O AilSSlAlhin 3HI e THC UBftACT OF o o Of CAltfOKNtA JUK3AiNn 3H1 iO AKWJfSH SH4 \ o TKt ifftSAtv OF o SANTA BARBARA c \ e Of CMfFORNiA a THE UBRABT OF o so *v)n 3m NTA BAR&AfcA \ / Of CALIFORNIA jo Anvaeti 3tu THE UB8A8Y Of wiMQVSMwv W . C , ^ ,, A I? U THE TELESCOPE/ A FAMILIAR SKETCH COMBINING A SPECIAL NOTICE OP OBJECTS COMING WITHIN THE BANGS OT A SMALL TELESCOPE, WITH A DETAIL OP THB MOST INTERESTING DISCOVEBXBS WHICH HATE BEEN MADE WITH THE ASSISTANCE OP POWEBPITL TELESCOPES, COSCEBXIXG THE PHENOMENA OF THE HEAVENLY BODIES. BY THE HON. MBS. WARD. / ILLUSTRATED BY THE AUTHOR'S ORIGINAL DRAWINGS. THIRD EDITION. LONDON: GEOOMBEIDGE AND SONS, 5, PATERNOSTER ROW. MDCCCLXIX. PEINTED BY J. E. ADLABD, BARTHOLOMEW CLOSE. TO THE EARL OF ROSSE. IN thanking you for the permission which you have kindly given me to dedicate to you this little hook on Astronomy, I am reminded that my earliest attempts to observe the wonders of the heavens were made in consequence of your having, many years ago, commended the two-inch Telescope in my possession as being good, so far as its limited powers extended. I have now gratefully to record a somewhat similar verdict which you have given in favour of these pages, encouraging my hope that some who read them may be led by their perusal to study and observe for themselves the wonders which I have endeavoured to describe. But I am aware that anything which I can offer is as much exceeded by the scientific treatment of which the subject is capable, as my two-inch Dollond is surpassed by that noble and unrivalled TELESCOPE, with which some of my happiest recollections are M. W. TBIMLESTOH HOUSE, NEAB DFBLIIC. CONTENTS. CHAPTER I. PAGE THE OBSEBVEB'S APPABATLTS, AND WHAT TO OBSBBVH . 1 CHAPTER n. THE SUN . ' . . . .22 CHAPTER III. THB EABTH . . . . . .28 CHAPTER IY. THE MOON . . . . . .36 CHAPTER V. ECLIPSES OP THE SUN AND MOON . . .60 CHAPTER YL MEBCUBY AND VENTS . 69 Contents. CHAPTER VH. CHAPTER VIII. JUPITEB . . . m CHAPTER IX. SATTTBN CHAPTER X. CHAPTER XI. SHOOTING STAES AND OTHEE LUMINOUS METEOES CHAPTER XII. FIXED STAES . CHAPTER XIII. CLUSTEES OP STAES AND NEBULE PAGB 71 . 122 PREFACE. CAN Astronomy be presented as an entertaining study ? Has any one attempted to cull from treatises addressed to the not wholly unlearned in science, facts, and anecdotes, the " light literature " of this sublime study, and to tell these things in simple words ? And to give the interest of reality to these facts, has it been sug- gested to those who can admire and wonder at the splendour of the firmament, to try how much they can improve their view of star or planet, by examining them with the help of a small telescope, such as one may see, perchance, at every sixth window, on a fine summer's day, at a watering-place, its object-glass, capable of better things, idly directed to fishing-boat or distant steamer, or still more idly, to unconscious group on the pier ? As we believe that these attempts, namely, to relate a few of the discoveries of the learned, in words which the unlearned can under- stand, and to tell how much may be seen of the heavenly bodies with a small telescope, have not been hitherto combined, we now venture on the task. This little book does not attempt to teach Astronomy, it deals prin- cipally with observation; showing how the stars appear in their season, coming back year after year in their appointed time, while the stately planets move in their solemn paths, changing their places gradually among the unchanging stars, as they have done before our time, and will do when we have passed away. Happy should we be could we impart the very great pleasure which even this humble form of Astronomy can give. The warm interest, the almost personal affection that can be felt for the well-known planet, the familiar constellation, the double star that has been scanned with the little telescope is no matter of speculation with the author of this slight treatise. The delight at the first appearance in the autumn of viii Preface. glorious Orion, seen by chance at midnight, the satisfaction when Jupiter is again descried, after being some months concealed by the neighbourhood of the Sun's beams, are feelings yearly experienced by us, and little influenced by time, place, or even by circumstances. From foreign lands, from crowded cities, from the open windows of our quiet home, from tho silent road leading from some scene of festivity, they are seen with nearly the same thoughts and feelings. They seem like friends. The distant planets are the solemn way-marks of the years that have passed since we first observed their positions; the southern horizon hides from our view a firmament unseen by us, but nightly spread over those we know and love in distant lands. The faint comet-like spots that appear to our eyes when accustomed to the darkness, are clusters of stars, discernible even through our little telescope. But what of that wondrous belt which traverses the sky, the Milky Way ? Our eyes and our little instrument are alike unable to decipher it ; but as we look on it we remember what has been revealed about it by a powerful telescope, namely this, that it con- sists "entirely of stars scattered by millions, like glittering dust, on the bkck ground of the general heavens."* Stars each, perhaps, a Sun I Far, far away from this earth and its troubles is the mind carried by such thoughts and remembrances. And still farther may it be uplifted in this quiet hour, even to the throne of Him whom the heaven of heavens cannot contain, but who yet looks so lovingly on his creature man, from the place of his habitation. "He healeth the broken in heart, and bindeth up their wounds. He telleth the number of the stars ; he calleth them ALL by their names." Psa. cxlvii. 3, 4. * Herschel's Treatise on Astronomy,' p. 163. THE TELESCOPE. CHAPTER I. THE OBSERVER'S APPARATUS; AND, WHAT TO OBSERVE. JO point out how we may see for ourselves, and to relate a little of what has been observed by others; these are the objects of this little book. The latter will be attempted in succeeding chapters, and the former will form the subject of the present one. We will suppose the reader, already interested in the appearance of the starry heavens, and acquainted, perhaps, with one or two constellations, inquiring how he may learn more, and what apparatus will be necessary for making observations. We would answer, you should have a set of maps of the stars, an Almanack with tables of the positions of the planets, and other astronomical information, and a telescope which you can fix steadily ; we will suppose it is a good telescope, but with an object-glass only two inches in diameter,* or even less. If you are privileged * Technically known as " two inches in aperture" 1 2 The Telescope. to use a more powerful instrument at any future time, you will value it all the more from having first learned to work with a small telescope. We have indicated the apparatus in the order which it is most desirable that the beginner should observe in using them. First, the maps, by means of which you by degrees become acquainted with the relative position of the various stars, and in consequence able to detect the progress amongst them of one of those wandering stars, the five visible planets. Second, the almanack, which directs the observer already instructed in the bearings of the stars, where to expect and find any given planet. Third, the telescope, to scan the stars now familiar, and therefore additionally interesting, and to observe the planets which have been identified. But we do not forbid the learner to reverse this order occasionally, long before the maps are mastered, and while the columns of the almanack still seem little better than a dull array of figures. He may lawfully encourage himself in his studies by looking through the telescope, pointing at random to one of the brilliant specks which he fancies may be a planet from its calm steady light. It may chance to be a discovery to him that the same telescope which enables him to read the name of a merchant brig at half a mile's distance, is also able to make the difference between a star and a planet strikingly apparent. The planet Saturn is, while I am observing it, in a part of the heavens not far removed, in apparent The Observer's Apparatus. 