Answers upon several heads in philosophy first drawn up for the private satisfaction of some friends : now exposed to publick view and examination / by William Marshall, Dr. of physick of the colledge of physicians in London. Marshall, William, 17th cent. 1670 Approx. 330 KB of XML-encoded text transcribed from 133 1-bit group-IV TIFF page images. Text Creation Partnership, Ann Arbor, MI ; Oxford (UK) : 2005-12 (EEBO-TCP Phase 1). A52075 Wing M809A ESTC R32413 12673620 ocm 12673620 65524 This keyboarded and encoded edition of the work described above is co-owned by the institutions providing financial support to the Early English Books Online Text Creation Partnership. This Phase I text is available for reuse, according to the terms of Creative Commons 0 1.0 Universal . The text can be copied, modified, distributed and performed, even for commercial purposes, all without asking permission. Early English books online. (EEBO-TCP ; phase 1, no. A52075) Transcribed from: (Early English Books Online ; image set 65524) Images scanned from microfilm: (Early English books, 1641-1700 ; 1531:3) Answers upon several heads in philosophy first drawn up for the private satisfaction of some friends : now exposed to publick view and examination / by William Marshall, Dr. of physick of the colledge of physicians in London. Marshall, William, 17th cent. [24], 237 p., 2 folded leaves of plates : ill. Printed by T.L. for Nathaniel Brooke ..., London : 1670. Errata on preliminary p. [23] Pages 1-14 bound out of order. Reproduction of original in the University of Illinois (Urbana-Champaign Campus). Library. Created by converting TCP files to TEI P5 using tcp2tei.xsl, TEI @ Oxford. Re-processed by University of Nebraska-Lincoln and Northwestern, with changes to facilitate morpho-syntactic tagging. Gap elements of known extent have been transformed into placeholder characters or elements to simplify the filling in of gaps by user contributors. 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Finxerunt animi , raro & per pauca loquentis : . Hor. LONDON , Printed by T. L. for Nathaniel Brooke , at the Angel in Cornh●● near the Royal Exchange and at Gresham Colledge . 1670. To the right Honorable William , Lord Viscount Bronker President , and the rest of the learned members , of the Royal Society . To the Incomparably learned Dr. Francis Glisson President , and the rest of the learned fellows of the , Colledge of Physicians in London . To the worthily famous Professors of Gresham Colledge in London . The Author wisheth all happines , submitting these his Philosophical answers to their grave censure . THe things here presented , and which shall be hereafter presented of the like nature , will vindicate mee from both suspition in you , and expectation in the Reader , of a dedicatory piece of flattery : I every where manifestly using a Philosophical freedome . 〈…〉 so ill a servant either to 〈◊〉 Honours , or to noble truths , which are the choice food of refined minds , to make this address unto you for the protection of any thing which may deserve a black censure . Let every line bear its own fate in its own bosom . Only being well assured , that these things in difference , and thus discussed between me and some friends ; as they have been contrarily taught by persons worthily had in singular veneration , both in the present and former ages ; so they concern some heads of Philosophy , which are of no small consequence unto true learning ; and besides , lying deeper in the pit of obscurity then the first fadom , they ought to receive the ablest decision ; I knew not therefore how more candidly to strip my self of any concern pervicatiously to defend any thing in these papers , then by laying them and their fate at the feet of so noble and able Judges . Possibly the thanks of private friends may have begot in me a 〈◊〉 opinion of some of these things the● they may deserve : your judgment may correct the errour of their indulgence . As all that desire to learn , ought to wait upon you and your honourable societies , as being together with the famous Universities and our Law Colledges , I mean our Innes of Court , as the soul and spirits of the Nation ; so these Papers wait upon you , not presuming in the least to inform , but submissely craving rather to learn of you what they ought to think of themselves : according to the noble method of Philosophy in some of your societies lately instituted and pursued , not seeking for a precarious allowance , as a Rogue and Felone may find refuge and safety at an holy sanctuary ; but ( however without the overweening dotage of self opinion ) either by their own fair truth and clearness to be justifyed , or else willingly to embrace the flames , which their errours have deserved . I know you will pardon the hasty rude dresse , or rather nakednes , ( best suiting the pursuances of truth ) in which these Answers to the questioning letters of some private friends , were first of all conceived : which without falsiifyng could not afterwards be altered : and their highest ambition then was only private satisfaction , though now , except I will leave those , for whose satisfaction they were first written , unsatisfied , they must proceed to put themselves upon the test for publick , either justification , or disallowance . The which I am the more easily perswaded to , observing it a method allow'd and practiced both by antients and moderns to preserve and deliver scattered points of Philosophy by way of Dialogues and Epistles . And indeed this method hath this special advantage in it ; we may in a word present what we have to say that is new , without loading the Reader with an unsavoury crambe , which hath been a thousand times before in the press . As if these paters be able , which I leave to your serious censure , to justify themselves : it is scarce possible for them to fall into the hands of any Reader , who shall not herein , if he read them diligently and with understanding , find , not only somewhat which is new , but as well that is memorable , and beyond all doubting , certain , and perhaps neither by himself formerly thought of , nor possibly every where in that vast Ocean of Books , which are in the world , to be met with . In these philosophical oppositions , till I be called to account , I have for the honour I bear them , spared those great and venerable names both moderns and antients , which I have herein opposed : it being my method in private , to pursue what is publickly in you exemplary Viz. to weigh controversies and questions in philosophy , not by parties and factions , time and continuance , or number and opinion , but as near as possibly I can , by observing how the scales bear between the opposite reasons : and I wish the method might be so happy , as to become more common . For the same reasons I have suppressed the names of my ingenious friends , in opposition to some of whose thoughts these things were first of all written . Every day make your names more illustrious for clearness of judgment in the mysteries of nature . Being the desire of all , and doubtless expectation of most and particularly of your Orator and servant William Marshal . To his worthy and learned friends with whom these things were first debated ; the Authors apology for the publication of these his papers . TO some of you the name of an Apology might seem almost unintelligible , or little less then mockery : your interest being no less in the birth , then in the first conception of these philosophical discourses . Your quaerying curiosity at first impraegnated the mind , with what your present importunity will not rest without committing to the Press . To the rest of you , my wish is , that with the favour of others , I might not have stood in need of this Apology . However let not the publication be mis-construed , as if I accounted all here debated to be peremptorily concluded , or all that I have opposed , conquered . The yet dissenting of several of you from several of the things here by me own'd , might make a more hardy confidence then , I hope , I shall ever be guilty of , ●o become modestly jealous of its own judgment . If the things here made publick should not be able to indure the piercing aire of this knowing age , however our free and mutual intercourse upon such and the like philosophical doubts cannot want its justification . The publishing sometimes of a mistake is an occasion of leading others into the right way . And because every one cannot see cross the Mediterranean , we are not therefore to walk either with hooded eyes , or to dis-own the seeing of any thing at all , or what appearances things make unto us . Though the mind , which is the souls bed , be neither in all of the samesize , nor in all equally luminous , or conceptive , yet each is equally concerned diligently according , to the proportion of his window , to take a view of the goodly scenes of nature . In these things't is better to erre then to be idle : as I am sure you are equally perswaded with Your faithfull friend and servant WILLIAM MARSHAL . TO THE READER . THe publishing these papers hath now made thee my judge and censor : and they were no otherwise designed , but for every one freely to exercise his judgment about them . Most of these Problemes are more frequently upon the Anvile then they are found easily malleable into fair , clear , doubtless conclusions . Therefore if we misse the goale , it is but allowing one more in these sublime things to run a planetary course . I shall in a word tell the worst , which can justly be laid to their charge ; some of the few things here discoursed , have left the commonly troden path ; not as affecting novelty , against which upon other oc●asions I appear for the antients , but as chusing to follow reason rather then the name of any Authour . First therefore examine their reasons , and then give unbiassed judgment for the truth ; which for the truths sake I shall be ready to accept , though against me . For if those to whom and against whom , though in a vayled way , these papers were first written , are supposed not to be exempted from errour , there is no room left but only for weak minds in these secrets of nature to arrogate unto themselves an infallibility . If any complain of obscurity , as both hast , and brevity , and the subject matter , and the manner of writing , and the quality of the persons for whom these things were first of all pen'd , may make them thereunto lyable enough , however I shall be ready to give both my account , and if valuable , my assistance to any who shall des●re it relating either to the obscurity , or intricacy of any passage ; and to accept from them any reasons they shall be pleased to produce to the contrary , Thine W. M. From my Study in Nags head Court in Gray's Church Street . A SYLLABE of the CONTENTS of these two SECTIONS . In the first Section . In the first Answer ; is treated Concerning the several Originals of Springs . Concerning the irregular Ebbings and Flowings of diverse particular Springs . Of Chymical multiplication , or the encreasing of the quantity of liquours by destillation . Of the possibility of a persons learning , in an hour or two , to write his mind in a language he is ignorant of : so as , what hee writeth in the unknown language , shall be constantly without errour in the Grammatical concerns of it , and the sense good and continued . In the second Answer ; is treated Concerning sympathyes between several parts of Animal bo●yes . Particularly , of the sympathy which is between the breasts and womb : and whether it be founded upon inosculations of the Epigastrick and Mammary veins and arteryes . Whether from view of the Breasts , judgment may be made concerning the sex of an unborn conception ? Of the Sympathetick relation of parts of the same side . Of the forming of the Phases and Shapes of the Moon from its mutuatitious light , and the proportion in which it hath its situation to the eye : and why the Moon appeareth to the eye rather plane then Sphaeral . In the Third Answer . Fresh-water Springs are asserted at the bottom of the Sea. Whether by frequent transhaping , and working upon Mercury , somewhat be not lost irrecoverably , beyond all possibility and hope of reduction ? That the doctrine of the four Elements as uncompounded bodyes , cannot acquit it self , against many rational doubtings and material controversyes , to be a Doctrine unquestionable . That the four Elements cannot be the first Elements . Of the difficulty of bringing the firs● Elements to view . That , in the Doctrine of the Ancients , seemeth a greater number of first Elements asserted , then four . What may have been the true rational intendment of the Ancients , in their introducing the Doctrine of the four Elements . In the Fourth Answer ; is treated Of the Sutures in the skull : and their distinctness according to their several kinds , number , and order . How in the distinction of the futures , both as to their number and order , is a certain latitude , admitting variety in the method of their account , and the Anatomical Doctrine of them . The like latitude is observable in several parts both of Concrete , and Abstract Mathematicks . Whether the praeeminence of right-side parts above the left , be natural or arbitrary . In the Fifth answer ; is treated Of the