sixty sucli villages as that near which our ships an¬ chored j and allowing five persons to each house, there would be in evei’y village, five hundred, or thirty thou¬ sand upon the island. This number is by no means exaggeiated ; for there tvere sometimes three thousand people at least collected upon the beach, when it could not be supposed that above a tenth part of the natives were present. ATRA Bilis, Black Bile, or Melancholy. According to the ancients it hath a twofold origin: 1st, From the grosser parts of the blood, and this they called the melancholy humour. 2d, From yellow bile being highly concocted. Dr Perceival, in his Essays Med. and Exp. suggests, that it is the gall rendered acrid, by a stagnation in the gall-bladder, and rendered viscid by the absorption of its fluid parts. Bile in this state discharged into the duodenum, occasions universal disturbance and disorder until it is evacuated : it oc¬ casions violent vomiting, or pui'ging, or both j and pre¬ vious to this the pulse is quick, the head aches, a deli¬ rium comes on, a hiccough, intense thirst, inward heat, and a fetid breath. Some describe this kind of bile as being acid, harsh, corroding, and when poured on the ground, bubbling up and raising the earth after the manner of a ferment. Dr Percival says, that by the use of the infus. sence Union, warmed with the., tInct. columb. he had checked the vomitings occasioned by this matter. Atra dies, in antiquity, denotes a fatal r/cy where¬ on the Romans received some memorable defeat. The word literally imports a black day; a denomination taken from the colour which is the emblem of death and mourning. Whence the Thracians had a custom of marking all their happy days with white stones or calculi, and their unhappy days with black ones 5 which they cast, at the close of each day, into an urn. At the person’s death the stones were taken out; and from a comparison of the numbers of each complexion, a judgment wras made of the felicity or infelicity of his course of life. The dies atree or atri were after¬ wards denominated nefasti and posteri. Such in parti¬ cular was the day when the tribunes were defeated by the Gauls at the river Allia, and lost the city 5 also that whereon the battle of Cannse was fought j and se¬ veral others mai'ked in the Roman calendar, as atree or unfortunate. ATRACTYLIS, Distaff Thistle. See Botany Index. ATRiETI, in Medicine, infants having no perfo¬ ration in the anus, or persons imperforated in the vagina or urethra. ATRAGENE. See Botany Index. ATRAPHAXIS. See Botany Index. ATREBATII, a people of Britain, seated next to the Bibroci, in part of Berkshire and part of Ox¬ fordshire. This was one of those Belgic colonies which had come out of Gaul into Britain, and there retained their ancient name. For the Atrebatii were a tribe of the Belgse, who inhabited the country which is now called Artois. They are mentioned by C&esar among the nations which composed the Belgic confe¬ deracy against him: and the quota of troops which they engaged to furnish on that occasion was 15,900.. Comius of Arras was a king or chieftain among the Atrebatii in Gaul in Caesar’s time : and he seems to have A T R r 2 Atrebatii have possessed some authority, or at least some influence, || over our Atrebatii in Britain ; for lie was sent by Caesar Atrip. t0 persuade them to submission. This circumstance makes it probable that this colony of the Atrebatii had not been settled in Britain very long before that time. The Atrebatii were among those British tribes which submitted to Caesar : nor do we hear of any remarkable resistance they made against the Homans at their next invasion under Claudius. It is indeed probable, that before the time of this second invasion they had been subdued by some of the neighbouring states, perhaps by the powerful nation of the Cattivellauni, which may be the reason they are so little mentioned in history. Cal- liva Atrebatum, mentioned in the seventh, twelfth, thirteenth, and fourteenth Itinera of Antoninus, and called by Ptolemy Calcula, seems to have been the ca¬ pital of the Atrebatii 5 though our antiquaries differ in their Sentiments about the situation of this ancient city, some of them placing it at Wallingford, and others at Ilchester. ATREUS, in fabulous history, the son of Pelops and Hippodamia, and the father of Agamemnon and Mene- laus, is supposed to have been king of Mycenae and Ar¬ gos about 1228 years before the Christian era. He drove his brother Thyestes from court, for having a cri¬ minal commerce with iErope his wife: but understand¬ ing that he had had two children by her, he sent for him again, and made him eat them j at which horrid action, the sun, it is said, withdrew his light. ATRI, a town of Italy, in the farther Abruzzo, in the kingdom of Naples, with the title of a duchy ; it is the see of a bishop, and is seated on a craggy moun¬ tain, four miles from the Adriatic sea. E. Long. 13.8. N. Lat. 42. 45. ATRIENSES, in antiquity, a kind of servants or officers in the great families at Rome, who had the care and inspection of the atrias and the things lodged therein. These are otherwise called atriarii, though some make a distinction between atrienses and alriarii; suggesting that the latter were an inferior order of servants, per¬ haps assistants of the atrienses, and employed in the more servile offices of the atrium, as to attend at the door, sweep the area, &c. The atrienses are represented as servants of authority and command over the rest: they acted as procurators, or agents, of their master, in selling his goods, &c. To their care were committed the statues and images of the master’s ancestors, &c. which were placed round the atrium j and which they carried in procession at fune¬ rals, &c. In the villas, or country houses, the atrienses had the care of the other furniture and utensils, particularly those of metal, which they were to keep bright from rust. Other things they were to hang from time to time in the sun, to keep them dry, &c. They were clothed in a short white linen habit, to distinguish them, and prevent their loitering from home. ATRIP, in nautical language, is applied either to the anchor or sails. The anchor is atrip, when it is drawn out of the ground in a perpendicular direction, either by the cable or buoy-rope. The topsails are atrip, when they are hoisted up to the mast-head, or to their utmost extent. 4 ] A T R ATRIPLEX, Orach, or Arach. See Botany Index. ATRIUM, in ecclesiastical antiquity, denotes an open place or court before a church, making part of what was called the narthex or antetemple. The atrium in the ancient churches was a large area or square plat of ground, surrounded with a portico or cloyster, situated between the porch or vestibule of the church and the body of the church. Some have mistakenly confounded the atrium with the porch or vestibule, from which it was distinct j others with the narthex, of which it was only a part. The atrium was the mansion of those who were not suffered to enter farther into the church. More parti¬ cularly, it was the place where the first class of peni¬ tents stood to beg the prayers of the faithful as they went into the church. Atrium is also used in the canon law, for the ceme- try or churchyard. In this sense we find a law prohi¬ biting buildings to be raised inatrio ecclesice, except for the clergy : which the glossary explains thus, id est in cemeterio, which includes the space of forty paces around a large church, or thirty round a little church or chapel. ATROPA, Deadly Nightshade. See Botany Index. Buchanan gives an account of the destruction of the army of Sweno the Dane, when he invaded Scot¬ land, by mixing a quantity of the belladonna berries with the drink which the Scots were, according to a treaty of truce, to supply them with. This so intoxi¬ cated the Danes, that the Scots fell upon them in their sleep, and killed the greatest part of them, so that there were scarcely men enough left to carry off their king. There have also been many instances in Britain of children being killed by eating berries of a fine black colour, and about the size of a small cherry, which are no other than those of belladon¬ na. When an accident of this kind is discovered in time, a glass of warm vinegar will prevent the bad effects. Naturalists tell strange stories of this plant : but set¬ ting aside its soporiferous virtue, the modern botanists will scarce warrant any of them, nor even that human figure ordinarily ascribed to its roots, especially since the discovery of the artifice of charlatans in fashioning it, to surprise the credulity of the people. Moses informs us (Gen. xxx. 14.) that Reuben the son of Leah, being in the field, happened to find mandrakes, which he brought home to his mother. Rachel had a mind to them, and obtained them from Leah, upon condition that she should consent that Ja¬ cob should be Leah’s bedfellow the night following. The term DahVi, dudaim, here made use of by Mo¬ ses, is one of those words of which the Jews at this day do not understand the true signification. Some translate it violets, others lilies, or jessamine. Junius calls it agreeable jlowers ; Codurquus makes it truffle, or mushroom ; and Calmet will have it to be the citron. Those that would support the translation of mandrakes plead, that Rachel being barren, and having a great desire to conceive, coveted Leah’s mandrakes, it may be presumed, with a view to its prolific virtues. The ancients have given to mandrakes the name of the ATT. [2 yopa apples of love, and to Venus the name of Mandrago- || ritis; and the emperor Julian, in his epistle to Ca- Aii.eotti. lixenes, says, that lie drinks the juice of mandrakes to excite amorous inclinations. ATROPHY, in Medicine, a disease, wherein the body or some of its parts, does not receive the neces- sary nutriment, but wastes and decays incessantly. See Medicine Index. ATROPOS, in fabulous history, the name of the third of the Parcre, or Pates, whose business it was to cut the thread of life. ATTACHMENT, in the Law of Kngland, im¬ plies the taking or apprehending a person by virtue of a writ or precept. It is distinguished from an arrest, by proceeding out of a higher court by precept or writ ; whereas the latter proceeds out of an inferior court by precept only. An arrest lies only on the body of a man ; whereas an attachment lies often on the goods only, and sometimes on the body and goods. An attachment by writ differs from distress, in not extending to lands, as the latter does ; nor does a distress touch the body, as an attachment does. Attachment out of the Chancery, is obtained upon an affidavit made, that the defendant was served with a subpoena, and made no appearance ; or it issues upon not performing some order or decree. Upon the re¬ turn of this attachment by the sheriff, qtiod non est in¬ ventus in balliva sun, another attachment, with a pro¬ clamation, issues j and if he still refuses to appear, a commission of rebellion. Attachment of the Forest, is one of the three courts held in the forest. The lowest court is called the court of attachment, or wood-mote court; the mean, swan- mote, and the highest, the justice in eyre^s seat. The court of attachments has its name from the verdurers of the forest having no other authority in it, but to re¬ ceive the attachments of offenders against vert and ve¬ nison taken by the foresters, and to enroll them, that they may be presented or punished at the next justice in eyre’s seat. This attachment is by three means : by goods and chattels •, by body, pledges, or main- prize ; or by tbe body only. This court is held every 40 days throughout the year; and is thence called forty days court. Foreign Attachment, is an attachment of money or goods found within a liberty or city, to satisfy some creditor within such liberty or city. By the custom of London, and several other places, a man can attach money or goods in the hands of a stranger, to satisfy himself. ATTACK, a violent attempt upon any person or thing, an assault, or the act of beginning a combat or dispute. Attack, in the military art, is an effort made to force a post, break a body of troops, &c. Attack of a Siege, is a furious assault made by the besiegers with trenches, covers, mines, &c. in order to make themselves masters of a fortress, by storming one of its sides. If there are two or three attacks made at the same time, there should be a communication betwixt them. See War. A TTACOTTI, an ancient people of Britain, men¬ tioned by Ammianus Marcellinus and St Jerome, as well as in the Notitia Imperii. They are represented as allies and confederates of the Scots and Piets, and 115 ] ATT therefore probably their neighbours : though their AUacotti precise situation has not been determined by anti- Attainder. quaries. ' ATTAINDER, in Law. When sentence of death, the most terrible and highest judgment in our laws, is pronounced, the immediate inseparable consequence by the common law is attainder. For when it is now clear beyond all dispute, that the criminal is no longer fit to live upon the earth, but is to be exterminated as a monster and a bane to human society, the law sets a note of infamy upon him, puts him out of its protec¬ tion, and takes no farther care of him than barely to see him executed. He is then ca\\e& attaint, attinctus, stained or blackened. He is no longer of any credit or reputation \ he cannot be a witness in any court ; nei¬ ther is he capable of performing tbe functions of an¬ other man : for by an anticipation of his punishment, he is already dead in law. This is after judgment: for there is a great difference between a man convicted and attainted; though they are frequently through inac¬ curacy confounded together. After conviction only, a man F liable to none of these disabilities : for there is still in contemplation of law a possibility of his inno¬ cence. Something may be offered in arrest of judge¬ ment : the indictment may be erroneous, which will render his guilt uncertain, and thereupon the present conviction may be quashad : he may obtain a pardon, or be allowed the benefit of clergy } both which sup¬ pose some latent sparks of merit, which plead in exte¬ nuation of his fault. But when judgment is once pro¬ nounced, both law and fact conspire to prove him com¬ pletely guilty j and there is not the remotest possibility left of any thing to be said in his favour. Upon judge¬ ment, therefore, of death, and not before, the attain¬ der of a criminal commences: or upon such circum¬ stances as are equivalent to judgment of death 5 as judgment of outlawry on a capital crime, pronounced for absconding or fleeing from justice, which tacitly con¬ fesses the guilt j and therefore, upon judgment either of outlawry, or of death, for treason or felony, a man shall be said to be attainted. A person attainted of high treason forfeits all his lands, tenements, and hereditaments ; his blood is cor¬ rupted, and he and his posterity rendered base ; and this corruption of blood cannot be taken off but by act of parliament. * * See the Attainders may be reversed or falsified (i. e. proved to be false) by writ of error, or by plea. If by writ ofand £ error,* it must be by the king’s leave, &c.; and when by ruption of plea, it must be by denying the treason, pleading a par- -Blood, don by act of parliament, &c. Persons may be attainted by act of parliament.-— Acts of attainder of criminals have been passed in se¬ veral reigns, on the discovery of plots and rebellions, from the reign of King Charles II. when an act was made for the attainder of several persons guilty of the murder of King Charles I. Among acts of this na¬ ture, that for attainting Sir John Fenwick, for con¬ spiring against King William, is the most remarkable ; it being made to attaint and convict him of high trea¬ son on the oath of one witness, just after a law had been enacted, “ That no person should be tried or at¬ tainted of high treason where corruption of blood is incurred, but by the oath of two lawful witnesses, un¬ less the party confess, stand mute, &c.” Stat. 7 and 8 W. HE ATT [2 Attali der, W. III. cap. 3. But in the case of Sir John Fen- Attaint. wick there was something extraordinary ; for he was 1 V 1 indicted of treason on the oaths of two witnesses, though but only one could be produced against him on his trial. ATTAINT, is a writ that lies after judgment against a jury of twelve men that have given false ver¬ dict in any court of record, in an action real or personal, where the debt or damages amounted to above 40s. stat. 5 and 34 Edw. III. c. 7. It is called attaint, because the party that obtains it endeavours thereby to stain or taint the credit of the jury with perjury, by whose ver¬ dict he is grieved. The jury who are to try this false verdict must be twenty-four, and are called the grand jury ; for the law wills not that the oath of one jury of twelve men should be attainted or set aside by an equal number, nor by less indeed than double the former. And he that brings the attaint can give no other evidence to the grand jury, than what was originally given to the petit. For as their verdict is now trying, and the question is whe¬ ther or no they did right upon the evidence that ap¬ peared to them, the law adjudged it the highest absur¬ dity to produce any subsequent proof upon such trial, and to condemn the prior jurisdiction for not believing evidence which they never knew. But those against whom it is brought are allowed, in the affirmance of the first verdict, to produce new matter : because the petit jury may have formed their verdict upon evidence of their own knowledge, which never appeared in court; and because very terrible was the judgment which the common law inflicted upon them, if the grand jury found their verdict a false one. The judgment was, 1. That they should lose their liberam legem, and be¬ come for ever infamous. 2. That they should forfeit all their goods and chattels. 3. That their lands and tenements should be seized into the king’s hands. 4. That their wives and children should be thrown out of doors. 5. That their houses should be razed and thrown down. 6. That their trees should be rooted up. 7. That their meadows should he ploughed. 8. That their bodies should be cast into jail. 9. That the party should be restored to all that he lost by reason of the unjust verdict. But as the severity of this punishment had its usual effect, in preventing the law from being executed, therefore by the statute 11 Hen. VII. c. 24. revived by 23 Hen. VIII. c. 3. and made perpetual by 13 Eliz. c. 25. it is allowed to be brought after the death of the party, and a more moderate punishment was inflicted upon attainted jurors : viz. perpetual in¬ famy, and if the cause of action were above 40I. value, a forfeiture of 20I. a-piece by the jurors j or, if under 40I. then 5I. a-piece ; to be divided between the king and the party injured. So that a man may now bring an attaint either upon the statute or at common law, at his election ; and in both of them may reverse the former judgment. But the practice of setting aside l6 ] ATT Atalnt verdicts upon motion, and granting new trials, has so superseded the use of both sorts of attaints, that there is hardly any instance of an attaint later than the 16th Attention, century. Attaint, among farriers, a knock or hurt in a horse’s leg, proceeding either from a blow with ano¬ ther horse’s foot, or from an over-reach in frosty wea¬ ther, when a horse, being rough shod, or having shoes . with long caulkers, strikes his hinder feet against his fore leg. ATTAINTED, in Law, is applied to a person’s being under attainder. See Attainder. ATTALICiE VESTES, in antiquity, garments made of a kind of cloth of gold. They took the de¬ nomination from Attalus, surnamed Philomater, a wealthy king of Pergamus, who was the first, accord¬ ing to Pliny, who procured gold to be wove into cloth. ATTALUS, the name of several kings of Perga¬ mus. See Pergamus. ATTELABUS. See Entomology Index. ATTENTION, a due application of the ear, or the mind, to any thing said or done, in order to acquire a knowledge thereof. The word is compounded of ad, “ to,” and tendo, “ I stretch.” Attention of mind is not properly an act of the un¬ derstanding, but rather of the will, by which it calls the understanding from the consideration of other ob¬ jects, and directs it to the thing in hand. Neverthe¬ less, our attention is not always voluntary : an interest¬ ing object seizes and fixes it beyond the power of con- troul. Attention, in respect of hearing, is the stretching or straining of the membrana tympani, so as to make it more susceptible of sounds, and better prepared to catch even a feeble agitation of the air. Or it is the adjusting the tension of that membrane to the degree of loudness or lowness of the sound to which we are at¬ tentive. According to the degree of attention, objects make a stronger or weaker impression (a). Attention is re¬ quisite even to the simple act of seeing: the eye can take in a considerable field at one look ; but no object in the field is seen distinctly but that singly which fixes the attention: in a profound reverie that totally occu¬ pies the attention, we scarce see what is directly before us. In a train of perceptions, no particular object makes such a figure as it would do singly and apart; for when the attention is divided among many objects, no particular object is entitled to a large share. Hence the stillness of night contributes to terror, there being nothing to divert the attention. Horror ubique animos, simul ipsa silentia terrent. JEn. Tiara. Silence and solitude are ev’rywhere ! Through all the gloomy ways and iron doors That hither lead, nor human face nor voice Is (a) Bacon, in his natural history, makes the following observations. “ Sounds are meliorated by the intension of the sense, where the common sense is collected most to the particular sense of hearing, and the sight suspend¬ ed. Therefore sounds are sweeter, as well as greater, in the night than in the day 5 and I suppose they are sweeter to blind men than to others ; and it is manifest, that between sleeping and waking, when all the senses are bound and suspended, music is far sweeter than when one is fully waking.” ATT [ ; Alteon Is seen or heard. A dreadful din was wont To grate the sense, when enter’d here, from groans Attd'Q'T And howls of slaves condemn’d, from clink of chains, And crash of rusty bars and creaking hinges ; And ever and and anon the sight was dash’d With frightful faces, and the meagre looks Of grim and ghastly executioners. Yet more this stillness terrifies my soul, Than did that scene of complicated horrors. Mourning Bride, act v. sc. 3. In matters of slight importance, attention is mostly directed by will 5 and for that reason, it is our own fault if trifling objects make any deep impression. Had we power equally to withhold our attention from mat¬ ters of importance, we might be pro'of against any deep impression. But our power fails us here: an interesting object seizes and fixes the attention beyond the possibi¬ lity of controul ; and while our attention is thus forci¬ bly attached to one object, others may solicit for admit¬ tance ; but in vain, for they will not be regarded. Thus a small misfortune is scarcely felt in presence of a greater: Lear. Thou think’st ’tis much, that this conten¬ tious storm Invades us to the skin : so ’tis to thee: But where the greater malady is fix’d, The lesser is scarce felt. Thou’dst shun a bear j But il thy flight lay tow’rd the roaring sea, Thou’dst meet the bear i’ th’ mouth. When the mind’s free, The body’s delicate : the tempest in my mind Doth from my senses take all feeling else, Save what beats there. King Lear, act iii. sc. 5. ATTENUANTS, or Attenuating Medicines, are such as were supposed to subtilize and break the hu¬ mours into finer parts j and thus dispose them for mo¬ tion, circulation, excretion, &c. ATTENUATION, the act of attenuating ; that is, of making any fluid thinner, and less consistent, than it was before. The word is compounded of ad, ‘ to,’ and tenuis, 1 thin.’ Attenuation is defined more generally by Chavin, the dividing or separating of the minute parts of any body, which before, by their mutual nexus or implication, formed a more continuous mass. Ac¬ cordingly, among alchemists, we sometimes find the word used for pulverization, or the act of reducing a body into an impalpable powder, by grinding, pounding, the like. ATTERBURY, Dr Francis, son of Dr Lewis Atterbury, was born at Milton in Buckinghamshire, 1662 j educated at Westminster; and from thence elected to Christ-church in Oxford, where he soon di¬ stinguished himself by his fine genius and turn for polite literature. 'The year he was made M. A. 1687, he exerted himself in the controversy with the Papists, vin¬ dicated Luther in the strongest manner, and showed an uncommon fund of learning, enlivened with great viva¬ city. In 1690 he married Miss Osborn, a distant rela¬ tion of the duke of Leeds ; a lady of great beauty, but with little or no fortune, who lived at or in the neigh¬ bourhood of Oxford. . 1° Feb. 1690-1, we find him resolved to “ bestir himself in his office in the house that of censor pro- Vol. HI. Part I. f 517 ] ATT bably, an officer (peculiar to Christ-church) who pre¬ sides over the classical exercises ; he then also held the catechetical lecture founded by Dr Busby. About this period it must have been that he took or¬ ders, and entered into another scene, and another sort of conversation : for in 1691 he was elected lecturer of St Bride’s church in London, and preacher at Bridewell chapel. An academic life, indeed must have been irk¬ some and insipid to a person of his active and aspiring temper. It was hardly possible that a clergyman of his fine genius, improved by study, with a spirit to exert his talents, should remain long unnoticed ; and we find that he was soon appointed chaplain to King William and Queen Alary. The share he took in the controversy against Bentley (about the genuineness of Phalaris’s Epistles) is now ve¬ ry clearly ascertained. In one of the letters to his no¬ ble pupil, dated “ Chelsea 1698 (he says), the matter had cost him some time and trouble. In laying the de¬ sign of the book, in writing above half of it, in review¬ ing a good part of the rest, in transcribing the rvhole, and attending the press (he adds), half a year of my life went away.” “ In 1700, a still larger field of activity opened, in which Atterbury was engaged four years with Dr AVake (afterwards archbishop of Canterbury) and others, concerning “ the Rights, Powers, and Privi¬ leges of Convocations:” in which, however the truth of the question may be supposed to lie, he displayed so much learning and ingenuity, as well as zeal for the interests of his order, that the lower house of convocation returned him their thanks, and the uni¬ versity of Oxford complimented him with the degree of D. D. January 29. 1700, he was installed arch¬ deacon of Totness, being promoted to that dignity by Sir Jonathan Trelawney, then bishop of Exeter. The same year he was engaged, with some other learned di¬ vines, in revising an intended edition of the “ Greek Testament,” with Greek “ Scholia,” collected chiefly from the fathers, by Air Archdeacon Gregory. At this period he was popular as preacher at the Rolls chapel; an office which had been conferred on him by Sir John Trevor, a great discernerof abilities, in 1698, when he resigned Bridewell, which he had obtained in 1693. Upon the accession of Queen Anne in 1702, Dr Atterbury was appointed one of her majesty’s chaplains in ordinary; and, in October 1704, was ad¬ vanced to the deanery of Carlisle. About two years after this, he was engaged in a dispute with Air Hoad- ly, concerning the advantages of virtue with regard to the present life ; occasioned by his sermon, preached August 30. 1706, at the funeral of Air Thomas Ben- net a bookseller. In 1707, Sir Jonathan Trelawney, then bishop of Exeter, appointed him one of the ca¬ nons residentiaries of that church. In 1709, he was engaged in a fresh dispute with Mr Hoadly, concern¬ ing “ Passive Obedience ;” occasioned by his Latin Sermon, entitled “ Concio ad Clerum Londinensem, habita in Ecclesia S. Elphegi.” In 1710, came on the famous trial of Dr Sacheverell, whose remarkable speech on that occasion was generally supposed to have been drawn up by our author, in conjunction with Dr Smalridge and Dr Freind. The same year Dr Atter¬ bury was unanimously chosen prolocutor of the lower house of convocation, and had the chief management E e of ATT [ 2i u ry. of affairs in that house. May n. 1711, he was ap- ' pointed by the convocation, one of the committee for comparing Mr Whiston’s doctrines with those of the church ot England ; and in June following, he had the chief hand in drawing up “ A Representation of the Present State of Religion.” In 1712, Dr Atterbury was made dean of Christ-church, notwithstanding the strong interest and warm applications of several great men in behalf of his competitor Dr Smalridge. The next year saw him at the top of his preferment, as well as .ot his reputation : for, in the beginning of June 1713, the queen, at the recommendation of Lord Chan¬ cellor Harcourt, advanced him to the bishopric of Ro¬ chester, with the deanery of Westminster, in commen- dam j he was confirmed July 4. and consecrated at Lambeth next day. At the beginning of the succeeding reign, his tide of prosperity began to turn ; and he received a sen¬ sible mortification presently after the coronation of King George I. when, upon his offering to present Lis majesty (with a view, no doubt, of standing better in his iavour) with the chair of state or royal canopy, his own perquisites as dean of Westminster, the offer was rejected, not without some evident marks of dislike to bis person. During the rebellion in Scotland, when the Pre¬ tender’s declaration was dispersed, the archbishop of Canterbury, and the bishops in or near London, had published a Declaration of their abhorrence of the pre¬ sent Rebellion, and an Exhortation to the Clergy and People to be •zealous in the discharge of their duties to his majesty K ing George : but the bishop of Rochester refused to sign it j and engaged Bishop Smalridge in the same refusal, on account of some reflections it con¬ tained against the high church party. He appeared ge¬ nerally among the protestors against the measures of the ministry under the king, and drew up the reasons of the protests with his own hand. In 1716, we find him advising Dean Swift in the management of a refractory chapter. April 26. 1722, he sustained a severe trial in the loss of his lady j by whom he had four children j Francis, who died an in¬ fant ; Osborn, student of Christ-church •, Elizabeth, who died September 29. 1716, aged 17*, and Mary, who had been then seven years married to Mr Mo- rice. In this memorable year, on a suspicion of his being concerned in a plot in favour of the Pretender, he was apprehended August 24. and committed prisoner to the Tower. Two officers, the under secretary, and a messenger, went about two o’clock in the afternoon to the bi¬ shop’s house at Westminster, where he then was, with orders to bring him and his papers before the council. He happened to be in his nightgown when they came in j and being made acquainted with their business, he desired time to dress himself. In the mean time his se¬ cretary came in j and the officers went to search for his papers j in the sealing of which the messenger brought a paper, which he pretended to have found in his close stool, and desired it might be sealed up with the rest. His Lordship observing it, and believing it to be a forged one of his own, desired the officers not to do it, and to bear witness that the paper was not found with him. Nevertheless they did it j and 3 8 ] ATT though they behaved themselves with some respect to Attcrh him, they suffered the messengers to treat him in a very -y~ rough manner, threatening him, if he did not make haste to dress himself, they would carry him away un- drest as he was. Upon which he ordered his secretary to see his papers all sealed up, and went himself direct¬ ly to the Cock-pit, where the council waited for him. The behaviour of the messengers, upon this occasion, seems to have been very unwarrantable, if what the au¬ thor of “ A Letter to the Clergy of the Church of England,” &c. tells us be true, that the persons, di¬ rected by order of the king and council to seize his lordship and his papers, received a strict command to treat him with great respect and reverence. However this was, when he came before the council, he behaved with a great deal of calmness, and they with much ci¬ vility towards him. He had liberty to speak for him¬ self as much as he pleased, and they listened to his de¬ fence with a great deal of attention ■, and, what is more unusual, after he was withdrawn, he had twice liberty tore-enter the council chamber, to make for himself such representations and requests as he thought proper. It is said, that, while he was under examination, he made use of our Saviour’s answer to the Jewish coun¬ cil, while he stood before them j “ If I tell you, ye will not believe me ; and if I also ask you, ye will not answer me, nor let me go.” After three quarters of an hour’s stay at the Cock-pit, he was sent to the Tower privately, in his own coach, without any manner of noise or observation. This commitment of a bishop upon a suspicion of high treason, as it was a thing rarely practised since the Reformation, so it occasioned various speculations among the people. Those who were the bishop’s friends, and pretended to the greatest intimacy with him, laid the whole odium of the matter upon the mi¬ nistry. They knew the bishop so well, they said, his love to the constitution, and attachment to the Prote¬ stant succession, his professed abhorrence of Popery, and settled contempt of the Pretender, and his caution, prudence, and circumspection, to be such, as would never allow him to engage in an attempt of subverting the government, so hazardous in itself, and so repug¬ nant to his principles; and therefore they imputed all to the malice and management of a great minister of state or two, who were resolved to remove him, on account of some personal prejudices, as well as the constant molestation he gave them in parliament, and the particular influence and activity he had shown in the late election. The friends to the ministry, on the other hand, were strongly of opinion, that the bishop was secretly a favourer of the Pretender’s cause, and had formerly been tampering with things of that na¬ ture, even in the queen’s time, and while his party was excluded from power; but upon their re-admis¬ sion, had relinquished that pursuit,, and his confede¬ rates therein, and became a good subject again. They urged, that the influence which the late duke of Or¬ mond had over him, assisted by his own private ambi¬ tion and revenge, might prompt him to many things contrary to his declared sentiments, and inconsistent with that cunning and caution which in other cases he was master of. And to obviate the difficulty, ari¬ sing from the bishop’s aversion to Popery, and the Pretender’s bigotry to that religion, they talked of a new ATT [ 219 1 ATT / r'-itiry new inven^ei^ sc^eme of f>'s> n°t to receive the Pre- - - > tender, whose principles were not to be changed, but his son only, who was to be educated a Protestant in the church of England, and the bishop to be his guar¬ dian, and lord protector of the kingdom, during his minority. These, and many more speculations, amu¬ sed the nation at that time ; and men, as usual, judged of things by the measure of their own affections and prejudices. March 23. 1722 3, a bill was brought into the house of commons, for “ inflicting certain pains and penalties on Francis Lord Bishop of Rochester j” a copy of which was sent to him, with notice that he had liberty of counsel and solicitors for making his defence. Under these circumstances, the bishop ap¬ plied by petition, to the house of lords, for their direction and advice as to his conduct in this conjunc¬ ture } and April 4. he acquainted the speaker of the house of commons, by a letter, that he was determined to give that house no trouble in relation to the bill de¬ pending therein ; but should be ready to make his de¬ fence against it when it should be argued in another house, of which he had the honour to be a member. On the 9th the bill passed the house of commons, and was the same day sent up to the house of lords for their concurrence. May 6th being the day appointed by the lords for the first reading of the bill, Bishop Atterbury was brought to Westminster to make his defence. The counsel for the bishop were, Sir Constantine Phipps and William Wyne, Esq.; for the king, Mr Reeve and Mr Wearg. The proceedings continued above a week; and on Saturday May nth, the bishop was permitted to plead for himself. This he did in a very eloquent speech : which he feelingly opens by com¬ plaining of the uncommon severity he had experienced in the Tower; which was carried to so great a length, that not even his son-in-law Mr Morice was permitted to speak to him in any nearer mode than standing in an open area, whilst the bishop looked out of a two- pair-of-stairs window. In the course of his defence he observes, “ Here is a plot of a year or two standing, to subvert the government with an armed force ; an invasion from abroad, an insurrection at home : just when ripe for execution, it is discovered; and twelve months after the contrivance of this scheme, no con¬ sultation appears, no men corresponding together, no provision made, no arms, no officers provided, not a man in arms ; and yet the poor bishop has done all this. What could tempt me to step thus out of my way ? Was it ambition, and a desire of climbing into a higher station in the church ? There is not a man in my office farther removed from this than I am. Was money my aim ? I always despised it too much, considering what occasion I am now like to have for it ; for out of a poor bishopric of 500I. per annum, I have laid out no less than xoool. towards the repairs of the church and episcopal palace ; nor did I take one shilling for dilapidations. The rest of my little income has been spent, as is necessary, as I am a bishop. Was I in¬ fluenced by any dislike of the established religion, and secretly inclined towards a church of greater pomp and power ? I have, my lords, ever since I knew what Bopery was, opposed it; and the better l knew it, the more I opposed it. I began my study in divinity, when the Popish controversy grew hot, with that im- Atterbnry. mortal book of Tillotson’s, when he undertook thet<—v-~—* Protestant cause in general ; and as such, I esteemed him above all. You will pardon me, my lords, if L mention one thing: Thirty years ago, I writ in de¬ fence of Martin Luther ; and have preached, expres¬ sed, and wrote to that purpose from my infancy ; and whatever happens to me, I will softer any thing, and by God’s grace, burn at the stake, rather than depart Irom any material point of the Protestant religion as professed in the church of England. Once more i Can I be supposed to favour arbitrary power P The whole tenor of my life has been otherwise S I was al¬ ways a friend to the liberty of the subject; and, to the best of my power, constantly maintained it. I may have been thought mistaken in the measures I took to support it; but it matters not by what party I was called, so my actions are uniform.” Afterwards, speaking of the method of proceeding against him as unconstitutional, he says i “ My ruin is not of that moment to any number of men, to make it worth their while to violate, or even to seem to violate, the constitution in any degree, which they ought to pre¬ serve against any attempts whatsoever. Though I am worthy of no regard, though whatsoever is done to me may for that reason be looked upon to be just; yet your lordships will have some regard to your own last¬ ing interests and that of posterity. This is a proceed¬ ing with which the constitution is unacquainted ; which, under the pretence of supporting it, will at last effec¬ tually destroy it. For God’s sake, lay aside these ex¬ traordinary proceedings ; set not up these new and dangerous precedents. I, for my part, will voluntarily and cheerfully go into perpetual banishment, and please myself that I am in some measure the occasion of put¬ ting a stop to such precedents, and doing some good to my country: I will live, wherever lam, praying for its prosperity ; and do, in the words of Father Paul to the state of Venice, say, esto perpetua. It is not my departing from it I am concerned for. Let me de¬ part, and let my country be fixed upon the immoveable foundation of law and justice, and stand for ever.” After a solemn protestation of his innocence, and an appeal to the Searcher of Hearts for the truth of what he had said, he concludes thus : If, on any account, there shall still be thought by your lordships to be any seeming strength in the proofs against me ; if, by your lordships judgments, springing from unknown motives, I shall be thought to be guilty ; if, for any reasons or ne¬ cessity of state, of the wisdom and justice of which I am no competent judge, your lordships shall proceed to pass this bill against me ; I shall dispose myself quietly and tacitly to submit to what you do ; God’s will be done : Naked came I out of my mother’s womb, and naked shall I return ; and, whether he gives' or takes awav, blessed be the name of the Lord !” On Monday the 13th he was carried for the last time from the Tower to hear the reply of the king’s counsel to his defence. These were both men of great knowledge and sagacity in law, but of different talents in point of eloquence. Their speeches on this occa¬ sion were made public ; and they seemed to have formed their “ Replies,” designedly, in a different way. The former sticks close.to the matter in evidence, and en¬ forces the charge against the bishop with great strength E c 2 and ATT [ 220 ] ATT Atterbury. and perspicuity : The latter answers all his objections, ' r—* and refutes the arguments brought in his defence, in an easy soft manner, and with great simplicity of rea¬ soning. Mr Reeve is wholly employed in facts, in comparing and uniting together circumstances, in or¬ der to corroborate the proofs of the bishop’s guilt : Mr Wearg is chiefly taken up in silencing the complaints of the bishop and his counsel, and replying to every thing they advance, in order to invalidate the allega¬ tions of his innocence. The one, in short, possesses the minds of the lords with strong convictions against the bishop : The other dispossesses them of any favour¬ able impression that might possibly be made upon them by the artifice of his defence. And accordingly Mr Reeve is strong, nervous, and enforcing 5 but Mr Wearg, smooth, easy, and insinuating, both in the man¬ ner of his expression and the turn of his periods. Mr Attcrh Wearg pays the highest compliments to the bishop’s'——r. eloquence ; but, at tbe*same time, represents it as em¬ ployed to impose upon the reason, and misguide the judgment of his hearers in proportion as it affected their passions 5 and he endeavours to strip the bishop’s de¬ fence of all its ornaments and colour of rhetoric. On the 15th the bill was read the third time; and after a long and warm debate, passed on the 16th, by a majority of 83 to 43. On the 27th, the king came to the house, and confirmed it by his royal assent. June 18. 1723, this eminent prelate, having the day before taken leave of his friends, who, from the time ef passing the bill against him to the day of his de¬ parture, had free access to him in the Tower (b), em¬ barked on board the Aldborough man of war, and landed (b) The following anecdote was first communicated to the public by the late Dr Maty, on the credit of Lord Chesterfield : “ I went (said Lord Chesterfield) to Mr Pope, one morning, at Twickenham, and found a large folio bible, with gilt clasps, lying before him upon his table; and, as I knew his way of thinking upon that book, I asked him, jocosely, if he was going to write an answer to it P It is a present, said he, or rather a legacy, from my old friend the Bishop of Rochester. I went to take my leave of him yesterday in the Tower, where I saw this bible upon his table. After the first compliments, the Bishop said to me, ‘ My friend Pope, considering your infirmities, and my age and exile, it is not likely that we should ever meet again ; and there¬ fore I give you this legacy to remember me by it. Take it home with you : and let me advise you to abide by it.’—‘ Does your Lordship abide by it yourself?’—‘ I do.’ ‘ If you do, my Lord, it is but lately. May I beg to know what new light or arguments have prevailed upon you now, to entertain an opinion so contrary to that which you entertained of that book all the former part of your life?’—The Bishop replied, ‘ We have not time to talk of these things ; but take home the book; I will abide by it, and I recommend vou to do so too ; and so God bless you.” These anecdotes Mr Nichols has inserted in the “ Epistolary Correspondence,” vol. ii. p. 79. with the profess¬ ed view of vindicating Atterbury, in the following words of an ingenious correspondent : “Dr War ton has revived this story, which he justly calls an ‘ uncommon’ one, in his last ‘ Essay on the Genius and Writings of Pope.’ It was indeed very uncommon ; and I have my reasons for thinking it equally groundless and invidious. Dr Warton, though he retails the story from ‘ Maty’s Memoirs,’ yet candidly ac¬ knowledges, that it ought not to be implicitly relied on. That this caution was not unnecessary, will, I appre¬ hend, be sufficiently obvious, from the following comparison between the date of the story itself and Mr Pope’s letters to the bishop. “ According to Lord Chesterfield’s account, this remarkable piece of conversation took place but a few days before the Bishop went into exile: and it is insinuated, that Mr Pope, till that period, had not even enter¬ tained the slightest suspicion of his friend’s reverence for the bible : Nay, it is asserted, that the very recom¬ mendation of it from a quarter so unexpected, staggered Mr Pope to such a degree, that in a mingled vein of raillery and seriousness, he was very eager to know the grounds and reasons of the Bishop’s change of senti¬ ment. “ Unfortunately for the credit of Lord Chesterfield and his story, there is a letter on record, that was wxitten nine months before this pretended dialogue took place, in which Mr Pope seriously acknowledged the Bishop’s piety and generosity, in interesting himself so zealously and afiectionately in matters which im¬ mediately related to his improvement in the knowledge of the holy scriptures. The passage I refer to is a very remarkable one ; and you will find it in a letter, dated July 27- 1722. It appears undeniably from this letter, that the Bishop had earnestly recommended to Mr Pope the study of the bible ; and had softened his zeal with an unusual urbanity and courtesy, in order to avoid the imputation of ill-breeding, and remove all occasion of disgust fiom a mind so ‘ tremblingly alive as Mr Pope’s.’ I will transcribe the passage at large. ‘ I ought first to prepare my mind tor a better knowledge even of good profane writers, especially the moralists, &c. be¬ fore I can be worthy of tasting the Supreme of books, and Sublime of all writings, in which, as in all the intermediate ones, you may (if your friendship and charity towards me continue so far) be the best guide to Yours, A. Pope.’ ' h The last letter of IVIr I ope to the Bishop, previous to his going into exile, was written very early in June 1^23. It must have been about this time that Pope paid his farewel visit to the Bishop in the Tower. But whether such a conversation as that which hath been pretended actually took place, may be left to the determination of every man of common sense, after comparing Lord Chesterfield’s anecdote with Mr Pope’s letter. “ 1 here must have been a mistake, or a wilful misrepresentation, somewhere. To determine its origin, or to mark minutely the various degrees of its progress, till it issued forth into calumny and falsehood, is impossible- 2 I ATT [ 221 ] ATT landed the Friday following at Calais. When he went on shore, having been informed that Lord Bolingbroke, who had, after the rising of the parliament, received the king’s pardon, was arrived at the same place on his return to England, he said, with an air of pleasant¬ ry, “ Then I am exchanged ?” And it was, in the opinion of Mr Pope on the same occasion, “ a sign of the nation’s being cursedly afraid of being overrun with too much politeness, when it could not regain one great man but at the expence of another.” But the severity of his treatment did not cease even with his banishment. The same vindictive spirit pursued him in foreign climes. No British subject was even per¬ mitted to visit him without the king’s sign manual, which Mr Morice was always obliged to solicit, not only for himself, but for every one of his family whom he carried abroad with him, for which the fees of office were very high. When Bishop Atterbury first entered upon his ba¬ nishment, Brussels was the place destined for his resi¬ dence ; but, by the arts and instigations of the British ministers, he was compelled to leave that place, and retire to Paris. There being solicited by the friends of the Pretender to enter into their negociations, he changed his abode for Montpelier in 1728 ; and, after residing there about two years, returned to Paris, where he died Feb. 15. 1731-2. The affliction which he sustained by the death of his daughter in 1729, was thought to have hastened his own dissolution. The former event he hath himself related in a very affecting manner, in a letter to Mr Pope : “ The earnest desire of meeting one I dearly loved, called me abruptly to Montpelier; where, after continuing two months un¬ der the cruel torture of a sad and fruitless expectation, I was forced at last to take a long journey to Toulouse ; and even there I had missed the person I sought, had she not, with great spirit and courage, ventured all night up the Garonne to see me, which she above all things desired to do before she died. By that means she was brought where I was, between seven and eight in the morning, and lived 20 hours afterwards ; which time was not lost on either side, but passed in such a manner as gave great satisfaction to both, and such as, on her part, every way became her circumstances and character : For she had her senses to the very last gasp, and exerted them to give me, in those few hours, greater marks of duty and love than she had done in all her lifetime, though she had never been wanting in either. The last words she said to me were the kindest of all ; a reflection on the goodness of God, which had allowed us in this manner to meet once more, before we parted for ever. Not many minutes after that, she laid herself on her pillow, in a sleeping posture, Placidaque ibi donum morte quievit. Judge you, Sir, what I felt, and still feel, on this occa¬ sion, and spare me the trouble of describing it. At my age, under my infirmities, among utter strangers, how shall I find out proper reliefs and supports ? I can have none, but those with which reason and religion furnish me ; and those I laid hold on, and grasp as fast as I can. I hope that He who laid the burden upon me (for wise and good purposes no doubt) will enable me to bear it in like manner, as 1 have borne others, with some degree of fortitude and firmness.” How far the bishop might have been attached in his inclinations to the Stuart family, to which he might be led by early prejudices of education, and the divided opinions of the times, it is not necessary here to inquire: But that he should have been weak enough to engage in a plot so inconsistent with his station, and so clum¬ sily devised (to say the least of it, and without entering into his solemn asseveration of innocence), is utterly inconsistent with that cunning which his enemies al¬ lowed him. The duke of Wharton, it is well known, was violent against him, till convinced by his unanswer¬ able reasoning* It has been said that Atterbury’s wishes reached to the bishopric of London, or even to York or Canter¬ bury. But those who were better acquainted with his views, knew that Winchester would have been much more desirable to him than either of the others. And there are those now living, who have been told from respectable authority, that that bishopric was offered to him whenever it should become vacant (and till that event should happen, a pension of 5000I. a-year, be¬ sides an ample provision for Mr Morice), if he would cease to give the opposition he did to Sir Eobert Wal¬ pole’s administration, by his speeches and protests in the house of lords. When that offer was rejected by the bishop, then the contrivance for his ruin was deter¬ mined on. In his speech in the house of lords, the bishop men¬ tions his being “ engaged in a correspondence with two learned men (Bishop Potter and Dr Wall) on settling the times of writing the four gospels.” Part of this correspondence is still in being, and will soon be pub¬ lished. The same subject the bishop pursued during his exile, having consulted the learned of all nations, and had nearly brought the whole to a conclusion when he died. These laudable labours are an ample con¬ futation of Bishop Newton’s assertion, that Atterbury “ wrote little whilst in exile but a few criticisms on French authors.” His body was brought over to England, and in¬ terred on the 12th of May following in Westminster abbey, in a vault which in the year 1722 had been prepared by his directions. There is no memorial over his grave ; nor could there well be any, unless his friends would have consented (which it is most pro¬ bable they refused to do) that the words implying him to have died bishop of Eochester should have been omitted on his tomb. Some I have simply stated matters of fact as they are recorded ; and leave it to your readers to settle other points not quite so obvious and indisputable, as they may think fit. My motives in this very plain narration arose from an honest wish to remove unmerited obloquy from the dead. I should sincerely rejoice if the cloud which in other respects still shades the character of this ingenious prelate could be removed with equal facility and success. I am, dear Sir, your faithful humble servant, Samuel Badcock.” • A T T [2 Atterhury. Some time before bis death, be published a vindi- —v—’ cation of himself, Bishop Smalridge, and Dr Aldrich, from a charge brought against them by Mr Oldmixon, of having altered and interpolated the copy of Lord Clarendon’s “ History of the Rebellion.” Bishop Atterbury’s “ Sermons” are extant in four volumes in octavo: those contained in the two first were published by himself, and dedicated to his great patron Sir Jona¬ than Trelawney bishop of Winchester ; those in the two last were published after his death by Dr Thomas Moore, his lordship’s chaplain. Four admirable “ Vi¬ sitation Charges” accompany his “ Epistolary Corre¬ spondence.” As to Bishop Atterbury’s character, however the moral and political part of it may have been different¬ ly represented by the opposite parties, it is universally agreed, that he was a man of great learning and un¬ common abilities, a fine writer, and a most excellent preacher. His learned friend Smalridge, in the speech he made when he presented him to the upper house of convocation, as prolocutor, styles him Vir in nullo Hterarum genere hospes, in plerisque artibus et studiis diu et feliciter exercitatus, in maximeperfectis literarum disciplinisperfectissimus. In his controversial writings, he was sometimes too severe upon his adversary, and dealt rather too much in satire and invective 5 but this his panegyrist imputes more to the natural fervour of his wit than to any bitterness of temper or pre¬ pense malice. In his sermons, however, he is not only every way unexceptionable, but highly to be com¬ mended. The truth is, his talent as a preacher was so excellent and remarkable, that it may not impro- 2 ] ATT perly be said, that he owed his preferment to the pul- ... pit. “ He has,” says an author in the Tatler, “ so par- ^ ticular a regard to his congregation, that he commits Attica, to his memory what he has to say to them ; and has so't- soft and graceful a behaviour, that it must attract your attention. His person, it is to be confessed, is no small recommendation ^ buthe is tobehighlycommendedfor not losing that advantage, and adding to propriety of speech (which might pass the criticism of Longinus) an action which would have been approved by Demosthenes. He never attempts your passions, till he has convinced your reason. All the objections which you can form are laid open and dispersed before he uses the least vehemence in his sermon ; but when he thinks he has your head, he very soon wins your heart, and never pre¬ tends to show the beauty of holiness, till he has convin¬ ced you of the truth of it.”—In his letters to Pope, &c. Bishop Atterbury appears in a pleasing light, both as a writer and as a man. ATTESTATION, the act of affirming or witness¬ ing the truth of something, more especially in writing. ATTIC, any thing relating to Attica, or to the city of Athens : thus Attic salt, in philology, is a delicate poignant sort of wit and humour peculiar to the Athe¬ nian writers j Attic witness, a witness incapable of cor¬ ruption, &c. Attic Order. See Architecture. Attic Base, a peculiar kind of base used by the ancient architects in the Ionic order; and by Palladio, and some others in the Doric. Attic Story, in Architecture; a story in the upper part of a house, where the windows are usually square. ATTICA. Attica, A TTICA, an ancient kingdom of Greece, situated 1^ — > J- L along the north coast of the gulf of Saron ; bound- Boundaries et^ °n ^ WeSt ^ ^egara> Mount Cithseron, and part of extent &c! ®oeo^a j on north by the strait of Euripus, now Stretto di negro ponte, and Bceotia; and on the east by the Euripus. It extends in length from north-west to south-west about 60 miles ; its breadth from north to south was 56, decreasing as it approached the sea. The soil of this country was naturally barren and craggy, though by the industry of its inhabitants it 2 produced all the necessaries of life. On this account Inhabitants Attica was less exposed to invasions than other more thought to fertile countries; and hence it preserved its ancient in¬ habitants beyond all the other kingdoms in its neigh¬ bourhood : so that they were reputed to be the sponta¬ neous productions of the soil ; and as a badge of this, Thucydides tells ns, they wore golden grasshoppers in their hair. The chief cities in the kingdom of Attica were Athens the capital ; next to it Eleusis, situated on the same gulf, near the coast ofMegara; and next to that Rhamnus, famed for the temple of Amphiaraus and the Cecrops the sta^ue the goddess Nemesis. first king. first king of this country, of whom we have any be produ¬ ced from the soil. . . 3 Cities. distinct account, was Cecrops. Others indeed are said Attio*. to have reigned before him, particularly one Actaeus,u'1^' whose daughter Cecrops married, and in her right laid the foundation of his new monarchy. Cecrops is said to have been the first who deified Jupiter, set up altars and idols, and instituted marriage among the Greeks. He is likewise affirmed to have taught his subjects naviga¬ tion ; and for the better administration of justice, and promoting intercourse among them, to have divided them into the first four tribes, called Cecropis, Autochthon, Actea and Par alia; and he is also by some said to be the founder of the Areopagus. From this monarch the Athenians affected to call themselves Cecropidce till the reign of Erectheus their sixth king, after whom they took the name of Erecthydce. Cecrops dying after a reign of 50 years, left three Cranaw daughters ; by marrying one of whom, probably, Cra- naus a wealthy citizen ascended the throne. He enjoy¬ ed his crown peaceably for ten years; till, having mar¬ ried one of his daughters named Attis, to Amphictyon the son of Deucalion, he was by him dethroned, and ’ forced to lead a private life to the last. From this^*^ daughter, the country, which before had been called wasca||ei Actea, took the name of Attica. Aftev ATT Aca_ After a reign of loor 12 years, Amphictyon was Uwn ' Iiimself deposed by Erictbonius, said to be the son of Vulcan and Tethys. Being lame of both bis feet, be En’an»n II. Cecrops II. was succeeded by his son Pandion II. and he was likewise driven out by Metion, who assumed the government. Pandion in the mean time fled into Megara, where he married Peiia the daughter of Pylas king of that place, and was appointed successor to the kingdom. Here he had four sons, who returning to Athens, whether with or without their father is uncer¬ tain, expelled the sons of Metion, and after the decease of Pandion their father, divided the government among themselves; notwithstanding which, the royal dignity did in effect remain with yEgeus the eldest. -Ego. iEgeus, when he ascended the throne, finding him¬ self despised by his subjects because he had no sons, and sometimes insulted by his brother Pallas, who had no less than fifty, consulted the oracle of Apollo at Del¬ phi. Receiving here, as was commonly the case, an answer which could not be understood without a com¬ mentator, he applied to Pittheus king of Troezen, fa¬ mous for his skill in expounding oracles. This prince easily prevailed with him to lie with his daughter aE- thra, who proved with child 5 and as none but these three were privy to the secret, iEgeus, before his re¬ turn to Athens, hid a sword and a pair of shoes under a stone, leaving orders with the princess, that if the child proved a boy, she should send him to Athens with these* tokens as soon as he was able to lift up that stone. He charged her moreover to use all imaginable secrecy, lest the sons of his brother Pallas should waylay and murder xi him. ilesi‘5 iEthra being delivered of a son, Pittheus gave out 0ni*1 tliat Neptune was the father of it. This child was named Theseus, and proved one of the most famous heroes of antiquity. Being arrived at the age of 16, his mother brought him to the stone above mentioned j and he having lifted it with ease, was desired to take up the sword and shoes and prepare himself to go to his father. He was advised to go by sea rather than by land, as, ever since the departure of Hercules, the roads had been exceedingly infested by banditti. The- I C A. 223 seus, however, who had already begun to discover Attica, marks of uncommon strength and courage, no sooner t., —.1 li-eard the name of Hercules mentioned, than he be¬ came desirous of imitating so great a pattern; and after performing a number of glorious exploits, for which see the article Theseus, he arrived safe at his father’s capital. _ 14 The great atchievements of our young hero pro-Is made cured him a welcome reception at the court of A£gens, known to though his birth was unknown to all except Medea, to^sfal^er- whom the king had lately been married. This queen being a sorceress, it is not to be supposed any thing could be concealed from her : she therefore, by her diabolical penetration, quickly found out that Theseus was the king’s son ; after which she became so jealous of h im on account of his valour, that she persuaded her old husband to invite the young stranger to a banquet, and poison him in a glass of wine. The poison was ac¬ cordingly prepared, and Theseus invited ; but the prince suddenly drawing bis sword, it was immediately recognised by iEgeus to be the same he had formerly buried below the stone. Upon this he stepped forward to Theseus, throwing down the poisoned draught in his way ; and, embracing him with much tenderness, own¬ ed him for his son before all the court. At this time the king of Athens had great occasion for such a champion as Theseus. The sons of Pallas, who had all along behaved with great insolence, upon Theseus being discovered to be the king’s son, and heir apparent to the crown, broke out in open rebel¬ lion. They were soon discomfited ; but iEgeus and i5 the whole country of Attica were still in great distress He kills the on the following account. Some years before, Andro- Minotaur, geus, the son of Minos king of Crete, came to A- thens to be present at one of their feasts. During this visit he contracted such an intimacy with the fifty sons of Pallas, that jEgeus, fearing some fatal consequen¬ ces, caused him to be privately murdered. Accord¬ ing to others, Androgeus having undertaken to en¬ counter the Marathonian hull, was killed by it. Be this as it will, Minos having received news of his son’s death, imputed it to the people of Attica ; and there¬ fore, after several unsuccessful attempts to revenge his own quarrel, prayed to the gods to do it for him.. The Athenians, in consequence of this prayer, were vi¬ sited with earthquakes, famine, and pestilence ; on ac¬ count of which they applied to the oracle. Here they were informed, that no relief was to be had till they were reconciled to the Cretan king. Minos resolving to make them pay dear for their deliverance, imposed upon them a tribute of seven young men and as many virgins, whom he condemned to be devoured by the Minotaur, a monster feigned by the poets to have been halt man and half bull. This bloody tribute bad been twice paid, and Minos had already sent his messengers the third time, when Theseus willingly oflered himself to he one of the unhappy victims ; and embarking with them in one ship, he gave the pilot two sails, the one black to sail with, and the other white to he hoisted up at his return incase he came oft’victorious. Our hero had all the success he could wish : he killed the Minotaur, prevailed with Minos to remit the tribute, and his daughter Ariadne to run away with him ; but her he left with child in the isle of Naxos. Unfortu¬ nately, however, for AEgeus, the joy of Theseus and Ins-, 2 24 ATTICA. Attica, 16 Death of ^Dgeus. Theseus king of At¬ tica, iS New mo¬ dels the gO' vermnent. t9 , Defeats the Amazons, kills the Centaurs, and carries off Helena. his company was so great, that at their return they forgot to hoist the white flag in token of their victory : upon which the old king, taking for granted that his son was killed, threw himself into the sea, which ever since has from him been called the JEgeun Sea. Theseus being thus left in possession of the kingdom of Attica, began immediately to think of indulging his warlike genius, and rendering the civil affairs of his kingdom as little troublesome as possible. To accom¬ plish this purpose, he began with gathering most of the people of Attica into the old and new town, which he incorporated into one city. After this he divested himself of all his regal power, except the title of king, the command of the army, and the guardianship of the laws. The rest he committed to proper magistrates chosen out of three different orders of the people, whom he divided into nobles, husbandmen, and artificers. The first he invested with the power of interpreting and executing the laws, and regulating whatever related to religion. The other two chose their inferior magistrates from among themselves, to take care of whatever rela¬ ted to their separate orders : so that the kingdom was in some measure reduced to a commonwealth, in which the king had the greatest post, the nobles were next to him in honour and authority, the husbandmen had the greatest profit, and the artists exceeded them in number. He likewise abolished all their distinct courts of judicature, and built one common council hall called Prytaneum, which stood for many ages afterwards. Having thus new-modelled the government, his next care was to join to his dominions the kingdom of Me- gara, in right of his grandfather Pandion 11. who had married the daughter of Pylas, as above mentioned. ,On this occasion he erected the famous pillar in the isthmus, which showed the limits of the two countries that met there. On the one side of this pillar was inscribed, “ This is not Peloponnesus, but Ionia and on the other, “ This is Peloponnesus, not Ionia.” After this he undertook an expedition against the Amazons, whom he overcame, took their queen Hippolita, and afterwards married her. Soon after this, Theseus con¬ tracted an intimacy with Perithous the son of Ixion : and being invited to his nuptials, assisted him in kill¬ ing a number of Centaurs, or rather Thessalian horse¬ men (who in their cups had offered violence to their female guests), and drove the rest out of the country. Our two associates then proceeded to Sparta, where I heseus fell in love with the famed Helena, at that time not above nine years old, while he himself w'as upwards of fifty. Her they carried oft’: and of the rape there are various accounts j but the following one, which is given by Plutarch, is generally allowed to be the most authentic. According to that historian, they stole this beauty, the greatest in the world at that time, out of the temple of Diana Ortia, where Helena happened to be dan¬ cing. They were pursued as far as Tegea, but made their escape out of Peloponnesus } and thinking them¬ selves now secure of their prey, they agreed to cast lots for her, upon condition that he to whose lot she fell should assist the other in procuring some celebrated beauty. Fortune having declared for Theseus, lie as¬ sisted his companion in the like attempt upon Proser¬ pina daughter of Aidonius king of the Mollossi in Epirus j who, being the next beauty to Helena, was Attica, ' Dmen guarded by the dog Cerberus, which had three heads, and was consequently a very formidable enemy. Her father, however, understanding that they designed to steal aw-ay his daughter, threw Perithous to be torn in pieces by Cerberus, and put Theseus in prison, from 1 whence he was afterwards relieved at the intercession of Hercules. . ^ ofEpiiui, After this misfortune, Theseus at length returned to Athens, but found himself very coolly received by his subjects. Mnestheus, the son of Pteus, and great- grandson of Erectheus, had made use of the king’s ab¬ sence to ingratiate himself with the people j and, upon the commencement of a war with Castor and Pollux, the two brothers of Helena, he persuaded the people of Athens to open their gates to the two brothers. Up- pon this, Theseus was under the necessity of conveying of Atheus. away himself and family with all possible privacy. This he luckily accomplished ; and designed to have sailed to Crete, to have obtained assistance from Deucalion son of Minos, and now brother-in-law to Theseus himself, he having lately married Phaedra sister to Deucalion. Unfortunately, however, our hero was shipwrecked on the island of Scyros. Here he was at first kindly re- 21 ceived by Lycomedes the king of that island $ but wasHisdeai soon after killed by a fall from a high rock, over which some say he was pushed by Lycomedes himself, who had been prevailed on to destroy Theseus in that manner by Mnestheus, that he might with the more se¬ curity enjoy the kingdom of Athens. ^ Mnestheus reigned 24 years, but lost his life at the Mnestkus, siege of Troy } and w’as succeeded by Demophon one Demopb, of the sons of Theseus by Phaedra, who was likewise at&0' the siege of Troy, but had the good fortune to return in safety. In his reign was erected the famous court of the Ephetse •, consisting originally of 50 Athenians and as many Argives, for trying of wilful murders. By this court the king himself afterwards submitted to be tried for having accidentally killed one of his subjects. He reigned 33 years, and was succeeded by his son, according to some, or according to others his brother, Oxyntes, who reigned 12 years. Oxyntes wras suc¬ ceeded by his son Aphydes, who was murdered by Thymsetes the bastard son of Oxyntes. 24 This king discovered many base qualities unworthy Thy™*1'5 of his^dignity ; and at last was deposed by his subjects on the following occasion. Xanthus king of Bceotia had a contest with the Athenians about one of their frontier towns. He offered to decide the matter by single combat with the king; but this w’as declined by Thymsetes. It happened, that at that time one Me- lanthus a Messenian, who had been driven out of his country by the Heraclidae, was come to Athens; who accepted the king of Boeotia’s challenge. At the first onset, Melanthus asked his adversary, why he had, con¬ trary to the articles, brought a second into the field with him P and as Xanthus immediately looked about to see who was behind him, Melanthus run him through with his lance. This victory, though it did little honour to him who gained it, was so agreeable to the Athenians, that they deposed their cowardly king Thymsetes, af¬ ter he had reigned 8 years ; and appointed" Melanthus in his stead, who after a reign of 37 years left the king¬ dom to his son Codrus. This prince reigned about 21 years ; during which time the Dores and Heraclidse had regained all Pelo¬ ponnesus, S Hi til,, «Ini ATT At(;a ponnesus, and were upon the point of entering into ugrt Attica. Codrus, being informed that the oracle had ■ promised them victory provided they did not kill the i tdn die ^[rig 0f Athenians, came immediately to a resolu- .jttf tion of dying for his country. Disguising himself, msi for therefore, like a peasant, he went into the enemy’s ligcjutiy. camp, and quarrelling with some of the soldiers, was killed by them. On the morrow, the Athenians know¬ ing what was done, sent to demand the body of their king j at which the invaders were so terrified, that they decamped without striking a blow, iepuiean Upon the death of Codrus, a dispute which happened oycj: among his sons concerning the succession, furnished the uentiitro-Athenians with a pretence for ridding themselves of licctf their kings altogether, and changing the monarchical form of government into a republican one. It was im¬ probable, they said, that they should ever have so good a king as Codrus 5 and to prevent their having a worse, they resolved to have no king but Jupiter. That they might not, however, seem ungrateful to the family of Codrus, they made his son Medon their supreme magi¬ strate, with the title of archon. They afterwards ren¬ dered that office decennial, but continued it still in the family of Codrus. The extinction of the Medontidse at last left them without restraint; upon which they not only made this office annual, but created nine archons. By the latter invention they provided against the too great power of a single person, as by the former they took away all apprehension of the archons having time to establish themselves, so as to change the constitution. In a word, they now attained what they had long sought, viz. the making the supreme magistrates dependant on the people. We have a list of these archons for upwards of 600 years, beginning with Creon, who lived about 684 years before Christ, to Herodes, who lived only 60 years before that time. The first archon of whom we .hear any thing worth notice, is named Draco. He reigned in the second, or, as others say, in the last year of the 39th Olympiad, when it is supposed he publish¬ ed his laws : but though his name is very frequently mentioned in history, yet no connected account can be found either of him or his institutions ; only, in gene¬ ral, his laws were exceedingly severe, inflicting death for the smallest faults; which gave occasion to one De¬ filades an orator to observe, that the laws of Draco were written with blood, and not with ink. For this extraordinary severity he gave no other reason, than that small faults seemed to him to be worthy of death, and he could find no higher punishment for the great¬ est. He was far advanced in years when he gave laws Athens ; and to give his institutions the greater weight, he would not suffer them to be called nomoi, or laws, but thesmoi, or sanctions proceeding from more than human wisdom. "Ihe extreme severity of these laws, however, soon made the Athenians weary both of them and the author of them ; upon which Draco was obliged to retire to TEgina. Here he was received with the highest honours: but the favour of the inhabitants of this place proved more fatal to him than the hatred of the Athenians; for coming one day into the thea¬ tre, the audience, to show their regard, threw, as the lei'i. custom then was, their cloaks upon him; and the mul¬ titude of these being very great, they stifled the old man, who was too weak to disengage himself from their load. Vol. III. Part I. + 21 racotttn itorii then: 25,1 i'elltt cltj) 30 I C A. 225 After the expulsion of Draco, nothing remarkable Aitica. happened at Athens till the year before Christ 606 v~— when we find the republic engaged in a war with the . 31 Mitylenians about the city Sigaeum, situated near the 11,1' mouth of the river Scamander. The Athenian army was commanded by Phrynon, a person equally' remark¬ able for the comeliness of his person and the generosity of his mind. The Mitylenians ivere commanded by Pittacus, one of the celebrated sages of Greece. As these commanders looked upon the honour of their re¬ spective countries to be concerned, they exerted them¬ selves to the utmost. At last they met in single com¬ bat ; wherein Phrynon depended on his valour only : but Pittacus concealed behind his shield a net, where- with he suddenly entangled his antagonist, and easily slew him. This, however, not putting an end to the war, Periander tyrant of Corinth interposed ; and both parties having submitted to his arbitration, he decreed that Sigaeum should belong to the Athenians. About seven years after this war, a conspiracy was Cylon’s formed by Cylon son-in-law to Theagenes ty’rant of conspiracy. Megara, who, having by his affable behaviour procured many friends, formed a design of seizing the sovereignty of Athens. Having consulted the oracle as to the most proper time, he was directed to make the attempt when the citizens of Athens were employed in celebrating their highest feasts to Jupiter. When many of the citizens therefore were gone to the Olympic games, Cylon and his associates made themselves masters of the citadel. Here they were instantly besieged by Mega- cles at that time archon, and soon reduced to great distress for want of water. The chief, together witlx his brother, found means to make their escape, but the meaner sort were left to shift for themselves. In this extremity they fled to the temple of Minerva; from whence Megacles with much ado prevailed upon them to come down and submit themselves to the mercy of their country. Having at last assented to this, they tied a cord to the image of the goddess, and carried the clue with them, to demonstrate, that though they were out of the temple they were still under Minerva’s protection. Unfortunately tor them, however, as they passed the temple of the Furies, the line snapt of itself; which Megacles construing into a renunciation by the goddess, caused his men to fall upon them and despatch as many as they could find. Such as were without the Conspira- temple were immediately massacred, and those who fled tors massa- thither again were murdered in their sanctuary. Incredby short, none escaped but such as bribed the wives of^effacles» the officers of justice. This carnage, however, did not put an end to the sedition. The remains of Cylon’s faction created great disturbances, by insinuating that the violation of Minerva’s sanctuary had drawn down the anger of the gods; and these discourses had such who'is t*e an effect, that Megacles and his officers were styled crated by execrable, and held to be persons under the displeasure the people, of heaven. During the time of this confusion, the Megarensians tt 25 attacked Nisea, which they took, as well as Salamis ; fu^war' S" and so completely routed the Athenians in every at-with Me- tempt to recover the latter, that a law was at last pas-gara. sed, by which it should be capital for any one to pro¬ pose the recovery of Salamis. About the same time the city was disturbed by reports of frightful appear¬ ances, and filled with superstitious fears; the oracle at U f Delphi 226 Attica. Epkneni- des’s expia tion and prophecy. 37 Solon the wise legi- lator. 33 Salamis re¬ covered by his means. ATT Delphi was therefore consulted, and an answer return¬ ed that the city behoved to be expiated. Upon this, Epimenides the Phestian was sent for from Crete, to perform the necessary ceremonies, he being reputed a holy man, and one that was deeply skilled in all the mysteries of religion. Ills expiation consisted in ta¬ king some black, and some white sheep, turning them all loose, and directing some persons to follow them to those places where they couched, and there to sacrifice them to the local deity. He caused also many temples and chapels to be erected, two of which have been pax1- ticularly noted, viz. the chapel of Contumely and that of Impudence. This man is said to have looked wist¬ fully on the port of Munychia for a long time, and then to have spoke as follows to those that w’ere near him : “ How blind is man to future things ! for did the Athenians know what mischief will one day be deri¬ ved to them from this place, they would eat it with their teeth.” This prediction was thought to be ac¬ complished 270 years after, when Antipater constrained the Athenians to admit a Macedonian garrison into that place. About 597 years before Christ, Solon the famed Athenian legislator began to show himself to his coun¬ trymen. He is said to have been lineally descended from Codrus; but left by his father in circumstances rather necessitous, which obliged him to apply to mer¬ chandise ; it is plain, however, both from his words and wi'itings, that he was a disinterested patriot. The shameful decree, that none under pain of death should propose the recovery of Salamis, grieved him so much, that having composed an elegy of 100 verses, such as he thought would be most proper to inflame the minds of the people, he ran into the market-place as if he had been mad, with his night-cap on his head, i'e- peating his elegy. A crowd being gathered round the pretended madman, his kinsman Pisistratus mingled among the rest, and observing the people moved with Solon’s words, he also seconded him with all the elo¬ quence he was master of j and between them they pre¬ vailed so far as to have the law repealed, and a war was immediately commenced against the people of Me- gara. Who was commander in this expedition is not ceitain 5 but the city was recovered, according to the most general account, by the following stratagem. So¬ lon coming with Pisistratus to Colias, and finding there the women busy in celebrating, according to custom, the feast of Ceres, sent a confidant of his to Salamis, who pretended to be no friend to the people of Attica, telling the inhabitants of Salamis, that if they had a mind to seize the fairest of the Athenian ladies, they might now do it by passing over to Colias. The Mega- rensians giving easy credit to what the man said, imme¬ diately fitted out a ship; which Solon perceiving from the opposite shore, dismissed the women, and having dressed a number of beaxalless youths in female habits, under which they concealed every one a dagger, he sent them to the sea-side to dance and divert themselves as the women were wont to do. When those who came from Salamis saw these voung persons skipping up and down, they strove who should be first on shore ; but were every one of them killed, and their vessel seized ; aboard which the Athenians embarking, sailed immedi¬ ately to Salamis and took it. On the return of Solon to Athens, he was greatly I C A. honoured by the people, to whom another occasion of ^uics 1 admiring his wisdom was quickly afforded. The in-* habitants of Cirrha, a town situated in the bay of Co- 39 rinth, after having by repeated incursions wasted the territory of Delphi, at last besieged the capital itself, with a view of making themselves masters of the trea-Sion’s " sures contained in the temple of Apollo. Advice of wisdom, this intended sacrilege being sent to the Amphictyons, who were the states-genei’al of Greece, Solon advised that the matter should be universally resented, and that all the states should join in punishing the Cirrhseans, and saving the Delphic oracle. This advice was complied with, and a genex-al war against Cirrha declared. Cly- sthenes, tyrant of Sicyon, commanded in chief, and Alc- maeon was general of the Athenian quota. Solon went as assistant or counsellor to Clysthenes, and by follow¬ ing his advice the war was conducted to a prosperous issue. For when the Greek army had besieged Cirrha for some time without any appearance of success, the oracle at Delphi was consulted, from whence the follow¬ ing answer was returned : “ In vain you hope to take the place before “ The sea’s blue waves x’oll o’er the hallowed shore.” This answer struck the whole army with surprise, till Solon advised Clysthenes to consecrate solemnly the whole territory of Cirrha to the Delphic Apollo ; so as that was a maritime counti’y, the sea must then wash the saci'ed coast. According to Pausanias, the city was reduced by the following stratagem, likewise in¬ vented by Solon. He caused the river Plistus, which run through Cirrha, to be turned into another chan¬ nel, hoping thereby to have distressed the inhabitants for want of water: but finding they had many wells within the city, and were not to be reduced by that means, he caused a vast quantity of roots of hellebore to be thrown into the river, which was then suffered to re¬ turn into its former bed. The inhabitants, overjoyed at the sight of running water, came in troops to drink of it: whereupon an epidemic flux ensued, and the ci¬ tizens being no longer able to defend the walls, the town was easily taken. ,, On the return of Solon to Athens he found thingsAthensis again in the utmost confusion. The remnant of Cy-greatcon- Ion’s faction gave out, that all sorts of misfortunes had^5100, befallen the republic on account of the impiety of Me- gacles and his followers ; which clamour was heighten¬ ed by the retaking of Salamis about this time by the Megarensians. Solon interposed, and persuaded those who wei'e styled execrable to abide a trial, and 300 per- 41 sons were chosen to judge them. The event vyas, that-Megaclen 300 of Megacles’s party who were alive were sent in-P?^*’ to pex-petual banishment, and the bones of such as were dead were dug up and sent without the limits of their country. 41 Though this decision restox-ed the public quiet for thelbreefe present, it was not long before the people were divided d0BSiit8rl into three factions, contending about the proper formnP‘ of govex-nment. These were called the Diacrii, Pedicel, and Parali; the first of these were the inhabitants of the hilly country, who declared positively for demo¬ cracy ; the second, dwelling in the lower parts, and who were far more opulent than the former, declared for an oligarchy, as supposing the government would fall mostly into their hands j the third party, who lived 1 i 1 ill i* siar i:* on ATT a on the sea-coast, were people of moderate principles, > and therefore were for a mixed government. Besides the disturbances raised on this account, others were occasioned by the rich oppressing the poor. According to Plutarch, the poor being indebted to the rich, ei¬ ther tilled their grounds and paid them the sixth part of the produce, or engaged their bodies for their debts, so that many were made slaves at home, and many sold into other countries j nay, some were obliged to sell their children to pay their debts, and others in despair quitted Attica altogether. The greatest part, how¬ ever, were for throwing off the yoke, and began to look about for a leader, openly declaring that they in¬ tended to change the form of government, and make a repartition of lands. In this extremity, the eyes of all the citizens were cast upon Solon. The most prudent were for offering him the sovereignty ; but be perceiving their intentions, behaved in such a manner as to cheat both parties, and showed a spirit of patriotism perhaps never equalled. He refused the sovereignty as far as it might have benefited himself; and yet took upon him¬ self all the care and trouble of a prince, for the sake of h his people. lolonho- He was chosen archon without having recourse to ea ahon. lots, and after his election disappointed the hopes of both parties. It was Solon’s fundamental maxim, That those laws will be best observed which power and jus¬ tice equally support. Wherever, therefore, he found the old constitution consonant to justice in any tole¬ rable degree, he refused to make any alteration at all, and was at extraordinary pains to show the reason of the changes he did make. In short, being a perfect judge of human nature, he sought to rule only by showing his subjects that it was their interest to obey, and not by forcing upon them what he himself esteem¬ ed best. Therefore, to a person who asked whether he had given the Athenians the best laws in his power, he replied, “ I have established the best they could re¬ ceive.” ettb uli *° ^ie ma‘n cause of sedition, viz. the oppressed isorrs. state of the meaner sort, Solon removed it by a contri¬ vance which he called sisachthia, i. e. discharge ; but what this was, authors are not agreed upon. Some say that he released all debts then in being, and prohi¬ bited the taking any man’s person for payment of a debt for the future. According to others, the poor were eased, not by cancelling the debts, but by lower¬ ing the interest, and increasing the value of money j a mina, which before was made equal to 73 drachms only, being by him made equal to 100; which was of great advantage to the debtor, and did the creditor no hurt. It is, however, most probable that the sisachthia was a general remittance of all debts whatever, otherwise So¬ lon could not have boasted in his verses that he had re¬ moved so many marks of mortgages (b) as were every¬ where frequent; that he had freed from apprehension 1 such as were driven to despair, &c. ifaans the midst of all Solon’s glory, an accident eha^ur hefel him, which, for a time, hurt his reputation, and fhwhreehad almost entirely ruined his schemes. He had con- leno J I C A. 227 suited Conon, Clinias, and Hipponicus, his three Attica friends, on an oration prepared with a view to engage —y— the people’s consent to the discharge j and these three men, thus knowing there was to be a general discharge of debts, basely took the opportunity of borrowing vast sums before the law was promulgated, in conse¬ quence of which they were never obliged to return them. This was thought at first to have been done with Solon’s consent, and that he had shared in the money ; but this aspersion was quickly wiped off when it ap¬ peared that the lawgiver himself was a very consider¬ able loser by his own law. His friends, however, could never recover their credit, but were ever after¬ wards stigmatized with the opprobrious appellation of chreocopidce, or debt-sinkers. ^ The Athenians were as little pleased with Solon’s Solon bla- management as with their former condition; the rich med at first, thinking he had done too much in cancelling the mo-^utafte®* ney-debts due to them, and the poor that he had done too little, because he had not divided the lands of At-and chosen tica equally. In a short time, however, they acquies-legislator, ced in the new institutions, and gave a more public token of their repentance than they had before shown of their displeasure, instituting a solemn sacrifice under the name of Sisachthia, at the same time that Solon was unanimously elected legislator of Athens, with full power to make laws, and alter or new-model the consti¬ tution as he thought fit. Solon being now invested with unlimited authority, Compiles & set about the arduous task of compiling new laws for new body the turbulent people of Attica; which having at ]a3t<)flaws» completed in the best manner he was able, or in the best manner the nature of the people would admit, he procured them to be ratified for 100 years. Such as related to private actions were preserved on parallelo¬ grams of wood, with cases which reached from the ground, and turned about upon a pin like a wheel. These were thence called axones ; and were placed first in the citadel, and afterwards in the prytaneum, that all the subjects might have access to them when they pleased. Such as concerned public institutions and sacrifices were contained in triangular tables of stone called cyrbes. The Athenian magistrates were sworn to observe both ; and in process of time these monuments of Solon’s wisdom became so famous, that all public acts were from them named Axones and Cyr- hes' . 