3 position, from the stars Castor and Pollux, or Procyon in the constellation of "the little Dog/' and to the unassisted eye is very similar to that star. But turn the telescope to each in succession ; Procyon appears a brilliant diamond point, how very bright and sparkling, but how small ! Now let us see Saturn ; behold ! there is the very planet of the astronomy books, with its round disc like a tiny moon, and its broad brilliant ring. Perhaps the seldom-used night eye-piece in the telescope-case (discarded long ago, because it turned the name of the merchant brig upside down, though it did make the letters somewhat larger), may improve our view of the planet. We screw it on, removing the day eye-piece, and we can now plainly see Saturn's shadow thrown on the brilliant surface of its ring, and can faintly descry its satellite " Titan" (Plate VIII) . They look very small, it is true, but the feeling that now indeed we see an object of which hitherto we had only heard, is always vividly experienced at a first sight of Saturn. The beauty, too, of the real planet never fails to strike the beholder in a way no pictured repre- sentation can. Possibly the reader exclaims here, " I wish I had any idea where to find Saturn, or that I even knew Castor and Pollux, and the little Dog." Then study your maps, and before long no large star visible in our latitude will be a stranger to you. We recommend maps rather than a globe for the purpose of learning the stars, for two plain practical reasons ; one is, that on the globe the stars are turned the contrary way, appearing as they would in a looking- glass, which arrangement, though necessary when the 4 The Telescope. concave firmament is represented as if viewed from outside, is very confusing to a beginner. The other reason in favour of maps is that they are portable. The observer, well wrapped up, at an open window, or fairly in the open air, can so easily carry about a thin book of maps, and studying for awhile by lantern-light some one group of stars represented in it, at once turn his eyes to the stars themselves, till the same group is found and its position committed to the memory.* A plain distinct set of maps, such as one would not mind half wearing out in the service, is much the best to learn with. The only set which the author ever used were those of Middleton's Celestial Atlas. In this work the stars visible in Great Britain are represented in five pages, engraved in the usual manner, with the lines of right ascension and declination, the equator and ecliptic, and the pictured figures of the constella- tions ; each page being faced by a blank map, in which the stars are vividly represented in white, on a black ground, and corresponding exactly in size and position to those on the " illustrated" page. * A Planisphere will also be found very useful. This is an ingenious arrangement of three discs of pasteboard, by means of which all the principal stars visible in Great Britain at any given day and hour will be indicated, and the times of their rising and setting clearly pointed out. The same information may be obtained (we need scarcely say) by a simple problem on the celestial globe; but for the mere purpose of studying the face of the heavens, the cheap and portable Planisphere is preferable. The beautiful precision and ingenious arrangements of a good celestial globe become, however, a source of great pleasure to those who have by a little persevering attention, made themselves acquainted with the actual movements of the heavens. The Observer's Apparatus. 5 The advantage of this plan consists in the blank map being unencumbered with lines, figures, or names of any kind, and in its simplicity and vivid contrast of black and white bearing a resemblance to the starry firmament which it represents. The names and posi- tions of the stars can at once be ascertained by referring to the neighbouring page. Very lately we have met with a popular guide to the constellations, in which this plan of clear and simple . maps form a prominent feature.* It is of small quarto size, and seems peculiarly well adapted for the purpose of teaching the constellations gradually, to persons hitherto acquainted with very few or with none of them ; and with a second atlas of the heavens, by the same author,f in which all the constellations are represented in four large and correct maps, would, if carefully studied on favorable evenings, from month to month, make the student thoroughly acquainted with every remarkable group, and each bright star in the glowing firmament. We have endeavoured to attract the reader's especial attention to the circumstance that the stars visible in this latitude cannot all be seen in the course of one night ; and we now wish to state the facts of the case, and, if possible, to state them so plainly that the reader may really know how the stars appear to move. We will suppose, reader, that with regard to the * 'An Easy Guide to the Constellations, with a Miniature Atlas of the Stars, and Key Maps.' By James Gall, jun. f 'The People's Atlas of the Stars, with Key Maps; being a com- panion to the Easy Guide to the Constellations.' 6 The Telescope. movements of the heavenly bodies, you know but one fact with absolute clearness and certainty, namely, that the Sun rises every day in the east, glorious and glow- ing from behind the horizon, and travels southwards in a sloping direction till about noon, and that, as the day goes on, he evidently travels downwards, and at last sinks behind the western horizon, leaving only radiant clouds to tell of his brightness ; and that the twilight gives way to night, and again, after some hours, night to twilight, and the Sun rises again. Nay, dear reader, be not offended at this low estimate of your knowledge ; we speak only of what you know with absolute clearness and certainty, and what you have had so many more opportunities of observing than you are likely to have enjoyed with regard to the fixed stars. For how few have followed in the track of the Chaldean shepherds, they who were among the earliest to collect and hand down to succeeding ages the facts of astronomy ! Did our usual occupations, like theirs, call us to spend the whole night under the blue vault of heaven, we should soon see for ourselves, and thoroughly com- prehend, that even as the Sun rises in the east, travels upwards to the south, and descends in the west, so do all the stars which we can see as we sit to watch them, facing the south, the direction where the Sun was at noon. All the night through we should observe that there are stars rising above the horizon at our left, others drifting slowly along opposite to us, others sinking, at our right. We might also perceive that those which The Observer's Apparatus. 7 rise but a little way eastward of the south point which we are facing, remain but a short time in our view, never rise to any great height, and set but a little way west of the southern point of the horizon, and then remain invisible for many hours. Whereas those which rise so far to the east that we must look exactly over our left shoulder to see them emerge above the horizon, rise to a great height overhead, set far to the west, and remain so long in sight (namely, twelve hours), that the morning twilight has almost come before they have sunk at our right hand. The stars still further removed from the south quarter of the horizon, what of them ? They are still longer above the horizon, and a shorter time below than those that rise in the east. Turning our eyes completely away from the southern to the northern horizon, what do we see ? Stars which merely descend for a brief interval, and again ascend ; and above them, stars which never set at all, but slowly revolve round the almost stationary Pole Star. But neither our present business, or we might say, the business of this little book, is with these northern stars, which indeed revolve like the others, but cannot be said to rise or set, as they are perpetually in sight on every cloudless night. "We again turn our eyes to the south, and endeavour to impress on the reader that if he spent the whole of one clear night in the open air, he would see stars rising and setting, as he sees the Sun do by day. Or, without rivalling the Chaldean astronomers by actually watching all night, he may prove the same thing by observing the rising of some 8 The Telescope. striking constellation, and tracing its progress occa- sionally during the night. Let