consistency of immense volatility with immense ponderousnes . Of making tinctures by materation without addition . Whether predictions may be concerning Comets before their appearance ? What is her●in to be judged , of Comets which are by new amassement ? What is her●in to be judged , of Comets which are supposed to be permanent Bodyes , and not to be new amassements . In the Sixth Answer ; is treated Of the motion of the Celestial Bodyes about their particular Axes . Whether such their Circumaxall motion afford a convictive demonstration and proof of the Copernican Systeme ? That the Earths motion is not sufficiently proved , upon the Hypothesis granted , That Comets are nearest the Earth , when they are in opposition unto the Sun. In the Second SECTION . In the Seventh Answer , is treated COncerning Angles of Contact . In order thereunto , are given several definitions of Plane Angles , and distinct names to them , according to those diversityes of their kinds and constitutions , which , in this Question , are more especially material and necessary to be distinguished . The state of the Question is set forth . It is shewn , that Recto-convexe Angles of Contact are truly Angles according to the definition of Plane Angles . That Recto-Convexe Angles of Contact are neither destitute of Quantity , nor their sides coincident . In what several wayes , one Quantity may be greater then another . Of Homogeneity . What kind of Homogeneity it is , that is requisite for proportionals ? That Angles have Figuration , as well as Quantity . That in Angles is observable an Homogeneity or Heterogeneity which is Mathematical , and also an Homogeneity or Heterogeneity which is not Mathematical , nor any way concerning their Quantity , but only their figuration , &c. How three Angles being all Equal ; the Equality between the first and second , may be more absolute then the Equality between the first and third being only respective . How some Angles are constituted by the Concrescency , Composition , and Annexion of several parts and Angles , which are Heterogeneal each to other . VVhether like Angles , in unequal Circles and in like segments of Circles be alwayes equal ; That all Equal Angles are not like . That all like Angles are not equal . VVhether this Controversy about the Recto-Convexe Angle of Contact , belong to Concrete or Abstract Mathematicks ? VVhat was the first mistake , that first ministred occasion for the starting of this controversy , which hath been so long reteined , in these Learnings , in which nothing is more monstrous and unusual then pertinacious controversy ; These Escapes of the Press crave the help of the Readers Pen. viz , PAg. 10. line . 11. read . aerial . p. 17. l. 2. r. heat . l. 16.17 . r. reason . p. 18. l. 10. r. easily . p. 14. l. 19. expunge the semicolon . p. 21. l. 28. r. Sympathy . p. 22. l. 15.16 . r. tumultuous . l. 24. r. those . p. 23. l. 29. r. concerning . p. 24. l. 18. r. falls . p. 29. l. 7. r. confessedly . p. 33. l. penult . r. flushing . p. 35. l. 13. r. that that . l. 28. r. fire . p. 36. l. 13. r. us . p. 39. l. 1. expunge the colon : l. 16. r. foetid . l. 26. r. their . l. 27 r. the. p. 41. l. 7. r. with the string . p. 43. l. 12. r. to the violating . p. 44. l. 2. and 7. r. inanimates . p. 49. l. 3. r. seame p. 56. l. 9. r. certainly . p. 57. l. 15. for is regularly . r. irregugularly . p. 61. l. 7. for if seeming . r. it seeming . l. 19. r. exact . p. 69. l. 5. r. limited . p. 71. l. 3. r. the Copernican . p. 75. l. 13. r. Jago . p. 80. l. 19. r. Lordships . p. 82. l. 17. r. like . p. 86. l. 5. r. BA . p. 89. l. 16. for mooving by . r. by mooving . p. 90. l. 2. r. an isoclitical . l. 28. r. Be again . p. 92. l. 30. for AHH . r. AHF . p. 100. l. 6. r. even . l. 19. r. say . p. 101. l. 1. r. one or each . p. 124. l. 29. r. recto-concave . p. 155. l. 26. and 28. r. crooked-lined . p. 160. l. 18. r. not other . p. 187. l. 26. r. a mixt-lined secant angle or of p. 200. l. 26. r. crooked-lined . p. 232. l. 1. r. constant . The faults of the Orthography are referred to the Readers ingenuity . The First SECTION of PHILOSOPHICAL ANSWERS CONTEINIHG The first Six Answers upon several heads in Philosophy . By WILLIAM MARSHAL LONDON , Printed by T. L. for Nathaniel Brooks , at the Angel in Cornhil near the Royal Exchange . 1670. ANSWERS Upon several heads in PHILOSOPHY The first Answer . Concerning the original of Springs : that all Springs have not the same nor the like original : that all Springs are not from the Sea : that several things may by the way contribute as originals to the same Spring , whether by way of dissolution , or condensation . Also of the ebbings and flowings of particular Springs : in some more especially observed to be in an unaccountable irregularity . Also of Chymical multiplication , or the distilling of liquors , so as by distillation to encrease their quantity to any given proportion . That Mercury is not explicable by the Doctrine of the four Elements . That in an hour or two's time a person of indifferent parts , able to read and write his native language only , may be taught to write his mind in a forein language , so as what he writeth shall be true in the forein language , and the sense good and continued . AS Nature in generation worketh the first beginnings of things usually in a very dark loom , not permitting common eyes to have a view of its un●aught art in ordering and warping its first filaments , covering with shells and membranes and divers veils the mysterious nature of first productions : The same judgement may be of Springs , which though every where obvious to the eye , by their pleasant murmurings , crystalline pureness , and perpetual flux , delighting the mind , as well as the sense ; yet whence these Rise , and how they are fed , and wherewith furnished , is more obscure and aenigmatical than to be resolved , as many easily imagine , in a word . And yet I suppose , an erroneous Hypothesis may be the chief ground of difficulty in this Question , while many generally expect that all Springs should be of the same or like original . But why is that more reasonable than to expect that all Springs should send forth waters of the same taste , colour , or virtue ? Too many Instances , Examples and Experiments may be produced of Springs owing their original to the Sea , percolated thorow the Earth , to deny , or call in question so evident a Truth , without a manifest crazing of our own judgement : yet that the Sea by such percolations is not the original of all Springs , is as manifest , as true , and confirm'd by as many and weighty Experiences ; not only of fresh Springs near the Sea , and in-land salt-springs ; but especially if we consider the numerous Springs , which are in the tops , or sides of several Mountains , vastly above the Seas level ; and therefore not possible in any Channel to be naturally raised so high , without all stay , or impediment of percolation . Of which I have observed a special instance in a low , somewhat rocky , wedge-like Mountain , situate along the brim of the full Sea ; but on the Land-side , at a little distance , set about with numerous and vast Mountains : in which little wedge-like Mountain , though most part immediately encompassed with a Plain , very considerably above the level of the highest , aequinoctial , or other Tides ; was a perpetual Spring of most lympid , clear water , not unfamed for its singular medical vertues . It is scarce consentaneous to sense , reason and experience , to derive such Fountains out of the Sea only by way of percolation ; which though it be allowed to contribute , in some places , to the sweetning of the fountainous flux , cannot be conceived apt to raise the water to an higher level than it had before . Not disallowing the former therefore in its place ; there is yet besides it some other Original of Springs to be inquired after . And how perpetual Springs should come to be in the tops of the highest Mountains of all , as the case of most difficult explication , cannot with greater reason and clearness be explain'd , than by bringing the waters thither , not in a watry form , but as vapours and exhalations , at leastwise the most constantly , and in the greatest proportion ; after the manner of a Distillation , ordered and managed by the institutes of Nature ; and this without Espousing the Tenets of our new Platonists , that will have several perpetuous continued Orbes of Fires , diversly graduated , for special Theological ends , contained still between two and two perpetuous and continued Crusts , or sphaeral shels of Earth , the one above the fire , the other beneath it , in respect of the Earths Center . And those that know how under the surface of the Earth , whether plain , or mountainous , are frequent stores , both of Materials , and naturally formed Cavities , and other Instruments , easily accommodable to such a work , will not conclude that to be a conjecture of fancy , which not only for its possibility , but the high degree of its probability , may justly claim to be entertain'd as a most real and undoubted physical Truth . For what doubt can be made of subterraneous heats and fires ? and hot Baths and Springs , attest the , not only warmth , which is sufficient for our purpose , but even the actual , and frequently intense , heat , and ebullition of liquors within the Caverns of the Earth , and the perpetuity , or constant continuance of such ebullitions : and as the Earth is well known to be furnished with many natural Caverns , so in those Caverns , for shape , proportion , situation , and other the like circumstances , we cannot but imagine there is great diversity . So how variously and plenteously the Earth is watered with subterraneous juyces , and moistures , cannot be denied by the observant , who almost every where under ground find lesser veins of water dispersed up and down the Body of the Earth , and in many places large concealed Rivers , elsewhere unfathomable Vaults , and Abysses : Sometime seen Rivers in their proper and perpetual Channels , make a dark course and discharge of their waters into the unseen Bowels of the Earth . Upon the whole , in the method of this explication , waters are , in the same manner secretly within the Earth , raised to the top of the Mountains , in which , to our view , they are raised in the open Air to those regions , from whence they fall back again upon us in the form of rain . And in such vapid exhalations , it cannot be denied but in some places , and at some times , the Mountain springs ranging in a much higher level , may by possibility be furnished from the percolated sea-water : but as the possibility of this is admitted , so the universal and absolute necessity of it , may not be averred : it seeming hard to say , that the Mountain-springs what distance soever from the Sea , have no other way of being furnished , but only from thence . And , I suppose , it will as uneasily obtain credit , that the Sea should run as fast every way , under the Earth , to the Originals of Springs , as the Springs generally do in seeking out their way unto the Sea. I doubt not , but besides the Seas , there are under the earth many other liquors , contributing to the origination of Springs , some having their first rise from dissolution , others from condensation , whence , and from the passages thorough which they run , and are percolated , rise very often those special vertues and dangers of some peculiar Springs : and sometimes in a seeming praeposterous way , though very consentaneous to the true nature of things , Springs adjoyning to the Sea are fresh , and at a vast distance from the Sea , in in-land Countreys sometimes salt . But besides both the Seas , & those other waters bred under the earth ; it s more than probable ▪ the rains falling down in showers from Heaven , adde not a little to the flushing and continuance of the Springs . So medical Springs after rains are noted for a while to be of less virtue ; and in long droughts , 't is usual for very many Springs to be quite dried up , till rains fall again : and where , by long obscure dens , caverns and passages under ground , access may be had to subterraneous Rivers ; such Rivers , though lying vastly deep under the Earths surface , they are sound to swell at after rains , and by their accession unto the wonted stream , frequently do make a most hideous and horrid noise , full of terrour to those in the Cave● mouth , and at other times unusual . From all which , seriously and impartially weighed , is made undeniably apparent , that rains , in no contemptible proportion furnish forth matter to be ordinarily by channelly veins convey'd , or else extraordinarily by a natural distillation wrought up into the Springs . And as this much discussed Question is resolved in these easie things , every where offering themselves to view in Nature ; so I doubt not , upon the same principles might also many other things , seeming at first sight to be very mysterious , in the concern of Springs , as that which with so much admiration is by the rude ignorant people cryed up and observed in some , having , as they term it , their Ebbings and Flowings in such irregular frequency as by no art can possibly be reduced to any certainty of account , or order : for the more special and clear observing of which they are wont