4$ After the promulgation of the laws, Solon found He goe* himself obliged to leave Athens, to prevent his being abroad foe continually teazed for explanations and alterations often years* them. He therefore pretended an inclination to mer¬ chandise, and obtained leave to absent himseJf for 10 years, during which time he hoped the laws would be grown familiar. From Athens Solon travelled into Egypt, where he conversed with Psenophis the He- liopolitan, and Sonchis the Saite, the most learned priests of that age. From these he learned the situa¬ tion of the island Atlantis, of which he wrote an ac¬ count in verse, which Plato afterwards continued gee F f 2 From lantis. (b) The Athenians had a custom of hanging up billets to show that houses were engaged for such and such sums of money. 228 ATTICA. Attica. .49 Things fall into disor¬ der in his absence. 50 He returns to Athens, but refuses to resume Ms office* . -5I Pisistratus assumes the sovereign¬ ty- From Egypt he went to Cyprus, where lie was ex¬ tremely well received by one of the petty kings. This prince lived in a city called Apeia, built by Demo- phon the son of Theseus, on an eminence near the ri¬ ver Clarius, but in a soil craggy and barren. Solon observing a very pleasant plain below, engaged the king to remove thither $ assisted in executing the Scheme he had formed ; and succeeded so well, that a new city wras formed, which soon became populous, and out of gratitude to the Athenian legislator was called Solos. But while Solon was thus travelling in quest of wis¬ dom, and with a view to benefit those among whom he came, his countrymen, who seem to have resolved on being dissatisfied at all events, had again divided them¬ selves into three factions. Lycurgus put himself at the head of the country people *, Megacles the son of Alcmaeon was at the head of those who lived on the sea coast; and Pisistratus put himself at the head of the poorer sort, to protect them, as he pretended, from tyranny, but in reality to seize on the sovereignty for himself. All the factions pretended to have a vast re- ' gard for Solon and his laws, at the same time that they were very desirous of a change j but how they were to he bettered, none of them knew, or pretended to know. In the midst of this confusion the legislator returned. Each of the factions paid their court to him, and af¬ fected to receive him with the deepest reverence and respect j beseeching him to reassume his authority, and compose the disorders which they themselves kept up. This Solon declined on account of his age, which, he said, rendered him unable to speak and act for the good of his country as formerly j however, he sent for the chiefs of each party, beseeching them in the most pathetic manner not to ruin their common parent, but to prefer the public good to their own private inte¬ rest. Pisistratus, who of all the three had perhaps the least intention to follow Solon’s advice, seemed to be the most affected with his discourses •, hut as Solon perceiv¬ ed he affected popularity by all possible methods, he easily penetrated into his designs of assuming the so¬ vereign power. This he spoke of to Pisistratus him¬ self, at first privately j but as he saw that his admoni¬ tions in this way had no effect, he then said the same things to others, that the public might be on their guard against him. All the wise discourses of Solon, however, were lost upon the Athenians. Pisistratus had got the meaner sort entirely at his devotion, and therefore resolved to cheat them out of the liberty which they certainly tie- served'to lose. With this view he wounded himself, and, as Herodotus says, the mules that drew his cha¬ riot; then he drove into the market-place, and there showed his bleeding body, imploring the protection of the people from those whom his kindness to them had rendered his implacable enemies. A concourse of peo¬ ple being instantly formed, Solon came among the rest, and suspecting the deceit, openly taxed Pisistratus with his perfidious conduct ; but to no purpose. A general assembly of the people was called, wherein it was mo¬ ved by one Ariston, that Pisistratus should have a guard. Solon was the only person present who had resolution enough to oppose this measure $ the richer Athenians, perceiving that the multitude implicitly followed Pi- sistratus, and applauded every thing he said, remaining - ‘ silent through fear. Solon himself, when he saw he could prevail nothing, left the assembly, saying he was wiser than some, and stouter than others. A guard of 400 men was now unanimously decreed to Pisistratus, as we are told by Solon himself. This inconsiderable body he made use of to enslave the people, hut in what manner he accomplished his purpose is not agreed. Certain it is, that with his guard he seized the citadel 5 but Polyaenus hath given an account of a very singular method which he took to put it out of the power of the Athenians to defend themselves even against such a small number. He summoned an assembly to be held at the Anacium, and directed that the people should come thither armed. They accordingly came j and Pisistratus harangued them, but in a voice so low that they could not tell what he said. The people com¬ plaining of this, Pisistratus told them that they were hindered from hearing him by the clangour of their arms •, but if they would lay them down in the por¬ tico, he would then be heard distinctly. This they did j and while they listened very attentively to a long and eloquent oration, Pisistratus’s guard conveyed away their arms, so that they found themselves depri- ved of all power of resistance. During the confusion Solon which followed this event, another assembly was held,^es wherein Solon inveighed bitterly against the meanness* 1S’ of his countrymen, inviting them to take up arms in defence of their liberty. When he saw that no¬ thing would do, he laid down his own arms, saying, that he had done his utmost for his country and his laws. According to Plutarch, he refused to quit the city; but the most probable opinion is, that he imme¬ diately retired from the dominion of Athens, and re¬ fused to return, even at the solicitation of Pisistratus himself. 53 1 Pisistratus having thus obtained the sovereignty, did Pis‘stratl» not overturn the laws of Solon, but used his ppwerg“T“sa with the greatest moderation. It is not to he expect-m0(]era. ed, however, that so turbulent a people as the Athe-tion. nians could be satisfied by any method of government he could lay down. At the beginning of his admini¬ stration, Megacles and his family retired out of Athens to save their own lives, yet without despairing of being able some time or other to return. With this view Megacles and his associates entered into a treaty with Lycurgus ; and having brought him and his party into a scheme for deposing Pisistratus, they concerted mat- ^ ters so well, that Pisistratus was soon obliged to seek priven«»“ for shelter somewhere else, and, on his departure, the by Mega- Athenians ordered his goods to be sold. Nobody, how-cles* ever, except one person (Callias') would venture to buy any ol them, from an apprehension, no doubt, that they would soon be restored to their proper owner, which ac¬ cordingly happened in a very short time. 55 ; As Megacles and his party had negociated with Ly-Who soon curgus to turn out Pisistratus, so they now entered into aftw ^ a treaty with Pisistratus to reinstate him in his princi-states pality, as soon as they found Lycurgus would not be implicitly governed by them. To accomplish this, they fell upon a very ridiculous project 5 which, however, was attended with the desired success. They found out a woman whose name was Phya, of a mean family and fortune, but of a great stature, and very handsome. > Her 6 DrlJn out a *iond tim; ATT Her they dressed in armour, placed her in a chariot, and having disposed things so as to make her appear with all possible advantage, they conducted her towards the city, sending heralds before, with orders to speak to the people in the following terms : “ Give a kind reception, O Athenians, to Pisistratus, who is so much honoured by Minerva above all other men, that she herself condescends to bring him back to the citadel.” The report being universally spread that Minerva was bringing home Pisistratus, and the ignorant multitude believing this woman to be the goddess, addressed their prayers to her, and received Pisistratus with the utmost joy. When he had recovered the sovereignty, Pisi¬ stratus married the daughter of Megacles as he had promised, and gave the pretended goddess to his son Hipparchus. Pisistratus did not long enjoy the kingdom to which he had been restored in so strange a manner. He had married the daughter of Megacles, as already observed j but having children by a former wife, and remembering that the whole family of Megacles was reprobated by the Athenians, he thought proper to let his new spouse remain in a state of perpetual widowhood. This she patiently bore for some time, but at last acquainted her mother. An affront so grievous could not fail to be highly resented. Megacles instantly entered into a treaty with the malecontents, of whom there were al¬ ways great plenty at Athens whatever was the form of government. This Pisistratus being apprized of, and perceiving a new storm gathering, he voluntarily quit¬ ted Athens, and retired to Eretria. Here having con¬ sulted with his sons, it was resolved to reduce Athens by force. With this view he applied to several of the Greek states, who furnished him with the troops he de- 7 sired, but the Thebans exceeded all the rest in their butiturns liberality j and with this army he returned to Attica, wnuu according to Herodotus, in the i ith year of his banish¬ ment. They first reduced Marathon, the inhabitants of which had taken no measures for their defence, though they knew that Pisistratus was preparing to at¬ tack them. The republican forces in the mean time marched out of Athens to attack him 5 but behaving in a secure and careless manner, they were surprised by Pisistratus, and totally routed. While they were en¬ deavouring to make their escape, he caused his two sons to ride before him with all speed, and tell those they came up with that nobody had any thing to fear, but that they might every one return to his own home. This stratagem so effectually dispersed the republican Irft'armJb ^,a,: was impossible to rally them, and Pisi- c stratus became a third time absolute master of Attica. His iib- Pisistratus being once more in possession of the sove- ject till reignty, took a method of establishing himself on the diicutent- throne directly opposite to what Theseus had done, wit! ^nstead of collecting the inhabitants from the country '“g > mo-!n^° Clties5 Pisistratus made them retire from the cities derfl:)i). lnt° the country, in order to apply themselves to agri¬ culture. This prevented their meeting together, and caballing against him in such bodies as they had been accustomed to do. By this means also the territory of Athens was greatly meliorated, and great plantations of olives were made over all Attica, which had before not only been destitute of corn, but also bare of trees. He also commanded, that, in the city, men should wear He 60 I C A. a kind of sheep-skin vest, reaching to the knees ; but so intolerable were the laws of Pisistratus to his sub¬ jects, that this kind of garment in succeeding times be¬ came proverbially the habit of slavery. As prince of Athens, Pisistratus received the tenth part of every man’s revenues, and even of the fruits of the earth ; and this also, though for the service of the state, seemed to the Athenians a most grievous bur¬ den. In short, though Pisistratus behaved in all re¬ spects as a most excellent prince, his subjects fancied themselves oppressed by tyranny, and were perpetual¬ ly grumbling from the time be first ascended the throne to the day of his death, which happened about 33 years after he had first assumed the sovereignty, of which time, according to Aristotle, he reigned 17 years. Pisistratus left behind him two sons named Tlippar- Hipparchus chus and Hippias, both men of great abilities, who and Hip- shared the government between them, and behaved with Pias‘ lenity and moderation. But though by the mildness of their government the family of the Pisistratidse seemed to be fully established on the throne of Athens, a con¬ spiracy was unexpectedly formed against both the bro¬ thers, by which Hipparchus was taken olf, and Hippias narrowly escaped. The most material facts relating to this conspiracy are what follow. 6, There were at that time in Athens two young men, Conspiracy called Harmodius and Aristogiton ; the former of these of Harmo- was exquisitely beautiful in bis person, and on that c*tu.s an? account, according to the infamous custom of the Greeks, violently beloved of the other. This Harmo- * . dins was also beloved of Hipparchus ; who, if W’e may believe Thucydides, forced him. This was grievously resented, and revenge determined on j to hasten which, another accident concurred. Hipparchus, finding that Harmodius endeavoured to avoid him, publicly af¬ fronted him, by not suffering his sister to carry the of¬ fering of Minerva, as if she was a person unworthy of that office. The two young men, not daring to show any public signs of resentment, consulted privately with their friends ; among whom it was resolved, that at the approaching festival of Panathenaea, when the citizens were allowed to appear in arms, they should attempt to restore Athens to its former liberty. In this they imagined that they should find themselves se¬ conded by the whole body of the people. But when the day appointed was come, they perceived one of their number talking very familiarly with Hippias ; and g3 fearing that they were discovered, they immediately Hipparchus fell upon Hipparchus, and despatched him with a mul-killed, titude of wounds. In this exploit the people were so far from seconding them, as they expected, that they suffered Harmodius to be killed by Hipparchus’s guards, and seizing Aristogiton themselves, delivered him up to Hippias. Some time afterwards, however, the respect they paid to these two young men exceeded all bounds. They caused their praises to be sung at the The con- PanathenEea, forbade any citizen to call a slave by either spirators of their names, and erected brazen statues to them inextrava- tlie forum *, which statues were afterwards carried into^^j 10 Persia by Xerxes, and sent back from thence by A- lexander the Great, Antiocbus, or Seleucus, for au¬ thors are not agreed by which. Several immunities and privileges were also grauted to the descendants of these <*3 230 Attica. 64 Cruelty of Ilippias. <>5 He is dri¬ ven out of Athens; ATT these two patriots, and all possible means were taken to render their memory venerable and respected by poste¬ rity. Hippias being now sole master of Athens, and proba¬ bly exasperated by the murder of his brother, began to alter his conduct greatly, and treat his subjects in an oppressive and cruel manner. Heiegan with torturing Aristogiton, in order to make him confess his accompli¬ ces : but this proved fatal to his own friends : for Aris¬ togiton impeaching such as he knew to be best affected to Hippias, they were immediately put to death j and when he had destroyed all those he knew, at last told Hippias, that now he knew of none that deserved to suf¬ fer death except the tyrant himself. Hippias next vent¬ ed his rage on a woman named Lecena, who was kept by Aristogiton. She endured the torture as long as she could ; but finding herself unable to bear it any longer, she at last bit off her tongue, that she might not have it in her power to make any discovery. To her the Athe¬ nians erected the statue of a lioness, alluding to her name, without a tongue, on which was engraved a suit¬ able inscription. After the conspiracy was, as Hippias thought, tho¬ roughly quashed, he set himself about strengthening his government by all the means he could think of. He contracted leagues with foreign princes, increased his revenues by various methods, &c. But these precau¬ tions were of little avail; the lenity of Pisistratus’s government had alone supported it 5 and Hippias pursuing contrary methods, was deprived of his so¬ vereignty in less than four years after the death of his brother. Th is revolution was likewise owing to the family of Megacles, who were styled Alcmceonida, and had set¬ tled at Lipsydrum. In times of discontent, which at Athens were very frequent, this family was the com¬ mon refuge of all who fled from that city *, and at last they thought of a method of expelling the Pisistratidte altogether. The method they took to accomplish their purpose was as follows. The agreed with the Amphictyons to rebuild the temple at Delphi j and being possessed of immense riches, they performed their engagement in a much more magnificent manner than they were bound to do ; for having agreed only to build the front of common stone, they built it of Parian marble. At the same time they corrupted the pro¬ phetess Pythia, engaging her to exhort all the Lace¬ daemonians that came to consult the oracle either in behalf of the state, or their own private affairs, to at¬ tempt the delivery of Athens. This had the desired ef¬ fect : the Lacedaemonians, surprised at hearing this ad¬ monition incessantly repeated, at last resolved to obey the divine command, as they imagined it to be ; and sent Anchimolius, a man of great quality, at the head of an army, into Attica, though they were at that time in league with Hippias, and accounted by him his good friends and alies. Hippias demanding assistance from the Thessalians, they readily sent him 1000 horse, under the command of one of their princes named Si- neas. The Lacedaemonians being landed, Hippias fell upon them so suddenly, that he defeated them with great slaughter, killed their general, and forced the shattered remains of their army to fly to their ships. The Spartans, incensed at this unfortunate expedition, determined to send another army into Attica \ which I C A. they accordingly did soon after under their king Cleo- . „ menes : and lie having, at his entrance into the Athe- < nian territories, defeated the Thessalian horse, obliged l1 Hippias to shut himself up in the city of Athens, which he was soon after forced to abandon altogether. He was, however, in no want of a place of refuge ; the Thessalian princes inviting him into their country, and the king of Macedon offering his family a city and territory, if they choose to retire into his dominions. ^ But Hippias chose rather to go to the city of Sigeum, au^ reti[[ which Pisistratus had conquered, and left to his own to Sigeiim, ] family. After the expulsion of the Pisistr'&tidte, the Atheni¬ ans did not long enjoy the quiet they had proposed to themselves. They were quickly divided into two fac-Two^ tions ; at the head of one was Clysthenes, one of the tions in chief of the Alcmseonidae j and of the other, Isagoras, Athent, a man of great quality, and highly in favour with the Athenian nobility. Clysthenes applied himself to the people, and endeavoured to gain their affection by in¬ creasing their power as much as possible. Isagoras per¬ ceiving that by this means his rival would get the bet¬ ter, applied to the Lacedaemonians for assistance, revi¬ ving at the same time the old story of Megacles’s sa¬ crilege, and insisting that Clysthenes ought to be ba¬ nished as being of the family of Megacles. Cleomenes ji,eSpa king of Sparta readily came into his measures, and sud-tinssuppcri denly despatched a herald to Athens with a dec]ara-bagM» tion of war in case all the Alcmmonidae were not im¬ mediately banished. The Athenians did not hesitate to banish their benefactor Clysthenes, and all his rela¬ tions ; but this piece of ingratitude did not answer their purpose. Cleomenes entered Attica at the head of a Spartan army j and, arriving at Athens, con¬ demned to banishment 700 families more than what had been sent into exile before. Not content with this, he would have dissolved the senate, and vested the go¬ vernment in 300 of the chief of Isagoras’s faction. This the Athenians would by no means submit to; and therefore took up arms, and drove Cleomenes and his troops into the citadel, where they were besieged for two days. On the third day Cleomenes surrendered on condition that all those who were in the citadel should retire unmolested. This, though agreed to, was not performed by the Athenians. They fell upon such as were separated from the army, and put them to death without mercy. Among the number of those slain on this occasion was Timesitheus the brother of Cleomenes himself. The Spartan king was no sooner withdrawn from.at Athens, than he formed a strong combination in fa-out metis vour of Isagoras. He engaged the Boeotians to at¬ tack Attica on the one side, and the Chalcidians on the other, while he at the head of a powerful Spartan army entered the territories of Eleusina. In this di¬ stress, the Athenians, not being able to. cope with so many enemies at once, resolved to suffer their terri¬ tories to be ravaged by the Chalcidians and Boeo¬ tians, contenting themselves with opposing the army commanded by Cleomenes in person. But this power¬ ful confederacy was quickly dissolved : the Corin¬ thians, who were allied with Cleomenes, doubting the justice ol their cause, returned home j his other allies likewise beginning to waver, and his colleague Ariston the other king of Sparta, differing in sentiments, Cleo- menei A T T menes was obliged to abandon the enterprise. The —^—1 Spartans and their allies being withdrawn, the Athe- 70: nians took a severe revenge of the Bceotians and Chal- cidians, totally routing their forces, and carrying off a ■ amie- great number of prisoners. The prisoners taken in this tod., war were put in irons, but afterwards set at liberty on paying a ransom of two minae per head. Their fetters were, however, hung up in the citadel; and the Athe¬ nians consecrating the tenth of what they had received for ransom, purchased a statue, representing a chariot and four horses, which they set up in the portico of the citadel, with a triumphant inscription in token of their victory. These indignities rousing the Boeotians, they imme¬ diately vowed revenge, and engaged on their side the people of AEgina, who had an hereditary hatred at the Athenians ; and while the latter bent all their atten¬ tion to the Boeotian war, the AEginetans landing a con- siderable army, ravaged the coasts of Attica, empiiof But while the Athenians were thus employed against the Boeotians and ^Eginetans, a jealousy sprung up on eKt- ^ie Par^ Lacedaemon, which was never afterwards 1 » eradicated. Cleomenes, after his unsuccessful expedi¬ tion against Attica, produced at Sparta certain oracles which he said he had found in the citadel of Athens while he was besieged therein : the purport of these oracles was, that Athens would in time become a rival to Sparta. At the same time it was discovered, that Ciysthenes had bribed the priestess of Apollo to cause the Lacedaemonians to expel the Pisistratidae from A- thens j which was sacrificing their best friends to those whom interest obliged to be their enemies. This had such an effect, that the Spartans, repenting their folly in expelling Hippias, sent for him from Sigeum, in order to restore him to his principality : but this not being agreed to by the rest of the states, they were forced to abandon the enterprise, and Hippias returned to Sigeum as he came. se os About this time, too,- Aristagoras the Milesian ha- war: ving set on foot a revolt in Ionia against the Persian 1 P*1' king, applied to the Spartans for assistance ; but they declining to have any hand in the matter, he next ap¬ plied to ^he Athenians, and was by them furnished with 20 shins under the command of Melanthus, a noble¬ man universally esteemed. This rash action cost the I Creeks very dear, as it brought upon them the whole power of the Persian empire ; for no sooner did the king of Persia hear of the assistance sent from Athens to his rebellious subjects, than he declared himself the sworn enemy of that city, and solemnly besought God that he might one day have it in his power to be re¬ venged on them. The Ionian war being ended, by the reduction of that country again under the Persian government, the king of Persia sent to demand earth and water as tokens of submission from the Greeks. Most of the islanders yielded to this command out of fear, and among the rest the people of TEgina *, upon which the Athenians accused the inhabitants of this island of treachery to¬ wards Greece, and a war was carried on with them for a long time. How it ended we are not informed j but its continuance was fortunate for Greece in general, as, by inuring them to war, and sea-aflairs in particu- lar, it prevented the whole of the Grecian states from I C A. . 231 being swallowed up by the Persians, who were now Attica, about to invade them. ■■ Besides the displeasure which Darius had conceived against the Athenians on account of the assistance they had afforded the lonians, he was further engaged to an expedition against Greece by the intrigues of Hippias. „„ Immediately on his returning unsuccessfully from La-Hippias ap. cedtemon, as above related, Hippias passed over intopb'es to the Asia, went to Artaphernes, governor of the adjacent.*>ers,ans' provinces belonging to the Persian king, and excited him to make war upon his country, promising to be obedient to the Persian monarch provided he was re¬ stored to the principality of Athens. Of this the A- thenians being apprised, sent ambassadors to Arta- phernes, desiring leave to enjoy their liberty in quiet : but that nobleman returned for answer, that if they would have peace with the great king, they must im¬ mediately receive Hippias ; upon which answer the Athenians resolved to assist the enemies of Darius as much as possible. The consequence of this resolution was, that Darius commissioned Mardonius to revenge him of the insults he thought the Greeks had offered him. But Mardonius having met with a storm at sea, and other accidents which rendered him unable to do any thing, Datis and Artaphernes the son of Artapher¬ nes above mentioned, were commissioned to do what he was to have done. The Persian commanders, fearing again to attemptxheyIn¬ to double the promontory of Athos, where their fleet vade had formerly suffered, drew their forces into the plains Greece, of Cilicia : and passing from thence through the Cy¬ clades to F.ubcea, directed their course to Athens. Th eir charge from Darius was to destroy both Eretria and Athens j and to bring away the inhabitants, that 7- they might be at his disposal. Their first attempt wasEretria dt- on Eretria, the inhabitants of which sent to Athens stayed, for assistance on the first approach of the Persian fleet. The Athenians, with a magnanimity almost unparallel¬ ed at such a juncture, sent 4000 men to their assist¬ ance 5 but the Eretrians were so much divided amongst themselves, that nothing could be resolved on. One party among them was for receiving the Athenian suc¬ cours into the city ; another, for abandoning the city and retiring into the mountains of Euboea ; while a third sought to betray their country to the Persians for their own private interest. Seeing things in this situa¬ tion, therefore, and that no good could possibly be done, one -/Eschines, a man of great authority among the Eretrians, generously informed the Athenian com¬ manders that they might return home. They accord¬ ingly retired to Oropus, by which means they escaped destruction : for Eretria being soon after betrayed to the Persians, was pillaged, burnt, and its inhabitants sold for slaves. On the news of this disaster the Athenians immedi¬ ately drew together all the forces they were able, which after all amounted to no more than 9000 men. These, with 1000 Platseans who afterwards joined them, were commanded by ten general officers, who had equal power $ among whom were Miltiades, Aristides, and Themistocles, men of distinguished valour and great abilities. But it being generally imagined that so small a body of troops would be unable to resist the formidable power of the Persians, a messenger was des¬ patched 232 ATT Attica, patched to Sparta to entreat the immediate assistance of 1 v~~* that state. He communicated his business to the senate in the following terms : “ Men of Lacedaemon, the A- thenians desire you to assist them, and not to suffer the most ancient of all the Grecian cities to be enslaved by the barbarians. Eretria is already destroyed, and Greece consequently weakened by the loss of so consi¬ derable a place.” The assistance was readily granted $ 7 Integrity of After the battle, Aristides discharged the trust re- Austides. posed in him with the greatest integrity. Though there w?as much gold and silver in the Persian camp, and the tents and ships they had taken were filled with all sorts of riches, he not only forbore touching any thing himself, but to the utmost of his power prevented others from doing it. Some, however, found means to enrich themselves ; among the rest, one Callias, cousin- german to Aristides himself. This man being a torch- bearer, and, in virtue of his office, having a fillet on his head, one of the Persians took him for a king, and, fall¬ ing down at his feet, discovered to him a vast quantity of gold hid in a well. Callias not only seized, and ap¬ plied it to his own use, but had the cruelty to kill the poor man who dicovered it to him, that he might not mention it to others j by which infamous action he en¬ tailed on his posterity the name of Laccopluti, or enriched 7S by the well. Miltiades After the battle of Marathon, all the inhabitants of Iv treated' ^at0ea were declared free citizens of Athens, and Mil- by the A- tia^esi Themistocles, and Aristides were treated with thenians. possible marks of gratitude and respect. This, however, was but very short-lived ; Miltiades proposed an expedition against the island of Paros, in which ha¬ ving been unsuccessful, through what cause is not well known, he was, on his return, accused and condemned to pay 50 talents, the whole expence of the scheme ; and, being unable to pay the debt, was thrown into prison, where he soon died of a wound received at 79 Paros. Aristides'56 ^ ^ thing can exceed the enormity of such a pro¬ ceeding as this, it was the treatment Aristides next re¬ ceived. Miltiades had proposed an expedition, which had not proved successful, and in which he might pos¬ sibly have had bad designs $ but against Aristides not so much as a shadow of guilt was pretended. On the contrary, his extraordinary virtue had procured him the title of Just, and he had never been found to swerve from the maxims of equity. His downfal was occa¬ sioned by the intrigues of Themistocles ; who being a man of great abilities, and hating Aristides on account of the character he deservedly bore among his country- I C A. men, took all opportunities of insinuating, that his ri- val had in fact made himself master of Athens without u the parade of guards and royalty. “ He gives laws to the people (said he) ; and what constitutes a tyrant, but giving laws ?” In consequence of this strange ar¬ gument, a strong party was formed against the virtuous Aristides, and it was resolved to banish him for 10 years by the ostracism. In this case, the name of the person to be banished was written upon a shell by every one who desired his exile, and carried to a certain place within the forum enclosed with rails. If the num¬ ber of shells so collected exceeded 6000, the sentence w'as inflicted; if not, it was otherwise. When the agents of Themistocles had sufficiently accomplished their purpose, on a sudden the people flocked to the forum, desiring the ostracism. One of the clowns who had come from a borough in the country, bringing a shell to Aristides, said to him, “ Write me Aristides upon this.” Aristides, surprised, asked him if he knew any ill of that Athenian, or if he had ever done him any hurt ? “ Me hurt ! (said the fellow), no, I don’t so much as know him j but I am weary and sick at heart on hearing him everywhere called the just." A- ristides, thereupon, took the shell, and wrote his own name upon it; and when informed that the ostracism fell upon him, modestly retired out of the forum, say- ing, “ I beseech the gods that the Athenians may never see that day which shall force them to remember Aristi¬ des.” After the battle of Marathon, the war with ALgina wras revived with great vigour ; but the zEginetans generally had the superiority, on account of their great naval power. Themistocles observing this, was conti-The nually exhorting his countrymen to build a fleet, notc*esl only to make them an equal match for the Atginetans, but also because he was of opinion that the Persians^ would soon pay them another visit. At last, he had the boldness to propose, that the money produced by the silver mines, which the Athenians had hitherto divided among themselves, should be applied to the building of a fleet : which proposal being complied with, 100 galleys were immediately put upon the stocks ; and this sudden increase of their maritime power proved the means of saving all Greece from slavery. About three years after the banishment of Aristides, Xer; Xerxes king of Persia sent to demand earth and water :Ta(*c but rI hemistocles desiring to make the breach with that ,ie< monarch still wider, put to death the interpreter for publishing the decree of the king of Persia in the lan¬ guage of the Greeks j and having prevailed upon the several states to lay aside their animosities and provide for their common safety, got himself elected general of the Athenian army. When the news arrived that the Persians were ad¬ vancing to invade Greece by the straits of Thermopy¬ lae, and that they were for this purpose transporting their forces by sea, Themistocles advised his country¬ men to quit the city, embark on board their galleys, and meet their enemies while yet at a distance. -This they would by no means comply with ; for which reason Themistocles put himself at the head of the army, and having joined the Lacedaemonians, marched towards Tempe. Here, having received advice that the straits of Thermopylae were forced, and that both Boeotia and Thessaly ICS, 0. iiC! J. A T T I Thessaly had submitted to the Persians, the army re- turned without doing any thing. In this distress the Athenians applied to the oracle at Delphi: from whence they received at first a very severe answer, threatening them with total destruction 5 but after much humiliation, a more favourable one was delivered, in which, probably by the direction of The- mistocles, they were promised safety in walls of wood. This was by Themistocles and the greatest part of the 5 citizens interpreted as a command to abandon Athens, [heart- and put all their hopes of safety in their fleet. Upon this, the opinion of Themistocles prevailing, the great- lu"est part began to prepare for this embarkation; and had money distributed among them by the council of the Areopagus, to the amount of eight drachms per man : but this not proving sufficient, Themistocles gave out that somebody had stolen the shield of Mi¬ nerva ; under pretence of searching for which, he seized on all the money he could find. Some, how¬ ever, there were who refused to embark with the rest, but raised to themselves fortifications of wood ; under¬ standing the oracle in its literal sense, and resolving to wait the arrival of the Persians, and defend them¬ selves to the last. In the mean time Aristides was re¬ called, when the Athenians saw it their interest, lest he should have gone over to the Persians and assisted 8 them with his advice. iilu The Persians having advanced to Athens soon after - the inhabitants had deserted it, met with no opposition ns except from a few just now mentioned ; who, as they 8. would hearken to no terms of accommodation, were all ie.v cut in pieces, and the city utterly destroyed. Xerxes, however, being defeated in a sea fight at Salamis, was |anu forced to fly with prodigious loss. See Salamis. The- mistocles was for pursuing him, and breaking down the bridge he had cast over the Hellespont; but this advice being rejected, he sent a trusty messenger to Xerxes, acquainting him that the Greeks intended to break down his bridge, and therefore desired him to make all the haste he could, lest by that means he should be shut up in Europe. According to Herodo¬ tus, he also advised the Athenians to quit the pursuit and return home, in order to rebuild their ruined houses. This advice, though misinterpreted by some, was cer¬ tainly a very prudent one, as Xerxes, though once de¬ feated, was still at the head of an army capable of de- stroying all Greece ; and had he been driven to despair by finding himself shut up or warmly pursued, it was impossible to say what might have been the event. Af¬ ter this, Themistocles formed a scheme for the aggran¬ disement of Athens indeed, but a most unjust and in- ianious one. It was, in short, to make Athens mistress of the sea, by burning all the ships except those belong¬ ing to that republic. He told his countrymen, that he had something to propose of great consequence, but ivluch could not be spoken publicly : whereupon he 'vas desired to communicate it to Aristides, by whom the proposal was rejected; and Aristides having in- ormed the Athenians that what Themistocles had said was very advantageous but very unjust, they desired him to think no more of it. 85 lio- 1 the fleet returned to Salamis, extraordinary ed mnours were paid to Themistocles by the Lacedaemo- Lm mans. On his entering that city, they decreed him a lc“i >. Wreath of olives as the prize of prudence; presented him Vol. III. Part I. f 85 C A. with the most magnificent chariot in Sparta : and when he returned to Athens, he was escorted by 500 horse, an honour never paid to any stranger but himself. On his arrival at A thens, however, there were not want¬ ing some who insinuated that the receiving such honours from the Lacedaemonians was injurious to the republic ; but Themistocles, confiding in his innocence, treated these clamours with contempt, and exhorted his coun¬ trymen to entertain no doubts of their allies, but ra¬ ther endeavour to preserve the great reputation they had acquired throughout all Greece. The defeat ol Xerxes at Salamis made Mardonius, who was left to carry on the war by land, more ready to treat with the Athenians than to fight them ; and with this view he sent Alexander king of Macedon to Athens to make proposals of alliance with that repub¬ lic, exclusively of all the other Grecian states. This proposal, however, was rejected ; and the consequence Athens a was, that Athens was a second time destroyed, thesecoIul tune Spartans sending assistance so slowly, that the Athenians destg0yed‘ were forced to retire to Salamis ; but they were soon 'p}je per_ freed from all apprehensions by the total defeat and sians de¬ death of Mardonius at Plataea; where Aristides, andfeated at the body of troops under his command, distinguished Fiata3,a and themselves in a most extraordinary manner. The same day that the battle of Platgea was fought, the Persians were defeated in a sea-fight at Mycale in Ionia, wherein it was allowed that the Athenians who were there behaved better than any of the other Greeks ; but when it was proposed to transport the lonians into Europe, that they might be in perfect safety, and give them the territories of such Grecian states as had sided with the Persians, the Athenians refused to comply, fearing the lonians would rival them in trade, or refuse the obedience they used to pay them ; besides which, they would then lose the opportunity of plundering the Persians in case of any quarrel with Ionia. Before they returned home, however, the Athenians crossed over to the Chersonesus, and besieged Sestos. The siege was sg long and troublesome : but at last the garrison, being Sestos ta- pressed with hunger, and having no hopes of relief, ken by the divided themselves into two bodies, and endeavoured to Athenians, make their escape ; but were pursued, and all either killed or taken. Oibazus, one of their commanders, was sacrificed to a Thracian god ; and the other, call¬ ed Artyactes, impaled alive, and his son stoned before his face, because he had rifled the sepulchre of Prote- silaus. < _ 89 After the victories at Platsea and Mycale, the Athe-They re¬ mans returned without any apprehension, and began to kydd their rebuild their city in a more magnificent manner thancity* before. Here they were no sooner arrived than a dis¬ pute was ready to be commenced about the form of government. The commons, with Themistocles at their head, were for a democracy ; to which Aristides, rather than hazard the raising disturbances, consented. It was therefore proposed, that every citizen should have an equal right to the government; and that the archons should be chosen out of the body of the people, without preference or distinction: and this proposal being agreed to, put an end to all discontents for the present. At this time also Themistocles proposed that the city of Athens should be fortified in the best manner pos¬ sible, that it might not be liable to be again destroyed, G g when 234 ATT Attica when the Persians should take it into their heads to '——v ’ 1 invade Greece. At this proposal the Lacedaemonians were exceedingly alarmed 5 and therefore remonstrated, Tlit mis to t^a*' s^ou^ Athens once be strongly fortified, and the cles advises ^’ers*ans become possessed of it, it would be impossible to fortify to get them out of it again. At last, seeing these ar- Athens, guments had no effect, they absolutely forbade the A- oeiveifthe ^len*aiis to carry their walls any higher. This com- Spaitans man^ gave great offence but Themistocles, considering who oppose the power of Sparta at that time, advised the Athenians it. to temporize j and to assure the ambassadors that they should proceed no farther in their work, till, by an em¬ bassy of their own, satisfaction should be given to their allies. Being named ambassador at his own desire to Sparta, with some other Athenians, Themistocles set out alone, telling the senate that it would be for the interest of the state to delay sending the other ambassadors as long as possible. When arrived at Sparta, he put oft from time to time receiving an audience, on account of his colleagues not being arrived : but in the mean time the walls of Athens were building with the utmost ex¬ pedition 5 neither houses nor sepulchres being spared for materials ; and men, women, children, strangers, citizens, and servants, working without intermission. Of this the Lacedaemonians having notice, and the rest of the Athenian ambassadors being arrived, Themi¬ stocles and his colleagues were summoned before the ephori, who immediately began to exclaim against the Athenians for their breach of promise. Themistocles denied the charge : he said his colleagues assured him of the contrary : that it did not become a great state lo give heed to vague repoi’ts, but that deputies ought to be sent from Sparta to inquire into the truth of the matter, and that he himself would remain as a hostage, to be answerable for the event. This being agreed to, he engaged his associates to advise the Athenians to commit the Spartan ambassadors to safe custody till he should be released 5 after which he publicly avowed the whole transaction, took the scheme upon himself, and told the Lacedaemonians that “ all things are lawful for our country.” The Spartans, seeing no remedy, con¬ cealed their resentment, and sent Themistocles home in 9i sa^y- Makes the The next year, being the last of the 75th Olympiad, Pyraeus the Themistocles observing the inconvenience of the port poi t of Phalerum, thought of making the Pyraius the port of Athens. This he did not at first think proper to men¬ tion publicly ; but having signified to the people that he had something of importance to communicate, they appointed Xanthippus and Aristides to judge of his proposal. They readily came into his measures, and told the people that what Themistocles proposed would be of the utmost advantage to the state, at the same time that it might be performed with ease. Upon this they Were desired to lay the matter