him fix on one which is not too near the southern horizon, and remains a considerable time in sight, and let him view it from an east window of his house at the time of its rising, say seven o'clock in the evening, in December. He may watch it now and then till eleven o'clock, when it will have gone so much to his right that he will now find it easier to see it from the south side of the house. He chances to awake at one o'clock, and now the constellation is opposite the window which looks to the south, and is higher up than the observer has previously seen it. He now closes his shutters on the calm cold stars, but, true to his undertaking, seeks his constella- tion again in the faint grey of the morning, shortly before seven o'clock. It is then opposite a west window, and slowly disappearing below the horizon. Such is the progress of constellation during one night. We need hardly remind our readers that this apparent movement of the starry heavens is entirely caused by the real movement of the earth on its own axis. We now proceed to trace the progress of a constella- tion during a year. Here, we have no additional movement to describe ; the stars preserve one invariable interval between the times of their rising. All the year round they come back to their old positions in twenty-three hours, fifty-six minutes, four seconds, and one-tenth of another second; in other words, the earth takes exactly that time in making one turn on its axis. They rise at precisely the same point of the horizon The Observer's Apparatus. 9 all the year round. They mount the same height in the south, and they set at the same point of the western horizon.* Were there no brilliant SUN in our firmament to interpose its hours of daylight, and to constrain our Earth to circle round it once a year, our observations of the stars would take the following simple form. There would be perpetual night ! and the stars alone would mark the periods of time. "We should see them rising in uninterrupted succession ; and in one cloudless interval of twenty-three hours, fifty-six minutes, four seconds, and one-tenth, the whole of the constellations would pass before our eyes, excepting those near the Southern Pole ; these, as in the existing state of things, would be perpetually invisible. But our reader, whom we have disrespectfully supposed to be familiar with no movement of the heavenly bodies, except the rising and setting of the Sun, will naturally inquire here, " Can we not in the existing state of things see all the constellations, except those near the Southern Pole, every night ? And what has the Earth's annual movement round the Sun to say to the matter ?" Waiving the latter question for the present, we will answer the former by narrating the progress of a constellation during the several months of the year ; hoping thereby to give an idea how any persevering * The apparent or real motions of stars, enumerated in treatises on astronomy under the names of Aberration, Precession and Nutation, Proper Motion, and Parallax, are all so extremely slow as not sensibly to affect what is stated in the text. 10 The Telescope. observer can see for himself that the constellations in their turns rise in the day-time, and are for some time invisible, but that they re-appear in their appointed seasons. And to one who has watched them during even a short portion of his life, they suggest the various changes of the year almost as emphatically as the opening buds, the floral splendours, the golden harvests, and the bare and leafless forests of this earth. We have supposed an observer watching a constella- tion occasionally during a winter night. If he particularly noticed the minute at which one star of that constellation rose over the horizon on December 1st, he would find that this star rose near four minutes earlier on the following evening, and on December 3rd, nearly four minutes earlier still. By New Year's Day, this star, which rose at seven o'clock on December 1st, rises two hours earlier, is plainly descending to the west at one o'clock in the morning, and sets at five instead of seven.* By February 1st it rises quite in the day-time, and consequently he cannot see it till it is already high in the sky, and it sets long before the night is over. By March 1st it is rising at one in the day-time, and at one in the morning it is setting. By June 1st it is rising at seven in the morning, and is, of course, invisible all day long. At night it is below the horizon, and, therefore, invisible also. It remains visible only in the memory of the amateur astronomer. But still observing its own invariable * In this observation a star on the celestial equator is supposed, as it is stated, to be exactly twelve hours above the horizon. Such a star (see page 7) would rise due east of the observer. The Observer's Apparatus. 11 periods, a time comes when it rises at three in the morning, namely, about the 4th of August ; and should the astronomer look out for a little before the morning twilight he might see it again, soon, however, to lose it in the advancing rays of the Sun. Another month, and the star rises at one ; and thus steadily gaining its two hours a month, it at length rises at the old hour of seven in the evening, shines the whole night, and is thus again in a favorable position for observation. Some constellations are most conveniently placed in spring, others in autumn, others can scarcely be observed save in the short nights of summer. So whether he chooses it or not, the observer must learn his lesson progressively. Orion, invisible during the spring and summer, and only to be seen in autumn from. " the small hours of the night " till morning, glitters in the winter sky as soon as the Sun has gone far enough below the horizon. Leo brightens the southern firmament in March; and the red star of Scorpio glows in the brief interval between evening and morning in the summer months. The changes just described in the views which we obtain of the stars are entirely caused by the Earth's annual journey round the Sun. That brilliant luminary alters his position among the stars every day by a space about equal to twice his own apparent breadth. It is in reality the Earth which moves, making the Sun appear to travel between us and those stars which lie in that part of space which is in the same plane as the Earth's " orbit/' or path. 12 The Telescope. We cannot, it is true, see this change of position. The Sun's brightness illuminates our whole atmosphere, and conceals the stars, otherwise we should see him successfully adorning " the Ram, the Bull, the heavenly Twins/ 7 and all the famous constellations of the Zodiac. The stars surrounding the Sun, at least those which are most brilliant, have indeed been seen in the day- time during the brief interval of a total solar eclipse, and can at any time be detected by the accurately- adjusted telescopes, of an observatory. Our proof, however, that the Sun does thus move, or appear to move among the constellations, is, that those stars which we can see shortly after sunset, in that part of heavens opposite to the Sun, gradually diminish their distance from the region where he is placed at each successive sunset, or rather, he approaches them, till at the end of six months, they seem as if swallowed up in his beams, and are not visible at any part of the twenty- four hours. They are then behind the Sun, but time passes and they go on, and proceeding westward, have at length moved so far away, or, as we have said, the Sun has so far moved from in front of them, or has seemed to do so in consequence of the Earth's real movement, that they rise a little while before the Sun, and are visible again. The maps and guides to the stars, which we have recommended, indicate the best season for observing each constellation, and commence by pointing out those northern stars which are seen all night during the whole year; proceeding next to the adjoining The Observer's Apparatus. 