to receive the water from the Spring into some stone , or such like vessel proportionately bored in , or near the bottom : all which in truth is without any retrogradation and reciprocation of motion in its channelly veins ; being nothing else but an inaequality of the waters issuing from the Spring in equal times , either by reason of its more plenteous filling at some times the channelly veins of the Spring as it passeth , or else by reason it passeth with a greater or lesser impetus ; or possibly in some cases and places upon both grounds : which what it hath in it that is more admirable than the running of any ordinary Brook , sometimes with a fuller channel , sometimes with a stronger stream , I do not yet understand : and how easily , upon the former principles , this is explicable any one may readily perceive : that we may more justly wonder how some grave Authors came to be so transported with the sight or fame of some such springs , occurring up and down in the World , as in their reports to offer them to the thoughts of distant Students , and succeeding times , as containing in them little less than miracle . And if the studious would observe diligently what is in nature , possibly many other things , seemingly as intricate , might be capable of as easie explications ; especially considering the vast way a Spring may run under the Earth before it break forth ; fairly insinuated to us by the pure fresh water Springs , bursting up a great way within the floud marks of the Sea ; clearly intimating to us , how two Hills at a considerable distance may both be concerned in the same Spring and its Course . And whereas we number and place Springs ac-according as we observe them to break forth and shew themselves unto the day ; in the true aestimate , and upon laborious search , it hath many times appeared quite otherwise ; that the original of the Spring , has been at a great distance from the eruption , and the eruption has not been till after the confluction and meeting of , it may be three or four several Springs , every one carrying in it sometimes the dissolution , sometimes the spirit , or somewhat of the first rudiments of some special Mineral ; and altogether make up , not seldome , an almost inimitable composition . Your other Quaery concerning Chymical Multiplication , or the distilling of Water from a Pint to a Quart , if my Genius fail me not , when rightly proposed and understood , cannot want some affinity with the matters we have already been treating of . For if any would impose that the same Water as by way of expansion , without other additional water or matter , might by distillation be brought to a double , treble , and so a thousand times as large dimensions as before , as Wines , Vinegars , and other Liquors , have in them , without any further addition , so much Phlegme , and so much Spirit of such a strength , whether fixed , or volatile ; it would require a very credulous judgement to allow the veracity , or possibility of such a Probleme : and I am clearly free , to disown the skill or power of any such Chymistry ; which once admitted , were it not for the shortness of humane life , and the hopelesness of obtaining Vessels , and Instruments large enough for the work , and conveniency to place them , the world might be in danger of Drowning from the lofty Artist ; as once it was hypothetically threatned , with shaking by the noble and ingenious Mechanist . But I had rather understand a Probleme favourably , so as it may carry truth , possibility , and reason along with it : and so methinks may this be interpretable , to wit , subtilly to contrive , find out , and order expedients , ingenious helps , and advantages , to condense free , and open exhalations into a watery form with dispatch and expeditely , especially at any season , or time of the year : so as by this Art out of the arrial vapours within a limited time to give any limited measure of water , which reason can expect from Art , or without abjuring and putting off its own nature , handsomely make demand of . And that this is the Philosophy of Nature appears in every days dewes , the trickling moisture hanging on the chamber-side of the Glass , when the Air is very sharp , and full of a nitrous coldness without : and we cannot rightly conceive the Idea of that famously known and frequently mentioned and in hot Countries , though rare , yet sometimes by sad experience attested disease , the Diabetes , without admitting both the possibility of such a Chymistry , and of Expedients for the more ready dispatch of it : for without an aptness to imbibe , attract and condense the vapid exhalations , which successively come to be near and about the Patient , and that with very singular advantages for expedition , how possibly should the Patients Urine come in a few weeks to weigh more than all , both the drinks and meats taken by the Patient all along that time , and all the weight of the Body , whensoever it was heaviest during that time besides ? To contract all into few , the possibility of the Probleme , according to this explication , needs not be doubted , being an every where obvious work of Nature ; as in the other sense it seems vain and frivolous . And in researches about expedients for dispatch ; it is possible , here , as in other pieces of that ingenious Art , several Artists may have several methods and contrivances , to suck in still more vapours in a continued succession , and proportionably to condense them when sucked in ; also to dispose the vapours , before they are sucked in , for more expedite and easie condensation at after : as every one has his peculiar Still , his peculiar Solvent , Bath , Ferment and Furnace . And that this point of Philosophy were a little more cultivated were to be wished , for the advantage of natural Philosophy , and the concernes of it in some practical Arts : for so hereby the difference of the Airs at several seasons , or at the same season in several places , might come in some measure to be known , by the Taste and Eye , as well as by the Nostril : and the concerns of Rokes , Fogs , Mists , and Airs any wayes altered , or infected , may be hereby more happily discovered in relation to the health and sickliness of Man , and so of other Animals : so what difference there is between the Breathings of several Animals of the same , or several Sexes and Kinds , or of the same Animal at several times of its age , rest , motion , fear , joy , hope , love , anger , health , sickness , peculiar conditions , or evacuations : and the discriminations between simple Airs , and the Airs altered by sprinklings , strewings , fumigations , from Minerals , Vegetables , Animals , may be made more evident . Your tying up Mercury to the old Elemental Laws , is a true semblance of the old Mezentian cruelty ; and I should pity the poor Fugitive , were I not ascertained from his constant course , that as a slippery Hocas , he will never leave transhaping himself till , to your own confession , he has slipt the Collar . Four qualities will assoon solve all questions , as four Elements ; which some of the learned Antients , vainly hoped , not to say , foolishly boasted , to do . As Philosophers distinguish between the sights of Age and Time ; Age first sees without , and after not without Spectacles : Time first sees with them , and after better without them : the Elements were as Spectacles in the Beginnings of those times , when men first set themselves about the studies of Arts , that helped them in a sort to conceive somewhat of Bodies ; but now the Eye of time grown clearer , seeth much more happily , as is by many supposed , without them . More crass and thin , solid and fluid parts are not denyed , but apparently to be seen , offering themselves to view in several plain and easie methods of analysing Bodies ; but the simplicity of those parts , obtained in such Analysmes , is not yet demonstrated . The strange Monster reported with so much averment to you , which seems so much to have startled your patience , to wit , that a person of parts , educated only to read and write the Language of the Nation wherein he was born , may in an hours time be taught to set down any matter , secret , or other , in another language , as Latine , Greek , French , &c. and the Latine , or other Language to be true , and the sense good and continued ; believe me , though it be true , as it is , yet it is not to be esteemed worthy your least discomposure : it may be done many several wayes , and yet when all is done , it is but a slight of the Brain ; like many of the mimical Miracles , performed by nimble handed Egyptians . That there may be no room for distrust of the truth of it , if affiance in me may so far prevail ▪ you may be assured , I have seen the whole Model and Systeme of it , in several Languages , besides our own : and but that it would make my Letter of too great a Bulk , should herewith have sent you a Transcript of one of them . In this , as in the foregoing Probleme of multiplying Chymistry ; in words speaking and containing truth , something seems to be offered to the understanding of the hearer , which is an Herculian shot beyond it . Pardon the length in which I have laboured discursively to send back all the Quaeries and Objections of your last fully answered . The Second Answer . Wherein of Sympathies between several parts of the same Animal Body in general and particularly of the Sympathy which is between the Breasts and the Womb : and that the ground of that Sympathy is not founded upon the inosculations of the Epigastrick and Mammary Veins and Arteries . That that Sympathy instructs not from the sight of the Breast concerning the Sex of the unborn Conception . Yet parts of the same side more especially Sympathize one with another , than those that are on contrary sides . That to found the Sympathy between the Breasts and Womb ; is no necessity of vessels passing directly between the one part and the other : but the grounds of their Sympathy may be several other wayes clearly explicable , by manifest Arteries , Sinews , and other Vessels . That the several shapes of the Moon have their original , forming , and alteration , from the parts of its mutuatitious light , and their situation in respect of our Eye . That there is not one general original of all light . And why the enlightned part of the Moon is still toward the Sun. And why the Moon appears plane and not sphaeral . I should wrong the truth , if I should not acknowledge , all your Arguments and Instances prove fairly the Sympathies , which nature has lodged in us , between some special parts above others ; to which may be added by way of Declaration ; that though no part in the whole animal Body , but is of affinity and concern unto all the rest , yet some , besides their general relation as of the same animal Body , have sometimes not only one , but several other more special grounds of Sympathy , to tye & link them one to another ; whether from homogeneity of substance , or commonness of original , or unity and concurrence in the same work , or concern in the same branchings of vessels , whether Arteries , Sinews , or Veins , of what kind soever ; each of which heightens the general relation which is between the parts : and the more of these are found inter-curring between any two parts , their relation is so much the more fortifyed . But of all other , the Sympathy which you urge , between the Breasts and Womb , in animals is too universally known , and variously evident to be denyed , or doubted . How oft , among prying and suspitious Women , has the state of the Womb been discovered from the colour of the Nipples , and condition of the Breasts ? And the judgements of Physicians justified and admired , when upon the manifest intercourse between these two parts , easily transferring humours , whether natural , or praeter-natural , from the one to the other , they have sometimes predicted long before the diseases of the Breasts , or Womb ? So upon expectation of the ones evacuation , the cure of the other has been ordered , and the event and time of recovery foreseen ? and observing how they grow and lessen together , heal and fade together , become firm & flaccid together , replenish and empty together , except when the one drains the other , the intercourse between them , and their common concern is manifest ; however the grounds and passages wherein this intercourse is founded and carried on , possibly may not be so very clear , as by many is presumed . And though I honour you for honouring the Antients ; it is now especially less clear then ever ; that the undeniable consent and sympathy , which is between these two parts , has its foundation in the inosculations of the epigastrick veins and arteries with the mammeryes : Except we will so farr degrade the examinations of reasons , and trials of experience , as to make what is antient , to be therefore indisputably authentick ; Concerning the sympathy of the Breasts and womb as held by the Antients ) there are two things well deserving serious & further consideration : For hath not this sympathy been rackt beyond its nature , and tentered beyond the truth , of what it is able to bear , or discover ; when , upon the view of the Breasts , declarations and predictions are made , not only of conceptions , & abortions in