before the senate 5 who coming unanimously into their measures, ambassa¬ dors were depatched to Sparta to insinuate there how proper it would be for the Greeks to have some great port, where a fleet might always watch the designs of the Persians; and thus having prevented any umbrage from their first undertakings, the work was set about with such expedition, that it was finished before the La¬ cedaemonians knew well what they were about. At this time also the sovereignty of the sea was transferred from Sparta to Athens, through the haugh- Athens. I C A. ty behaviour of Pausanias the Lacedaemonian. He ^ had commanded at Plataea, and still enjoyed the su- - preme authority in the war which was all this time carrying on against the Persians ; but being elated with^0Vfl f- his success at Plataea, and having entered into a trea-^ sonable correspondence with the enemy, he treated theferrei captains under his command with the greatest haugh-Alhe tiness, giving the preference to the Spartans in such a manner that the rest of the Greeks could no longer bear his insolence. On the contrary, Aristides, and Cimon the son of Milthades, who commanded the Athenians, by their obliging behaviour gained the favour of every body $ so that the allies, having publicly affronted Pan• sanias, put themselves under the protection of the A- thenian republic ; and thenceforward the Athenians, and not the Lacedaemonians, had the supreme com¬ mand. The Greeks being now sensible that they would al-^r;stj ways have occasion to be on their guard against the taxes Persians, and that it was necessary to establish a fundG)ee' by a common taxation of all the states, Aristides pitched upon as the only person that could be trusted^ with the power of allotting to each of the states its proper quota. This difficult task he undertook, and executed in a manner unparalleled in the annals of hi¬ story. All parties were pleased, and his taxation was styled the happy lot of Greece. The gross amount of it was 450 talents. ■ It now came to the turn of Themistocles to experi-Theni ence the ingratitude of his countrymen. His servicesclesb had been so essential, that the treatment he received^ may perhaps be a sufficient excuse for modern patriots when they connect their own interest with the service of their country. Themistocles had plainly saved the state from ruin by his advice j he had distinguished him¬ self by his valour ; had rendered Athens, by his policy, superior to the other states of Greece $ and entirely subverted the Lacedaemonian scheme of power. Yet, notwithstanding all this, he was banished by the ostra¬ cism, without the smallest crime pretended, unless that he was hated by the Lacedaemonians, and that he had erected a temple, near his own house, dedicated to Diana, the giver of the best counsel; intimating that he himself had given the best counsel for the safety both of Athens and of all Greece, which was no more than the truth. Nay, he was not only driven out of Athens, but out of all Greece ; so that he was forced to seek shelter from the king of Persia, against whom he had fought with so much valour. That monarch gave him a gracious reception } and he was never recalled, be¬ cause the Greeks had no occasion for his services. $ The war with Persia was not yet discontinued ; thesmee Greeks found their advantage in plundering and en-Cinf riching themselves with the spoils of the kingofPer-®U sia’s subjects. For this reason, in the end of the 77^ Olympiad, they equipped a navy, under a pretence of relieving such of the Greek cities in Asia as were sub¬ ject to the Persians. Of this fleet Cimon, the son of Miltiades by the daughter of the king of Thrace, was appointed commander in chief. He had already tasted the justice and generosity of his countrymen, having been thrown into prison for his father’s fine, from which he was released by Callias, whom his sister Elpinice married on account of his great wealth procured by n° very honourable means. He accepted of the command, however, 9*1 sullies Cli iio- US. : h however, and gained such immense booty in this expe¬ dition, that the Athenians were thereby enabled to lay the foundation of those long-extended walls which united the port to the city. The foundation was laid in a moorish ground j so that they were forced to sink it very deep, and at a great expence j but to this Cimon himself contributed out of his own share of the spoils, which was very considerable. He also adorned the fo¬ rum with palm trees, and beautified the academy with delightful walks and fountains. The Persians having soon after this expedition invaded the Chersonesus, and with the assistance of the Thracians made themselves masters of it, Cimon was sent against them in a great hurry. He had only four ships 5 but nevertheless with these he took 13 of the Persian gal¬ leys, and reduced the whole of the Chersonesus. After this he marched against the Thracians, who revolting against the Athenians, had made themselves masters of the gold mines lying between the rivers Nyssus and Strymon. The Thracians were quickly obliged to yield ; after which the Athenians sent a great colony to Amphipolis, a city of Thrace, which for some time made a considerable figure, but afterwards attempting to pene¬ trate into the country of the Edones, great part of them were destroyed. Cimon also fell upon the following expedient to make Athens irresistible at sea by the other states of Greece. Many of the Greek states, by virtue of A- ristides’s taxation, were bound to furnish men and gal¬ leys as well as to pay the tax for their support. But when they saw themselves out of danger from the Per¬ sians, most of them were very unwilling to furnish their quota of men. This the Athenian generals being of¬ fended with, were for having recourse to force ; but Cimon permitted such as were desirous of staying at home to do so, and accepted a sum of money in lieu of a galley completely manned. By this means he in¬ ured the Athenians, whom he took on board his galleys, to hardship and discipline ; while the allies who re¬ mained at home became enervated through idleness, and from being confederates, dwindled into tributaries, and almost slaves. In the last year of the 77th Olym¬ piad, Cimon was sent to assist the Lacedaemonians against their Helotes, who had revolted from them. In this he was attended with his usual success $ but, some time after, the Lacedaemonians being engaged in the siege of Itnome, sent again to the Athenians for succour, and Cimon was a second time sent to their relief; but the Spartans having received a sufficient support of troops from other quarters before the arrival of the A- 1 Ionian general, he and his men were dismissed withoilt doing any thing. This grievously offended the people of Athens, who thenceforward hated not only the La- c.e ^'jwnians, hut all their own citizens wlio were thought to be friends to that state. It was not possible, however, that any person who m served the state should escape banishment at A- thens. Cimon had gained great wealth both to the pu 1 ic and to himself. In his public character he had e aved with unimpeached honesty, and as a private citizen he dedicated his wealth to the most excellent purposes. He demolished the enclosures about his grounds and gardens, permitting every one to enter M 1 f , 'vlliU ^ru^.s tliey P'eaSf,d ; he kept an open ,a e? vv‘ieie both rich and poor were plentifully en- cr atned. If he met a citizen in a tattered suit of ATTICA. 235 clothes, he made some of his attendants exchange with Attica, him j or if the quality of the person rendered that ,J“"“ kindness unsuitable, he caused a sum of money to be privately given iiim. All this, however, was not suf¬ ficient : he did not concur with every measure of the commonalty j and therefore the popular party deter¬ mined not to banish him, but to put him to death. 1 he crime laid to his charge was, that by presents from the Macedonians he was prevailed upon to let slip a manifest opportunity of enlarging his conquests, after- taking from the Persians the gold mines of Thrace. To this accusation Cimon replied, that to the utmost of his power he had prosecuted the war against the Thracians, and other enemies of the state of Athens; but that, it was true, he had not made any inroads into Macedonia, because he did not imagine he was to act as a public enemy of mankind, and because he was struck with respect for a nation modest in their car¬ riage, just in their dealings, and strictly honourable in their behaviour towards him and the Athenians : that if his countrymen looked upon this as a crime, he must abide their judgment; but, for his part, be could never be brought to think such conduct amiss. Elpi- nice, Cimon’s sister, used all her interest in his behalf, and amongst others spoke to Pericles the celebrated statesman and orator. He was indeed Cimon’s rival, and had no doubt assisted in stirring up the prosecution against him; but he did not desire his death; and there¬ fore, though appointed to accuse him, Pericles spoke in such a manner that it plainly appeared he did not think him guilty ; and, in consequence of this lenity, Cimon was only banished by the ostracism. The Athenian power was now risen to such a height, that all the other states of Peloponnesus looked upon this republic with a jealous eye, and were continually watching every opportunity of making war upon it when the state was engaged in troublesome affairs, and seemed to be less able to resist. These attempts, how¬ ever, so far from lessening, generally contributed to in¬ crease, the power of the xlthenians ; but in the year before Christ 458, the republic entered into a Avar with warbe- Sparta, which was scarcely put an end to but by the de- tween A- struction of the city of Athens. For this war, there thens and was no recent provocation on the part of the Spartans. Sp*11*8, They had sent a great army to assist the Dorians against the Phocians, and the Athenians took this opportunity to revenge themselves of former quarrels. Having therefore drawn in the Argives and Thessalians to be their confederates, they posted themselves on the isth¬ mus, so that the Spartan army could not return with¬ out engaging them. The Athenians and their con¬ federates amounted to 14,000, and the Spartans tb 11,500. The Spartan general, however, not very will¬ ing to hazard a battle, turned aside to Tanagra, a city in Boeotia, where some of the Athenians who inclined to aristocracy entered into a correspondence with him. / & But before their designs were ripe for execution, the Athenians Athenian army marched with great expedition to Ta-defeated, nagra, so that a battle became inevitable. When the armies were drawn up in order of battle, Cimon pre¬ sented himself befort? his countrymen in complete ar¬ mour, and went to take post among those of his own tribe ; but the popular party raised such a clamour against him, that he was forced to retire. Before he departed, hotvever, he exhorted Euthippus and the rest of his friends to beha\Te in such a manner that they G g 2 might 236 ATTICA. Attica. They gain great ad¬ vantages over the Spartans. 102 Cimon re¬ called. *33 His death. might wipe off1 the aspersion thrown upon him, as if he J had designed to betray his country’s cause to the La¬ cedaemonians. Euthippus desired him to leave his ar¬ mour, which he did ; and a battle ensuing, the Atheni¬ ans were defeated with great loss, and Euthippus with the rest of Cimon’s friends were all killed in defence of his armour which they had surrounded. Another engagement soon followed, wherein both armies suffer¬ ed so much, that they were glad to conclude a short truce, that each might have time to recruit their shat¬ tered forces. The scale of fortune now seemed to turn in favour of the Athenians. The Thebans, who had been de¬ prived of the command of Bosotia on account of their having sided with Xerxes, were now restored to it by the LacedEemonians. At this the Athenians were so displeased, that they sent an army under Myronides the son of Callias into Boeotia to overturn all that had been done. That general was met by the Thebans and their allies^ who composed a numerous and well-disciplined army. Nevertheless, though the Athenian army was but a handful in comparison of their enemies, Myroni¬ des gained a complete victory over the allies, in some sense more glorious than either that of Marathon or Plataea. In these battles they had fought against effe¬ minate and ill-disciplined Persians, but now they en¬ countered and defeated a superior army composed of the bravest Greeks. After this victory, Myronides marched to Tanagra, which he took by storm, and ra¬ zed to the ground : he then plundered Boeotia ; defeated another army which the Boeotians had drawn together to oppose him j then fell upon the Locrians ; and ha¬ ving penetrated into Thessaly, chastised the inhabitants of that country for having^revolted from the Atheni¬ ans ; and from thence returned to Athens laden with riches and glory. The next year Tolmides the Athenian admiral in¬ vaded Laconia, where he made himself master of seve¬ ral places $ and on the back of this, Pericles invaded Peloponnesus with great success, burning, spoiling, or taking, whatever places he attempted. On his return he found the people greatly out of humour on account of Cimon’s banishment j so he was immediately re¬ called. Cimon was no sooner returned than he fell to his old employment of plundering the Persians ; and, accord¬ ing to Plutarch, he had now nothing less in view than the conquest of the whole Persian empire. The Per¬ sian monarch finding he could have no rest, at last sent orders to Artabazus and Megabizus, his commanders, to conclude a treaty •, which was done on the following conditions : 1. That the Greek cities in Asia should be free, and governed by their own laws. 2. That the Per¬ sians should send no army within three days journey of the sea. 3. That no Persian ship of war should sail be¬ tween Thesalis and Cyrene, the former a city of Pam- phylia, and the latter of Lycia. While this treaty was going on, Cimon died, whe¬ ther of sickness or of a wound he had received is not known j and after his death the Athenian affairs be¬ gan to fall into confusion. It was now the misfortune of this state to be alike hated by her enemies and allies ; the consequence of which was, that the latter were per¬ petually revolting whenever they thought they had an opportunity of doing so with impunity. The Mega- 2 rians, at this time, who had been long under the pro- au l tection or dominion of Athens, thought proper for' some reason or other to disclaim all dependence on their former protectors, and have recourse to Sparta, with which state they entered into a strict alliance. This the Athenians revenged by ravaging the country of the Megarians; which soon brought on a renewal of the Lacedaemonian war that had been for a little time suspended. Pericles, however, procured the return of the first Lacedaemonian army, without bloodshed, by bribing Chandrides the young king of Sparta’s tutor. In the winter, Tolmides resolved to undertake an expe¬ dition into Bceotia with a small body of troops : which design he put in execution contrary to the advice of Pericles 5 and his rashness was soon punished by his own death and the total defeat of his army. Notwithstand- ic ing this misfortune, however, Pericles soon after inva-A ddr ded and reduced Euboea ; and the LacedEemonians,^^ lc* finding it was not for their interest to carry on the£,acecm war, concluded a truce with the Athenians for 30nians. years. About this time Psammiticus, king of Egypt, sent by way of present to the people of Athens 40,000 bushels of wheat; which proved a great misfortune to the city: for Pericles, out of spite to Cimon, who had(;rueiJn children by an Arcadian woman, bad preferred a lawperjci whereby the Athenians of the half blood were disfran¬ chised 5 and this law, on account of the distribution of the corn above mentioned, was prosecuted with such severity, that no less than 5000 persons, who till then had been considered as free men, were sold for slaves. y,inih. f This piece of cruelty has been of great service to the^g • critics, as by means of it we know exactly the numberniam . of Athenian citizens, which at this time amounted tozens‘ no more than 14,040 persons, though Athens was now aiming at no less than erecting an universal mo¬ narchy. Six years after the conclusion of the peace between Athens and Sparta, a war broke out between the Sa¬ mians and Milesians about the city of Priene, seated under Mount Mycale in Ionia. How this war came to affect the Athenians is not certainly known j but, some¬ how or other, this republic was induced to take the part of the Milesians j and the island of Samos was reduced by Pericles, who established there a democracy, and left an Athenian garrison. He was no sooner gone, I07 however, than the Samians disliking their new form of government, drove out the garrison he had left; butperjc] Pericles quickly returning, besieged and took their ci¬ ty, demolished their walls, and fined them of the whole expence of the war ; part of which he obliged them to pay down, and took hostages for the remainder. When Pericles returned, he procured himself to be appointed to pronounce the public oration in honour of those who fell: which he did with such eloquence, that when he came down from the pulpit the women gathered about him, took him by the hand, and crowned him with garlands. ^ A little after this commenced the war between the War t Corcyrians and Corinthians, which by degrees brought tween" the Athenians into those engagements that proved the ruin of their state. The causes of this war were thean following. An intestine war breaking out in the little territory of Epidamnum, a city of Macedonia, found¬ ed by the Corcyrians, one party called in to their as¬ sistance tliiaHs* Attic a. 109 Athens sides with the Corey- rians. no ’otid*a be. ^ed by Athe- “aiis. ATT sistance the Illyrians, and the other the Coreyrlans. ■> The latter neglecting the matter, Corinth was applied to, as the Corcyrians were a colony from that place. The Corinthians, partly out of pity to the Epitlam- nians, and partly out of spleen to the Corcyrians, sent a very great fleet to the assistance of the former, by which means that party which had applied to Corinth was thoroughly established. This being resented by the Corcyrians, they sent a fleet to Epidamnum to sup¬ port the exiles •, and accordingly this fleet began to act offensively on its entering the port, the chief com¬ manders having instructions to propose terms of accom¬ modation, to which the Corinthians would by no means agree. The next year the Corcyrians defeated at sea the Corinthians and their allies, and took Epidamnum by storm j after which they wasted the territories of the allies of the Corinthians, which greatly exasperated the latter, At Corinth, therefore, they began to make great preparations for carrying on the war, and pressed their confederates to do the same, that they might be in a condition to retrieve the honour they had lost, and humble this ungrateful colony which had thus insulted her mother city. The Corcyrians were no sooner acquainted with these proceedings, than they despatched ambassadors to Athens with their complaints j and these were quickly followed by others from Corinth on the same errand. At first the people of Athens inclined to favour the Corinthians : but they soon changed their minds, and took part with the Corcyrians : they contented them¬ selves, however, with entering into a defensive alliance with that little state, whereby they promised to assist each other, in case either party should be attacked } and in consequence of this treaty, they furnished the Corcy¬ rians with ten galleys, under Lacedsemonius the son of Cimon, with whom were joined Diotenes and Proteus as colleagues. As soon as the season of the year permitted, the Corinthians sailed for the coast of Corcyra with a fleet of 150 ships, under the command of Xenoclides, as¬ sisted by four other Corinthian admirals j each squa¬ dron of their allies being commanded by a chief of their own. The Corcyrian and Athenian fleet amount¬ ed to 120, but the Athenians had orders to give as little assistance as possible. The action was very brisk for some time : the Corcyrian right wing broke the left of the Corinthian fleet; and forcing some of the ships on shore, landed, pillaged their camp, and made a great number of them prisoners ; on the other hand, the Corinthian ships in the right wing beat the Cor¬ cyrian ships there, they being but very faintly assisted by the Athenians, till the latter were at last obliged to defend themselves, which they did so well, that the Corinthians were glad to retire. The next day pre¬ parations were made on both sides for another engage¬ ment ; but 20 ships coming from Athens to the assist¬ ance of the Corcyrians ; the Corinthians declined the combat. . As soon as the Corcyrian war broke out, the Athe¬ nians sent orders to the citizens of Potidsea to demolish a part of their wall, to send back the magistrates they had received from Corinth, and to give hostages for their own behaviour. Potidsea was a town in Mace¬ donia, founded by the Corinthians, but at that time m alliance with the Athenians.—Perdiccas king of I C A. 237 Macedon, who hated the Athenians, took this oppor- Attica, tunity to persuade the Potidseans to revolt. Accor- '—-v—— dingly they sent ambassadors to Athens to entreat the revocation of these orders ; but at the same time sent deputies to Sparta, to join with the Corinthians and Megarians in their complaints against the Athenians. The Athenians upon this sent a considerable fleet against Potidaea, under the command of Callias, a no¬ bleman of great courage. The Corinthians on their part despatched one Aristeus with a considerable body of troops to the assistance of that city. An engage¬ ment following, the Athenians were victors, but with the loss of their general. Phormio, who succeeded in the command, invested the city in form, and shut up its port with his fleet; but the Potidseans dreading to fall into the hands of the Athenians, made a most ob¬ stinate defence, while in the mean time they warmly solicited the Corinthians to perform their promises, and engage the rest of the states of Peloponnesus in their quarrel. Iir The Lacedaemonians having heard what the Corin- The Spar- thians and other little states of Greece had to say tans de- against the Athenians, sent ambassadors to the latter, demanding reparation for the injuries, with orders, in ^eTnjtu-ies case of a refusal, to declare war. The terms demand- offered to ed were, in the first place, the expulsion of those A-the states of thenians who were allied to the family of Megacles so Greece, often mentioned. This article was on account of Pe¬ ricles ; for he was the son of Xanthippus the Athenian commander at Mycale by Agariste niece to the famous Clysthenes, who corrupted the priestess of Apollo in order to procure the expulsion of the Pisistratidae. They next insisted that the siege of Potidsea should be raised ; thirdly, that the inhabitants of ^Egina should be left free; and lastly, that a decree made against the Megarians, whereby they were forbid the ports and markets of Athens, should be revoked, and all the Grecian states under the dominion of Athens set at Hberty. . .112 These terms the Athenians were persuaded by Peri-Their terms cles to reject. The arguments used by him were in sub-rejected by stance as follows : That whatever the Lacedaemonians al*v?ce °'f might pretend as to the injustice of the complaints of the *’cac*€S’ allies, the true ground of this resentment was the pro¬ sperity of the Athenian republic, which the Spartans always hated, and now sought an opportunity of hum¬ bling : that it must be owing to the Athenians them¬ selves if this design succeeded, because for many rea¬ sons Athens was better able to engage in a long and expensive war than the Peloponnesians. He then laid before the people an exact account of their circum¬ stances ; putting them in mind, that the treasure brought from Delos amounted to 10,000 talents ; and that though 4000 of these had been expended on the stately gate of their citadel, yet that 6000 were still in hand ; that they were also entitled to the subsidies paid by the confederate states ; that the statues of their gods, the Persian spoils, &c. were worth immense sums; that private men were arrived at vast fortunes; and that, considering their trade by sea, they had a certain annual increase of wealth ; that they had on foot an army of 12,000 men, and in their colonies and garrisons 17,000 ; that their fleet consisted of 300 sail; whereas the Peloponnesians had no such advantages. For these reasons he proposed as the most feasible and likewise • 238 ATT Attica. II3 Attempt of the The¬ bans on Plataea. 1x4 They are massacred, “S Account of the allies | on both sides. likewise the most equitable satisfaction that could be given, that they would reverse their decree against Me- gara, if the Lacedaemonians would allow free egress and regress in their city to the Athenians and their al¬ lies 5 that they would leave all those states free who were free at the making of the last peace with Sparta, provided the Spartans would also leave all states free who were under their dominion ; and that future dis¬ putes should be submitted to arbitration. In case these offers should be rejected, he advised them to hazard a war; telling them, that they should not think they ran that hazard for a trifle, or retain a scruple in their minds as if a small matter moved them to it, because on this small matter depended their safety, and the reputa¬ tion of their constancy and resolution ; whereas, if they yielded in this, the next demand of the Lacedaemonians would be of a higher nature ; for having once discover¬ ed that the Athenians were subject to fear, they would thence conclude that nothing could be denied to Spar¬ ta ; whereas a stiff denial in this case would teach them to treat Athens for the future on terms of equality. He enforced these reasons by showing that their ancestors had always acted on the like principles, and in all cases preferred their glory to their ease, and their liberty to their possessions. This was the origin of the Peloponnesian war, which makes so great a figure in ancient history. The im¬ mediate preliminary to general hostilities was an at¬ tempt of the Thebans to surprise Platsea. With this view they sent Eurymachus with 300 Thebans to assist such of the Plataeans as they had drawn over to their interest, in making themselves masters of the place. In this design, they succeeded very well at first, the Plataeans, who had promised to open the gates, keeping their words exactly, so that they were instantly in pos¬ session of the city. The other party, however, per¬ ceiving how small a number they had to contend with, unanimously rose upon them, killed a great many, and forced the rest to surrender themselves prisoners of war. Another party came from Thebes to assist their countrymen ; but they arrived too late : the Pla- taeans, however, foreseeing that they would waste their country, promised to release their prisoners if they would forbear to spoil their lands. On this the The¬ bans withdrew ; and the Plataeans cruelly put to death all their prisoners, to the number of 180, with Eury¬ machus their chief, alleging that they had not pro¬ mised their release but in case of peace. The Athe¬ nians, as soon as they had notice of this attempt of the Thebans, caused all the Boeotians in their terri¬ tory to be arrested ; and when they understood how the Platseans had delivered themselves, they sent a great convoy of provisions to that city, and a numerous body of troops to escort their wives and children to Athens. Both parties now prepared in earnest for war, both sent ambassadors to the Persians, and both sought to rouse them allies. Most of the Greek states inclined to favour the Spartans, because they acted on this occa¬ sion as the deliverers of Greece, and because they either had been, or feared that they would be, oppressed by the Athenians. With the Spartans joined all the Pe¬ loponnesians, except the Argives and pait of the A- chseans ; without Peloponnesus, the Megarians, Pho- cians, Locrians, Boeotians, Ambraciots, Leucadians, I C A. and Anactorians, declared themselves on their side. On the other hand, the Chians, Lesbians, Plateeans, Messe-y nians, Acarnanians, Corcyrians, Zacynthians, Carians, Dorians, Thracians, most part of the islands, and all the Cyclades excepting Melos and Thera, with Euboea and Samos, joined the Athenians. g. The Peloponnesian war commenced 431 years before First mi Christ. The Lacedaemonian army was assembled at the°ftliear isthmus, and consisted of no less than 60,OOO men ; but before Archidamus king of Sparta, who commanded in chief, would enter Attica, he despatched a herald to Athens. The herald was sent back without any an¬ swer, by which all hopes of peace were cut off. As Archidamus was a friend to Pericles, the latter appre¬ hended that he might forbear plundering his estates. With this he immediately acquainted the people ; tell¬ ing them at the same time, that in such a case he made a present of his lands to the public. He then advised the citizens to take no care of defending their country- seats, but to attend only to the city, busy themselves in the equipping of ships, and settle a thorough resolution not to be intimidated with the first evils of war. This proposal the Athenians readily complied with, and ap¬ pointed Pericles commander in chief, with nine more generals to assist him. The first year, the Spartan army committed great ravages in Attica, Pericles having no force capable of opposing it, and refusing to engage on disadvantageous terms, notwithstanding prodigious clamours were raised against him by his countrymen. The allies, however, had no great reason to boast of the advantages they gained this year: an Athenian fleet ravaged the coasts of Peloponnesus ; another infested the Locrians, drove out the inhabitants of .ZEgina, and repeopled the island from Athens. They likewise reduced Cephalenia, and some towns in Acarnania and Leucas which had decla¬ red for the Lacedsemonians ; and in the autumn, when the Peloponnesians were retired, Pericles entering the Megarian territory, did all the mischief that could be expected from a provoked enemy. „ The spring of the second year was very fatal to A- Secon thens, by a dreadful plague which destroyed great num-year. bers of the citizens, while the Peloponnesians under fi°r the place had surrendered before the tbenians. ^eet could come to its assistance. Paches, the Athe¬ nian commander, likewise chased away the Peloponne¬ sian fleet upon its arrival ; and returning to Lesbos sent the Lacedaemonian minister, whom he found in Mi¬ tylene, together with a deputations, to Athens. On their arrival, the Lacedaemonian was immediately put to death ; and in a general assembly of the people, it was resolved, that all the Mitylenians who were ar¬ rived at man’s estate should be put to death, and the women and children sold for slaves. The next day, however, this cruel decree was reversed, and a galley sent with all expedition to countermand the bloody or¬ ders. This last vessel, however, could not get before the other: but Paches, being a man of great humani¬ ty, had taken a day to consider on the orders he had received $ during which time the last-mentioned galley arrived j in consequence of which, only about 1000 of the most forward rebels were put to death 5 the walls of the city were also demolished, their ships taken away, and their lands divided among the Athenians, who let them again to their old masters at very high rents. The same summer the Athenians seized the island of Mino- as> tying over against the territory of Megaraj and I C A » 239 likewise the port of Nisaea, which last they fortified, Attica. and it proved afterwards a place of the utmost import- 1 —' ance to them. x\t this time also the Plataeans, driven^ *24 to the last extremity, surrendered to the Lacedaemoni-taj5eiA,1(j ans, by whom they were, to the number of 208, in- eluding 25 Athenians, put to death, and their women sold for slaves. Their city was soon after razed by their implacable enemies the Thebans, who left only an inn to show where it stood. The fame of Plataea, however, induced Alexander the Great afterwards to rebuild it. I2^ In this year happened the famous sedition of Cor-Sedition of cyra, whence other seditions, when their effects ren- Corcyra. dered them terrible, have been called Corcyrian. It hath been already observed, that the war between the Corcyrians and Corinthians brought on the general war throughout Peloponnesus. A great number of Corcy¬ rians were in the beginning of this war carried away prisoners into Peloponnesus, where the chief of them were very well treated, but the rest sold for slaves. The reason of this conduct of the Corinthians was a de¬ sign they had formed of engaging these Corcyrians to influence their countrymen to side with them and their allies. With this view they treated them with all ima¬ ginable lenity and tenderness, instilling into them by degrees a hatred of democratic government; after which they were told, that they might obtain their li¬ berty upon condition of using all their influence at home in favour of the allies, and to the prejudice of Athens. This the Corcyrians readily promised and en¬ deavoured to perform. At first, those who were for an aristocracy prevailed, and murdered all those of the opposite party that fell into their hands, in which they were assisted by a fleet of Peloponnesians : but the A- thenians sending first one fleet and then another to the assistance of the distressed party, the Peloponnesians were forced to withdraw j after which the democratic party sufficiently revenged themselves, and destroyed their antagonists without mercy. The worst of all was, that this example once set, the several states of Greece \ felt in their turns the like commotions, which were al¬ ways heightened by agents from Sparta and Athens j the former endeavouring to settle aristocracy, and the latter democracy, wherever they came. I2(j While the Athenians were thus engaged in a war Athenians wherein they were already overmatched, they foolishly engage in engaged in anew one, which in the end proved morea"!ar fatal than all the rest. The inhabitants of Sicily were ,CI split into two factions $ the one called the Doric, at the head of which was the city of Syracuse ; the other the Ionic, which owned the Leontines for their chiefs : the latter perceiving themselves too weak without fo¬ reign aid, sent one Gorgias, a celebrated oratoi’, to apply to Athens for relief 5 and he by his fine speeches so captivated the giddy and inconstant Athenians, that they ran headlong into a war which they were unable to maintain while engaged with all the Peloponnesi¬ ans. Enticed by this new prospect, therefore, and grasping at the conquest of Sicily, as well as of all Greece, they sent a fleet to the assistance of the Le¬ ontines, under the command ofLachetes and Chabrias; and they were no sooner sailed than another fleet for the same purpose was begun to be fitted out. All this time the plague continued to rage with great violence at Athens, cutting off this year 4000 citizens, be¬ sides,. A T T I O A. ''-7 Sixth year. izS Seventh yea'-, Pylus forti¬ fied by the Athenians 129 Besieged. 130 Spartan fleet de¬ stroyed. Treachery of the Athenians. 132 They at¬ tack SphaC' teria. *33 Cleon the orator ap¬ pointed general. sides a much greater number of the meaner sort of people. The sixth year of the Peloponnesian war was remark¬ able for no great exploit: Agis the son ot Archida- mus, king of Sparta, assembled an army in order to invade Attica, but was prevented from so doing by many great earthquakes which happened throughout Greece. The next year, however, he entered Attica with his army, while the Athenians on their part sent a fleet under the command of Demosthenes, to infest the coasts of Peloponnesus. As this fleet passed by La¬ conia, the commander took notice that the promonto¬ ry of Pylus, which was joined to the continent by a narrow neck of land, had before it a barren island a- bout two miles in circumference, in which, however, there was a good and safe port, all winds being kept off by the headland, or by the isle. These advantages made him apprehend, that a garrrison left here would give the Peloponnesians so much trouble, that they would find it more advisable to protect their own coun¬ try than to invade that of their neighbours. Accord¬ ingly, having raised a strong fortification, he himself with five ships staid to defend it, while the rest of the fleet proceeded on their intended expedition. On the news of this event, the Peloponnesian army immedi¬ ately returned to besiege Pylus. When they arrived before the place they took possession of the harbour, and then caused a chosen body of Spartans take posses¬ sion of the island of Sphacteria, after which they at¬ tacked the fort with great vigour. Demosthenes and his garrison defended themselves with great valour j and an Athenian fleet arriving very seasonably, offer¬ ed battle to the Peloponnesian fleet. This being re¬ fused, the Athenians boldly sailed into the harbour, broke and sunk most of the vessels therein, after which they besieged the Spartans in Sphacteria. The Pelo¬ ponnesians now began to treat with their enemies, and a truce was concluded during the time that negocia- tions were carried on at Athens. One of the articles of this truce was, that the Peloponnesians should deli¬ ver up all their ships, on condition of having them punctually returned in case the treaty did not take ef¬ fect. The Athenians having heard the Spartan am¬ bassadors, were inclined to put an end to this destruc¬ tive war : but Cleon, one of their orators, a warm and obstinate man, persuaded his countrymen to insist on very unreasonable terms ; upon which the ambassadors returned, and by doing so put an end to the truce. The Peloponnesians then demanded their vessels j but the Athenians refused to deliver them, under pretence of their having broke the truce. Hostilities being thus recommenced on both sides, ■the Lacedaemonians attacked the Athenians at Pylus, while the latter attacked the Spartans at Sphacteria. The Spartans, though but a handful of men, and under every imaginable discouragement, behaved with such bravery, that the siege proceeded very slowly, so that the people of Athens became very uneasy. They be¬ gan then to wish they had embraced the offers of the Spartans, and to rail vehemently against Cleon, who, to excuse himself, said it would be easy for the gene¬ ral of the forces they were at that time sending to at¬ tack the Spartans in the isle, and reduce them at once. Nicias, who had been appointed to this command, re¬ plied that if Cleon believed he could, do such great things he would do well to go thither in person : the Att|ca latter imagining this only meant to try him, said he —— was ready to go with all his heart; whereby Nicias catched him, and declared that he had relinquished his charge. Cleon thereupon said, that he was no gene¬ ral j but Nicias told him that he might become one j and the people, pleased with the controversy, held the orator to his word. Cleon then advancing, told them he was so little afraid of the enemy, that, with a very inconsiderable force, he would undertake, in conjunc¬ tion with those already at Pylus, to bring to Athens the Spartans who gave them so much trouble in 20 days. The people laughed at these promises : however, t they furnished him with the troops he desired ; and to He takes their surprise, Cleon brought the Spartans prisoners to die place Athens within the time appointed. This summer, likewise, an Athenian fleet was sent End of di to Sicily, with instructions to put in at Corcyra, and Core.ynan assist the government against the Lacedsemonian fac-se tion which still subsisted in that island. This they ef¬ fectually performed ; for by their means the exiles fell into the hands of the other party : these they imprison¬ ed ; and then drew them out by 20 at a time, to suffer death, which was inflicted with all the circumstances of cruelty that party-rage could suggest. When only 60 remained, they entreated the Athenians to put them to death, and not to deliver them up to their country¬ men ; but upon this the Corcyrians surrounded the place where they were confined, endeavouring to bury them under their darts j upon which the unhappy cap¬ tives all put an end to their own lives. In the eighth year Nicias reduced the isle of Cythe- EiAth ra on the coast of Laconia j as likewise Thyrsea, on year, the confines of that country. The latter had been Success4 given to the AEginetans when expelled from their own tlie At'ie‘ country by the Athenians : and they were now con¬ demned to death, as inveterate enemies of the Atheni¬ an state and nation.—In Sicily, one Hermocrates of Syracuse persuaded all the inhabitants of the island to adjust their difierences among themselves; upon which the Athenian generals returned home, and for so doing two of them were banished, and the third sentenced to pay a heavy fine. The Athenians next laid siege to Megara under the conduct of Hippocrates and Demosthenes ; but Brasi- das a Spartan general coming to its relief, a battle en¬ sued, by which, though neither party got the better, the Lacedaemonian faction prevailed in Megara, and many who favoured the Athenians were forced to with- party [ire draw. After this, such as had been banished for ad-vails in hering to the Lacedaemonians were allowed to return, on Megars. their taking an oath to forget what was past, and attempt nothing that might disturb their country. As soon as they were settled, however, they forgot their oath ; and causing 100 of those who were most obnoxious to be ap¬ prehended, forced the people to condemn them to death. They then changed the whole form of government, in¬ troduced an oligarchy, and possessed themselves of the supreme power. ^5 In Boeotia some commotions were raised in favour of Athenia^ the Athenians; but their generals Hippocrates and lose their Demosthenes being defeated by the opposite party, allPower.am hopes ceased of the Athenian power being established ®ce0 in Bceotia. In the mean time Brasidas reduced the ci¬ ty of Amphipolis, which greatly alarmed the Atheni¬ ans, Attica. *3P Ninth year A truce concluded md broken. 140 'Icon de- eated and :illed by Jrasida'. 