13 constellations which can scarcely be said to set, as only a few of their stars dip for a brief period below the northern horizon. The constellations, however, which we would espe- cially commend to the learner's attention are those which comprise the twelve signs of the Zodiac. These signs of the Zodiac, which divide the Sun's track into twelve equal parts, do not correspond exactly with the constellations, partly owing to the unequal size of the latter and partly from another reason too complicated to be treated of in this little work. Still the Sun's path lies among these stars from west to east, and were we to mark his place in a map from day to day during a year, we should find we had traced that great circle of the heavens called " the Ecliptic." This circle, instead of being everywhere equally distant from that star which marks the celestial pole, runs far to the south in our winter, and lies among stars which rise but a little way, comparatively, above the horizon, approaches daily northward till the middle of June, when it lies among stars which mount high in the sky, and remain upwards of sixteen hours above the horizon. Still sweeping round the heavens, it soon begins to recede from the north pole, and travels south, till in the fol- lowing winter the circle is completed. By learning the zodiac well we shall obtain a vivid idea of the Sun's path, and rightly apprehend the reason why he appears so low in winter, so high in summer, and why we have equal day and night in the spring and autumn. Then, we shall see why the Moon, always opposite to the Sun when full, and like the Sun 14 The Telescope. always travelling in the zodiac, and rising and setting along with its neighbours for the time being, is seen towering in the sky during the long winter nights, but in summer merely skirting the southern horizon. Lastly, by knowing the zodiac, we know where to look for the five planets which are visible to the naked eye. For in that region of the heavens they pursue their course, appearing, as viewed from the Earth, like bright guests in the various constellations of the zodiac, rising and setting along with them, and appearing earlier and earlier each day, till with them they dis- appear behind the Sun for a while. Here, however, our well-worn book of maps is at fault. It directs us to the steady unchanging denizens of the firmament, the fixed stars, and recognises the existence of but one wanderer, the Sun, whose place from day to day is marked on the ecliptic. The other brilliant travellers, Mercury, Venus, Mars, Jupiter, and Saturn, must be sought in the almanack every year. For instance, if the reader will possess himself of ( Dietrichsen and Hannay's Almanack/ he will find the position of any of the above planets for every fifth day during the year, clearly given in " Right Ascension and Declination." He may find the map in which this spot of the heavens is contained, and just as we might mark the position of some remarkable spot on this earth, being given its longitude and latitude, he may neatly note the place of the planet among the stars, and forthwith prepare to search for and find it in the real heavens. The planet, thus identified, soon becomes a familiar acquaintance ; we watch it from week to week, The Observer's Apparatus. 15 and in time can observe that it has its own independent movement, has changed its place in the constellation, and will at last leave it altogether. Mars, Jupiter, and Saturn are the planets most frequently in sight, while Mercury and Yenus, " satellites of the Sun," as they have been termed, are seen only for a short time before the rising or after the setting of that luminary, and always in the same region of the heavens. Venus never appears further removed from the Sun than one- fourth of the celestial hemisphere ; and Mercury travels away but one-sixth, and is in fact very seldom seen, as the twilight soon conceals him from view. For a few mornings before the brighter stars have paled in the sunrise, and for a few evenings after the Sun has set, he may be seen, aptly realizing the title, " messenger of the gods," by his rapid movement. Venus is much longer in sight, occasionally remaining visible four hours after sunset, or preceding the rising of the Sun by that interval. But Mars, Jupiter, and Saturn can be seen in quite the opposite quarter of the heavens from the Sun, and are frequently visible during the whole night. Thus we can easily trace their paths, and note them from month to month, and year to year. These planets seem to move, like the Sun, round the zodiac from west to east through the main part of their journey, yet some- times they appear to stand still for a few days, then they actually go backward a little way, and then again they stand, then once more move eastward. The eastward movement is real, their own steady course round the Sun, but the little backward run and the two 16 The Telescope. pauses, are the result of our Earth's motion in her smaller path round the Sun making them appear to run in the opposite direction when in a particular position. Mercury and Venus also perform this little piece of retrograde movement, but as the neighbouring stars are not so often visible with them, as in the case of the three outer planets, it cannot be so easily watched. Very slowly and solemnly does the planet Saturn make its way round the Sun. When we first noted its position it was in the constellation Pisces, and two stars in Aries pointed downwards to it. That was in the spring of 1850; and thirty years from that period must elapse before the eye of man will see it there again. Since then it has passed through Aries and Taurus, and is now east of the principal stars in Gemini. Jupiter, taking only twelve years to travel round the Sun, has passed over eight of the constellations of the zodiac in the same period. Mars performs its circuit in a little more than two years, as viewed from the Earth. If the observer wishes to obtain a clear idea of the path of a planet, he cannot do better than note its successive places on his map by means of the almanacks for two or three years. Then drawing a line from point to point, he will observe that it is very similar to the Ecliptic, but at certain intervals there will occur a little loop or double, where the planet has stood still, gone back, and after a pause resumed its grand east- ward progress. The path of the Moon is free from these interruptions. Its apparent rapidity, too, is greater, almost beyond comparison, as it encircles the The Observer's Apparatus. 17 zodiac in a month. It moves farther north, and also farther south than the Sun, but follows the same direction, namely, from east to west. To give an idea how to use the almanack as a guide to the planets, we may mention as an example, their position on January 21st, 1857. On that evening, and also for a few evenings before and after it, all the five planets known to the ancients were visible for a short interval after sunset, a fact which we ascertained by conning page 6 of ' Dietrichsen and Hannay's Al- manack' for a few minutes. The lower part of this page was devoted to a table of the rising, southing, and setting of the planets, calculated for every fifth day during the month. It appeared that four of them set in the evening, as follows : Mercury at 6h. 6m. j Mars at 7h. 37m. ; Venus at 8h. 30m. ; Jupiter at lOh. 23m. On the same evening the Sun, according to a column in another part of the page, was to set at 4h. 27m., so that this gave an interval of one hour and thirty-nine minutes in which Mercury might be seen ; the three others being longer in sight. The next question was, Can Saturn possibly be also visible ? Yes, he will be quite high enough above the horizon, for he rose at 2h. 25m. in the afternoon. Referring now to the short columns at the top of the page, we find the " right ascensions " of the five planets for this day ; that is to say, their places answering to what we should call east Longitude* on the terrestrial * Longitude on the terrestrial globe is reckoned east and west of the " first meridian." Eight ascension is reckoned east only, and the reckoning begins j- 2 18 The Telescope. globe: they are as follows -.Mercury 21h. 20m. 26s.; Mars 22h. 22m. 53s.; Venus 23h. 4m. 59s.; Jupiter Oh. 18m. 50s.; Saturn 6h. 39m. 40s. "0," be it observed, is marked 24 on the map, and means the same thing, therefore the four first-mentioned planets are apparently near each other ; we find the numbers corresponding to the above all in the same map, but Saturn is far off, half way to the opposite part of the heavens. Next we found their declination, which answers to Latitude* on the terrestrial globe. It is given at the top of page 7 of the almanack, thus : Mercury 14h. 21m. 35s., south ; Mars lOh. 27m. 12s., south; Venus 