general , with a probable prognostick of the time and event of the feared abortion ; but also from the difference of the Breasts on each side , the sexe of the conception , or abortion is peremptorily limited ; and when twins of several sexes have been conceived , the twin of whether sexe shall alone be aborted is foreshewn ; in that rare & unusuall case of aborting one twin , and compleating the due months of gestation with the rest ? Not to alleadge more of these impertinent medical Enthusiasmes ; such groundlesse and inconsequent deductions , as they are casily received by the superstitious , who yawn after things novel and strange , and blindly swallow what is offered without either praeexamining by the eye of reason , or proving them by the praemastications of experience : so I doubt not but to sober minds they will appear an apish overhugging the truth , to the ruine and destruction of it : an overchurning a serious , secret , true , observation of nature into ranckness and falsity ; and a praeposterous grafting a wild , wandering fancy upon the most cultivated stock of sober , true and certain observation . For since men have set their minds to learn out of natures unwritten books , as well as out of the writings of Authours ; what hath been more usual than to find male and female conceptions indifferently on the one or other side , or horn of the womb ? And though against experience no Argument ought to avail ; we shall not stiffe what they seem to have to say for themselves ; That the left praeparing vein riseth from the Emulgent only , which may be suspected , to be a weakning of its power and influxion ; whereas the right praeparing , or spermatick vein riseth immediately from the great discending Trunk , of which the aforesaid Emulgent is but an offset . All this is generally and in most Bodies true : and in former Ages , with the glossiness of its probability , carryed away the minds and judgments of most : but now upon more curious searches made into the Bowels , and heart of nature , the sophistry , & weaknes of the former Argument manifestly appears : the spermatick veins , if any be so pleased to continue that name , being only reducing vessels , and carrying forth from the vital fountain nothing at all to the Testicles , womb , Ovaries , or other organes of generation ; as may appear by observing ; the motion of the juyces contain'd in them , notifyed from the side on which the tumour and fulnes suddenly upon an intercepting ligature gathereth . And the different rise of these spermatick veins is more aptly referred to the indirect situation of the discending Trunk there ; which usually at the loins inclines a little rather to the right side , making the left Emulgent accordingly , to be commonly a little longer than the right : so as for a long tender venal vessel to have had its original so obliquely remote , and sloping over the fore bodies of the Rack bones , might not seem sufficiently secure ; however in the more strongly coated arterial vessels , it is not withstanding otherwise ; the right and left spermatical arteries both rising constantly from the descending branch of the Aorta . That Argument of the right side parts being , stronger , hotter , nimbler , &c. than those on the left side ; annexeth an incohaerent sequel , to a Truth which is meerly accidental : the special strength of the right side parts not being any natural priviledge , but an advantage acquired by exercise , use and education ; and by the same method , as easily transferable to the other side . And if at any time Twin parts be not equally concern'd , it is because there is not equall relation to the sides : so the Ovary of that Side to which the Conception is more principally affixed , in many females is of a fleshy substance , of colour like Sanders , or somewhat brighter , the other all the while remaining without any alteration as a cluster of watery Blebs & vesicles . But more particularly in the Copulations of mankind , all such considerations of sides must of necessity be obliterated ; the right side of the one Parent being applyed to the left of the other , and so on the other side , the left to the right . In all this we deny not , but right side parts have more special relation to right side parts , where the parts twin , and are double : but to parts , which are single , and posited in the middle , Twin parts have equall relation . So as upon the whole matter , the diseases of each particular Breast are more prone to be transferred to the same respective side of the womb , and those of either side of the womb to the respective breast ; of which are most apparent footsteps in the fabrick of nature : for though in some vessels , as Blood-veins , water-veins , chyle-veins , arteries , &c. this distinction of sides be again lost and confounded by insertion into some common Trunk , before they can be traced from the one part , to the other collateral part ; yet in some other vessels without any such confusion in the midway , the same collateral vessels ramify themselves distinctly unto the parts all along on the same side : as is most manifest in the visceral sinew , or wandering pair : but yet hereby is not opened any window to see into the sex of unborn conceptions . And , as herein I desire to reverence antiquity , but follow reason ; so upon your more serious thoughts , I doubt not but you will judge , with me , another Point upon this subject very well worthy calling in Question : and that is the much noysed ground of this sympatly between the Breasts and womb ; said , and formerly thought , to be the inosculations of the mammary veins and Arteries with the Epigastriks . It is well known , how many lateral heterogeneal inosculations , between Arteries and Blood-veins , have been introduced by closet Anatomists ; while , in Bloudless speculations , they formed nature according to their reasonings , to solve appearing phaenomena's ; instead of forming their reasonings according to what they ought first to have observed in nature : the verity and authority of all which , among Anatomists at sharp , that carry their Eyes in their hands , and will believe no more than they see , is at present not much ; however formerly solemnly , and for singular purposes , placed in and very near several of the chief Bowels : yet the fumultous aestuation which this Hypothesis continually placeth nature under , like the meeting of two contrary seas , may be sufficient , in reason also , to decry and discard it : for which reason also lateral homogeneal inosculations of bloud-veins with bloud-veins , as they are frequently found , so they may as easily in reason be admitted . But the inosculations