141 fifty :ars peace 141 ew dis. intents. ATT arts, tvlio thereupon sent netv supplies of men, money, and ships to the Macedonian coast j hut all their care could not prevent a great desertion from their interest in those parts, where the conduct and valour of Brasidas carried all before him. In the ninth year, the Spartans made new proposals of peace, which the Athenians were now more inclined to accept than formerly j and finding their affairs very much unsettled by the loss of Amphipolis, a truce for a year was quickly agreed on, while negociations were in the mean time carrying on for a general peace. This pacific scheme, however, was very soon over¬ thrown by the following accident in Thrace. The ci¬ ty of Scione, and that of Menda, revolted to Brasi¬ das ; who, knowing nothing of the truce, sought to draw over Potidaea also. The Athenians, pretending that Scione revolted two days after the truce was con¬ cluded, made heavy complaints, asserting that this was a breach of the truce, and that both it and Menda should be restored to them. This not being effected by negociations, an army was sent against the two ci¬ ties by which Menda was reduced ) but Scione ma¬ king an obstinate defence, the siege was turned into a blockade. In the tenth year Brasidas made an attempt upon Po- tidaea j which having failed, the Athenians began to re¬ cover some courage. The truce expiring on the day of the Pythian games, Cleon persuaded the Athenians to send an army into Thrace under his own command. It consisted of 1200 foot and 300 horse, all Athenian citi¬ zens, who embarked on board 30 galleys. Brasidas had an army much inferior 5 but observing that the A- thenian general was become caredess, and neglected dis¬ cipline, he attacked him. In this engagement Cleon was killed, and the Athenians were defeated with the loss of 600 men, while the Spartans lost only seven ; hut among these was their brave commander Brasidas, whose death affected them almost as much as the loss of their army did the Athenians. As the death of Cleon deprived the Athenians of 'one of their best speakers, and one who had been very industrious in promoting the war, they were now much more disposed than formerly to hearken to terms of ac¬ commodation. Amongst the Spartans, too, there was a party, at the head of whom was Plistonax their king, who earnestly wished for peace j and as Nicias labour¬ ed no less assiduously at Athens to bring about this de¬ sirable event, a peace was at last concluded for fifty years between the two nations. The conditions were, that a restitution of places and prisoners should be made on both sides $ excepting that Nisaea should remain to the Athenians, who had taken it from the Megarians, and that Plataea should continue with the Thebans, be¬ cause they absolutely would not give it up. The Boeo¬ tians, Corinthians, and Megarians, refused to be in¬ cluded in this peace : but the rest of the allies yielded to it $ and it was accordingly ratified, receiving the name of the Nician peace, from Nicias who had so vi¬ gorously promoted it. By this means, however, tranquillity was far from being restored, buch of the states of Peloponnesus as were dissatisfied, began immediately to league among themselves, and to set on foot a new confederacy, the head of which was to be the state of Argos. The La¬ cedaemonians, too, found it impossible to perform ex- Vol. III. Part I. f 241 Attica. I C A. actly the articles of agreement j the city of Amphipolis, in particular, absolutely refused to return under the A- thenian government; for which reason the Athenians refused to evacute Pylus. In the winter, new negoci¬ ations were entered into on all sides, but nothing deter¬ mined, and universal murmuring and discontent took place. These discontents were not a little heightened Heightened by AScibiades, who now began to rival Nicias, and, by Aid. perceiving the Lacedaemonians paid their court mostly blades, to his rival, took all opportunities to incense his coun¬ trymen against that nation. Nicias, on the other hand, who wished for nothing so much as peace, used all his endeavours to bring about a reconciliation. The arti¬ fices of Alcibiades, however, added to the turbulent and haughty disposition of both nations, rendered this im¬ possible ; so that though Nicias went on purpose to Sparta, he returned without doing any thing. Alcibiades having thus disposed every thing accord-His ntea- ing to his wishes, and a war being inevitable, he began sures for to take the most prudent methods for preserving histlle sa.fet-v country in safety. With this view he entered into aof Allici- league for 100 years with the Argives, which he hoped would keep the war at a distance ; he next passed over into the territories of Argos, at the head of a consider¬ able army ; and laboured, both at that city and at Pa- trae, to persuade the people to build walls to the sea, that so they might the more easily receive assistance from the Athenians. But though great preparations for war were now made, nothing was undertaken this year; only the Argives thought to have made themselves mas¬ ters of Epidaurus, but were hindered by the Lacedae¬ monians putting a garrison into it. The next year (the 14th after the Peloponnesian war Fourteenth was first begun) a Spartan army, under the command year. War of Agis, entered the territory of Argos, where the con- renewed, federate army lay; but just as the engagement was about to begin, a truce was suddenly concluded by two of the Argive generals and the king of Sparta. With this neither party was pleased, and both the king and. generals were very ill treated by their citizens. On the arrival of some fresh troops from Athens, therefore, the I4e6 the aboli- up such high demands in the king of Persia’s name, ^tlica that the Athenians of themselves broke oft' the treaty, —L and thus Alcibiades preserved the friendship of both parties. Pisander having engaged the army at Samos in his scheme of overturning democracy, that form of go¬ vernment was abolished first in the cities subject to x_^ Athens, and lastly in the capital itself. Pisander’s new New form scheme was, That the old form ol government should g°vei'n- be totallv dissolved : that five prytanes should be elect-"jf"1 esta‘ ed : that these five should choose too : and that each u IsIiC ‘ of the hundred should choose three: that the 400 thus elected should become a senate with full power ; but should occasionally consult with 5000 of the most weal¬ thy citizens, who should thenceforward he esteemed on\y the people; and that no authority should remain with the lowest class. Though the people were not very fond of this change, those who conducted it, being men of great parts, found means to establish it by force ; for when the people were gone out of the city to their ordinary employments, the 400, hav¬ ing each a dagger concealed under his vest, attend¬ ed by a guard of 120 men, entered the senate house, dissolved the old senate, and without ceremony turn¬ ed them out; after which the commons, not knowing whom to submit to, or to whom to apply, made no op¬ position. The first step of the new governors was to destroy all tlieir enemies ; who, however, were not very nu¬ merous, so that little blood was shed. They next sent ambassadors to Agis to sue for peace ; but he, taking for granted that the Athenians would never defend an oligarchy, gave no answer to the ambassadors, but im¬ mediately marched towards the capital with a design to attack it. On his arrival, hov/ever, he was quickly convinced of his mistake, being repulsed with loss, and obliged to retire to his old post. In the mean time the Athenian army declared again The army for a democracy ; and having recalled Alcibiades, in-.declare for vested him with full power, and insisted on his imme-a^emo^ diate return to Athens to restore the ancient £overn‘ ment. This measure he refused to comply with, and^i^cs. persuaded them to stay where they were, in order to save Ionia : he also prevailed on them to allow some deputies, who had been sent from the new gover¬ nors of Athens, to come and deliver their message. To these deputies Alcibiades replied, that they should immediately return to Athens, and acquaint the 400, that they were commanded immediately to resign their power and restore the senate ; hut that the 5OCO might retain theirs, provided they used it with mode¬ ration. 155 By this answer the city was thrown into the utmost Great con- confusion ; but the new government party prevailing, ambassadors were despatched to Sparta with orders to procure peace on any terms. This, however, was not to he effected ; and Phrynicus, the head of the em¬ bassy, and likewise of the new government party, was murdered on his return. After his death, Theramenes, the head ol the other party, seized the chiefs of the 400 ; upon which a tumult ensued that had almost pro¬ ved fatal to the city itself. The mob, however, being at last dispersed, the 400 assembled, though in great fear, and sent deputies to the people, promising to set all things to rights. In consequence of this deputa¬ tion, ATT Utica. tf°n> a day was appointed for convoking a general as- v—v—sembly, and settling the state j but when that day came, news was brought that the Lacedaemonian fleet appear¬ ed in view, and steered directly for Salamis. Thus all was again thrown into confusion ; for the people, in¬ stead of deliberating on the subject proposed, ran in crowds down to the port, and perceiving the Spartans made towards Euboea, a fleet of 36 ships was immedi¬ ately despatched under the command of Thymochares, genian to engage tl'6 enemy. This fleet was utterly defeated, flU de- 22 of the Athenian ships being taken, and most of the sJpyed by others sunk or disabled ; but what was worse, this de- t! Spar- feat was followed by the revolt of all the country of Euboea except Orcus. When these dismal tidings arrived at Athens, every thing was given up for lost; and had the Lacedaemo¬ nians taken this opportunity of attacking the city, they had undoubtedly succeeded, and thus put an end to the war : but being at all times slow, especially in naval affairs, they gave the Athenians time to equip a new fleet, and to retrieve their affairs. One good ef¬ fect of this disaster, however, was the putting an end for a time to the internal dissensions of this turbulent people ; insomuch that Thucydides the historian is of opinion, that the republic never enjoyed so much quiet » as at this time. Edoits of Alcibiades now showed his abilities and inclination Afbiades. serve country in an eminent manner. By his intrigues he so effectually embroiled the Persians and Peloponnesians with each other, that neither party knew whom to trust. Thrasybulus, with 55 ships, gained a victory over the Peloponnesian fleet consisting of 73 : after which he took eight galleys coming from Byzantium j which city had revolted from the Athe¬ nians, but was soon after taken, and the inhabitants se¬ verely fined. The fleet being afterwards joined by Al¬ cibiades, nine more or the Peloponnesian galleys were taken, the Halicarnassians were constrained to pay a large sum ot money, and Cos was strongly fortified : which transactions ended the 21st year of the Pelo¬ ponnesian war. In the succeeding years of this famous war, the Athenians had at first great ads'antages. Thrasybulus gained a signal victory at sea j and Alcibiades gained two victories, one by sea and another by land, in one I •-$ day ; took the whole Peloponnesian fleet, and more T Spar- sP0,-l than his men could carry away. The Spartans ta;i sue were now humbled in their turn, and* sued for peace ; fo >eace. but the Athenians were so intoxicated with their suc¬ cess, that they sent back the ambassadors without an an- swer • which they soon had sufficient reason to repent T!y take ^l.ie ^ginning of the Athenian misfortunes was Pills. the taking of Pylus by the Spartans. The Athenians had sent a fleet under the command of one Auytus to its defence: but he was driven back by contrary winds ; upon which he was condemned to death, be¬ cause he could not cause the wind blow from what quarter he pleased : this sentence, however, was re¬ mitted on his paying a vast sum of money. This mis¬ fortune was quickly followed by another. The Me- garians surprised Nysaja; which enraged the Athe¬ nians so much, that they immediately sent an army into tnat country, who defeated the Megarians who opposed them with great slaughter, and committed horrid deva¬ stations. I C A. 243 These misfortunes as yet, however, were overbalan* Attica, ced by the great actions of Alcibiades, Thrasybulus,v——' and Theramenes. When Alcihiades returned, he .,(?0 brought with him a fleet of 200 ships, and such a load ^n^^’a^es of spoils as had never been seen in Athens since the thens in conclusion of the Persian war. The people left their triumph, city destitute, that they might crowd to the port, to behold Alcibiades as he landed j old and young blessed him as he passed ; and next day when he made a ha¬ rangue to the assembly, they directed the record of his banishment to be thrown into the sea, absolved him from the curses he lay under, and created him general with full power. Nor did he seem inclined to indulge I(,[ himself in ease, but soon put to sea again with a fleetHeisdis- of 100 ships. He had not been long gone, however, graced, before all this was forgot. Alcibiades sailed to the Hellespont with part of his fleet, leaving the rest un¬ der the command of Antiochus his pilot, but with strict orders to attempt nothing.before his return. This command the pilot paid no regard to, but provoked Lysander the Lacedaemonian admiral to an engage¬ ment, and in consequence of his temerity was defeated with the loss of 15 ships, himself being killed in the engagement. On the news of this defeat Alcibiades returned, and endeavoured to provoke the Lacedaemo¬ nians to a second battle ; but this Lysander prudently declined j and in the mean time, the Athenians, with unparalleled ingratitude and inconstancy, deprived Al¬ cibiades of his command, naming ten new generals in his room. 162 This was the last step the Athenians had to take forTheAthe- perfecting their ruin. Conon, who succeeded to the1113113 S^.11 command, was defeated by Callicratides, Lysander’s successor; but being afterwards strongly reinforeed,pUt six of the Lacedaemonians were entirely defeated with the loss their gene- of 77 ships. Such a victory might at this time have™1® 5° inspired the Athenians with some kind of gratitude to-deat wards the generals who gained it ; but instead of this, on pretence of their not having assisted the wounded during the engagement, eight of them were recalled j two were wise enough not to return ; and the six who trusted to the justice of their country were all put to death. i6. The next year Lysander was appointed commander They are of what fleet tiie Peloponnesians had left, with which utterly de- he took Thasus and Lampsacus. Conon was despatch-teate^ by ed against him with 180 ships, which being greatly Lysandci! ? superior to Lysander’s fleet, that general refused to come to an engagement, and was blocked up in the river iEgos. While the Athenians lay there, they grew quite idle and careless ; insomuch that Alcibiades, who had built a castle for himself in the the neighbour¬ hood, entreated them to be more on their guard, as he well knew Lysander’s abilities. They answered, that they wondered at his assurance, who was an exile and a vagabond, to come and give laws to them ; telling him, that if he gave them any farther trouble, they would seize and send him to Athens. At the same time they looked on victory as so certain, that they consulted what they should do with their prisoners ; which, by the advice of Philocles their general, was to ■ cut off all their right hands, or, according to Plutarch, their right thumbs ; and Adiamantus, one of their of¬ ficers, rendered himself very obnoxious by saying, that such idle discourse did not become Athenians. The H h 2 consequences 244 Attica. T I C A. 164 who takes Athens. Terms of peace. 166 The thirty tyrants. 167 Critias ami Therame- nes, their opposite characters. consequences of such conduct may be easily imagined. ' Lysander fell unexpectedly upon them, and gained a most complete victory 5 Conon, with eight galleys only, escaping to Cyprus 5 after which Lysander re¬ turned to Lampsacus, where he put to death Philocles with 3000 of his soldiers, and all the officers except Adiamantus. This execution being over, he reduced all the cities subject to Athens ; and with great civi¬ lity sent home their garrisons, that so the city might be overstocked with inhabitants, and destitute of pro¬ visions, when he came to besiege it j which he did soon after by sea, while Agis, with a great army, invested it by land. For a long time the Athenians did not so much as desire a peace ; but at last were forced to send depu¬ ties to Agis, who sent them to Sparta, where no terms could be granted except they consented to demolish their walls. They next sent to Lysander, who after a long attendance referred them to,Sparta j and thither Theramenes with some other deputies was immediately sent. On their arrival, they found the council of the confederates sitting, who all except the Spartans gave their votes that Athens should be utterly destroyed ; but they would not consent to the ruin of that city, which had deserved so well of Greece. On the return of Theramenes, peace was concluded, on condition that the long walls and the fortifications of the port should be demolished j that they should give up all their ships but 12, receive all they had banished, and follow the fortune of the Lacedaemonians. These se¬ vere terms were punctually executed. Lysander caused the walls to be pulled down, all the music in his army playing, on that very day of the year on which they had beat the Persians at Salamis. He likewise esta¬ blished an oligarchy expressly against the will of the people } and thus the ruin of Athens ended the 27th year of the Peloponnesian war, and the 404th before Christ. As soon as Lysander had demolished the long walls, and the fortifications of the Piraeus, he constituted a council of thirty, with power, as was pretended, to make laws, but in truth to subjugate the state. These are the persons so famous in history, under the title of t/ie thirty tyrants. They were all the creatures of Lysander ; who, as they derived their rise from conquest and the law of the sword, exercised their offices in a suitable manner; that is, with the highest testimonies of pride, insolence, and cruelty. Instead of making laws, they governed without them ; appointed a senate and magistrates at their will j and, that they might do all things without danger of controul, they sent for a garrison from Lace- dsemon ; which was accordingly granted them, under the command of Callidius, upon their promise to pay the soldiers regularly. One of the first steps they took was to punish all informers ; which, though severe, was po¬ pular; but when, through flattery and bribes, they had wholly drawn over Callidius to their party, they suffered bad men to live in quiet, and turned their rage against the good. Critias and Theramenes were at the head of the thirty, men of the greatest power and abilities in Athens. The former was ambitious and cruel with¬ out measure ; the latter was somewhat more merciful : the former pushed on all the bloody schemes framed by bis confederates; and carried into execution many of his own ; the latter always opposed them, at first with Attica, moderation, at last with vehemence. He said, that ■ power was given them to rule, and not to spoil, the commonwealth ; that it became them to act like shep¬ herds, not like wolves ; and that they ought to be* ware of rendering themselves at once odious and ridi¬ culous, by attempting to domineer over all, being such a handful of men as they were. The rest, disliking much the former part of his discourse, catched hold of the lat¬ ter, and immediately chose out 3000, whom they made the representatives of the people, and to whom they granted this notable privilege, that none of them should be put to death but by judgment of the senate, thereby openly assuming a power of putting any other of the Athenian citizens to death by their own authority. A glorious use they made of this new-assumed privilege; for as many as they conjectured to be no friends to the government in general, or to any of themselves in par¬ ticular, they put to death, without cause, and without mercy. Theramenes openly opposing this, and abso¬ lutely refusing to concur in such measures, Critias ac¬ cused him to the senate as a man of unsteady princi¬ ples, sometimes for the people, sometimes against them, always for new things and state-revolutions. Thera¬ menes owned, that he had sometimes changed his mea¬ sures, but alleged that he had always done it to serve the people. He said that it was solely with this view he made the peace with Sparta, and accepted the office of one of the thirty : that he had never opposed their measures while they cut off the wicked ; but when they began to destroy men of fortune and family, then he owned he had differed with them, which he conceived to be no crime against the state. ,55 While Theramenes was speaking, Critias withdrew, Thera- perceiving that the senate were thoroughly convinced ofmene,Put the truth of what Theramenes had said : but he quick-t0 (^eat*L ly returned with a guard, crying out, that he had struck Theramenes’s name out of the list of the 3000 ; that the senate had, therefore, no longer cognizance of the cause, when the thirty had already judged and con¬ demned him to death. Theramenes perceiving that they intended to seize him, fled to the altar, which was in the midst of the senate-house, and laying his hands thereon, said, “ I do not seek refuge here be¬ cause I expect to escape death, or desire it; but that, tearing me from the altar, the impious authors of my murder may interest the gods in bringing them to speedy judgment, and thereby restore freedom to my country.” The guards then dragged him from the altar, and car¬ ried him to the place of execution, where he drank the poison with undaunted courage, putting the people in mind with his last breath, that as they had struck his name out of the 3000, they might also strike out any of theirs. His death was followed by a train of mur¬ ders, so that, in a short time, 60 of the worthiest and most eminent citizens of Athens fell by the cruelty of the thirty. Among these, the most pitied was Ni- ceratus the son of Nicias; a man universally beloved for his goodness, and universally admired for his vir¬ tues. As for the Spartans, they, losing their former generosity, were extremely pleased'with these things, and, by a public decree, commanded that such as fled from the thirty tyrants should be carried back bound to Athens : which extraordinary proceeding frightened all Greece ; but the Argives and Thebans only had courage ATT Auica. courage to oppose it: the former received the Athenian exiles with humanity and kindness, the latter punished with a mulct such of their citizens as did not rise and rescue the Athenian prisoners, who in pursuance of the Lacedaemonian decree were carried bound through their territories, Thrasybulus, and such as with him had taken shelter in the Theban territory, resolved to hazard every thing, rather than remain perpetual exiles from their country j and though he had but 30 men on whom he could de¬ pend, yet considering the victories he had heretofore ob- 1S9 tained in the cause of his country, he made an irruption ira*ybu- jn^0 Attica, where he seized Phyla, a castle at a very ifS]aZeS snia^ distance from Athens, where in a very short space his forces wei’e augmented to 700 men j and though the tyrants made use of the Spartan garrison in their endeavours to reduce him and his party, yet Thrasybu¬ lus prevailed in various skirmishes, and at last obliged them to break up the blockade of Phyla, which they had formed. The thirty and their party conceiving it very advantageous for them to have the possession of Eleusina, marched thither, and having persuaded the people to go unarmed out of their city, that they might number them, took this opportunity most inhu¬ manly to murder them. The forces of Thrasybulus in¬ creasing daily, he at length possessed himself of the Pi¬ raeus, which he fortified in the best manner he could j but the tyrants being determined to didve him from thence, came down against him with the utmost force they could raise. Thrasybulus defended himself with great obstinacy j and in the end they were forced to re¬ treat, having lost before the place not only a great num- titias°kill-^er their men, but Critias the president of the thirty, another of the same body, and one who had been a cap¬ tain of the Piraeus. When they came to demand the dead from Thrasy¬ bulus, in order for their interment, he caused a crier he had with him to make a short speech in a very loud voice to the people, entreating them to consider, that as they were citizens of Athens without, so those against whom they fought, and those who sought to preserve themselves within the fort, were Athenian citizens also 5 wherefore, instead of thinking how to ruin and destroy their brethren, they ought rather to consult how all differences might be composed, and especially ought to lid themselves of those bloody tyrants, who, in the short time they had had the administration in their hands, had destroyed more than had fallen in the Pelo¬ ponnesian war. The people, though moved by these dis- vji courses, differed among themselves j the consequence of P* tyrants which was, that they expelled the thirty, and chose ten ' ed' men out of each tribe to govern in their stead, where¬ upon the tyrants retired to Eleusina. The citizens, however, though they changed the government, made no agreement with those in the Piraeus; but sent away deputies to Sparta, as did all the tyrants from Eleu¬ sina, complaining, that the Athenians had revolted, r and desiring their assistance to reduce them. The Spar- -Hlpt Ot * 1 l « r t||Spar. tans sent thereupon a large sum 01 money to encourage store- their confederates, and appointed Lysander commander - A- in chief, and his brother to be admiral *, resolving to ^iUme' Sena sea and land forces to reduce Athens a second time ; intending, as most of the Greek states suspected, to add it now to their own dominions. It is very pro- n ( I G A. 245 bable that this design of theirs would have taken effect, Attica, if Pausanias king of Sparta, envying Lysander, had not resolved to obstruct it. With this view, he procured another army to be raised against the Athenians, of which himself had the command, and with which he marched immediately to besiege the Piraeus. While hs lay before the place, and pretended to attack it, he en¬ tered into a private correspondence with Thrasybulus, informing him what propositions he should make in order to force the Lacedaemonians, who were suspected by their allies, to grant them peace. 175 The intrigues of Pausanias had all the success heHowfru*-’ could wish. The Ephori who were with him in the camptrate than Sylla. Tliis was Alaric king of the Goths : who, M—i under the emperors Arcatlius and Horiorius, overran Greece and Italy, sacking, pillaging, and destroying. Then the Peloponnesian towns were overturned, Arca¬ dia and Lacedaemon were laid waste, the two seas by the isthmus were burnished with the flames of Corinth, and the Athenian matrons were dragged in chains by barbarians. The invaluable treasures of antiquity, it is related, were removed j the stately and magnificent structures converted into piles of ruin ; and Athens was stripped of every thing splendid or remarkable. Syne- sius, a writer of that age, compares the city to a victim of which the body had been consumed, and the hide only remained. “ After this event, Athens became an unimportant place, and as obscure as it once had been famous. We read that the cities of Hellas were put into a state of defence by Justinian, who repaired the walls, which at Corinth had been subverted by an earthquake, and at Athens and in Bceotia were impaired by age $ and here we take a long farewell of this city. A chasm of near 700 years endues in its history, except that, about the year XI30, it furnished Roger the first king of Sicily with a number of artificers, whom he settled at Palermo, where they introduced the culture of silk, which then passed into Italy. The worms had been brought from India to Constantinople in the reign of Justinian. “ Athens, as it rvere, re-emerges from oblivion in the 13th century, under Baldwin, but besieged by a general of Theodorus Lascaris, the Greek emperor. It was taken in 1427 by Sultan Morat. Boniface, mar¬ quis of Montferrat, possessed it with a garrison j after whom it was governed by Delves of the house of Ar- ragon. On his death, it was seized, with Macedonia, Thessaly, Boeotia, Phocis, and the Peloponnesus, by Bajazet 5 and then, with the island Zante, by the Spa¬ niards of Catalonia in the reign of the Greek emperor Andronicus Palseologus the elder. These were dispos¬ sessed byReinerius Acciaioli, a Florentine; who,leaving no legitimate male issue, bequeathed it to the state of Ve¬ nice. His natural son, Antony, to whom he had given Thebes with Boeotia, expelled the Venetians. He was succeeded in the dukedom by his kinsman Nerius, who was displaced by his own brother named dntomj, but recovered the government when he died. Nerius, lea¬ ving only an infant son, was succeeded by his wife. She was ejected by Mahomet on a complaint from Francus son of the second Antony, who confined her at Me- gara, and made away with her ; but her son accusing Sytl him to Mahomet the Second, the Turkish army under 'ink Omar advanced, and he surrendered the citadel in 1455 j the Latins refusing to succour him unless the Athe¬ nians would embrace their religious tenets. Mahomet, it is related, when he had finished the war with the despot of the Morea, four years after, surveyed the city and Acropolis with admiration. The janizaries informed him of a conspiracy; and Francus Acciaioli, who re¬ mained lord of Bceotia, was put to death. In 1464 the Venetians landed at the Piraeus, surprised the city, and - carried off their plunder and captives to Euboea. “ It is remarkable, that after these events Athens was again in a manner forgotten. So lately as about the middle of the 16th century, the city was commonly be¬ lieved to have been utterly destroyed, and not to exist, except a few hqts of poor fishermen. Crusius, a learned I C A. 247 and inquisitive German, procured more authentic in- Attica, formation from his Greek correspondents residing in v — Turkey, which he published in 1584, to awaken curio¬ sity and to prompt farther discoveries. One of these letters is from a native of Naupiia, a town near Argos in the Morea. This writer says that he had been olten at Athens, and that it still contained many things wor¬ thy to be seen, some of which be enumerates, and then subjoins ; “ But why do I dwell on this place ? It is as the skin of an animal which has been long dead.” It now remains to give some idea of the charac¬ ter, government, and religion of this once so famous people. _ . The Athenians, says Plutarch, are very subject to character violent anger ; but they are soon pacified. They are 0f the an- likewise easily impressed with humanity and compassion, cient Athe- That this was their temper, is proved by many lustori-nians* cal examples. We shall produce a few. The sentence of death pronounced against the inhabitants of Mity- lene, and revoked the next day : The condemnation of Socrates, and that of the ten chiefs, each followed by quick repentance and most pungent grief. The minds of the same people, adds Plutarch, are not formed for laborious researches. They seize a sub¬ ject, as it were, by intuition ; they have not patience and phlegm enough to examine it gradually and mi¬ nutely. This part of their character may seem sur¬ prising and incredible. Artisans, and other people of their rank, are in general slow of comprehension. But the Athenians of every degree were endowed with an inconceivable vivacity, penetration, and deli¬ cacy of taste. Even the Athenian soldiers could re¬ peat the fine passages of the tragedies of Euripides. Those artisans and those soldiers assisted at public de¬ bates, were bred to political affairs, and were equally acute in apprehension and in judgment. We may in¬ fer the understanding of the hearers of Demosthenes from the genius of his orations, which were laconic and poignant. As their inclination, continues Plutarch, leads them to assist and support people of low condition, they like discourse seasoned with pleasantry, and productive of mirth. The Athenians patronize people of low de¬ gree ; because from them their liberty is in no clanger, and because such patronage tends to support a derno- cratical constitution. They love pleasantry ; which turn of mind proves that they are a humane social people, who have a taste for raillery and wit, and are not soured with that reserve which marks the despot or the slave. They take pleasure in hearing themselves praised ; but they can likewise patiently bear raillery and cen¬ sure. We know with what art and success Aristo¬ phanes and Demosthenes applied their praise and their irony to the Athenian people. When the republic enjoyed peace, says the same Plutarch in another place, it encouraged the adulation of its orators : but when it had important affairs to discuss, when the state was in danger, it became serious; and preferred to its eloquent sycophants, the honest orators who opposed its follies and its vices ; such ingenious and bold patriots as a Pericles, a Phocion, and a Demos¬ thenes. The Athenians, continues Plutarch, often make their governors tremble, and show great humanity to their v 24B ATT Attica, tlieir enemies. They were very attentive to the infer- —y~—' mation and instruction of those citizens who were most eminent for their policy and eloquence *, but they were on their guard against the superiority of their talents 5 they often checked their boldness, and repressed their exuberant reputation and glory. T-hat this was their temper, we are convinced by the ostracism : which was established to restrain the ambition of those who had great talents and influence, and which spared neither the greatest nor the best men. he detestation of ty¬ ranny and of tyrants, which was inherent in the Athe¬ nians, rendered them extremely jealous of their privi¬ leges, made them zealous and active in defence of their liberty, whenever they thought it was violated by men in power. As to their enemies, they did not treat them with rigour. They did not abuse victory by a brutal inhu¬ manity to the vanquished. The act of amnesty, which they passed after the usurpation of the 30 tyrants, proves that they could easily forgive injuries. It was this mildness, this humanity of disposition, which made the Athenians so attentive to the rules of politeness and decorum. In their war with Philip, having sei¬ zed one of his courtiers, they read all the letters he bore, except one from Olympias to her husband, which they sent back unopened. Such was their ve¬ neration of love and conjugal secrecy j those sacred rights, which no enmity, no hostility, warrants us to violate 1 The views of conquest cherished by a small republic, were extensive and astonishing ; but this people, so great, so ambitious in their projects, were, in other respects, of a different character. In the expences of the table, in dress, in furniture, in houses, in short, in private life, they were frugal, simple, modest, poor; but sumptuous and magnificent whenever the ho¬ nour of the state was concerned. Their conquests, their victories, their riches, their connections with the inhabitants of Asia Minor, never reduced them to luxury, to riot, to pomp, to profusion. Xenophon remarks, that a citizen was not distinguished from a slave by his dress. The wealthiest citizen, the most renowned general, was not ashamed to go himself to market. The taste of the Athenians, for all the arts and sci¬ ences, is well known. When they had delivered them¬ selves from the tyranny of Pisistratus, and after this had defeated the vast efforts of the Persians, they may be considered as at the summit of their national glory. For more than half a century afterwards they main¬ tained, without controul, the sovereignty of Greece ; and that ascendant produced a security, which left their minds at ease, and gave them leisure to cultivate every thing liberal or elegant. It was then that Peri¬ cles adorned the city with temples, theatres, and other beautiful public buildings. Phidias, the great sculp¬ tor, was employed as his architect, who, when he had erected edifices, adorned them himself, and added sta¬ tues and basso-relievos, the admiration of every be¬ holder. It was then that Polignotus and Myro paint¬ ed ; that Sophocles and Euripides wrote j and not long after, that they saw the divine Socrates. Human affairs are, by nature, prone to change $ and states, as well as individuals, are born to decay. Jealousy and ambition insensibly fomented wars, and I C A.' success in these wars, as in others, was often various. The military strength of the Athenians was first im¬ paired by the Lacedaemonians ; after that it was again humiliated, under Epaminondas, by the Thebans : and last of all it was wholly crushed by the Macedonian Philip. Nor, when their political sovereignty was lost, did their love of literature and the arts sink along with it. Just at the close of their golden days of empire flou¬ rished Xenophon and Plato, the disciples of Socrates 5 and from Plato descended that race of philosophers called the Old Academy. Aristotle, who was Plato’s disciple, may be said not to have invented a new phi¬ losophy, but rather to have tempered the sublime and rapturous mysteries of his master with method, order, and a stricter mode of reasoning. Zeno, who was himself also educated in the principles of Platonism, only differed from Plato in the comparative estimate of things, allowing nothing to be intrinsically good but virtue, nothing intrinsically bad but vice, and consi¬ dering all other things to be in themselves indifferent. He too and Aristotle accurately cultivated logic, but in different ways ; for Aristotle chiefly dwelt upon the simple syllogism } Zeno upon that which is derived out of it, the compound or hypothetic. Both too, as well as other philosophers, cultivated rhetoric along with logic j holding a knowledge in both to be requi¬ site for those who think of addressing mankind with all the efficacy of persuasion. Zeno elegantly illustrated the force of these twTo powers by a simile taken from the hand : the close power of logic he compared to the fist, or hand comprest: the diffuse power of logic, to the palm, or hand open. The new academy was founded by Arcesilas, and ably maintained by Carneades. From a mistaken imi¬ tation of the great parent of philosophy Socrates (par¬ ticularly as he appears in the dialogues of Plato), be¬ cause Socrates doubted some things, therefore Arcesilas and Carneades doubted all.—Epicurus drew from an¬ other source } Democritus had taught him atoms and a void : by the fortuitous concourse of atoms he fancied he could form a world j while by a feigned veneration he complimented away his gods, and totally denied their providential care, lest the trouble of it should im¬ pair their uninterrupted state of bliss. Virtue he re¬ commended, though not for the sake of virtue, but pleasure ; pleasure, according to him, being our chief and sovereign good. See Aristotle, Epicurus, Plato, Socrates, &c. We have already mentioned the alliance between philosophy and rhetoric. This cannot be thought won¬ derful, if rhetoric be the art by which men are per¬ suaded, and if men cannot be persuaded without a knowledge of human nature : for what but philosophy can procure us this knowledge ? It was for this reason the ablest Greek philosophers not only taught, but wrote also treatises upon rhetoric. They had a farther induce¬ ment, and that was the intrinsic beauty of their lan¬ guage as it was then spoken among the learned and po¬ lite. They would have been ashamed to have deliver¬ ed philosophy, as it has been too often delivered since, in compositions as clumsy as the common dialect of the mere vulgar. The same love of elegance, which made them at¬ tend to their style, made them attend even to the pla¬ ces Attica, ATT itica. ccs where their philosophy was taught. Plato deli¬ vered his lectures in a place shaded with groves, on the hanks of the river Ilissus •, and which, as it once be¬ longed to a person called Academus, was called after his name, the Academy. Aristotle chose another spot ol a similar character, where there were trees and shade 5 a spot called the Lyceum. Zeno taught in a portico or colonnade, distinguished from other buildings of that sort (of which the Athenians had manv) by the name of the Variegated Portico, the walls being decorated with various paintings of Polygnotus and Myro, two capital masters of that transcendant period. Epicurus addressed his hearers in those well known gardens, call¬ ed, after his own name, The gardens of Epicurus. These places of public institution were called among the Greeks by the name of Gymnasia; in which, what¬ ever that word might have originally meant, wei’e taught all those exercises, and all those arts, which tended to cultivate not only the body but the mind. As man was a being consisting of both, the Greeks could not consider that education as complete, in which both were not regarded, and both properly formed. Hence their Gymnasia, with reference to this double end, were adorned with two statues, those of Mercury and of Hercules, the corporeal accomplishments being patronized (as they supposed) by the god of strength, the mental accomplishments by the god of ingenuity. It was for the cultivation of every liberal accom¬ plishment that Athens was celebrated (as we have said) during many centuries, long after her political influence was lost and at an end. She was the place of education, not only for Greeks but for Romans. It was hither that Horace was sent by his father j it was here that Cicero put his son Mar¬ cus under Cratippus, one of the ablest philosophers then belonging to that city. The sects of philoso¬ phers which we have already described, were still ex¬ isting when St 1 aul came thither. We cannot enough admire the superior eloquence of that apostle, in his manner of addressing so intelligent an audience. We cannot enough admire the sublimity of his exordium ; the propriety of his mentioning an altax which he had found there ; and his quotation from Aratus, .one of their well known poets. Nor was Athens only cele¬ brated for the residence of philosophers, and the insti¬ tution of youth : men of rank and fortune found plea¬ sure in a retreat, which contributed so much to their liberal enjoyment. We shall finish this picture of the Athenians by the addition of one object more, to which every one" will admit they have a right; an object which was promi¬ nent and striking, in all their actions and in all their enterprises: We mean their ardent love of liberty. Tins was their predominant quality j the main spring of their government. From the beginning of the Pe£ sian war, they sacrificed every thing to the liberty of Greece. They left, without hesitation, their cities, their houses, to fight at sea the common enemy, from whom they were in danger of servitude. What a glo¬ mus day was it for Athens, when all her allies, growing flexible to the advantageous offers which were made to them by the king of Persia, she replied by Aristides, to the ambassadors of that monarch,—“ That it was impossible for all the gold in the world to tempt the re¬ public of Athens : to prevail with her to sell her liher- Vol, HI. Part I. i I C A. ty, and that of Greece.” ft was by these generous sentiments that the Athenians not only became the bulwark of Greece, but likewise guarded the rest of Europe from a Persian invasion. 249 Attica. Ihese great qualities were blended with great fail¬ ings, seemingly incompatible with patriotism. For the Athenians, notwithstanding their tenacious jealousy of the rights of their country, were a volatile, inconstant, capricious people. ^ Ihere never was a people more attentive to the wor-Religion, snip of the gods than the Athenians. The worship of then principal deities wras diffused over all Greece, and even beyond its limits. Each temple had its particular religious rites : the pomp, the ceremonies, the duration, and the succes¬ sion of the solemn feasts were all appointed by fixed rules. I he worship paid to each divinity, whether public or private, w'as founded on traditions, or on laws constantly obeyed. The feast of Bacchus, the Pana- thenaea, the feast of the mysteries of Eleusis, were ce¬ lebrated according to established rules, most of which were as ancient as the feasts themselves. The old cu¬ stoms, of which the priests were the guardians, were observed in the temples. It is probable that the priests were consulted on affairs in which the worship of a deity was interested, and that their answ'er was decisive. Me are certain that the Eumolpidae had this authority. They were the interpreters of the ancient laws on which the worship of Ceres was founded, its magnificence, and its mode—laws which were not written, as Lysias informs us, but were perpetuated by a constant observa¬ tion. The abuses which had gradually crept into the celebration of those feasts, had given rise to several new regulations ; to that of the orator Lycurgus, for ex¬ ample, and to the law of Solon, which enjoined the senate to-repair to Eleusis on the second day of the feast : but neither these, nor the other particular regu¬ lations which we find in Samuel Petit’s collection of Attic laws, could make a religious code. There was no general system which comprehended all the branches of their religion, which, by combining all its articles, might regulate their belief and conduct, and direct the judges in their decisions. lSr Crimes against religion were only punished as they Crimes a~ affected the state; and consequently they were tried bySainst bli¬ the magistrate. Mere raillery, though somewhat pro-£l0n’ fane, was thought productive ol no worse consequence than offending the ministers of the gods. The Athe-with seve- mans acknowledged no other religion than the heredi-rity. tary public worship; no other gods than those they nad received from their ancestors; no other ceremonies but those which had been established by the laws of the state, and practised by their country from time im¬ memorial. They were only solicitous to preserve this worship, which was closely interwoven with their go¬ vernment, and made a part of its policy. They were likewise attentive to the ceremonial pomp; because or¬ der, the regular vigour of legislation, depends greatly on the awe impressed by externals. But as to the in¬ consistent and monstrous romance of fable, foreign opi¬ nions, popular traditions, and poetical fictions, which formed a religion quite different from that of the state —in it they were very little interested, and allowed every one to think of it as he pleased. This explanation will reconcile a seeming contradic- ^ ^ tioa 250 ATT Attica, tion in the conduct of the Athenians, who gave great license to their poets, and severely punished the ci¬ tizens who were guilty of impiety. Aristophanes, who made as free with the gods as with the great, was applauded by the Athenians. They condemned So¬ crates to death, who revered the Deity, but disapproved the public manner of worshipping him. The life of j'Eschylus was in danger, from a suspicion that he had revealed some of the secrets of Eleusis in one of his pieces. The wit of Aristophanes’s drama was unpu¬ nished. The priests were not confined to the care of the al¬ tars; they who were vested with the sacerdotal dignity, which was only incompatible with professions merely useful and lucrative, might likewise hold the most im¬ portant offices of the commonwealth. This we could prove by a great number of examples ; we shall cite that of Xenophon the illustrious historian and philosopher: he was likewise a famous general, and he was a priest. He was performing the sacerdotal function when he received the news of his son’s death, who was killed at the battle of Mantinea. The sacred ministry was not only compatible with civil offices, but likewise with the profession of arms. The priest and the soldier were often blended. Cal- lias, the priest of Ceres, fought at Platsea. This cu¬ stom was not peculiar to the Athenians. The La¬ cedaemonians, after the battle which we have just men¬ tioned, made three graves for their slain ; one for the priests, one for the other Spartans, and one for the Helots. As the ordinary business of life was incompatible venues, See. with the sacerdotal dignity, the priests had a revenue fixed to their office. We know that a part of the vic¬ tims was their right, and that apartments were assigned them near the temples. But, besides these advantages, they had a salary proportioned to the dignity of their functions, and to the rank of the deities whom they served. Their salary was probably paid from the re¬ venue of the temples. 