6h. 54m. Is., south; Jupiter Oh. 42m. from a line running through the first point of the sign Aries, which, however, is about the centre of the constellation Pisces. Right ascension is marked in hours, and sometimes in degrees also. There are fifteen degrees to an hour. In ' Middleton's Atlas ' hoth divisions are given. lu ' Dietrichsen and Hannay's Almanack,' hours, minutes, and seconds only are given ; and in ' Gall's Atlas,' degrees only. We recommend the student to mark the hours also on the margin of these maps. * Latitude on the terrestrial glohe is reckoned north and south of the equator. Declination is reckoned north and south also, and the reckoning is from the celestial equator, that great imaginary circle which is every- where equally distant from the poles of the heavens. In ' Dietrichsen and Hannay's Almanack,' and in ' Middleton's Atlas,' the places of the stars are given in declination ; but in some other almanacks, and in 'Gall's Atlas,' they are given in north polar distance, by which measure the stars on the celestial equator would be marked as in ninety degrees of north polar distance, those ten degrees south declination as in one hundred degrees, and so on. We recommend the student to mark the numbers in declination at every tenth degree, on the margin of Gall's maps, and with a hard pencil to rule lines across the map from each of these, and similar ones from the hours of right ascension. The Observer's Apparatus. 19 59s., north; Saturn 22h. 37m. 6s., north. We now marked the exact points on the maps, and also noted the Sun's place on the ecliptic; and clearly proved to ourselves that the four neighbouring planets would be arranged nearly in a line, slanting upward, Jupiter being the most distant from the Sun, and Mercury nearest to him. It was a fine evening, and from no better observatory than a railway carriage, we watched the Sun descending below the horizon, and, allowing for the sloping course he was still pursuing, though concealed from our eyes, knew where to expect Jupiter and Venus to appear in the increasing darkness. There they were ; and as star by star shone out in the blue concave, our eyes suddenly detected Mars a little way to the west of Venus, and then Mercury, gleaming brightly close to the last rays of the Sun. We next sought out Saturn, and a glance from the east window of the carriage showed him, ornamenting the con- stellation of Gemini. This reminiscence of January, 1857, may sufficiently serve as a hint how to use the almanack. It only remains now to point out, in a general way, some of the more interesting subjects for observation with a small TELESCOPE. We will do so in the form, of a list, premising that nearly all the phenomena noted here are predicted in the almanack. The constantly changing positions of Jupiter's satel- lites. The apparent widening and narrowing of Saturn's ring during fifteen years. 20 The Telescope. The phases of Mercury and Venus, and of Mars, the two former of which frequently appear crescent- shaped, and the latter gibbous, or not quite circular. The variety in the apparent diameters of the planets depending on their distance from the Earth. The diameter of Venus appears nearly six times more at some periods than at others. The apparent size of Jupiter varies in a much less degree, the difference being in the proportion of about three to four and a half. Eclipses of the Sun and Moon. Occultations of the stars, and occasionally of planets, by the Moon passing in front of them ; for instance, the Moon concealed Jupiter for more than an hour on January 2nd, 1857, and the planet's re-appearance formed a beautiful spectacle through the telescope. Conjunctions of any of the planets ; that is to say, the apparent meeting or near approach of any two or more of them, are at all times striking and beautiful, and enable observers to compare them, and to trace their subsequent wanderings with renewed interest. Of Astronomical phenomena, not noted in the alma- nack, but particularly suited for observation with the telescope, we may name the following : The spots on the Sun, showing the rotation of that luminary on its axis in twenty-five days. The craters and elevations of the Moon, with their sharply-defined shadows, moving as the Sun's light gradually shines on them. The irregular belts of Jupiter, showing his rotation on his axis. The Observer's Apparatus. 21 Some objects among the fixed stars are also seen more clearly with a small telescope than with the un- assisted eye ; namely, a few clusters of stars, the great nebular in Orion, and some of the more conspicuous double stars. Finally, the observer may chance to find a Comet, not with his telescope, in the starry heavens, but humbly in the newspaper, and studying the printed tables, mark its place on the map for several successive days, and then watch for it in the same manner as if it were a planet. We will now conduct our reader to those heavenly bodies which we have observed from year to year, and at the same time endeavour to impart some of the dis- coveries of the learned in connection with each. 22 The Telescope. CHAPTER II. THE SUN. us place at the beginning of our observa- tions this magnificent orb. It is, of all the heavenly bodies, the one most frequently in our thoughts. It is the brightest thing which the Lord of Glory has been pleased to show us in this life. It is the source of light and heat to our earth. First let us describe its appearance as seen through our little instrument, and then proceed to narrate some of the discoveries which, by means of the telescope, have hitherto been made concerning this stupendous globe. We must place a piece of dark- coloured glass before the eye-piece of the telescope, as the Sun is far too bright to be looked at without this protection. There are two other little precautions which we would recom- mend to the observer ; firstly, to point the telescope by observing its shadow on a piece of paper, held to receive it ; when this shadow is perfectly round, it will be found that the instrument is exactly pointing to the Sun; secondly, prepare a flat piece of pasteboard, with a hole cut through it of the diameter of the telescope, and when the instrument is properly adjusted, slip on the paste- board to screen the unemployed eye and the head and PARTIAL ECLIPSE OF THE MOON. THE MOON, ilays and lirrntij-one hours after AVie. OTTivr Sun, as seen with the naked bUl\, eye, through smoked glass. un March l&fh., 1858, shetctng a remarkable spot on its surface. ManK9.1S5S 9.A. .13 _. 18 SPOTS, OBSERVED AT VARIOUS TIMES. Si,,i. .bsn-vrd ,\])i-il l.i to 21, 1854. Fig 2. Sror, close to the Pun's eclpo, April 12, 185-1. I {ft '' SPOT, May 11, 1R54. Fifr. 4. SPOT, observed on two successive clnys. .'> Ltinunous nuuks on the Sun, March 10, 1858. Hg. 6. -SPOT, March 10 to 22, 1858. The Sun. 23 face from the heat of the Sun. The first precaution is recommended to save the observer from being dazzled in vain endeavours to " hit the Sun " in the ordinary way, and both are more easily and quickly done in practice than in description. Looking now through the telescope, should the dark glass used be of a reddish shade, we shall see a round orange-coloured disc in a black sky. On this disc there are generally a few black spots, somewhat resembling small blots or splashes of ink. When examined with care the larger spots prove to be not uniformly black, and not circular in shape, but of two dark shades, and of irregular outline. It. is somewhat practicable to look at the sun through a fog or thin cloud without using the coloured glass. Its disc then appears white, and the spots are of two shades of brown. The opinion generally held by astronomers concern- ing these spots is, that they are the comparatively dark solid body of the Sun, laid bare to our view by immense fluctuations in its luminous atmosphere ;* that the Sun has at least two atmospheres, upper and lower, and that the darker part of the spots is where the sun is seen through a rent in both layers of atmosphere ; the lighter, where one layer still covers it.* Recent observations have indicated that there are three gradations of shade, in some spots at least, the centre being the darkest.f The solar spots are not permanent. When watched from day to day, they are observed to enlarge or con- tract, to change their forms, and at length to disappear * Herschel's ' Treatise/ p. 208-9. f Johnston's ' School Atlas of Astronomy,' p. 4. 24 The Telescope. altogether; and new ones appear where previously there were none. These changes can be detected with a very small telescope. Another phenomenon on the Sun's disc is the occasional appearance of certain branching streaks of light on its luminous surface, curved in shape, and distinguished by their superior brightness. These are called facula, and are often observed in the neigh- bourhood of great spots, or on parts of the solar disc, where spots shortly afterwards break out. These have been supposed to be the ridges of immense waves in the luminous regions of the Sun's atmosphere, indica- tive of violent agitation in their vicinity.* With powerful instruments the whole surface of the Sun may be seen to be finely mottled with minute dark dots or pores, which fluctuate in their appearance like the rest of the markings.* The solar disc can be exhibited in a very agreeable manner by holding a screen or sheet of paper at a proper distance from the eye-piece of the telescope, and slightly altering the focus of the instrument, when the bright image of the Sun will be shown, with all the spots distinctly appearing. The effect will be heightened by darkening the room, as, for instance, by having a hole made in the window-shutter for the telescope, and closing every other aperture. The faculae show particu- larly well in this way, and their presence may often be thus detected when the fatigued eye has failed to observe them by a direct scrutiny. With this contri- vance, however, the spots will be reversed, as in a camera obscura; but they may be noted down on * Herschel's 'Treatise,' p. 208. The Sun. 25 paper, and afterwards traced on the other side, when they will appear in their true positions. The changes in these spots are truly surprising when we consider the size of the Sun ; and its size is known with considerable exactness, having been calculated by comparing its apparent diameter by its known dis- tance.* And how is the Sun's distance known? It is no doubt difficult to conceive the way in which the dis- tance of any inaccessible point can be ascertained. Surveyors use an instrument by which they can tell the direction of any far-off tree or building, as seen from each end of a line, which they have actually measured on the ground, and knowing the two directions, and the length of the " base line," they can by arithmetical calculations tell the distance of a tree or building ;f and it is by a nearly similar process, on a far larger scale, and performed with excellent instruments, that the distances of the Sun and planets have been com- puted. The base'line, answering to the surveyor's line measured on the ground, has been as long as from Britain to the Cape of Good Hope, or from Lapland to Otaheite.J And the Sun is so far off that its light takes more than eight minutes to reach the Earth, and yet light requires but one second to travel one hundred and ninety- two thousand miles. |( * Herschel's ' Treatise/ p. 192. t Ibid., p. 147, and see chap, xii of this little book. J Airy's ' Lectures on Astronomy,' p. 139. ' Cosmos,' vol. iii, p. 269. || Herschel's ' Treatise.' p. 297. 26 The Telescope. It must then be of stupendous size to appear so large as it does at such a distance. Some spots have fre- quently appeared on it large enough to be visible to the naked eye.* One of these was forty-five thousand miles in diameter, three times as long as the voyage from England to Australia \ " That such a spot should close up in six weeks' time (for they hardly ever last longer) its borders must approach at the rate of more than a thousand miles a day." f The solar spots were discovered by Galileo in 1610.J It was soon observed that besides changing their shapes in the way above described, they always approached the Sun's edge with a motion of the same kind as that which an island on a globe would seem to have, if we fixed our eyes on it, while we slowly turned the globe. This movement proves that the Sun revolves on its axis, a fact which could not otherwise have been easily ascertained. A spot of great size, and for some days visible to the naked eye is shown in Plate II, fig. 2. The course of these spots varies with the period of the year at which they are observed. From this fact astronomers have discovered that the Sun's axis is not perpendicular to the Earth's annual orbit. In Sep- tember the Sun's north pole is most turned towards us; in March its south pole is similarly situated, and the spots pursue a curved course, corresponding with these positions ; whereas in June and December they appear * ' Cosmos,' vol. in, p. 275. t Herschel's Treatise,' p. 208. J ' Martyrs of Science,' p. 36. Arago's ' Lectures on Astronomy,' p. 18. The Sun. 27 to traverse the disc in straight lines.* The time of the Sun's rotation on its axis is twenty-five days and eight hours.* It is a remarkable circumstance that the solar spots always occur near the Sun's equator, where his rotation must be quickest; a region corresponding to the tropics of this Earth, where the fiercest whirlwinds and hurricanes of our atmosphere occur.f We have now described at some length the Sun's thinly-scattered spots, but what shall we say of its brightness, its radiant beams, which return to our eyes in such splendour even when reflected from the far- distant orb of Saturn? What of its genial life- dispensing heat ? "The question, * Whence are thy beams, O Sun?' remains as unanswered now as in the days of Ossian, and the manner in which this perpetual light and heat are kept uudimmed, is as great a mystery as life itself."! A mystery to us, but no mystery to " the Father of Lights," who " maketh his Sun to rise on the evil and on the good." * Johnston's ' School Atlas.' t Nichol's ' Cyclopaedia of Physical Science,' p. 710. J Breen's ' Planetary Worlds,' p. 39. The Telescope. CHAPTER III. THE EARTH. JOES our reader complain that we have already departed from the province of this little book, as stated in our introduction ? We have promised to treat only of those heavenly bodies which we can observe, and are we not already following in the track of the school-books, and placing old mother Earth among the heavenly bodies for mere custom's sake? Reader, we cannot, it is true, direct our little telescope so as to gain a bird's-eye view of this world. Neither we, nor any of the human race, can at any one time behold more than an insignificant portion of its surface. In this matter, as well as in that of self-knowledge how difficult it is " To see ourselves as others see us !" Yet, though we cannot see the Earth, we can now and then see in the moon-lit heavens its silhouette, a portion of its round black portrait, clearly suspended before our eyes ; and again at another time, the reflection of The Earth. 29 its brightness though not of its form comes to our eyes, " as in a mirror, darkly." Thus we may place it among observed phenomena, as in a collection of portraits from life, we might admit the silhouette and the shadowy photograph, rather than altogether exclude one whose likeness is not to be had in any form. The Earth exhibits its black portrait at the time of a lunar eclipse. That dark shade with a curved edge, which glides on those occasions over the Moon's bright disc, is no other than the shadow of this round world, (Plate 1, fig. 1). It would be exhibited at every full moon, but that on account of the Moon's moving in a path which is not exactly in the same plane with that of the Earth, it but seldom happens that Earth, Moon, and Sun, are in a straight line. To the observer who is favoured with a clear sky on the occasion of an eclipse of the Moon, it is a striking and suggestive sight. The accuracy with which it commences at its predicted time, and the distinctly- rounded form of the shadow, produce a strong feeling of the truth of Astronomy. The other sight in the heavens, which tells us not of the Earth's form, but of its brightness, is that lovely spectacle, popularly called " the old moon in the young moon's arms." Shortly before and shortly after new Moon, when the illuminated portion of our satellite seems only like a narrow bow, a pale ashy light plays on the remainder of the disc, rendering it faintly visible, (Plate I, fig. 2). That is Earthlight on the Moon, " the reflection of a reflection." For then the Earth is (so to