'Those revenues, which kept the temples in repair, and defrayed the sacrificial expences, were very considerable. They were of many different kinds. A great part of the sacred revenues arose from fines, which individuals were condemned to pay for various ollences ; fines, of which the tenth part was appro¬ priated to Minerva Polias, and the fiftieth to the other gods, and to the heroes whose names their tribes bore. Besides, if the Prytanes did not hold the assemblies conformably with the laws, they were obliged to pay a fine of 1000 drachms to the goddess. If the Proe- dri, i. e. the senators whose office it was to lay before the assembly the matters on which they were to delibe¬ rate, did not discharge that duty according to the rules prescribed to them, they were likewise condemned to pay a fine, which, as the former, was applied to the use of Minerva. By these fines her temple must have been greatly enriched. Besides this revenue, which was the common pro¬ perty ot the gods, and which varied according to the number and degrees of the misdemeanours, the temples had their permanent revenues : We mean the produce of the lands which were consecrated to the deities. We do not here allude to the lands consecrated to the gods, which were never to be cultivated : such as the 3 I C A. territory of Cirrha, proscribed by a solemn decree of Attica the Amphictyons ; the land betwixt Megara and At- -—y-— tica, which was consecrated to the goddesses of Eleu¬ sis, and many others. We would speak only of those which were cultivated, the fruits of which enriched the temples. There were likewise lands belonging to the state, the produce of which was destined to defray the expence of the sacrifices which were offered in the name of the re¬ public. There were likewise first fruits which the pub¬ lic officers levied on all lands, for the use of the gods. All these emoluments made a part of the revenue of the temples. The gods, besides the revenues immediately apper¬ taining to their temples, had gertain rights which were granted them by particular compact. The Lepreatse, for instance, were obliged to pay every year a talent to Olympian Jupiter, on account of a treaty of alliance which they made with the Eleans in one of their wars. The inhabitants of Epidaurus, to obtain leave from the Athenians to cut down olive-trees for statues, which the Pythian priestess had commanded them to make, engaged to send deputies every year to Athens, to oft’er sacrifices in their name to Minerva and to Nep¬ tune. But this prerogative was rather honorary than lucrative. The tenth part of the spoils taken in war was like¬ wise the property of Minerva. Sacred vessels were bought with the eftects of the 30 tyrants. In short, the gods were profited by almost every public accident. But what contributed most to enrich the famous tem¬ ples of Greece, was the money which was constantly brought to them by individuals, in consequence of vows they had made, or to pay for sacrifices which were offered in their names. The credulity of the people was an inexhaustible fund. That credulity en¬ riched the temples of Delos and Eleusis, and supported the magnificence of Delphi. And those immense trea¬ sures which were the fruit of superstition, were often a prey to avarice. These revenues were not deposited with the priests; nor did they expend them. A moderate salary was all their gain ; and to offer sacrifices to the deities whose ministers they were, was all their employment. It is very probable that all the sacred revenues were paid into the hands of officers who were appointed to receive them, and who were to give an account of the discharge of their trust. Nay, we cannot doubt of this, after reading a passage in Aristotle, who, speak¬ ing of the officers ot the temples, expressly mentions those who are intrusted with the money appertaining to the gods. Citizens, without doubt, of approved inte¬ grity, were chosen to this office ; and their duty must have been, to keep the temples in repair and order, and to disburse and keep an account of the ordinary sacred expences. As to the solemn (easts, which were incredibly mag¬ nificent, such as the feast of Bacchus, and the Pana- thenaea, they were celebrated at the expence of the choregus ; i. e. ot the chief of the choir of each tribe ; for each tribe had its poet and its musicians, who sung, emulating each other, hymns in honour of the deity. 1 he richest citizens were appointed chiefs of the dif¬ ferent choirs ; and as their office was very expensive, to indemnify them in some degree, the choregus of 1 Si Priests, tjieir duty 153 Sacred re- ATT y uica. Victorious tribe had the privilege of engraving his ■‘-V—^ name on the tripod which that tribe suspended to the roof of the temple. Ihis office, though ruinous, was eagerly solicited j and naturally, in a republican state. It led to honours, like the curule dignity at Rome ; and it greatly tended to ingratiate its possessor with a people who were more affected with pleasures than with essential services, and who, consequently, would more highly esteem a profuse choregus than a victo¬ rious general. With regard to the fines, which were in the whole, or in part, the property of Minerva and of the other deities, there were at Athens public treasurers appointed to re¬ ceive them. They were ten in number, and they were nominated by lot. They were called Treasurers of the goddess, or Receivers of the sacred money. That money they received in the presence of the senate j and they were empowered to diminish or to annihilate the fine, if they thought it unjust. The statue of Minerva, that of the Victories, and the other invaluable pledges of the duration of the state, were deposited with them. The treasury in which the money consecrated to the gods was kept, was in the citadel, behind the temple of Minerva Polias; and from its situation it was termed Opisthodomus. It was surrounded wiih a double wall. It had but one door, the key of which was kept by the Lpistates, or chief of the Prytanes: his dignity was very considerable; but it lasted only one day. In this treasury a register was kept, in which were written the names of all those who were indebted to the state ; he who owed the smallest fine was not omitted. If the debtors proved insolvent, they were prosecuted with ex¬ treme rigour, and often punished with a cruelty which religion could not excuse ; though the interest of the gods was the motive, or rather the pretext. The sa¬ cred treasurers held a considerable rank among the ma¬ gistrates who received the public finances. Of these magistrates there were many kinds, as there were many *orts of revenues. The Athenian priests did not compose an order di¬ stinct and separate from the other orders of the state. 1 hey did not form a body united by particular laws, under a chief whose authority extended to all his infe¬ riors. The dignity of sovereign pontiff was unknown at Athens; and each of the priests served his particular ' temple, unconnected with his brethren. The temples, indeed, of the principal deities ; those of Minerva, for instance, of Neptune, of Ceres, and of Proserpine, had many ministers; and in each of them a chief presided, who had the title of High Priest. The number of sub¬ altern ministers was in proportion to the rank of the deity ; but the priests of one temple were altogether a separate society from those of another. Thus at Athens there was a great number of high priests, because many deities were worshipped there, whose service required many ministers. 1 he power of each priest was confined to his temple ; and there was no sovereign pontiff, the minister general of the gods, and the president at all the feasts. It naturally follows from this account, that the mi¬ nisters of the gods at Athens were not judges in matters of religion. J hey were neither authorized to take cognizance of crimes committed against the deity, nor to punish them. Their function was to offer sacrifices to the gods, and to entreat their acceptance of the I C A. 251 adorations of the people. But the punishinent of impie- Attica, tv, of sacrilege, of the profanation of mysteries, and of '—1—v— other irreligious crimes, was not entrusted to their zeal. I he priests were not only incapable of avenging crimes against religion by a criminal process ; they even could not, without an express order either from the senate or the people, exercise their right of de¬ voting criminals to the infernal gods. It was in con¬ sequence of a civil sentence pronounced against Alci- biades, that the Eumolpidse launched their anathema against him. It was in virtue of another decree that they revoked their imprecations, when his countrymen wanted his service, and therefore restored him to their favour. Religious causes, according to M. de Bougainville, fell under the jurisdiction of the Heliastee. I he government, though often altered, continued pretty much on the plan established by Solon. 1S4 I he people of Athens w'ere freemen, sojourners, or People di¬ slaves. The citizens, called in Greek Politai, were ve-v'Ae^ ry numerous; but what may seem strange, were as ma- ny in the time of Cecrops as in the most flourishing state of the commonwealth, hardly ever exceeding 20,000. It was Solon who decreed that none should be accounted free but such as were Athenians both by fa¬ ther and mother. After his time it fell into desuetude, till revived by Pericles ; and was again at his instance repealed. After the expulsion of the 30 tyrants, Solon’s law was restored. A person born of a stranger was styled Nothos, a bastard ; whereas the son of a free wo¬ man was called Cnesios, i. e. legitimate. There was in Cynosarges a court of judicature, to which causes of il¬ legitimacy properly belonged; and the utmost care was taken to prevent any from being enrolled Athe¬ nian citizens, who bad not a clear title thereto. The citizens were divided by Cecrops into four tribes : the first called Cecropes, from Cecrops ; the second, Au¬ tochthon, from a king of that name; the third, Actai, from Acteus, another king of Athens, or rather from Acte, which signifies a shore; the fourth, Puralia: these names were altered by Cranaus, and agajn by Ericthonius. In the reign of Erictheus, they were again changed; the soldiers were called Ohlitai, the craftsmen Ergatai, the farmers Georgoi, the graziers and shepherds Adgicorai.: in this state they were when Solon settled the commonwealth,'and appointed the se¬ nate to be composed of 400, 100 out of each tribe. Clystbenes increased the number of the tribes to ten ; and made the senate consist of 500, taking 50 out of each tribe. In succeeding times, two other tribes were added. Each tribe was subdivided into its Demoi or wards : and with respect to these it was that Solon in¬ stituted the public feasts before-mentioned, at which sometimes the whole tribe assembled, sometimes several wards, and sometimes only the inhabitants of one ward. The second sort of inhabitants we mentioned were called Metoicoi, i. e. sojourners; these were persons who lived always at Athens, yet were not admitted free denizens : as for such as did not constantly reside in Athens, they were styled Xenoi; i. e. strangers. The sojourners were obliged to choose out of the citi¬ zens protectors, who were styled Patrons ; they paid services to the state, and besides these an annual tribute of ^2 drachms for every man, and six for every wo¬ man ; but such as had sons, and paid for them, were I i 2 exempted; 252 ATT Attica, exempted. If people fell to poverty, and were not "v—able to pay the tribute, they were seized by the tax- masters, and actually sold for slaves •, which, as Dio¬ genes Laertius tells us, was the fate of Xenocrates the philosopher. The sojourners in Attica were under the same law as those in Athens. As to servants, they were freemen, who through indigency were driven to receive wages, and while they were in this state had no vote in the assembly. As to slaves, they were abso¬ lutely the property of their masters, and as such were used as they thought fit: They were forbidden to wear clothes, or to cut their hair like their masters 5 and, which is indeed amazing, Solon prohibited them to love boys, as if that had been honourable : They were likewise debarred from anointing or perfuming them¬ selves, and from worshipping certain deities : They were not allowed to be called by honourable names j and in most other respects were used like dogs. They stigmatized them at their pleasure, that is, branded them with letters in the forehead and elsewhere. How¬ ever, Theseus’s temple was allowed them as a sanctuary, whither, if they were exceedingly ill used, they might fly, and thereby oblige their owners to let them be transferred to another master. In this and many other respects the Athenian slaves were in a much better con¬ dition than those throughout the rest of Greece : they wrere permitted to get estates for themselves, giving a small premium to their masters, who were obliged to make them free if they could pay their ransom *, thev likewise obtained the same favour from the kindness of their masters, or for having rendered military services to the states. When they were made free, they were obliged to choose patrons 5 and had likewise the privi¬ lege of choosing a curator, who, in case their patrons jg- injured them, was bound to defend them. General as- The general assembly of the people, which Solon sembly of made the dernier resort, was called the Ecclesia ; and the people. cons;sted of all the freemen of Athens, excepting such as were atimoi or infamous. The meetings of these as¬ semblies were either ordinary or extraordinary. The ordinary were such as were appointed by law, the ex¬ traordinary such as necessity required. Of the first there were four in 35 days. In the first assembly they approved or rejected magistrates, heard proposals for the public good, and certain causes. In the second they received petitions, and heard every man’s judge¬ ment on the matters that were before them. In the third they gave audience to foreign ambassadors. The fourth was employed altogether in affairs relating to the gods and their worship. The extraordinary meet¬ ings were appointed by the magistrates when occasion required, whereas to the ordinary assemblies the peo¬ ple came of their own accord. The first were held ei¬ ther in the market-place, in the Pnyx a place near the citadel, or in the theatre of Bacchus : as to the latter, the magistrates who appointed the extraordinary meet- ing appointed also the place where it should be held. If any sudden tempest rose, or any earthquake hap¬ pened, or any sign notoriously inauspicious appeared, the assembly was immediately adjourned, to prevent the people from apprehending unhappy consequences from their deliberations. But if the weather was fair and serene, and nothing.happened out of the ordinary course of things, they proceeded to purify the place where the assembly was held, which was done by sprinkling 2 I C A. it round with the blood of young pigs ; then the crier Attica, made a solemn prayer for the prosperity of the republic,'y—. and that heaven would bestow a happy issue on their counsels and undertakings : he then pronounced a bit¬ ter execration against any who should in that assembly propound what might be disadvantageous to the state. Those ceremonies being over, they proceeded to busi- ness' . 1% There were several magistrates wdio had the oversee- Method of j ing and regulating these assemblies. These were, first, giving their the Epistate, or president of the assembly, who was0P*ni°ns* chosen by lot out of the Proedri: his office was to give the signal for the people’s voting. Next to him were the Prytanes, i. e. a committee of the senate, who of course were present on this occasion : by their order a programma, or scheme of the business to be proposed at the assembly, was previously set up in some public place, that every man might know what business to apply liis thoughts to. The Proedri were nine in num¬ ber, appointed by lots out of all the tribes to which the Prytanes did not belong : they had the right of pro¬ posing to the people what they w'ere to deliberate up¬ on, and their office ended with the assembly j there sat with them assessors, who were to take care that nothing they proposed was detrimental to the common¬ wealth. The first step to business was the crier’s read¬ ing the decree of the senate whereon the assembly was to deliberate j when he had finished this, he made pro¬ clamation in these words : Who of the men above 50 will make an oration .§ When the old men had done speaking, the crier made proclamation again that any Athenian might then offer his sentiments, whom the law allowed so to do ; that is, all such as were above 30 years old, and were not infamous. If such a one rose up to speak, the Prytanes interposed, and bid him be silent and if he did not obey them, the lictors pull¬ ed him down by force. When the debates were over, the president permitted the people to vote; which they did by casting first beans, but in after times pebbles, into certain vessels: these were counted, and then it was declared that the decree of the senate was either rejected or approved: after which, the Prytanes dis¬ missed the assembly. The senate was instituted by Solon to prevent theThesenate. dangerous consequences of leaving the supreme power in the people. At the time of his institution, it was to consist of 400, 100 out of each tribe ; it was increased to 500, when the tribes were augmented to 10 j and when they came to 12, it was also swelled to 600. They were elected by lots after this manner: At a day appointed, towards the close of the year, the president of each tribe gave in a list of such persons belonging thereto, as were fit for and desired to appear for this dignity : these names were engx-aven on tables of brass, and a number of beans equal to the number of the amount of them, among which were 100 white ones, put into a vessel •, and then the names of the candidates and the beans were drawrn one by one, and such as were drawn by the white beans were received into the senate. After the senate was elected, they proceeded to appoint the officers who were to preside in the se¬ nate : these were the Prytanes before mentioned j and they were elected thus : The names of the ten tribes were thrown into one vessel, and nine black beans and a white one into another vessel. Then the names of the tribes A T T tribes were drawn with tlie beans. The tribe to which ■ 1‘a^f'a' , the white bean answered, presided first j and the rest according to the order in which they were drawn. ] tunes P»Ttanes> while the senate consisted of 500, were 50 in number. For the farther avoiding of con¬ fusion, therefore, 10 of these presided a week, during which space they were called Proedri', and out of these an Epistate or president was chosen, whose office lasted but one day, and by law no man could hold it more than once : the reason of this was, that he had in his custody the public seal, the keys of the citadel, and the charge of the exchequer. The reader must distinguish between the Epistates and Proedri last mentioned, and those spoken of in the former paragraph, because, though their titles were the same, their offices were perfectly di¬ stinct. The senate assembled by direction of the Pry- tanes once every day, excepting festivals, and some¬ times oftener, in the senate-house, which was thence calk ed Pnjtaneum. ] ws how When a member of the senate made a motion for a < iblished, new law, it was immediately engraven on tablets, that Vf the members when they came next might be prepared to speak to it. At the subsequent assembly the Epi¬ states opened the matter; after which every senator that pleased delivered his sentiments 5 then any of the Prytanes drew up the decree, and repeated it aloud : after which they proceeded to vote $ and if there was a majority of white beans, then it became psephisma, and w^as afterwards propounded to the people : if they approved it, it became a law } otherwise it was of no force longer than the senate who decreed it subsisted. The power of the senate was very great; for they took the account of magistrates at the expiration of their of¬ fices \ they directed the provisions made for poor citi¬ zens out of the public treasure j they had the superin¬ tendency of public prisons, and a power of punishing ■ such as committed acts morally evil, though not prohi¬ bited by any Iawr 5 they had the care likewise of the fleet 5 and besides all these they had many other branches of authority, which it is not necessary for us to men¬ tion. Before they took their seats, they were con¬ strained to undergo a very strict examination, wherein the whole course of their lives was inquired into ; and if the least slur on their reputation appeared, they were set aside. When this examination w'as over, they took an oath, whereby they bound themselves to promote in all their counsels the public good, to advise nothing contrary to the laws, and to execute their functions ex¬ actly. The highest fine the senate could impose was 500 drachms : if they thought the ofl’ender deserved a heavier mulct, they then transmitted the cause to the Thesmothetae, who punished them as they thought fit. The senators, when their year was out, gave an ac¬ count of their management to the people : but that they might have the less to do, they always punished such of their number as they found had offended by expulsion ; and in this they were mighty exact. Yet an expelled senatoiMvas notwithstanding eligible to any other office, the most trivial omission being sufficient to occasion a dismission from the senatorial dignity ; and therefore, when the tribes chose their senators, they also chose a certain number of subsidiaries, out of which, when a senator was expelled, another was sub¬ stituted in his place. Each senator was allowed a drachm every day: for it was a constant rule with the I C A. Athenians, that the public ought to pay for every man’s Attica, time j and therefore such of the poor Athenians as -v—-—■* thought fit to demand it, had three obolh for going to the assembly. If during their administration any ships of war were built, the senators had crowns decreed them j but if not, they were forbid to sue for them. Next to the senate was the court of Areopagus 5 for a description of which see that article. I$0 I he chief magistrates of Athens were Archons, and Arclions, inferior to them there were many others j of whom itNomophy- will be necessary to mention some. In the first place saces’ ^!'c‘ they had Nomophylaces, who were also styled the eleven, because they were so many in number, one chosen out of each tribe, and a clerk or secretary who made up the eleventh. Their duty it was to look to the exe¬ cution of the laws : they had authority to seize robbers and other capital offenders ; and if they confessed, to put them to death. Dr Potter thinks they resembled our sheriffs. The Phylarchi were the presidents of the Athenian tribes j but in time this became a military title. The Philobasileus was an officer in each tribe, who did the same things within his jurisdiction as the Basileus did with respect to the state. The Demarchi were the principal magistrates in wards. The Lexar- chi were six in number, and were bound to take care that the people came duly to the assemblies ; in their custody was the public register of the citizens names. They had under them Toxotse, who were lictors or bailifs ; they were sometimes 1000 in number: these men were necessary : but, like most of their sort, were in a manner infamous, as may be gathered from the comedies of Aristophanes 5 they were generally Scy¬ thians, raw-boned, brawny fellows, ready to execute any thing they were commanded. The Nomothetae were 1000 in number ; their business was to watch over and inspect into the laws. There were two sorts of orators in the service of the state. Some were ap¬ pointed to defend an old law, when a motion was made to repeal it; these had their fee from the state, but the same man was incapable of being elected twice. Be¬ sides these, there were 10 settled orators called Prieto- res, elected by lot; their business was to plead public causes in the senate house. For this they had their sta¬ ted fees ; and with respect to their qualifications, the l9£ law run thus: “Let no one be a public orator who Laws re- hath struck his parents, denied them maintenance, or garding shut them out of his doors $ who hath refused to serveoratols“ in the army ; who hath thrown away his shield j who hath been addicted to lewd women, notoriously effe- * minate, or has run out his patrimony. If any man who has been guilty of these crimes dare to deliver an ora¬ tion, let him be brought to trial upon the spot. Let an orator have children lawfully begotten, and an estate within Attica ; if in his oration he talks imperti¬ nently, makes idle repetitions, affects an unbecoming raillery, digresses from the point in question, or, after the assembly is over, abuses the president, let the Pro¬ edri fine him 50 drachms ; and if that is not thought enough, let him be brought before the next assembly and fined again.” We shall conclude this draught of the Athenian go- Courts vernment with an account of their courts of justice, which, exclusive of the Areopagus, were 10 in num¬ ber ; four had cognizance of criminal, and six of civil causes, These 10 courts were numbered with the 10 first :54 A T T I C A. Attica, first letters of the alphabet, and were thence styled, Alpha, Beta, Gamma, &c. When an Athenian was at leisure to hear causes, he wrote his own name, that of his father, and the ward to which he belonged, up¬ on a tablet 5 this he presented to the Thesmothetse, who returned it again to him with another tablet, with the letter which fell to his lot ; then he went to the crier of the court, who presented him a sceptre, and gave him admission. When the causes were over, every judge went and delivered his sceptre to the Prytanes, and received a stated fee for every cause that was tried. But this w7as intended only to compensate their loss of time so that there might be no appearance of covetous¬ ness, a man was forbid to sit in two courts on the same day. The first criminal court after the Areopagus was that of the Ephctce. It consisted of 51 members, all up¬ wards of 51 years old. Draco gave it a very extensive jurisdiction $ but Solon took away from them the power of judging in any other causes than those of manslaugh¬ ter, accidental killing, and lying in wait to destroy: the Basileus entered all causes in this court. The second criminal court was called Delphinium, because it was held in the temple of Apollo Delphinius ; it had cog¬ nizance of such murders as were confessed by the crimi¬ nal, but at the same time justified under some pretence or other. rIhe Prytaneum was the third criminal court. It held plea of such cases where death ensued from inanimate things ; causes were heard here with the same solemnity as in other courts ; and on judgment given, the thing, whatever it was, that had occasioned the death of a man, was thrown out of the territory of Athens. Ihe last criminal court was styled P/rrerrfrm. It sat in a place near the sea shore j and such persons were brought before this court as had committed murders in their own country and fled to Attica ; the proceed¬ ings of this court were so severe, that they did not per¬ mit the criminal to come on shore, but obliged him to plead his cause in his vessel ; and if he was found guilty, he was committed to the mercy of the winds and seas. Of the judicatures for hearing civil causes, the first was the Parabaston, so called, as some think, because in it no matter could be heard if the cause of action was above one drachm. The Cainon, or new court, was the second tribunal. The third was styled the coui't of Lycus, because it assembled in a temple dedi¬ cated to that hero, whose statue, represented with the face of a wolf) was set up in all courts of justice. The Trigonon was so called, because it was triangular in its form. The court Metidius derived its appellation from the architect who built it. The sixth and last court w'as called Helicea; it w'as by far the greatest, and is generally believed to have derived its name from the judges sitting in the open air exposed to the sun. All the Athenians who were free citizens were allowed by law to sit in these courts as judges; but before they took their seats were sworn by Apollo Patrius, Ceres, and Jupiter the king, that they would decide all things righteously and according to law, where there was any law to guide them $ and by the rules of natural equity, where there was none. The Helaeastic court consisted at least of 50, but its usual number was 300, judges j when causes of very great consequence were to be tried, 1000 sat therein j and now and then the judge® were increased to IJOO, and even to 2000. Attici, ATT Atticus. AfriCUS, Titus Pomponius, one of the most Attila. honourable men in ancient Rome. He understood the ' art of managing himself with such address, that with¬ out leaving his state of neutrality, he preserved the esteem and aff ection of all parties. His strict friendship with Cicero did not hinder him from having great in¬ timacy with Hortensius. The contests at Rome be¬ tween Cinna’s party and that of Marius induced' him to go to Athens, where he continued for a long time. He was very fond of polite learning, and kept at his house several librarians and readers. He might have obtained the most considerable posts in the government 5 but chose rather not to meddle, because in the corrup¬ tion and faction which then prevailed he could not dis¬ charge them according to the laws. He wrote Annals. He married his daughter to Agrippa; and attained to the age of 77. AT IILA, king of the Huns, surnamed the scourge of God, lived in the filth century. He may be ranked amongst the greatest conquerors, since there was scarce¬ ly any province of Europe which did not feel the weight of his victorious arms. Gibbon's Attila deduced his noble, perhaps his regal, de- Rome, scent from the ancient Huns, who had formerly con- vol. iii. tended with the monarchs of China. His features, ac- P’ 357’ cording to the observation of a Gothic historian, bore the stamp of his national origin : and the portrait of Attila exhibits the genuine deformity of a modern Calmuck j a large head, a swarthy complexion, small deep-seated eyes, a flat nose, a few hairs in the place ATT of a beard, broad shoulders, and a short square body, of nervous strength, though of a disproportioned form.y— The haughty step and demeanour of the king of the Huns expressed the consciousness of his superiority above the rest of mankind $ and he had a custom of fiercing rolling his eyes, as if he wished to enjoy the terror which he inspired. Yet this savage hero was not inaccessible to pity his suppliant enemies might confide in the assurance of peace or pardon; and At¬ tila was considered by his subjects as a just and indul¬ gent master. He delighted in war: but after he had ascended the throne in a mature age, his head, rather than his hand, achieved the conquest of the north j and the fame of an adventurous soldier was usefully ex¬ changed for that of a prudent and successful general. The effects of personal valour are so inconsiderable, except in poetry or romance, that victory", even among barbarians, must depend on the degree of skill, with which the passions of the multitude are combined and guided for the service of a single man. The arts of Attila were skilfully adapted to the character of his age and country. It was natural enough, that the Scythians should adore with peculiar devotion, the god ol war; but as they were incapable of forming either an abstract idea, or a corporeal representation, they worshipped their tutelar deity under the symbol of an iron scimitar. One of the shepherds of the Huns perceived, that a heifer, who was grazing, had wound¬ ed herself in the foot •, and curiously followed the track of the bloocf, till he discovered, among the long grass, ATT [2 Mtila. the point of an ancient sword ; which he dug out of y 1 t|ie ground, and presented to Attila. That magnami- mous, or rather that artful, prince, accepted with pi¬ ous gratitude, this celestial favour ; and, as the right¬ ful possessor of the stvord of Mars, asserted his divine and indefeasible claim to the dominion of the earth. If the rites of Scythia were practised on this solemn occa¬ sion, a lofty altar, or rather pile of faggots, 300 yards in length and in breadth, was raised in a spacious plain; and the sword of Mars was placed erect on the summit of this rustic altar, which was annually conse¬ crated by the blood of sheep, horses, and of the hun¬ dredth captive. Whether human sacrifices formed any part of the worship of Attila, or whether he propitia¬ ted the god of war with the victims which he continu* ally offered in the field of battle, the favourite of Mars soon acquired a sacred character, which rendered his conquests more easy and more permanent; and the barbarian princes confessed, in the language of devo¬ tion or flattery, that they could not presume to gaze with a steady eye on the divine majesty of the king of the Huns. His brother Bleda, who reigned over a considerable part oFthe nation, was compelled to re¬ sign his sceptre and his life. Yet even this cruel act was attributed to a supernatural impulse ; and the vi¬ gour with which Attila wielded the sword of Mars, con¬ vinced the world that it had been reserved alone for his invincible arm. But the extent of his empire affords the only remaining evidence of the number and impor¬ tance of his victories; and the Scythian monarch, how¬ ever ignorant of the value of science and philosophy, might perhaps lament that his illiterate subjects were destitute of the art which could perpetuate the memory of his exploits. If a line of separation were drawn between the civi¬ lized and the savage climates of the globe ; between the inhabitants of cities who cultivated the earth, and the hunters and shepherds who dwelt in tents ; Attila might aspire to the title of supreme and sole monarch of the Barbarians. He alone, among the conquerors of ancient and modern times, united the two mighty kingdoms of Germany and Scythia : and those vague appellations, when they are applied to his reign, may¬ be understood with an extensive latitude. Thuringia, which stretched beyond its actual limits as far as the Danube, was in the number of his provinces : he in¬ terposed, with the weight of a powerful neighbour, in the domestic affairs of the Franks ; and one of his lieu¬ tenants chastised, and almost exterminated, the Bur¬ gundians of the Rhine. He subdued the islands of the ocean, the kingdoms of Scandinavia, encompassed and divided by the waters of the Baltic ; and the Huns niight derive a tribute of furs from that northern re¬ gion, which has been protected from all other conque¬ rors' by the severity of the climate, and the courage of the natives. Towards the east, it is difficult to cir¬ cumscribe the dominion of Attila over the Scythian de¬ serts : yet we may be assured, that he reigned on the banks of the ^ olga; that the king of the Huns was dreaded not only as a warrior but as a magician ; that he insulted and vanquished the khan of the formi¬ dable Geougen ; and that he sent ambassadors to nego- ciate an equal alliance with the empire of China. In the proud review of the nations who acknowledged the sovereignty of Attila, and who never entertained du- 55 ] ATT ring his lifetime the thought of a revolt, the Gepidse Attiln and the Ostrogoths were distinguished by their num- || hers, their bravery, and the personal merit of . their Attorney, chiefs, i he renowned Ardaric king of the Gepidre, was the laithful and sagacious counsellor of the mo¬ narch ; who esteemed his intrepid genius, whilst he lo¬ ved the mild and discreet virtues of the noble Walamir king of the Ostrogoths. The crowd of the vulgar kings, the leaders of so many martial tribes, who served under the standard ot Attila, were ranged in the sub¬ missive order ol guards and domestics round the person of their master. They watched his nod ; they trembled at his frown : and at the first signal of his will, they ex¬ ecuted without murmur or hesitation his stern and ab¬ solute commands. In time of peace, the dependent princes, with their national troops, attended the royal camp in regular succession ; but when Attila collected his military force, he was able to bring into the field an army ot five, or, according to another account, of seven hundred thousand Barbarians. I he death of Attila was attended with singular cir¬ cumstances. He had married a new wife, a beautiful virgin named lldico. His nuptials were celebrated with great festivity, at his palace beyond the Danube, and he retired late to bed oppressed with wine. In the night, a blood-vessel burst in his lungs, which suf¬ focated him. rIhe bride was found in the morning sit¬ ting by the bedside, lamenting his death and her own danger. The body of Attila was exposed in the plain, while the Huns, singing funeral songs to his praise, marched round it in martial order. The body, enclo¬ sed in three coffins, of gold, silver, and iron, was pri¬ vately interred during the night; and to prevent the violation of his remains by the discovery of the place where he was buried, all the captive slaves who were employed in the solemnity were barbarously massacred. This happened about the year 453. With Attila end¬ ed the empire of the Huns. His sons, by dissension and civil war, mutually destroyed each other, or were dispossessed by more powerful and independent chief¬ tains. For a farther account of his exploits, see the article Huns. ATTIRE, in hunting, signifies the head or horns of a deer. The attire of a stag, if perfect, consist of bur, pearls, beam, gutters, antler, sur-antler, royal, sur- royal, and crotchets ; of a buck, of the bur, beam, brow- antler, advancer, palm, and spellers. ATTITUDE, in Painting and Sculpture, the gesture of a figure or statue ; or it is such a disposition of their parts as serves to express the action and sentiments of the person represented. ATTIUM, in Ancient Geography, a promontory on the north-west of Corsica, (Ptolemy). It still retains some traces of its ancient name, being now called Pun- ta di Acciuolo (Cluverius). . ATTLEBURY, a town in the county of Norfolk in England. E. Long. o. 40. N. Lat. 52. 23. ATTOLLENS, in Anatomy, an appellation given to several muscles, otherwise called levatores and eleva¬ tor es. See Anatomy, Tables of the Muscles. ATTORNEY at law, answers to the Procurator or Proctor of the civilians and canonists : And he is one who is put in the place, stead, or turn, of ano¬ ther, to manage his matters of law. Formerly every suitor ATT [ 256 ] ATT Attorney, suitor was obliged to appear in person, to prosecute or ' v-*—' defend his suit (according to the old Gothic constitu¬ tion), unless by special license under the king’s letters patent. This is still the law in criminal cases. And an idiot cannot to this day appear by attorney, but in person 5 for he hath not discretion to enable him to appoint a proper substitute: and upon his being brought before the court in so defenceless a condition, the judges are bound to take care of his interests, and they shall admit the best plea in his behalf that any one present can suggest. But, as in the Roman law, cum glim in usu fuisset, alterius nomine agi non posse, sed quia hoc ■non minimum incommoditatem habebat, cozperunt homi¬ nes per procuratores litigare; so, with us, on the same principle of convenience, it is now permitted in gene¬ ral, by divers ancient statutes, whereof the first is sta¬ tute West. 2. c. 10. that attorneys may be made to prosecute or defend any action in the absence of the parties to the suit. These attorneys are now formed into a regular corps j they are admitted to the execu¬ tion of their office by the superior courts of Westmin¬ ster hall ; and are in all points officers of the respec¬ tive courts in which they ai’e admitted ; and as they have many privileges on account of their attendance there, so they are peculiarly subject to the censure and animadversion of the judges. No man can practise as an attorney in any of those courts, but such as is ad¬ mitted and sworn an attorney of that particular court: an attorney of the court of king’s bench cannot prac¬ tise in the court of common pleas j nor vice versa. To practise in the court of chancery, it is also neces¬ sary to be admitted a snlicitor therein : and by the sta¬ tute 22 Geo. II. c. 46. no person shall act as an attor¬ ney at the court of quarter-sessions, but such as has been regularly admitted in some superior court of re¬ cord. So early as the statute 4 Hen. IV. c. 18. it was enacted, that attorneys should be examined by the judges, and none admitted but such as were virtuous, learned, and sworn to do their duty. And many sub¬ sequent statutes have laid them under farther regula¬ tions. Letter of attorney pays by different acts, 6s. By 25 Geo. III. c. 80. the following duties are to be paid by every solicitor, attorney, notary, proctor, agent, or procurator, viz. for every warrant to prosecute for a debt of 40s. or to defend, a stamp duty of 2s. 6d. And they are to take out certificates annually ; and if resident in London, Westminster, the bills of mor¬ tality, or Edinburgh, they are now obliged to pay 5I. for the same ; and in every other part of Great Bri¬ tain, 3I. The duties are under the management of the commissioners of stamps : and every acting solici¬ tor, and other persons as above, shall annually deliver in a note of his name and residence, to the proper offi¬ cer of the court in which he practises \ the entering officers are to certify notes delivered, and issue annual certificates, stamped as above, which must be renewed ten days before the expiration. Refusing to issue, or improperly issuing certificates, is a penalty of 50I. and damages to the party aggrieved. Acting without a certificate, or giving in a false place of residence, is a penalty of 50I. and incapacity to sue for fees due. A stamped memorandum shall be given to the proper officer, of the names of the parties in every action ; and in such cases as used to require precipes. Officers who receive stamped memorandums, are to file the same, Attorney on penalty of 50I. and persons not acting conformable || to this act forfeit 5I. , Attraction, ATTQRNEY-General, is a great, officer under the ' V""J king, made by letters patent. It is his place to exhibit informations, and prosecute for the crown, in matters criminal 5 and to file bills in the exchequer, for any¬ thing concerning the king in inheritance or profits j and others may bring bills against the king’s attorney. His proper place in court, upon any special matters of a criminal nature, wherein his attendance is required, is under the judges on the left hand of the clerk of the crown : but this is only upon solemn and extraordinary occasions j for usually he does not sit here, but within the bar in the face of the court. ATTOURNMENT, or Attornment, in Law, a transfer from one lord to another of the homage and sex-vice a tenant makes $ or that acknowledgment of duty to a new lord. ATTRACTION, in Natural Philosophy, a general term used to denote the cause by which bodies tend to¬ wards each other, and cohere till separated by some other power. The principle of attraction, in the Newtonian sense of it, seems to have been first surmised by Copernicus, “ As for gravity,” says Copernicus, “ I. consider it as nothing more than a certain natural appetence (appe- tentia) that the Creator has impressed upon all the parts of matter, in oi’der to their uniting or coalescing into a globular form, for their better preservation 5 and it is credible that the same power is also inherent in the sun and moon, and planets, that those bodies may constantly retain that round figure in which we behold them.” De Rev. Orb. Ccelest. lib. i. cap. 9. And Kepler calls gra¬ vity a corporeal and mutual affection between similar bodies, in order to their union. Ast. Nov. in Introd. And he pronounces more positively, that no bodies w-hatsoever were absolutely light, but only relatively so j and consequently, that all matter was subjected to the law of gravitation. Ibid. The first in this country who adopted the notion of attraction was Dr Gilbert in his book De Magtiete ; and the next was the celebrated Lord Bacon, Nov. Or¬ gan. lib. ii. aphor. 36. 45. 