speak) nearly full of the Moon, and its light 30 The Telescope. reflected from the Sun, shines on the Moon, and that with sufficient brilliancy to make it visible to us after a second reflection. With these two phenomena before our eyes, we see, and we feel anew, constrained to believe that this Earth is indeed no level plain, but a globe, and that it shines like Venus, Mars, and the other planetary worlds. And yet it seems strange, as we look at the solid substance of this Earth, that it could under any cir- cumstances appear like a Star! But as Sir John Herschel remarks in stating that the Moon's light is entirely derived from reflection, it need not be thought surprising " that a solid substance should appear to shine." " It is no more than a white cloud does standing off upon the clear blue sky. By day the Moon can hardly be distinguished in brightness from such a cloud ; and in the dusk of evening clouds catching the last rays of the Sun appear with a dazzling splendour, not inferior to the seeming brightness of the moon at night/' Thus we may conceive how the Earth illuminated by sunshine may be seen from far, gleaming like the Moon or a planet. The first European records of astronomy are those of Alonzo the Tenth, King of Castile, A.D. 1250. He was the greatest patron of astronomy in his age, and it is related that he objected to the complicated system devised by Ptolemy. It remained for Copernicus, a Danish astronomer, nearly to unfold the true theory of the planets. He applied himself to astronomy in 1500, but his work, the name of which was "On the Bevolutions of the The Earth. 31 Heavenly Bodies," was not published till 1543. He died that very year. Three years afterwards was born the illustrious Tycho Brahe, who at the age of fourteen began to study astronomy, and was the best observer since Hipparchus. His observations guided Kepler in the discovery of the famous "laws" of astronomy which bear his name. Contemporary with Kepler was Galileo, who made a Telescope in 1609 ; and who was the first to answer certain serious objections to the theory of Copernicus. From this time down to the present day we meet with numerous illustrious names in the annals of astronomy, and pre-eminent among them all is that of NEWTON. Others had laboured at the edifice of Truth, contributing to its perfection from age to age, but as it were in darkness, waiting for the dawn of light. He first dispersed the shades of night, and shed on the beauteous structure the bright beams of intellect, placing it in perpetual sunshine. No reader of this little work will require to be informed that Newton's great discovery was that of Universal Gravitation. It may, however, be well to state what was the distinctive feature of this discovery, as peculiarly belonging to Newton. It was this ; that he demonstrated, by studying the motions and distances of the Sun, Moon, and planets, that this grand, all-pervading force of attraction, exercised by each particle of matter on every other particle, is an absolute fact, a great law of nature, and not a mere theory suggested without proof as a way of accounting for observed phenomena.* * ' Penny Cyclopaedia,' article " Astronomy." 32 The Telescope. In 1666 Newton began particularly to reflect on the force which makes bodies fall to the surface of the Earth, and to conjecture that the same force might even influence the far-off Moon. It is possible, thought he, that the Earth attracts the Moon, and that this in connexion with an original " projectile" force, is what causes it to move in the curved path, and with the variable velocity which have been observed. The next question was, " Does the Moon advance towards the Earth in the exact proportion in which it ought to advance, if it be indeed influenced by the same force which draws a stone or an apple to the ground ?" He compared the measures of the Moon's distance and the Earth's diameter, according to the computations which had been made at that period ; and it appeared to him that the force of the Earth's attraction would not be sufficient to account for the observed motion of the Moon. He had therefore not found the proof he sought ', and his biographers relate that for sixteen years he discarded the theory of universal gravi- tation.* But in 1682 he heard the particulars of a more correct measurement of the Earth than that from which he had previously calculated. He resumed his investigations, and found that his former ideas were based on truth. He followed out the subject in its various bearings, established unerring rules for calcu- lating the effects of gravitation, and proved, in suc- cessive sections of his great work, the ( Principia/ that * ' Penny Cyclopaedia,' article " Newton." The Earth. 33 these rules hold good alike for objects on the Earth, and for the Moon, planets, and comets. * Succeeding mathematicians have applied these rules to the minutest details of the most intricate planetary motions ; and, to quote Professor Airy's works, when we " compare the observed place of a planet with the place which was calculated beforehand, according to the law of gravitation, it is found that they agree so nearly as to leave no doubt of the truth of the law. The motion of Jupiter, for instance, is so perfectly calculated, that astronomers have computed ten years beforehand the time at which it will pass the meridian of different places, [that is to say the instant at which we, for instance, should see it exactly opposite a south window,] and we find the predicted moment correct within half a second of time."f We will not now enter into these achievements of science further than to give three simple proofs of the globular% form of the Earth, and to allude in a few words to the beautiful arrangement which causes the change of seasons. Firstly, the sharp horizon line at sea, not fading away in the distance, as would be the case if the sea extended over a level plain, but forming round our station a circle, behind which receding vessels disap- pear, just as'if they descended below the brow of a hill. Secondly, the fact that as we travel long distances to the south, stars which as seen from the British Isles * ' Penny Cyclopaedia,' article " Principia." t Ibid., article " Gravitation." J More correctly speaking " spheroidal," the earth being slightly flattened at its poles. 3 34 The Telescope. merely skirted the southern horizon, appear high in the heavens, and new stars, never before beheld by us, come into view. Still further south these newly seen constellations shine directly overhead, and those surrounding the northern pole have disappeared from our view. Again, as we travel northward of the British Isles the northern stars rise higher than we have hitherto seen them, and always in exact proportion to the latitude from which they are observed. Thirdly, people have sailed round the Earth. Magellan first accomplished this feat; it was next done by Sir Francis Drake, and every one has heard of the voyage of Captain Cook. Ships are now ' ' almost daily prosecuting such voyages. It is a common thing for ships to sail in an easterly direction to Australia, and to return by continuing their eastward course, and not by coming back the same way they set out."* This last forms the strongest practical proof of all, and gained by direct experiment and observation, that our world is round. The diameter of the Earth is nearly eight thousand miles. Any inequalities on its surface must therefore bear a very minute proportion to the whole size of the planet. " The highest mountain does not exceed five miles in perpendicular elevation ; this is only one sixteen hundredth part of the Earth's diameter ; conse- quently on a globe of sixteen inches in diameter, such a mountain would be represented by a protuberance of no more than one hundredth part of an inch, which is * Airy's ' Lectures.' The Earth. 35 about the thickness of ordinary drawing-paper."