48. Sylv. cent. i. exp. 33. In France it was received by Fermat and Roberval j and in Italy by Galileo and Borelli. But till Sir Isaac Newton appeared, this principle was very imperfectly defined and applied. It must be observed, that though this gx-eat author makes use of the word attraction, in common with the school philosophers j yet he very studiously distinguishes between the ideas. The ancient attraction was sup¬ posed a kind of quality, inherent in certain bodies themselves, and arising from their particular or specific forms. The Newtonian attraction is a more indefinite principle j denoting not any particular kind or man¬ ner of action, nor the physical cause of such action ; but only a tendency in the general, a conatus accedcndi, to whatever cause, physical or metaphysical, such ef¬ fect be oxving, whether to a power inherent in the bodies themselves, or to the impulse of an external agent. Accordingly, that author, in his Philosoph. Nat. Prin. Afath. notes, “ that he uses the xvords attraction, impulse, propension to the centre, indif¬ ferently ; and cautions the reader not to imagine that ATT [ ; traction, by attraction be expresses the modus of the action, or —~v~— the efficient cause thereof, as if there were any proper powers in the centres, which in reality are only ma¬ thematical points j or as if centres could attract.” Lib. i. p. 5. So he “ considers centripetal powers as attractions, though, physically speaking, it were per¬ haps more just to call them impulses.” lb. p. 147. He adds, “ that what he calls attraction may possibly be effected by impulse, though not a common or corporeal impulse, or after some other manner unknown to us.” Optic, p. 312. Attraction, if considered as a quality arising from the specific forms of bodies, ought, together with sym¬ pathy, antipathy, and the whole tribe of occult quali¬ ties, to be exploded. But when we have set these aside, there will remain innumerable phenomena of na¬ ture, and particularly the gravity or weight of bodies, or their tendency to a centre, which argue a principle of action seemingly distinct from impulse, where at least there is no sensible impulsion concerned. Nay, what is more, this action in some respects differs from all impulsion we know of $ impulse being always found to act in proportion to the surfaces of bodies, whereas gravity acts according to their solid content, and consequently must arise from some cause that pe¬ netrates or pervades the whole substance thereof. This unknown principle, unknown we mean in respect of its cause, for its phenomena and effects are most obvious, with all the species and modifications thereof, we call attraction ; which is a general name, under which all mutual tendencies, where no physical impulse appears, and which cannot therefore be accounted for from any known laws of nature, may be ranged. And hence arise divers particular kinds of attrac¬ tion j as, Gravity, Magnetism, Electricity, &c. which are so many different principles acting by different laws, and only agreeing in this, that we do not see any physical causes thereof j but that, as to our senses, they may really arise from some power or efficacy in such bodies, whereby they are enabled to act even upon di¬ stant bodies, though our reason absolutely disallows of any such action. Attraction may be divided, with respect to the law it observes, into two kinds. I. That which extends to a sensible distance. Such are the attraction of gravity, found in all bodies j and the attraction of magnetism and electricity, found in particular bodies. The several laws and phenomena of each, see under their respective articles. The attraction of gravity, called also among mathe¬ maticians the centripetal force, is one of the greatest and most universal principles in all nature. We see and feel it operate on bodies near the earth, and find by observation that the same power (i. e. a power winch acts in the same manner, and by the same rules, viz. always proportionably to the quantities of matter, and as the squares of the distances reciprocally) does also obtain in the moon, and the other planets primary and secondary, as well as in the comets ; and even that this is the very power whereby they are all retained in their orbits, &c. And hence, as gravity is found in all the bodies which come under our observation, it is easily inferred, by one of the settled rules of philoso¬ phizing, that it obtains in all others: and as it is found to be as the quantity of matter in each body, it must Vol. III. Part I, f 157 ] ATT be in every particle thereof’, and hence every particle Attraction, in nature is proved to attract every other particle, &c. See Attraction, Astronomy Index. From this attraction arises all the motion, and con¬ sequently all the mutation, in the material world. By this heavy bodies descend, and light ones ascend ; by this projectiles are directed, vapours and exhalations rise, and rains, &c. fall. By this rivers glide, the air presses, the ocean swells, &c. In effect, the motions arising from this principle make the subject of that extensive branch of mathematics, called mechanics or statics, with the parts or appendages thereof, hydrostatics, pneuma¬ tics, &c. 2. Ihat which does not extend to sensible distances. Such is found to obtain in the minute particles where¬ of bodies are composed, which attract each other at or extremely near the point of contact, with a force much superior to that of gravity, but which at anv distance from it decreases much faster than the power of gravity. This power a late ingenious author chooses to call the attraction of cohesion, as being that whereby the atoms or insensible particles of bodies are united into sensible masses. This latter kind of attraction owns Sir Isaac New¬ ton for its discoverer ; as the former does for its im¬ prover. The laws of motion, percussion, &c. in sen¬ sible bodies under various circumstances, as falling, projected, &c. ascertained by the later philosophers, do not reach to those more remote intestine motions of the component particles of the same bodies, whereon the changes of the texture, colour, properties, &c. of bodies depend : so that our philosophy, if it were on¬ ly founded on the principle of gravitation, and carried so far as that would lead us, would necessarily be very deficient. But beside the common laws of sensible masses, the minute parts they are composed of are found subject to some others, which have been but lately taken no¬ tice of, and are even yet imperfectly known. Sir Isaac Newton, to whose happy penetration we owe the hint, contents himself to establish that there are such mo¬ tions in the minima nature?, and that they flow from certain powers or forces, not reducible to any of those in the great world. In virtue of these powers, he shows, “ That the small particles act on one another even at a distance ; and that many of the phenomena of nature are the result thereof. Sensible bodies, we have already observed, act on one another divers ways : and as we thus perceive the tenor and course of nature, it appears highly probable that there may be other powers of the like kind ; nature being very uniform and consistent with herself. Those just men¬ tioned reach to sensible distances, and so have been observed by vulgar eyes ; but there may be others which reach to such small distances as have hitherto escaped observation ; and it is probable electricity may reach to such distances, even without being excited by friction. The great author just mentioned proceeds to confirm the reality of these suspicions from a great number of phenomena and experiments, which plainly argue such powers and actions between the particles, e. g. of salts and water, sulphuric acid and water, nitric acid and iron, sulphuric acid and nitre. He also shows, that these powers, &c. are unequally strong between diffe- K k rent ATT [2, Attraction, vent bodies ; stronger, e. g. between the particles of —v-—potash and those of nitric acid than those of silver, be¬ tween nitric acid and zinc than iron, between iron and copper than silver or mercury. So sulphuric acid acts on water, but more on iron or copper, &c. The other experiments which countenance the exist¬ ence of such principle of attraction in the particles of matter are innumerable. These actions, in virtue whereof the particles of the bodies above mentioned tend towards each other, the author calls by a general indefinite name atti'action; which is equally applicable to all actions whereby di¬ stant bodies tend towards one another, whether by im¬ pulse or by any other more latent power : and from hence he accounts for an infinity of phenomena, other¬ wise inexplicable, to which the principle of gravity is inadequate. \ “ Thus (adds our author) will nature be found very conformable to herself and very simple ; performing all the great motions of the heavenly bodies by the attraction of gravity, which intereides those bo¬ dies, and almost all the small ones of their parts, by some other attractive power diffused through the par¬ ticles thereof. Without such principles, there never would have been any motion in the world ; and with¬ out the continuance thereof, motion would soon perish, there being otherwise a great decrease or diminution thereof, which is only supplied by these active princi¬ ples. We need not say how unjust it is in the generality of foreign philosophers to declare against a principle which furnishes so beautiful a view, for no other reason but because they cannot conceive how one body should act on another at a distance. It is certain, philosophy allows of no action but what is by immediate contact and impulsion (for how can a body exert any active power there where it does not exist ? to suppose this of any thing, even the Supreme Being himself, would per¬ haps imply a contradiction) : yet we see effects without seeing any such impulse; and where there are effects, we can easily infer there are causes, whether we see them or not. But a man may consider such effects witnout entering into the consideration of the causes, as indeed it seems the business of a philosopher to do . for to exclude a number of phenomena which we do see, will be to leave a great chasm in the history of nature j and to argue about actions which we do not see, will be to build castles in the air.——It follows, therefore, that the phenomena of attraction are matter of physical consideration, and as such entitled to a share in the system of physics ; but that the causes thereof will only become so when they become sensible, i. e. when they appear to be the effect of some other higher' causes (for a cause is no otherwise seen than as itself is an effect, so that the first cause must from the nature of things he invisible) : we are therefore at liberty to suppose the causes of attraction what we please, with¬ out any injury to the effects—The illustrious author himself seems a~ little irresolute as to the causes; incli¬ ning sometimes to attribute gravity to the action of an immaterial cause (Optics, p. 343, &c.) and sometimes to that of a material one (fb. p. 325.). In his philosophy, the research into causes is the last thing, and never comes under consideration till the Jaws and phenomena of the effect be settled ; it being 58 ] ATT to these phenomena that the cause is to be accommo- AttI,a dated. The cause even of any, the grossest and most ,jCt" sensible action, is not adequately known. How im- Attribut pulse or percussion itself produces its effects, i. e. how motion is communicated by body to body, confounds the deepest philosophers ; yet is impulse received not only into philosophy, but into mathematics : and ac¬ cordingly the laws and phenomena of its effects make the greatest part of common mechanics. The other species of attraction, therefore, in which no impulse is remarkable, when their phenomena are sufficiently ascertained, have the same title to be pro¬ moted from physical to mathematical consideration; and this without any previous inquiry into their causes, which our conceptions may not be proportionate to : let their causes be occult, as all causes strictly speaking are, so that their effects, which alone immediately concern us, be but apparent. Our great philosopher, then, far from adulterating science with any thing foreign or metaphysical, as many have reproached him with doing, has the glory of ha¬ ving thrown every thing of this kind out of his system, and of having opened a new source of sublimer mecha¬ nics, which duly cultivated might be of infinitely great* er extent than all the mechanics yet known. It is hence alone we must expect to learn the manner of the changes, productions, generations, corruptions, &c. of natural things; with all that scene of wonders opened to us by the operations of chemistry. Some of our own countrymen have prosecuted the discovery with laudable zeal: DrKeill particularly has endeavoured to deduce some of the laws of this new action, and applied them to solve divers of the more general phenomena of bodies, as cohesion, fluiditv, elasticity, softness, fermentation, coagulation, &c.j and Hr Freind, seconding him, has made a further applica¬ tion of the same principles, to account at once for almost all the phenomena that chemistry presents : so that some philosophers are inclined to think that the new mechanics should seem already raised to a com¬ plete science, and that nothing now can occur but what we have an immediate solution of from the attractive force. But this seems a little too precipitate : A principle so fertile should have been further explored. Attrac¬ tion in the gross is so complex a thing, that it may solve a thousand different phenomena alike. The no¬ tion is hut one degree more simple and precise than action itself; and, till more of its properties are ascer¬ tained, it were better to apply it less and study it more. It may be added, that some of Sir Isaac New¬ ton’s foil owers have been charged with falling into that error which he industriously avoided, viz. of considering attraction as a cause or active property in bodies, not merely as a phenomenon or effect. For an account of the mathematical laws of attrac¬ tion, see Attraction, Supplement. Attraction of Mountains. See Mountains. Elective Attraction. See Chemistry Index. ATTREBATII. See Atrebatii. AT'I RIBUTE, in a general sense, that which agrees with some person or thing ; or a quality deter¬ mining something to be after a certain manner. Thus understanding is an attribute of mind, and extension an attribute of body. That attribute which the mind conceives A V A [ 259 ] A tf B Attribute conceives as the foundation of all the rest, is called its essential attribute; thus extension is by some, andsoli- Ava . dity by others, esteemed the essential attribute of body or matter. AT TRIBUTES, in Theology, the several qualities or perfections of the Divine nature. Attributes, in Logic, are the predicates of any subject, or what may be affirmed or denied of any thing. Attributes, in Tainting and Sculpture, are sym¬ bols added to several figures, to intimate their parti¬ cular office and character. Thus the eagle is an attri¬ bute of Jupiter j a peacock, of Juno j a caduce, of Mercury; a club, of Hercules; and a palm, of Vic¬ tory. ATTRIBU FIVES, in Grammar, are words which are significant of attributes; and thus include adjectives; verbs, and particles, which are attributes of substances; and adverbs, which denote the attributes only of attri¬ butes. Mr Harris, who has introduced this distribu¬ tion of words, denominates the former attributives of the first order, and the latter attributives of the second order. ATTRITION, the rubbing or striking of bodies one against another, so as to throw of}'some of their su¬ perficial particles. ATUR/E, an ancient town in the district of Novem- populana in Aquitania, cn the river Aturus ; now Aire in Gascony, on the Adour. E. Long. o. 3. N. Lat. 43. 40. ATWOOD, George, a mathematician and mecha¬ nician. See Supplement. AVA, a kingdom of Asia, in the peninsula beyond the Ganges. The king is very powerful, his dominions being bounded by Bengal and the sea on the west, Siam bn the south, Tonquin and Cochin China on the east, and by Tibet and China on the north. Several large rivers run through this country, which annually over¬ flow their banks like the Nile, and thus render it ex¬ tremely fertile. Here are mines of lead and copper, together with some of gold and silver, besides large quantities of the finest oriental rubies, sapphires, eme¬ ralds, &c. See Asia, N° 81, &c. Ava, formerly the metropolis of the kingdom of the same name, is situated in E. Long. 96. 30. N. Lat. 21. o. It is pretty large ; the houses built with timber or bamboo canes, with thatched roofs, and floors made of teak plank or split bamboo. I he streets are very straight, with rows of trees planted on each side. The king’s palace is an exact quadrangle, each side of which is 800 paces, and is surrounded with a brick wall ; but the palace itself is of stone. It has four gates: the golden gate, through which all ambassadors enter; the gate of justice, through which the people bring petitions, accusations, or complaints ; the gate of giace, through which those pass who have received any favours, or have been acquitted of crimes laid to their charge; and the gate of state, through which his majesty himself passes when he shows himself to the people. Ava ava, a plant so called by the inhabitants of O-» taheite, in the feouth sea, from the leaves of which they express an intoxicating juice. It is drunk very freely by the chiefs and other considerable persons, who vie with each other in drinking the greatest number of draughts. AVADOUTAS, a sect of Indian Bramins, who Avaclouhu in austerity surpass all the rest. The other sects retain |j earthen vessels for holding their provisions, and a stick Aubcnton to lean on ; but none of these are used by the Avadou- t*~*—v*——; tas ; they only cover their nakedness with a piece of cloth; and some of them lay even that aside, and go stark naked, besmearing their bodies with cow-dung. When hungry, some go into houses, and, without speaking, hold out their hand ; eating on the spot whatever is given them. Others retire to the sides of holy rivers, and there expect the peasants to bring them provisions, which they generally do very libe¬ rally. AVAIL of Marriage, in Scots Law, that casualty in wardholding, by which the superior was entitled to a certain sum from his vassal, upon his attaining the age of puberty, as the value or avail of his tocher. AVALANCHES, a name given to prodigious snow¬ balls that frequently roll down the mountains in Savoy, particularly Mount Blanc, to the extreme danger of such adventurous travellers as attempt to ascend those stupendous heights. Some of the avalanches are about 200 feet diameter; being fragments of the ice-rocks which break by their own weight from the tops of the precipices. See Mount Blanc. AVALON, a small but ancient city of France, in the department of the Yonne, and containing 4200 in¬ habitants in 1815. E. Long. 3. 50. N. Lat. 47. 48. A VANIA, in the Turkish legislature, a fine for crimes and on deaths, paid to the governor of the place. In the places wherein several nations live together un¬ der a Turkish governor, be takes this profitable method of punishing all crimes among the Christians or Jews* unless it be the murder of a Turk. AVARICUM, an ancient town of the Bituriges in Gallia Celtica, situated on the rivulet Avara, in a very fertile soil (Caesar.) Now Bourges, in Berry. E. Lone . 2. 30. N. Lat. 47. 10. ' AVAST, in the sea language, a term requiring to stop or to stay. AVAUNCHERS, among hunters, the second branch¬ es of a deer’s horns. AUB AGNE, a town of Provence in France, situated on the river Veaune, on the road from Marseilles to Toulon. The states formerly held their session at this place. E. Long. 5. 52. N. Lat. 43. 17. AUBAINE, in the old customs of France, a right vested in the king, by virtue of which he claimed the inheritance of all foreigners that died within his domi¬ nions, notwithstanding of any testament the deceased could ipake. An ambassador was not subject to the right of aubaine ; and the Swissj Savoyards, Scots, and Portuguese were also exempted. This ancient privi¬ lege of the crown was abolished in 1819. AUBE, a department in the east of France, compre¬ hending part of the ancient Champagne. It contains 305 square leagues, and had a population of 238,819 in 1815. Troyes is the chief town. AUBENAS, a town of France, in the department of Ardeche, situated on the river Ardeche, at the foot of the mountains called the Cevennes. E. Long. 4. 32. N. Lat. 44. 40. AUBENTON, a town of France, in the department of Aisne, situated on the river Aube. E. Long. 4. 2 c. N. Lat. 49. 51. K k 2 AUBETERRE; A U B Aiibeterre II Aubrey. AUBETERRE, a town of France, in the Angu- mois, on the river Dronne. E. Long. o. 10. N. Lat. ,45-M- AUBIGNE, a town of France, in the department of Cher, situated on the river Verre, in a flat and agreeable country. It is surrounded with high strong walls, wide ditches, and high counterscarps. The castle is within the town, and is very handsome. E. Long. 2. 20. N. Lat. 47. 29. AUBIN du comier, a town of Erance, in the de¬ partment of Isle and Vilaine. W. Long. 1. 15. N. Lat. 48' I5* Aubin, in Horsemanship, a broken kind of gait, be¬ tween an amble and a gallop, accounted a defect. AUBONNE, a town of Switzerland, in the can¬ ton of Bern. E. Long. 5. 54. N. Lat. 46. 30. It is situated near a river of the. same name, seven miles north of the lake of Geneva, upon an eminence which has a gentle declivity, at the foot of which runs the river with an impetuous torrent. The town is built in the form of an amphitheatre j on the upper part of which stands a very handsome castle with a fine court, and a portico supported by pillars of a single stone each ; above there is a covered gallery that runs round the court j and as the castle stands high, there is a most delightful prospect, not only of the town and neigh¬ bouring fields, but of the whole lake of Geneva and the land that surrounds it. At Thonen, in Savoy, on the other side of the lake, is a town covered with tin, which makes a glittering appearance when the sun is in a certain position •, and the castle of Aubonne has like¬ wise a tower of the same kind, which at certain hours makes a similar appearance to the Savoyards. The bailiage of Aubonne contains several villages, which are mostly at the foot of the mountain Jura. In one part of this mountain there is a very deep cave, where¬ in those that go down find a natural and perpetual ice¬ house. At the bottom is heard a great noise like that of a subterraneous river, which is supposed to be that of the river Aubonne, because it first appears, with se¬ veral sources, about 100 paces from the foot of that mountain. AUBREY, John, a famous English antiquary, de¬ scended from an ancient family in Wiltshire, was born in 1626. He made the history and antiquities of England his peculiar study and delight; and contri¬ buted considerable assistance to the famous Monasticon Anglicanum. He succeeded to several good estates j but law-suits and other misfortunes consumed them all, so that he was reduced to absolute want. In this ex¬ tremity he found a valuable benefactress in the Lady Long of Draycot in Wilts, who gave him an apart¬ ment in her house, and supported him to his death, which happened about the year 1700. He was a man of considerable ability, learning, and application, a good Latin poet, an excellent naturalist, but somewhat credulous, and tinctured with superstition. He left many works behind him. He wrote, 1. Miscellanies. 2. A Perambulation of the county of Surry, in five volumes, octavo. 3. The Life of Mr Hobbes of Malmsbury. 4. Monumenta Britannica, or a discourse concerning Stonehenge, and Roll Rich stones in Ox¬ fordshire. 5. Architectonica Sacra ; and several other works still in manuscript. [ 260 ] A U D AUBURN, a market-town of Wiltshire, in Eng- Aujmn land. W. Long. 1. 20. N. Lat. 53. 20. || AUBUSSON, a small town of France, in the pro- Audience, vince of La Marche, and the government of the Lyon-U“"Y'—■ nois, now the department of Creuse. Its situation is very irregular, on the river Creuse, in a bottom sur¬ rounded with rocks and mountains. A manufacture of tapestry-is carried on here, and the town contained a population of 3520 souls in 1815. E. Long. 2. 15. N. Lat. 45. 58. AUCAUGREL, the capital of the kingdom of Adel in Africa, seated on a mountain. E. Long. 44. 35. N. Lat. 9. 10. AUCH, a city of France, the capital of the coun¬ ty of Armagnac, now the department of Gers, and the metropolis of all Gascony. The archbishop formerly assumed the title of primate of Aquitain. It lies on the summit and declivity of a very steep hill, which is sur¬ rounded by other hills that rise at a small distance j and through the vale below runs a rivulet, called the Gers. The inhabitants amount to 8800 ; the buildings are mo¬ dern and elegant j the streets, though in general narrow, yet are clean and well paved. In the centre of the city stands the cathedral, which is one of the most mag¬ nificent in France, both as to its construction and the internal decorations. The painted windows are only inferior to those of Gouda in Holland. The chapels are of equal beauty, and ornamented at a prodigious expence. The revenues of the see of Audi amounted formerly to three hundred thousand livres per annum. It contains manufactures of serge and the coarse wool¬ lens called barat; there are also tanneries, and the en¬ virons are noted for producing the excellent pear called bon chretien. AUCTION, a kind of public sale, very much in use for household goods, books, plate, &c. By this method of sale the highest bidder is always the buyer. This was originally a kind of sale among the ancient Romans, performed by the public crier sub hasta, i. e.. under a spear stuck up on that occasion, and by some magistrate, who made good the sale by delivery of the goods. AUDEANISM, the same with anthropomorphism. See Anthropomorphites. AUDEUS, the chief of the Audeans, obtained the name of a heretic, and the punishment ol ba¬ nishment, for celebrating Easter in the manner of the Jews, and attributing a human form to the Dei¬ ty. He died in the country of the Goths, about the year 370. AUDIENCE given to ambassadors, a ceremony observed in courts at the admission of ambassadors or public ministers to a hearing. In England, audience is given to ambassadors in the presence chambers ; to envoys and residents, in a gal¬ lery, closet, or in any place where the king happens to be. Upon being admitted, as is the custom of all courts, they make three bows; after which they cover and sit down ; but not before the king is covered and sat down, and has given them the sign to put 011 their hats. When the king does not care to have them co¬ vered, and sit, he himself stands uncovered ; which is taken as a slight. At Constantinople, ministers usual¬ ly have audience of the prime vizier. a Audience Ludienoe II uiditores. A U D [ 261 ] A U D Audience is also the name of a court of justice established in the West Indies by the Spaniards, an¬ swering in effect to the parliament in France. These courts take in several provinces, called also audien¬ ces, from the name of the tribunal to which they be¬ long. Audience is also the name of an ecclesiastical court held by the archbishop of Canterbury, wherein differ¬ ences upon elections, consecrations, institutions, mar¬ riages, &c. are heard. AUDIENDO & TERMINANDO, a writ, or rather a commission to certain persons, when any insurrection or great riot is committed in any place, for the appeas¬ ing and punishment thereof. AUDIENTES, or Auditores, in church history, an order of catechumens j consisting of those newly in¬ structed in the mysteries of the Christian religion, and not yet admitted to baptism. AUDIT, a regular hearing and examination of an account by some proper officers, appointed for that pur¬ pose. AUDITOR, in a general sense, a hearer, or one who listens or attends to any thing. Auditor, according to our Laiv, is an officer of the king, or some other great person, who, by examin¬ ing yearly the accounts of the under officers, makes up a general book, with the difference between their receipts and charges, and their allowances to alloca¬ tions. Auditor of the Receipts, is an officer of the exche¬ quer who files the tellers bills, makes an entry of them, and gives the lord treasurer a certificate of the money received the week before. He also makes de¬ bentures to every teller, before they receive any money, and takes their accounts. He keeps the black book of receipts, and the treasurer’s key of the treasury, and sees every teller’s money locked up in the new treasury. Auditors of the Revenue, or of the exchequer, offi¬ cers who take the accounts of those who collect the re¬ venues and taxes raised by parliament, and take the accounts of the sheriffs, escheators, collectors, tenants, and customers, and set them down in a book, and per¬ fect them. Auditors of the Prest and Imprest, officers of the exchequer, who take and make up the accounts of Ire¬ land, Berwick, the mint, and of any money impressed to any man for the king’s service. They received pound¬ age on all accounts passed by them, which amounted to a prodigious sum, especially in time of war. But the office is now abolished, and 7000I. a-year given to the incumbents. Auditors Collegiate, Conventual, &c. officers for¬ merly appointed in colleges, &c. to examine and pass their accounts. AUDITORES, in church history. See Audi- ENTES. The auditores formed one branch of the Manichean sect, which was divided into elect and auditors; cor- responding, according to some writers, to clergy anA. laity ; and, according to others, to the faithful and ca¬ techumens among the Catholics. By the Manichean rule, a different course of life was prescribed to the elect from that of the auditors. The latter might eat flesh, drink wine, bathe, marry, traffic, possess estates, Auditores bear magistracy, and the like; all which things were [j forbidden to the elect. The auditors were obliged to , Andran. . maintain the elect, and kneeled down to ask their bles- sing. Beausobre observes, that the elect were ecclesi¬ astics, and in genera], such as made profession of ob¬ serving certain counsels, called evangelic ; such as the clergy and monks j and they were called the perfect by Theodoret. The auditors were the laity, and so denominated, because they heard in the church, whilst others taught and instructed. AUDITORIUM, in the ancient churches, was that part of the church where the audientes stood to hear and be instructed. The auditorium was that part now called navis ec- clesiee*. In the primitive times, the church was so*gee strict in keeping the people together in that place, that ptavs. the person who went from thence in sermon-time, was ordered by the council of Carthage to be excommuni¬ cated. AUDITORY, something relating to the sense of hearing. Auditory, or Audience, an assembly of people who attend to hear a person who speaks in public. Auditory is also used for the bench whereon a ma¬ gistrate or judge hears causes. Auditory, in ancient churches. See Audito¬ rium. Auditory Passage, (meatus auditoriusf, in Ana¬ tomy ; the entrance of the ear. See Anatomy In¬ due. Auditory Nerves. See Anatomy Index. AUDRAN, Claude, a French engraver, the first of the celebrated artists of that name, was the son of Lewis Audran, an officer belonging to the wolf-hun¬ ters, in the reign of Henry IV. of France ; and was born at Paris in 1592. He never made any great pro¬ gress in that art; so that his prints are»held in little or no estimation. Yet though he acquired no great re¬ putation by his own works, it was no small honour to him to be the father of three great artists, Germain, Claude, and Girard ; the last of whom has immorta¬ lized the name of the family. Claude Audran retired from Paris to Lyons, where he resided, and died in 1677. Audran, Carl, a very eminent engraver, was bro¬ ther to the preceding, though some assert ,he was only his cousin-german ; and was born at Paris in 1594. In his infancy he discovered much taste, and a great dispo¬ sition for the arts; and to perfect himself in engrav¬ ing, which he appears to have been chiefly fond of, he went to Rome, where he produced several prints that did him great honour. At his return, he adopt¬ ed that species of engraving which is performed with the graver only* He settled at Paris, wdiere he died in 1674, without having ever been married. The Abbe Maiolles, who always speaks of this artist with great praise, attributes 130 prints to him: amongst which, the annunciation, a middle-sized plate, upright, from Hannibal Carracci; and the assumption, in a circle, from Domenichino, are the most esteemed. In the early part of his life he marked his prints with C, or the name of Carl, till his brother Claude published some plates with the initial only of his bap¬ tismal i A U D [ 262 ] A U E> Atidran. Strutt's Diction¬ ary. tismal name; when, for distinction’s sake, he used the letter K, or wrote his name K.arl, with the K instead of the C. Audran, Germaine^ the eldest son of Claude, men¬ tioned in the preceding article but one, was born in 1631 at Lyons, where his parents then resided. Not content with the instructions of his father, he went to Paris,, and perfected himself under his uncle Carl; so that, upon his return to Lyons, he published several prints which did great honour to his graver. His me¬ rit was in such estimation, that he was made a mem¬ ber of the academy established in that town, and cho¬ sen a professor. He died at Lyons in 1710, and left behind him four sons, all artists; namely, Claude, Be- noist, John, and Louis. Audran, Claude, the second of this name, and se¬ cond son to Claude above mentioned, was born at Lyons in 1639, and went to Rome to study paint¬ ing ; where he succeeded so well, that at his return he was employed by Le Brun to assist him in the battles of Alexander, which he was then painting for the king of France. He was received into the Royal Academy io the year 1675, and died unmarried at Paris in 1684. His virtues (says Abbe Fontenai) were as praiseworthy as his talents were great. M. Heineken mentions this artist as an engraver, without specifying any of his works in that line. Audran, Girard, or Gerard, the most celebrated artist of the whole family of the Audrans, was the third son of Claude Audran mentioned in a preceding article, and born at Lyons in 1640. Fie learned from his father the first principles of design and engra¬ ving ; and following the example of his brother, he left Lyons and went to Paris, where his genius soon began to manifest itself. His reputation there brought him to the knowledge of Le Brun, who employed him to engrave the battles of Constantine, and the triumph of that emperor; and for these works he obtained apart¬ ments at the Gobelins. At Rome, whither he went for improvement, he is said to have studied under Carlo Maratti, in order to perfect himself in drawing; and in that city, where he resided three years, he engraved several fine plates. M. Colbert, that great encourager of the arts, was so struck with the beauty of Audran’s works whilst he resided at Rome, that he persuaded Louis XIV. to recal him. On his return, he applied himself assiduously to engraving ; and was appointed engraver to the king, from whom he received great encouragement. In the year 1681 he was named coun¬ sellor of the Royal Academy ; and died at Paris in 1703. He had been married ; but left no male issue behind him. The great excellency of this artist above that of any other engraver was, that though he drew admirably himself, yet he contracted no manner of his own ; but transcribed on copper simply, with great truth and spirit, the style of the master whose pictures he copied. On viewing his prints you lose sight of the engraver, and naturally say, it is Le Brun, it is Poussin, it is Mignard, or it is Le Sueur, &c. as you turn to the prints which he engraved from those masters. Let any one examine the battles above-mentioned from Le Brun, the preservation of the young Pyrrhus from Nichol as Poussin, the pest from Mignard, and the mar¬ tyrdom of St Lawrence from Le Sueur, and then judge 3 candidly of the truth of this observation. The fol- Audnui lowing judicious observations by the abbe Fontenai, —y—. taken chiefly from M. Basan* with some small %'aria- tion and additions, will fully illustrate the merits of Gerard Audran. “ This sublime artist, far from con¬ ceiving that a servile arrangement of strokes, and the too frequently cold and affected clearness of the gra¬ ver, were the great essentials of historical engraving, gave worth to his works by a bold mixture of free hatchings and dots, placed together apparently without order, but with an inimitable degree of taste; and has left to posterity most admirable examples of the style in which grand compositions ought to be treated. His greatest works, which have not a very flattering ap¬ pearance to the ignorant eye, are the admiration of true connoisseurs and persons of fine taste. He ac¬ quired the most profound knowledge of the art by the constant attention and study which he bestowed upon the science of design, and the frequent use he made of painting from nature. This great man always knew how to penetrate into the genius of the painter he copied from; often improved upon, and sometimes even surpassed him. Without exception, he was the most celebrated engraver that ever existed in the histo¬ rical line. We have several subjects which he engra¬ ved from his own designs, that manifested as much taste as character and facility. But, in the battles of Alex¬ ander, he surpassed even the expectations of Le Brun himself.” These consist of three very large prints, lengthwise, each consisting of four plates, which join together, from Le Brun ; namely, the passage of the Granicus; the battle of Arbela ; Porus brought to A- lexander, after his defeat. To this set are added two hiore large prints lengthwise, on two plates each, also from Le Brun, as follow : Alexander entering the tent of Darius ; and The triumphal entry of Alexander into Babylon. The former was engraved by Gerard Ede- link, and the latter by Gerard Audran. It is to be remarked of all these plates, that those impressions are generally most esteemed which have the name of Goy- ton the printer marked upon them. The Pest, from Peter Mignard, a large plate, lengthwise, also deserves particular notice. In the first impressions, the figure in , the clouds is Juno with her peacock behind her; in the latter, the peacock is obliterated, and the wings of an angel are added to the figure. Audran, Benoit, the second son of Germain Au¬ dran, was born at Lyons in 1661, where he learn¬ ed the first principles of design and engraving under the instruction of his father; But soon after going to Paris, his uncle Gerard Audran took him under his tuition ; and Benoit so greatly profited by his instruc¬ tions, that though he never equalled the sublime style of his tutor, yet he deservedly acquired great reputa¬ tion. Nay, the abbe Fontenai adds this eulogium : “ We admire in his works a share of those beauties which we find in the engravings of the illustrious Ge¬ rard.” He was honoured with the appellation of the king’s engraver, and received the royal pension. He was made an academician, and admitted into tlje coun¬ cil in 1715. He died unmarried at Louzouer, where he had an estate, in 1721. His manner was founded upon the hold clear style of his uncle. His outlines were firm and determined ; his drawing correct; the heads of his figures are in general very expressive ; and A U D [ 263 ] A V E iudran. tlie other extremities well marked. His works, when —y--—' compared with those of his uncle, appear to want that mellowness and harmony which are so conspicuous in the latter; they are more dry ; and the round dots with which he finished his flesh upon the lights are of¬ ten too predominant. In his most finished plates, we find the mechanical part of the engraving extremely neat, and managed with great taste and judgment. Among his neatest prints may he reckoned that which represents Alexander sick, drinking from the cup which his physician presents to him ; a circular plate, from Le Sueur. Audran, John, the third son of Germain Audran, was born at Lyons in 1667 \ and, after having receiv¬ ed instructions from his father, went to Paris to perfect himself in the art of engraving under his uncle Gerard Aud ran. At the age of 20 years, the genius of this great artist began to display itself in a surprising man¬ ner ; and his future success was such, that in 1707, he obtained the title of engraver to the king, and had a pension allowed him by his majesty, with apartments in the Gobelins j and the following year he was made a member of the Royal Academy. He was 80 years of age before he quitted the graver: and near 90 when he died at his apartments assigned him by the king. He left three sons behind him •, one of whom was also an engraver, as we shall see below. “ The most ma¬ sterly and best prints of this artist (in Mr Strutt’s opi¬ nion) are those which are not so pleasing to the eye at first sight. In these the etching constitutes a great part; and he has finished them in a bold rough style. The scientific hand of the master appears in them on exami¬ nation. The drawing of the human figure, where it is shown, is correct. The heads are expressive and fine¬ ly finished ; the other extremities well marked. He has not, however, equalled his uncle. He wants that harmony in the effect ; his lights are too much and too equally covered ; and there is not sufficient difference between the style in which he has engraved his back grounds and his draperies. This observation refers to a fine print by him of Athaliah, and such as he engra¬ ved in that style. At other times he seems almost to have quitted the point, and substituted the graver. But here I think he has not so well succeeded. The effect is cold and silvery : see, for example, the Andro¬ mache from Sylvestre. One of his best finished -prints, m this neat style, seems to me to be Cupid and Psyche from Ant. Coypel.” Audran, Loins, the last son of Germain Audran, was born at Lyons in 1670 ; from whence he went to Paris, after the example of his brothers, to complete his studies in the school of his uncle Gerard. He died suddenly at Paris in I7,2, before he had produced any great number of prints by his own hand. He assisted, it is presumed, his brothers in their more ex¬ tensive works. Among the most esteemed prints by this artist are the seven acts of mercy, on seven middling sized plates, lengthwise, from Sebastian Bourdon. Audran, Benoit, the second engraver of that name, was the. son of John Audran, and nephew to the for¬ mer Benoit: and was also established at Paris. He engraved but a few plates. It is necessary, however, to be careful not to confound him with his uncle. But a little attention will easily prevent this mistake ; ^or the second Benoit is vastly inferior to the first in point of merit. We have some few portraits by this And ran artist: and among other plates, the descent from the fj cross, from a picture of Poussin. Avelfino. AVLIRO, a considerable city of Portugal, seated ^ near the head of a small gulf formed by the tide at the mouth of the river Vouga. This river forms a small haven with a bar, over which vessels may pass that do not draw above eight or nine feet water. The city stands in a long plain well watered, and very fertile. This plain is nine miles broad, from Porto to Coimbra ; and is bounded on the east by a chain of mountains called Sara d'Alcoba, which reach from the one town to the other. Near this city there is salt made in suf¬ ficient quantity to serve two or three provinces. Here is a remarkable nunnery, where none are received but the daughters of the ancient nobility. The inhabitants of Aveiro have the singular privilege, that no stranger whatever can pass a night there without leave of the magistrate. W. Long. 8. 34. N. Lat. 40. 30. AVELLANE, in Heraldry, a cross, the quarters of which somewhat resemble a filbert-nut. Sylvanns Morgan says, that it is the cross which ensigns the mound of authority, or the sovereign’s globe. A\ELLINO, a city of Italy, in the kingdom of Naples, with a bishop’s see. It was almost ruined by an earthquake in 1694. It is, however, at present a pretty considerable place, extending a mile in length down the declivity of a hill, with ugly streets, but to¬ lerable houses. The churches have nothing to recom¬ mend them, being crowded with monstrous ornaments, in a barbarous style, which the Neapolitans seem to have borrowed from the Spaniards. The cathedral is a poor building, in a wretched situation, with little to attract the eye. The good people here need not run to Naples to see the blood of St Januarius : for they have a statue of St Lawrence, with a phial of his blood, which for eight days in August entertains them with a similar miraculous liquefaction. Their only edi¬ fice of note is a public granary, of the Composite or¬ der, adorned with antique statues, and a very elegant bronze one of Charles II. of Spain, while a boy, cast by Cavalier Cosimo. The number of inhabitants amounts to 8000, some say 10,000. The bishop’s re¬ venue is about 6000 ducats (1125I.) a year. The magistracy consists of a syndic and four eletti, ail annual ; which offices are engrossed by a certain num¬ ber of families of some distinction, that neither inter¬ marry nor associate with the rest of the burghers. There is a considerable manufacture of cloth here of various qualities and colours, but chiefly blue. Many wealthy merchants have a concern in this business, some with a capital of eighty thousand ducats (15,000!.). The poor women who spin the wool must work very hard to earn above four grana a-day. The second article of trade is maccaroni and paste of many kinds, which be¬ ing of an excellent quality, are in high repute all over the country. Wooden chairs are also made and sold here in great quantities. Avellino abounds writh pro¬ visions of every sort; each street is supplied with whole¬ some water; the wine is but indifferent. The soil of this district, which consists chiefly of volcanic substan¬ ces, produces little corn, but fruit in abundance, of which the apple is deservedly held in great esteem. The most profitable, however, of all its fruit-trees is the hazel. Nut bushes cover the face of the valley, and in , good- A V E [ 264 ] AYE 'Avelh'no good years bring in a profit of sixty thousand ducats |j (il,250l.)