* On the same scale fine sand or dust would represent smaller mountains, scratches and pin-holes imperceptible with- out a magnifier would suffice for the deepest mines, the depths of the sea would be imitated by a slight depres- sion in about the same proportion as the height of the mountains, and a mere film of liquid would represent the ocean. The subject of the seasons is clearly explained in every elementary book on astronomy, and proved to be a result of the oblique position of the Earth's axis. Had it been placed perpendicular to the plane of the Earth's path round the Sun, the following would have been the effect : There would have been equal day and night all over the globe, and at all times of year. By its being on the contrary, obliquely placed, the northern parts of the Earth have long days and short nights in summer ; the Sun at noon is high in the heavens, and throughout his daily course is the companion of those stars which set but for a short time (see page 13 ;) and the polar regions have for some weeks no night at all. In the southern latitudes they have short days and long nights at the time it is summer to the northern hemisphere. Six months afterwards, when there is winter in the north, there is summer south of the Equator, and at the intermediate periods of spring and autumn, there is equal day and night all over the world. We now once more take leave of our planet, and turn our attention to our nearest neighbour in space. * Herschel's ' Treatise,' p. 22. 36 The Telescope. CHAPTER IV. THE MOON. (HIS is the nearest of all the heavenly bodies. Its frequent changes of position and shape must attract every one's attention; both are the effect of its moving round the earth once in four weeks. The inequalities on its surface visible to the naked eye, become more and more interesting as we view them with more and more powerful telescopes. At the time of full Moon, when the Sun's light illuminates the whole lunar disc which is opposite to us, we of course see the greatest possible part of its surface, but we do not by any means see it to the best advantage. It is like viewing a large building with the light shining strongly in front of it, and making it appear without any shadows. It would be more picturesquely shown with the sunshine coming from one side, and bringing out the different prejections in light and shade. Accordingly the most favorable time for observing it is during eight or nine days before, and a similar period after new Moon. The Moon turns on its axis in exactly the time which it occupies in revolving round the Earth ; thus The Moon. 37 it keeps the same side continually directed towards us.* There are slight variations called " librations," in the direction in which we see the Moon ; a little more of its western side is brought into view at one time than at another, while a small portion of the eastern side is concealed, and vice versa ; also, owing to the fact that the Moon's axis is not quite perpendicular to the plane of her path round the earth, the Moon's north and south poles incline slightly towards the earth in their turns ; so that we are acquainted with the appearance of a little more than one hemisphere.f But the re- maining part is to us an impenetrable mystery. However, of the visible part of the Moon we can make a better map than of that " half of the Earth's surface which comprises the interior of Asia and Africa." J In fact such a map exists ; we allude to the large chart of the Moon, published by Beer and Madler, in 1834; a work of exquisite accuracy, "containing every winding of every bay, every rocky promontory, every steep defile, every mountain and vale, every hollow, plain, and river, if such a thing exists, until there is not a peculiar feature of her scenery " that is not recorded for our inspection. Of all the heavenly bodies, the Moon is beyond comparison that of whose physical constitution we can * Herschel's ' Treatise,' p. 230. f Ibid., p. 231. J ' Cosmos,' vol. iii, p. 359. This quotation is from Rev. J. Crampton's book, ' The Lunar World,' a highly interesting work, in which a very successful attempt is made to realize lunar landscape and scenery; and an instructive detail given of the many beneficent arrangements in connection with our satellite. 38 The Telescope. learn most. With the aid of even a small telescope, its highly diversified surface presents a strange and striking appearance, and one to which the observer must devote some time and study, before he can become even moderately familiar with its details. Riccioli, a distinguished savant of the seventeenth century, performed a piece of good service to the students of the Moon, by giving names to the various parts of its surface.* He styled the broad-shaded tracts seas, oceans, etc. ; for instance, there is the Sea of Serenity, the Sea of Showers, the Ocean of Storms. He called the mountains after the most celebrated astronomers of ancient and modern times ; and a few bear the names of well-known mountains in the Earth.* The observer soon becomes well acquainted with the conspicuous and brilliant summits of Tycho, Copernicus, Kepler, and Aristarchus; the strangely dark "craters" of Plato and Grimaldus, and the glittering ridge of the Lunar Appenines. (Plate III.) The lunar mountains are wonderfully numerous, occupying by far the larger portion of the surface. They are almost all of a circular or cup-shaped form. The larger ones have for the most part small, steep, conical hills rising up in their craters. " They offer, in short, in its highest perfection," says Sir John Herschel, " the true volcanic character, as it may be seen in the crater of Vesuvius, and in a map of the Campi Phlegrai or the Puy de Dome."f Herschel adds from his own observations, that decisive * ' Penny Cyclopaedia,' article " Moon." t Herschel's ' Treatise,' p. 229. The Moon. 39 marks of volcanic stratification, arising from successive deposits of ejected matter, may be clearly traced with powerful telescopes. It must, however, be remembered, that the craters of the Moon are of vastly larger dimensions than those of the Earth. For instance, a remarkable lunar crater called Tycho, is nearly fifty miles in diameter;* and this is by no means one of the widest. A few spots on the Moon shine with a peculiar brightness, which it has been suggested may be caused by some mirror-like concentration of rays. One of these, a crater called Aristarchus, is believed to be the same spot at which Sir William Herschel saw what he supposed to be a burning volcano. But Mr. Nasmyth, of Manchester, who has spent all the leisure of many years in examin- ing the Moon with powerful telescopes, and who has seen the effects of volcanic action in different parts of the Earth, is decidedly of opinion that not one of the numerous volcanos on the lunar surface is in action, or has been so for thousands of years past.f These hollow mountains prevail on almost all parts of the Moon's surface ; there are, however, some chains of mountains with exceedingly pointed summits. J When such summits appear near the shaded part of the Moon, that is, on the inner edge of the crescent, they shine like detached points on stars. This ap- pearance never fails to surprise an observer who looks for the first time at the Moon through a telescope. * Nichol's ' Cyclopaedia,' p. 515. t 'The Lunar World,' p. 99. J ' Cosmos,' vol. iii, p. 353. 40 The Telescope. (Plate I, fig. 2, and plate IV, figs. 5, 6.) The inner edge of the Moon seems like melting ice, with bright drops hanging from it. These drops are in fact the mountain tops on which the Sun has risen, while the valleys remain in shade. The height of the lunar mountains has been calcu- lated by observations made on the length of their shadows. The higher the mountain the longer the shadow.* It is interesting to observe the foreshortening of the mountains and valleys ; those opposite our eyes appearing round, and those near the Moon's edge elliptical.^ The lunar mountains are very high. Thirty-eight of them are higher than Mont Blanc ; J none, however, equal in height the loftiest summit of the Himalaya. But these mountains are very lofty in proportion to the Moon's size; its diameter being two thousand one hundred and sixty miles, || whereas that of the Earth is nearly eight thousand miles. It has been asked " why does the outer edge of the Moon appear so smooth, instead of bristling all round with these lofty mountains ?" To this we answer, that high as these mountains are, they still bear a very small absolute proportion to the dimensions of the Moon. Let the reader glance at our scale of English miles in Plate III, which, however, is chiefly applicable * Arago's ' Lectures,' p. 21. f Herschel's ' Treatise,' p. 229. J ' Cosmos,' vol. iii, p. 363. Ibid., p. 131. || Herschel's ' Treatise,' p. 214. 'fj*tt*p "V v .I- 1 "" I/.- i/ t L* iffi A X