* The nuts are mostly of the large round Aventine. species of filbert, which we call Spanish. These bushes U’“”’v were originally imported into Italy from Pontus, and known among the Homans by the appellation of 'Nux Pontica, which in process of time was changed into that of Nux Avcliana, from the place where they had been propagated with the greatest success. The pro¬ prietors plant them in rows, and by dressing, form them into large bushes of many stems. Every year they re¬ fresh the roots with new earth, and prune off the strag¬ gling shoots with great attention. AVE MARIA, the angel Gabriel’s salutation of the Virgin Mary, when he brought her the tidings of the incarnation.—It is become a prayer or form of de¬ votion in the Romish church. The chaplets and rosa¬ ries are divided into so many ave-marias, and so many pater-nosters, to which the Papists ascribe a wonderful efficacy. AVENA, Oats. See Botany Index. AVENACEOUS, something belonging to or par¬ taking of the nature of oats. AVENAGE, in Law, a certain quantity of oats paid by a tenant to a landlord, instead of rent or some other duties. AVENCHE, an ancient city of Switzerland, in the canton of Bern, formerly the capital of all Switzerland, but now shows its former greatness only by its ruins. E. Long. 7. 7. N. Lat. 46. 50. AVENES, a small but strong town in French Flan¬ ders, in the county of Hainault, seated on the river Thespis. It contains about 2700 inhabitants j but the houses are wretchedly built, and the streets irregular. It was fortified by M. Vaubian in a strong regular man¬ ner. About this place is a prodigious number of white stones proper for building, and used by sculptors for sta¬ tues : they are known by the name of Stones of Avenes. E. Long. 3. 50. N. Lat. 50. 10. AVENIO, an ancient town of the Cavares, and one of the most opulent in Gallia Narbonensis 5 now Avig¬ non, in Provence. See Avignon. AYENOE, an officer belonging to the king’s stables, who provides oats for the horses. He acts by warrant from the master of the horse. AVENS. See Cariophyllus, Botany Index. A\ENTINE, John, author of the Annals of Ba¬ varia, was born of mean parentage, in the year 1466, at Abensperg in the country just named. He studied first at Ingoldstadt, and afterwards in the university of Paris. In 1503, he privately taught eloquence and poetry at Vienna; and in 1507 he publicly taught Greek at Cracow in Poland. In 1509, he read lectures on some of Cicero’s works at Ingoldstadt: and in 1512, was appointed to be preceptor to Prince Louis and Prince Ernest, sons of Albert the Wise, duke of Bava¬ ria, and travelled with the latter of these two princes. After this he undertook to write the annals of Bava¬ ria; being encouraged by the dukes of that name, who settled a pension upon him, and gave him hopes that they would defray the charges of the book. This work, which gained its author great reputation, was first published in I554> by Jerome Zieglerus, professor of poetry in the university of Ingoldstadt; and afterwards at Basil in 1580, by Nicholas Cisner. An affront which Aventine received in the year 1529, stuck by him all the rest of his life : he was forcibly taken out of his sis- ter’s house at Abensperg, and hurried to jail; the true y ? cause of which violence was never known : but it would Avenue, probably have been carried to a much greater length, had not the duke of Bavaria interposed, and taken this learned man into his protection. Mr Bayle remarks, that the incurable melancholy which from this time pos¬ sessed Aventine, was so far from determining him to lead a life of celibacy, as he had done till he was 64, that it induced him perhaps to think of marrying. The violence of his new passion was not, however, so great, but that it suffered him to advise with two of his friends, and consult certain passages of the Bible relative to mar¬ riage. The result was, that it was best for him to marry ; and having already lost too much time, consi¬ dering his age, he took the first woman he met with, who happened to be his own maid, ill-tempered, ugly, and extremely poor. He died in 1534, aged 68 ; leav¬ ing one daughter, who was then but two months old. He had a son, who died before. AVEN L INES mons, one of the seven hills on which ancient Rome stood. The origin of the name Aventinus is uncertain : but this hill was also called Murcius, from Murcia the goddess of sloth, who had a little chapel there ; and Collis JDiance, from the temple of Diana; likewise Remonius, from Remus, who want¬ ed to build the city, and who was buried there. It was taken within the compass of the city by Ancus Mar- tius. To the east it had the city walls; to the south, the Campus Figulinus ; to the west, the Tiber; and to the north, Mons Palatinus : in circuit two miles and a quarter. AVENTURE, in law books, means a mischance causing the death of a person without felony. AVENUE, in Gardening, a walk planted on each side with trees, and leading to a house, garden-gate, wood, &c. and generally terminated by some distant object. All avenues that lead to a house ought to be at least as wide as the whole front of the house, if wider they are better still ; and avenues to woods, and prospects, ought not to be less than 60 feet wide. The trees should not be planted nearer to one another than 35 feet, especially if they are trees of a spreading kind ; and the same ought to be the distance, if they are for a regular grove. The trees most proper for avenues with us, are the English elm, the lime, the horse-chesnut, the common chesnut, the beech, and the abele. The English elm will do in all grounds, except such as are very wet and shallow; and this is preferred to all other trees, be¬ cause it w7ill bear cutting, heading, or lopping in any manner, better than most others. The rough or smooth Dutch elm is approved by some, because of its quick growth. This is a tree which will bear removing very well; it is also green almost as soon as any plant what¬ ever in spring, and continues so as long as any, and it makes an incomparable hedge, and is preferable to all other trees for lofty espaliers. The lime is valued for its natural growth add fine shade. The horse-chesnut is proper for all places that are not too much exposed to rough winds. The common chesnut will do very well in a good soil; and rises to a considerable height, when planted somewhat close ; though, when it stands single, it is rather inclined to spread than to grow tall. The A V E [ 265 ] AYE The beech is a beautiful tree, and naturally grows well with us in its wild state; but it is less to be chosen for 1 avenues than the before-mentioned, because it does not bear transplanting well, but is very subject to miscarry. Lastly, the abele is fit for any soil, and is the quickest grower of any forest-tree. It seldom fails in trans¬ planting 5 and succeeds very well in wet soils, in which the others are apt to fail. The oak is but little used for avenues, because of its slow growth. The old method of planting avenues was with re¬ gular rows of trees, and this has been always kept to till of late : but we have now a much more magnifi¬ cent way of planting avenues $ this is by setting the trees in clumps, or platoons, making the opening much wider than before, and placing the clumps of trees at about 300 feet distant from one another. In each of these clumps there should be planted either seven or nine trees ; but it is to be observed, that this is only to be practised where the avenue is to be of some considerable length, for in short walks this will not ap¬ pear so sightly as single rows of trees. The avenues made by clumps are fittest of all for parks. The trees in each clump should be planted about 30 feet asunder j and a trench should be thrown up round the whole clump, to prevent the deer from coming to the trees to bark them. AVENZOAR, Abu Merwan Abdalmalec ebn Zohr, an eminent Arabian physician, flourished about the end of the eleventh or the beginning of the twelfth century. He was of noble descent, and born at Se¬ ville, the capital of Andalusia, where he exercised his profession with great reputation. His grandfather and father were both physicians. The large estate he inherited from his ancesters, set him above practising altogether for gain : he therefore took no fees from the poor, or from artificers, though he refused not the pre¬ sents of princes and great men. His liberality was ex¬ tended even to his enemies j for which reason he used to eay, that they hated him not for any fault of his, but rather out of envy. Dr Freind writes, that he lived to the age of 135 j that he began to practise at 40, or (as others say) at 20 j and had the advantage of a longer experience than almost any one ever had, for he enjoyed perfect health to his last hour. He left a son, known also by the name of Ebn Zohr, who followed his father’s profession, was in great favour with A1 Mantur emperor of Morocco, and wrote several treatises of physic. Avenzoar was cotemporary with Averroes, who, ac¬ cording to Leo Africanus, heard the lectures of the former, and learned physic of him ; this seems the more probable, because Averroes more than once gives Aven- zoar a very high and deserved encomium, calling him admirable, glorious, the treasure of all knowledge, and the most supreme in physic from the time of Galen to his own. Avenzoar, notwithstanding, is by the generality of writers reckoned an empiric: but DrFreind observes, that this character suits him less than any of the rest of the Arabians. “ He was bred,” continues that author, “ in a physical family, his father and grandfather being both practitioners, whom he always remembers with great gratitude and honour. We have his own testimo¬ ny that he had a regular education ; and that he not only learned what properly belongs to a physician, but, out of a great desire of knowledge every thing besides Vol. III. Part I. t which relates to pharmacy or surgery.” Dr Freind afterwards observes, “ that he was averse to quackery, and rejects the idle superstitions of astrologers j and throughout all his works professes himself so much of the dogmatical or rational sect, which was directly op¬ posite to the empirical, that he has a great deal of rea¬ soning about the causes and symptoms of distempers ; and as in his theory he chiefly, if not only, follows Ga¬ len, so he quotes him upon all occasions, oftener than the rest of the Arabians do. Notwithstanding he is so Galenical, there are several particulars in him which seldom or ever occur in other authors j and there are some cases which he relates from his own experience, which are worth perusing.” He wrote a book entitled, Tayassir fdlm&dawat w'altadbir, i. e. “ The method of preparing medicines and diet 5” which is much esteemed. This work was translated into Hebrew, in the year of Christ 1280, and thence into Latin by Pa- ravicius, whose version has had several editions. The author added a supplement to it, under the title of Jdme, or a Collection. He also wrote a treatise Fi'lad- wiyat wdilaughdiyat, i. e. “ Of Medicines and Food j” wherein he treats of their qualities. AVERAGE, in Commerce, signifies the accidents and misfortunes which happen to ships and their car¬ goes, from the time of their loading and sailing to their return and unloading; and is divided into three kinds. 1. The simple or particular average, which consists in the extraordinary expences incurred for the ship alone, or for the merchandises alone. Such is the loss of anchors, masts, and rigging, occasioned by the common accidents at sea; the damages which happen to merchants by storm, prize, shipwreck, wet, or rot¬ ting $ all which must be borne and paid by the thing which suffered the damage. 2. The large and common average, being those expences incurred, and damages sustained, for the common good and security both of the merchandises and vessels, consequently to be borne by the ship and cargo, and to be regulated upon the whole. Of this number are the goods or money given for the ransom of the ship and cargo, things thrown overboard for the safety of the ship, the expences for unloading, for entering into a river or harbour, and the provisions and hire of the sailors when the ship is put under an embargo. 3. The small averages, which are the expences for towing and piloting the ship out of or into harbours, creeks, or rivers, one third of which must be charged to the ship, and two thirds to the cargo. Average is more particularly used for a certain con¬ tribution that merchants make proportionably to their losses, who have had their goods cast into the sea in the time of a tempest. It also signifies a small duty which those merchants, who send goods in another man’s ship, pay to the master for his care of them over and above the freight. Hence it is expressed in the bills of lading, paying so much freight for the said goods, with primage and average accustomed. AVERDUPOIS. See Avoirdupois. AVERNUS, a lake of Campania in Italy, near Baiae, famous among the ancients for its poisonous qualities. It is described by Strabo as lying within the Lucrine bay, deep and darksome, surrounded with steep banks that hang threatening over it, and only L1 accessible Avenzoar 11 Avernus. A V E [ 266 ] A V E Avernu*. accessible by the narrow passage through which you " ~ v sail in. Black aged groves stretched their boughs over the watery abyss, and with impenetrable foliage exclu¬ ded almost every ray of wholesome light; mephitic, vapours ascending from the hot bowels ot the earth, being denied free passage to the upper atmosphere, floated along the surface in poisonous mists. These circumstances produced horrors fit for such gloomy deities ; a colony of Cimmerians, as well suited to the rites as the place itself, cut dwellings in the bosom of the surrounding hills, and officiated as priests of Tar¬ tarus. Superstition, always delighting in dark ideas, early and eagerly seized upon this spot, and hither she led her ti’embling votaries to celebrate her dismal or¬ gies ; here she evoked the manes of departed heroes— here she offered sacrifices to the gods of hell, and at¬ tempted to dive into the secrets of futurity. Poets enlarged upon the popular theme, and painted its awful scenery with the strongst colours of their art. Ho¬ mer brings Ulysses to Avernus, as to the mouth of the infernal abodes ; and in imitation of the Grecian bard, Virgil conducts his hero to the same ground. Who¬ ever sailed thither, first did sacrifice; and endeavoured to propitiate the infernal powers, with the assistance of some priests who attended upon the place, and directed the mystic performance. Within, a fountain of pure water broke out just over the sea, which w^as fancied to be a vein of the river Styx ; near this fountain was the oracle : and the hot waters frequent in those parts were supposed to be branches of the burning Phlege- thon. The poisonous effluvia from this lake were said to be so strong, that they proved fatal to birds endea¬ vouring to fly over it. Virgil ascribes the exhalation not to the lake itself, but to the cavern near it, which was called Averting or Cave of the Sybil, and through which the poets feigned a descent to hell. Plence the proper name of the lake is Lacug Averni, the “ lake near the cavern,” as it is called by some ancient au¬ thors. The holiness of these shades remained unimpeached for many ages : Hannibal marched his army to offer incense at this altar; but it may be suspected he was led to this act of devotion rather by the hopes of surpri¬ sing the garrison of Puteoli, than by his piety. After a long reign of undisturbed gloom and celebrity, a sud¬ den glare of light was let in upon Avernus ; the horrors were dispelled, and with them vanished the sanctity of the lake : the axe of Agrippa brought its forest to the ground, disturbed its sleepy waters with ships, and gave room for all its malignant effluvia to escape. The viru¬ lence of these exhalations, as described by ancient au¬ thors, has appeared so very extraordinary, that modern writers, who know the place in a cleared state only, charge these accounts with exaggeration : but Mr Swin¬ burne thinks them entitled to more respect; for even now he observes the air is feverish and dangerous, as the jaundiced faces of the vine-dressers, who have suc¬ ceeded the Sibyls and Cimmerians in the possession of the temple, most ruefully testify. Boccacio relates, that during his residence at the Neapolitan court, the surface of this lake was suddenly covered with dead fish, black and singed, as if killed by some subaqueous erup¬ tion of fire. At present the lake abounds with tench ; the Lu- erine with eels. The change of fortune in these lakes is singular: In the splendid days of imperial Rome the Lucrine was the chosen spot for the brilliant parties of pleasure of a voluptuous court: now, a slimy bed of rushes covers the scattered pools of this once beautiful sheet of water ; while the once dusky Avernus is clear and serene, oftering a most alluring surface and charm¬ ing scene for similar amusements. Opposite to the tem¬ ple is a cave usually styled the Sibyl’s grotto; but ap¬ parently more likely to have been the mouth of a com¬ munication between Cuma and Avernus, than the abode of a prophetess; especially as the Sibyl is positively said by historians to have dwelt in a cavern under the Cu- mean citadel. AVERRHOA. See Botany Index. AVERROES, one of the most subtile philosophers that ever appeared among the Arabians, flourished at the end of the nth and beginning of the 12th centu¬ ry. He was the son of the high-priest and chief judge of Corduba in Spain : he was educated in the univer¬ sity of Morocco ; and studied natural philosophy, me¬ dicine, mathematics, law and divinity. After the death of his father, he enjoyed his posts; but notwith¬ standing his being exceeding rich, his liberality to men of letters in necessity, whether they were his friends or his enemies, made him always in debt. He was after¬ wards stripped of all his posts, and thrown into prison, for heresy ; but the oppressions of the judge who suc¬ ceeded him, caused him to be restored to his former employments. He died at Morocco in the year 1206. He was excessively fat, though he ate but once a-day. He spent all his nights in the study of philosophy ; and when he was fatigued, amused himself with reading poetry or history. He was never seen to play at any game, or to partake in any diversion. Pie was extremely fond of Aristotle’s works, and wrote commentaries on them ; whence he was styled the commentator, by way of emi¬ nence. He likewise wrote a work on the whole art of physic, and many amorous verses ; but when he grew old, he threw these last into the fire. His other poems are lost, except a small piece, in which he says, “ That when he was young, he acted against his rea¬ son ; but that when he was in years, he followed its dictates upon which he utters this wish ; “ Would to God I had been born old, and that in my youth I had been in a state of perfection !” as to religion, his opinions were, that Christianity is absurd ; Judaism, the religion of children ; Mahometanism, the religion of swine. A VERROISTS, a sect of Peripatetic philosophers, who appeared in Italy some time before the restoration of learning, and attacked the immortality of the soul. They took their denomination from Averroes, the celebrated interpreter of Aristotle (see the preceding article), from whom they borrowed their distinguishing doctrine. The Averroists, who held the soul was mortal, ac¬ cording to reason or philosophy, yet pretended to submit to the Christian theology, which declares it immortal. But the distinction was held suspicious ; and this di¬ vorce of faith from reason was rejected by the doctors of that time, and condemned by the last council of the Lateran under Leo X. AVERRUNCI (dei)); certain gods, whose business it was, according to the Pagan theology, to avert mis¬ fortunes. AUG .Terrunci *uge. fortunes. Apollo and Hercules were of the number of these gods among the Greeks j and Castor and Pollux among the Romans. 1 AVERSA, a town of Italy in the kingdom of Na¬ ples, with a bishop’s see. It is situated in a very fine plain, in E. Long. 14. 20. N. Lat. 41. o. AVERSION, according to Lord Karnes, is opposed to affection, and not to desire, as it commonly is. We have an affection to one person $ We have an aversion to another 5 the former disposes us to do good to its object, the latter to do ill. AVERTI, in Horsemanship, is applied to a regular step or motion enjoined in the lessons. In this sense they say pas averte, sometimes pas ecouti, and pas d'ecole, which all denote the same. The word is mere French, and signifies advised. AVES, one of the Carribbee islands, 451 miles south of Porto Rico, with a good harbour for careening of ships. It is so called from the great number of birds that frequent it. There is another of the same name lying to the northward of this, in N. Lat. 15. o. j and a third near the eastern coast of Newfoundland, in N. Lat. 50. 5. Aves, Birds, the name of Linnaeus’s second class of animals. See Ornithology. AVESBURY, Robert, an English historian, of whom little more is known than that he was keeper of the registery of the court of Canterbury in the reign of Edward III. and consequently that he lived in the 14th century. He wrote, Memorabilia gesta magnijici regis Anghce domini Edieardi tertii post conqueslum, procerumque ; tactis primitus quibusdam gestis de tem¬ pore patris sui domini Edwardi secitndi, qvcr in regnis Anghce, Scotice, et Francice, ac in Aquitania et Britan¬ nia, non humana sed Dei potentia, contigerunt, per Robertum de Avesbury. This history ends with the battle of Poictiers, about the year 1356. It continued in manuscript till the year 1720, when it was printed by the industrious Thomas Ilearne at Oxford, from a manuscript belonging to Sir Thomas Seabright. It is now become very scarce. AVEZZANO, a town of Italy in the kingdom of Naples, in the Farther Abruzzo. It is built on an al¬ most imperceptible declivity, one mile from the lake ot Celano, to which an avenue of poplar's leads from the baronial castle. This edifice stands at a little di¬ stance from the town, is square, and flanked with towers; it was erected by Virginio Orsini, to which family this and many other great lordships belonged, before they were wrested from them in times of civil war, and transferred to the Colonnas. Avezzano was founded in 860, and contains 2700 inhabitants, and two religious communities within its walls, which are indeed in a ruinous condition. The houses are in general mean ; but there are some large buildings and opulent families of the class of gentlemen, not possessed of fees held in capite. AUGE, formerly a territory of Normandy in France, which gave title to a viscount. It extends from Falaise and Argenton as far as the sea, between the rivers Hives, \ ie, and Tongues. The arable land is stiff, and produces but littie good corn : but they sow sainfoin ; which succeeds so well that they have five good crops successively; they likewise sow flax and hemp; and have a vast quantity of apples, with which they make cy- [ 267 ] AUG der. Horses are bred here in great numbers; and the inhabitants fatten the oxen which come from Poictou and Britanny. AUGEAS, in fabulous history, was king of Elis, and particularly famed for his stable, which contained 3000 oxen, and had not been cleaned for 30 years, Hercules was desired to clear away the filth from this stable in one day; and Augeas promised, if he per¬ formed it, to give him a tenth part of the cattle. This task Hercules is said to have executed by turning the course of the river Alpheus through the stable ; when Augeas refusing to stand by his engagement, Hercules slew him with his arrows, and gave his kingdom to Phyleus his son, who had shown an abhorrence of his father’s insincerity. AUGMENT, in Grammar, an accident of certain tenses of Greek verbs, being either the prefixing of a syllable, or an increase of the quantity of the initial vowels. AUGMENTATION, in a general sense, is the act of adding or joining something to another with a design to render it large. Augmentation is also used for the additament or thing added. Augmentation was also the name of a court erect¬ ed 27 Hen. VIII. so called from the augmentation of the revenues of the crowm, by the suppression of religi¬ ous houses ; and the office still remains, wherein there are many curious records, though the court has been dis¬ solved long since. Augmentation, in Heraldry, are additional char¬ ges to a coat-armour, frequently given as particular marks of honour, and generally borne either in the es¬ cutcheon or a conton ; as have all the baronets of Eng¬ land, who have borne the arms of the province of Ulster in Ireland. AUGRE, or Awgre, an instrument used by carpen¬ ters and joiners to bore large round holes ; and consist¬ ing of a wooden handle, and an iron blade terminated at bottom with a steel bit. AUGSBURG, a city of Germany, in the king¬ dom of Bavaria, seated near the confluence of the Ardech and Lech, in one of the most beautiful plains that can be imagined. It is one of the largest and handsomest cities of the empire ; but the fortifications are after the old manner, and very irregular ; the streets are broad and straight ; the houses mostly of timber, plastered and whitened without, or adorned with paint¬ ings; the rest are of freestone; the churches and foun¬ tains are generally ornamented with fine figures of brass. Many of the churches are stately, and adorned within with curious workmanship and paintings. That part of the city erected by the noble family of the Fuggers, who are lords of the adjacent country, consists of seve¬ ral streets crosswise, containing 106 houses : the poor people that inhabit them are maintained by an annual pension. Its magnificent town-house is little inferior to that of Amsterdam, being a vast square stone build¬ ing, with a marble portico ; at the top of the front, w'ithin the pediment, is a large spread eagle, hold¬ ing a sceptre and globe, in its talons, of brass gilt, said to weigh 2200 weight ; the great portal is of a very beautiful reddish marble, over which is a balcony of the same colour, supported by two pillars of white marble ; over the gate there are two large griffins of L 1 2 brass r AUG [ 268 ] AUG Augsburg brass; most of the rooms are wainscotted ami ceiled \r—■' with very fine timber : the great hall is very magnifi¬ cent, and paved with marble ; it is 110 feet long, 58 broad, and 52 high, and its roof is supported by eight columns of red marble : the ceiling of the upper wall is of very curious workmanship of polished ash, consist¬ ing of compartments, the squares and pannels of which are enriched with gilded sculptures, and filled with pictures and other ornaments 5 this is likewise support¬ ed by eight pillars, with bases and chapiters of brass : the other rooms are handsomely adorned with very fine paintings. In the square, near the town-house, is the fountain of Augustus, which is a marble bason, surrounded with iron ballustrades finely wrought: at the four corners are four brass statues, as big as the life, two of which are women and two men •, in the middle of the bason is a pedestal, at the foot of which are four large sphinxes squirting water out of their breasts ; a little above these are four infants holding four dolphins in their arms, which pour water out of their mouths : and over these infants are festoons and pine-apples all of brass ; upon the pedestal, is the statue of Augustus as large as the life. The fountain most remarkable next to this is that of Hercules, which is a hexagon bason with several brass figures, particularly Hercules engaging the hydra. Another curiosity is the secret gate, which was contri¬ ved to let in persons safely in time of war : it has so many engines and divisions with gates and keys, and apartments for guards at some distance from each other, where passengers are examined, that it is impossible for the town to be surprised this way $ the gates are bolted and unbolted, opened and shut, by unseen operators, insomuch that it looks like enchantment. The water- towers are also very curious, of which there are three seated on a branch of the river Lech, which runs through the city in such a torrent as to drive many mills, which work a number of pumps that raise the water in large leaden pipes to the tops of the towers j one of these sends water to the public fountains, and the rest to near IOOO houses in the city. The Lutherans have a college here, which is a vast square building, with a fine clock on the top of the front. In this there are seven different classes, a hall for public disputations, and a theatre for dramatic repre¬ sentations. The cathedral is a large, gloomy, Gothic building, with two spire steeples; it is adorned with paintings upon whimsical subjects, and has a great gate all of brass, over which are several scripture passages well represented in basso-relievo. The Jesuits had a splendid college here, with a church full of gilding, painting, and carving j and a fine library. Though half the inhabitants are Lutherans, there are a great many Popish processions. There are no Jews in the town, nor are they sufiered to lie there \ but they in¬ habit a village at about a league distance, and pay so much an hour for the liberty of trading in the day¬ time. The Benedictine abbey is a vast Gothic build¬ ing, the ceiling of which is said to be the highest in Germany, and overlooks all the rest of the churches j it is adorned with several statues, and has one very grand altar. The church of St Croix is one of the handsomest in Augsburg for architecture, painting, sculpture, gilding, and a fine spire. Hie inhabitants look upon Augustus Caesar as the founder of the town : it is true, that that emperor sent Augsburg, a colony there ; but the town was already founded, — though he gave it the name of Augusta Vindelicorum. Augsburg, indeed, is one of the oldest towns in Ger¬ many, and one of the most remarkable of them, as it is there and at Nuremberg that you meet with the oldest marks of German art and industry. In the 14th and 15th centuries, the commerce of this town was the most extensive of any part of south Germany, and contributed much to the civilization of the country, by the works of art and variety of necessaries to the com¬ fort and convenience of life which it was the means of introducing. Many things originated in this town which have had a great influence on the happiness of mankind. Not to mention the many important diets of the empire held here $ here, in 952, did a council confirm the order for the celibacy of priests j here, in I53°, was the confession of faith of the Protestants laid before the emperor and other estates of Germany j and here, in 1555, was signed the famous treaty of peace, by which religious liberty was secured to Ger¬ many. Though the Protestants were very powerful at Augs¬ burg, they could not keep their ground : for the Ba¬ varians drove them from thence: but Gustavus Adol¬ phus restored them again in 1632; since which time they have continued there, and share the government with the Catholics. In 1703, the elector of Bavaria took the city after a siege of seven days, and demolish¬ ed the fortifications: however the battle of Hochstedt restored their liberty, which they enjoyed under the go¬ vernment of their own magistrates, till the French re¬ volution. It was suffered to continue a free city in 1803, but was united to Bavaria in 1807. The chap¬ ter is composed of persons of quality, who are to bring proofs of their nobility, and the canons have a right of electing their own bishop. The police of the place is very good : and though the town has no territory, it has no debts. Augsburg is, however, no longer what it was. It no longer has a Fugger and a Welser in it to lend the emperor millions. In this large and handsome town, formerly one of the greatest trading towns in Germany, there are no merchants at present to be found who have capitals of more than 20,oool. The others, most of whom must have their coaches, go creeping on with capitals of 3000I. or 4000I. and do the business of brokers and commissioners. Some houses, however, carry on a lit¬ tle banking trade $ and the way through Tyrol and Graubundten occasions some little exchange between this place and Germany. After these brokers and doers of business by commission, the engravers, statu¬ aries, and painters, are the most reputable of the la¬ bouring part of the city. Their productions, like the toys of Nuremberg, go everywhere. There are al¬ ways some people of genius amongst them ; but the small demand for their art affords them so little en¬ couragement, that to prevent starving they are mostly confined to the small religious works which are done elsewhere by Capuchin monks. They furnish all Ger¬ many with little pictures for prayer books, and to hang in the citizens houses. There is an academy of arts instituted here under the protection of the magi¬ strates : the principal aim of which is to produce good mechanics, and preserve the manufactures of the citv. This AUG [ 269 ] AUG m^bnrg This town, which is nine miles and a half in circum- [] ference, contains, according to Mr Riesbeck, hardly Uigirale. 30,000 inhabitants : hut Mr Nicolai makes them about ~ 35.00.0' .... This city has its drinking water from the river Lech, which runs at some distance from it; and the aqueducts which convey the water are much to be admired. It is a central depositary of the Neckar, Tyrolese, Italian, and Greek wines. Another important branch of traf¬ fic here is that of bookselling and publishing, especially in Catholic literature. The Catholics have six churches and eight monasteries here, and the Lutherans six churches ; but the former considerably exceed the lat¬ ter in point of numbers. This city was first constituted the capital of the circle of the Lech, hut was joined in 1810 to that of the Iller, of which Kempten is now the chief town. The elector of Treves fixed his resi¬ dence here after the secularisation of his territeries. A wooden bridge of ingenious structure was built over the Lech at Augsburg in 1808. In the war of 1756, the citizens were divided into equal parties for the two courts. The Catholics considered the emperor as their god, and the Protestants did the same by the king of Prussia. The flame of religion had almost kindled a bloody civil war amongst them.—The bishop takes his name from this town, but resides at Dillingen. He has an income of about 20,oool. per annum. As a proof of the Catholicism of this place, the Pope through¬ out his whole progress met nowhere with such honours as he did here. This he owed to his friends the Je¬ suits, who had great influence in this place. E. Long. 10. 58. N. Lat. 48. 24. Augsburg Confession^ denotes a celebrated confes¬ sion of faith drawn up by Luther and Melancthon, on behalf of themselves and other ancient reformers, and presented in 1530 to the emperor Charles V. at the diet of Augusta or Augsburg, in the name of the evangelic body. This confession contains 28 chapters; of which the greatest part is employed in representing, with perspicuity and truth, the religious opinions of the Protestants, and the rest in pointing out the errors and abuses that occasioned their separation from the church of Rome. AUGUR, an officer among the Romans appointed to foretel future events, by the chattering, flight, and feeding of birds. There was a college or community of them, consisting originally of three members, with respect to the three tribes, the Luceres, Ramnenses, and Tatienses : afterwards the number was increased to nine, four of whom were patricians and five ple¬ beians. They bore an augural staff or wand, as the ensign ol their authority ; and their dignity was so much respected, that they were never deposed, or any substituted in their place, though they should be con¬ victed of the most enormous crimes. See Augury. AUGURAL, something relating to the augurs.— The augural instruments are represented on several ancient medals. Augural Supper, that given by a priest on his first admission into the order, called also by Varro Adjici- alis. Augural Books, those wherein the discipline and rules of augury were laid down. AUGURALE, the place in a camp where the ger neral took auspicia. This answered to the Augurato- Augural® Hum in the city. |] Augurale is also used in Seneca for the ensign or ^Uknil'-Y' badge of an augur, as the lituus. ~ v AUGU RATORIUM, a building on the Palatine mount, where public auguries were taken. AUGURY, in its proper sense, the art of foretelling future events by observations taken from the chatter¬ ing, singing, feeding, and flight, of birds ; though it is used by some writers in a more general signification, as comprising all the different kinds of divination. Augury was a very ancient superstition. We know from Hesiod, that husbandry was in part regulated bv the coming or going of birds : and most probably it had been in use long before his time, as astronomy was then in its infancy. In process of time, these animals seem to have attained a greater and very wonderful au¬ thority, till at last no affair of consequence, either oL private or public concern, was undertaken without consulting them. They were looked upon as the in¬ terpreters of the gods ; and those who were qualified to understand their oracles were held among the chief men in the Greek and Roman states, and became the assessors of kings, and even of Jupiter himself. How¬ ever absurd such an institution as a college of augurs may appear in our eyes, yet, like all other extrava¬ gant institutions, it had in part its origin from nature. When men considered the wonderful migration of birds, how they disappeared at once, and appeared again at stated times, and could give no guess where they went, it was almost natural to suppose that they retired somewhere out of the sphere of this earth, and perhaps approached the ethereal regions, where they might converse with the gods, and thence be enabled to predict events. It was almost natural for a super¬ stitious people to imagine this ; at least to believe it, as soon as some impostor was impudent enough to assert it. Add to this, that the disposition in some birds to imitate the human voice, must contribute much to the confirmation of such a doctrine. This institution of augury seems to have been much more ancient than that of aruspicy ; for we find many instances of the for¬ mer in Homer, but not a single one of the latter, though frequent mention is made of sacrifices in that author. From the whole of what has been observed, it seems probable that natural augury gave rise to religious au¬ gury, and this to aruspicy, as the mind of man makes a very easy transition from a little truth to a great deal of error. A passage in Aristophanes gave the hint for these observations. In the comedy of the Birds, he makes one of them say this : “ The greatest blessings which can happen to you mortals, are derived from us. First, we show you the seasons, viz. spring, winter, au¬ tumn. The crane points out the time for sowing, when she flies with her warning notes into Egypt; she bids the sailor hang up his rudder and take his rest, and every prudent man provide himself with winter garments. Next the kite appearing, proclaims another season, viz. when it is time to shear his sheep. After that the swallow informs you when it is time to-put on summer clothes. We are to you, (adds the chorus), Ammon, Dodona, Apollo : for, after consulting us, you undertake every thing; merchandise, purchases, marriages,,, j. AUG [ 270 ] AUG Augury marriages,” &c. Now, it seems not improbable, that 11 the same transition was made in the speculations of men Augusta, which appears in the poet’s words; and that they were easily induced to think, that the surprising foresight of birds, as to the time of migration, indicated something of a divine nature in them ; which opinion Virgil, as an Epicurean, thinks fit to enter his protest against, when he says, Hand equidem credo, quia sit divinitas Mis Ingenium. But to return to Aristophanes. The first part of the chorus, from whence the fore-cited passage is ta¬ ken, seems, with all its wildness, to contain the fabu¬ lous cant, which the augurs made use of in order to ac¬ count for their impudent impositions on mankind. It sets out with cosmogony ; and says, That in the be¬ ginning were Chaos and Night, and Erebus and Tar¬ tarus : That there was neither water, nor air, nor sky : That Night laid an egg, from whence, after a time* Love arose : That Love, in conjunction with Erebus, produced a third kind; and that they were the first of the immortal race, &c. AUGUST, (augustus'), in a general sense, something majestic, venerable, or sacred. The appellation was first conferred by the Roman senate upon Octavius, after his being confirmed by them in the sovereign power. It was conceived as expressing something divine, or elevated above the pitch of mankind, being derived from the verb augeo, “ I increase,” tanquam supra humanam sortem auctus. See Augustus. August, in Chronology, the eighth month of our year, containing 31 days. August was dedicated to the honour of Augustus Ceesar, because, in the same month, he was created consul, thrice triumphed in Rome, subdued Egypt to the Roman empire, and made an end of civil wars, being before called Sextilis, or the sixth month from March. AUGUSTA, or Austa, an island in the Adriatic sea on the coast of Dalmatia, near Ragusa, subject to Venice. E. Long. 17. 50. N. Lat. 42. 35. Augusta, a town of Georgia in North America. See Georgia. Augusta Ausciorum, a town of Aquitania, so na¬ med out of compliment to Augustus, being originally called Climberrum, which name it afterwards resumed. In the middle age, it took the name of the people^ Ausci; and is now called Auch, the capital of Gas¬ cony. Augusta Ementa, a town of Lusitania, on the river Anas,, the capital of the province : a colony of the Emeriti, or such soldiers as had served out their legal time, were men of experience, or had received marks of favour. The colony was founded by Augustus : and is now called Merida, a city of Spain, in Estremadura on the river Guadiana. See Merida. Augusta Pretoria, a town and colony of Gallia Cisalpina, and capital of the Salassi 5 seated at the foot . of the Alpes Graiae on the Duria. Now Aouste in Pied¬ mont. See Aouste. Augusta Rauracorum, a town of Gallia Belgica ; now a small village called August, at the bend o&f the Rhine northward j but from the ruins, which are still to be seen, it appears to have been a considerable 3 colony, at the distance of six miles from Basil to the Augusts east. i Augusta Suessonum, a town of Gallia Belgica on AuSustin. the Axona j so called from Augustus, and with great probability supposed to be the Noviodunum Suessonum of Caesar. Now Soissons, on the river Aisne, in the Isle of France. See Soissons. Augusta Taurinorum, a town of the Taurini at the foot of the Alps, where the Duria Minor falls into the Po; now Turin, the capital of Piedmont. Augusta Ireba, a town of the Aiqui, near the spring of the river Anio in Italy ; now Trevi, in Um¬ bria, on the east of the Campagna di Roma. Augusta Trevirorum, a town of the Treviri, a people inhabiting between the Rhine and the Meuse, but especially about the Moselle 5 now Triers, or Treves, in the circle of the Lower Rhine, on the Mo¬ selle. Augusta Vindelicorum, a town of the Licates on the LicuS $ called by Tacitus a noble colony of Rhce- tia ; now Augsburg, capital of Suabia. Augusta Historia is the history of the Roman em¬ perors from the time of Adrian to Carinus, that is, from the year of our Lord 157 to 285, composed by six Latin writers, JE\. Spartianus, Julius Capitolinus, All. Lampridius, \ ulcatius Gallicanus, Trebellius Pol- lio, and Flavius Vopiscus. . AUGUSTALES, in Roman antiquity, an epithet given to the flamens or priests appointed to sacrifice to Augustus after his deification ; and also to the ludi or games celebrated in honour of the same prince on the fourth of the ides of October. AUGUSTALIA, a festival instituted by the Ro¬ mans in honour of Augustus Caesar, on his return to Rome, after having settled peace in Sicily, Greece, Sy¬ ria., Asia, and Parthia 5 on which occasion they likewise built an altar to him, inscribed Fortunce reduci. AUGUSTALIS pigefectus, a title peculiar to a Roman magistrate who governed Egypt, with a power much like that of a proconsul in other provinces. AUGUSTAN confession. See Augsburg Con- Jession. AUGUSTIN, or Austin, St, the first archbishop of Canterbury, was originally a monk in the convent of St Andrew at Rome, and educated under St Gregory, afterwards Pope Gregory I. by whom he was des¬ patched into Britain with 40 other monks of the same order, about the year 596, to convert the English Saxons to Christianity. They landed in the isle of Thanet ; and having sent some French interpreters to King Ethelbert with an account of their errand, the king gave them leave to convert as many of his sub¬ jects at they could, and assigned their place of resi¬ dence, at Durovernum, since called Canterbury; to which they were confined till the king himself was con¬ verted, whose example had a powerful influence in pro¬ moting the conversion of his subjects j but though he was extremely pleased at their becoming Christians, he never attempted to compel them. He despatched a priest and a monk to Rome, to acquaint the pope with the success of his mission, and to desire his resolution of certain questions. These men brought back with them a pall, and several books, vestments, utensils, and ornaments for the churches. His holiness, by the same messengers, AUG [ 271 ] AUG ugu