in the Question being final ; I wave these that are lateral . And final inosculations are on all hands , agreed to be in a manner impossible to be shewn ; because , when granted to be , yet there where they are , the vessels are so minute , and slender , that it neither can be easy for the quickest sight , nor the most cautions hand , either , without hurting them , to come at the vessels , where they are inosculated , or to distinguish the vessels when heterogeneal at their inosculation , or to discern a final inosculation , whether of vessels of the same , or of different kinds . So that this whole Question about final inosculations being to receive its decision by the judgment of reason ; such final inosculations as are homogeneal , as of Arteries with Arteries , and Bloud-veins with Bloud-veins of the same Trunk , such as in this Point were understood and intended by the Antients , are no way capable of desence , allowance , or justification at the Barr of reason : for it experimentally , and to the eye , appears , that if any such inosculations should be supposed , the same Humours at the same time , from the same place , should move two contrary ways , to wit , both to , and from the heart , and in vessels rising from , or gathered at after into , the same trunk : in which account , the lung vein , the hollow vein , and the port vein , though all of them bloud-veins , yet because of the diversity of their Trunks , are to be esteemed as heterogeneal . And finall homogeneal inosculations generally , and therefore also between the Mammaryes and Epigastricks , being thus everted ; the old doctrine oncerning the ground of the sympathy between the Breasts and womb cannot be retained . And if any think by a short alteration of , and putting heterogeneal inosculations for , the rejected homogeneal , the ground of this sympathy will remain firm and clear as of old ; to wit by making humours to be transferred from the womb by the Epigastrick arteries and mammary veins to the Breasts , and by the mammary arteries , and Epigastrick veins from the breasts to the womb ; I suppose , that though such inosculations be not as the other , impossible , though undemonstrable to sense , yet upon mature considerations , these will not be judged sufficient to found this sympathy upon . If we lay the matter seriously in the ballance , even such heterogeneal and final inosculations do rather hinder the transferring of humours from the one part to the other : to be sure , look how much salls , or is any ways drawn into their capacities and cavities , cannot by them be so transferred , but is otherways disposed of : for the mammarie veins carry not to the breasts , but to the subclavians , and so to the heart , and the mammary arteries carry not to the breasts , but to the Muscles and parts on the forebelly . In like manner the womb will appear equally unconcerned in those veins and arteries : for the Epigastrick veins carry not bloud unto the womb but unto their collateral Iliacks , and so to the heart : and the Epigastrick arteries carry not bloud from the Iliacks to the womb , but to the Muscles lying on the fore part of the belly . And of themselves , neither mammary bloud-vessels reach the womb , nor either of the Epigastricks the breasts : so as , notwithstanding any thing in these vessels , we yet seem to be in the dark as to the grounds of this confessed sympathy . Not to add , that in many Animals some , and , in some all , the breasts are quite out of the way of the Mammaryes , on the same side of the Epigastricks with the womb , and , on that side , as farr removed from the capillar terminations of the Epigastricks and mammaries , as the womb it self . And professedly I understand not , upon what necessity the vessels founding , or contributing to the sympathy of these two parts , must needs pass directly between the one part and the other ; and may not as well here , as in the sympathy of other parts be admitted sufficient for this purpose , by their common concern and relation to some special branch , or general trunk , And vessells thus related , touching and terminating in these two parts , are not hard to be found in several kinds ; as arteries and sinews to convey like matter to both these parts : veins and sinews to reduce what is improper , superfluous , useless , or redundant in either , or meet and apt to be transferred from the one to the other : in which both cannot but be assisted by the agreement of their similar attractions , and that conformity of substance , which is either constant , or at some special times between some , or all of each of their parts : which as it may be a ground of the maturation & exalting of these parts together , so thereby the Bodies , pores , and passages , of both , are alike open , for the reception of like humours : and the same conform substance may be the cause why those vital emanations & irradiations which the generative parts receive from the parts which are principal ; when , I say , those vital emanations come to be remitted and reflected back again from the generative parts to all the rest of the body ; then , above all others , the breasts gather into themselves powerfully those forces of nature , which are so reflected back again from the generative parts universally to the parts of the whole . And such a course , as I have hinted , is both plain by view , undeniably certain , and familiar in the usual method of nature ; the breasts , above other parts , being exonerated by the evacuations of the womb and the evacuations of the womb , more especially then of other parts , being diverted by the excretions of the breasts : so that these being the common and trodden paths of nature , there cannot but remain an open way also for the translation of other matters . And though by the Mammaryes and Epigastricks , whether inosculated , or not inosculated , I have above shewn , that such conveyances cannot be made ; yet nothing hinders , nay 't is very apparent , that such translations may be aptly enough made , nay no doubt are made , by the thoracick and preparing vessels ; to wit , by the Arteries and some sinews directly , as bringing humours directly unto the parts , and by other sinews and veins more indirectly , as they are apt to carry , or not carry away what has by other vessels been transferred from one of these parts unto the other . I had discoursed these things shorter , if I had not been concerned to quit my self of rashness , with which you had attainted me for seeming herein to have made a defection from the Antients . I should assoon defend the Moons Eclipsses to be a celestiall fainting , and planetary sickness , and to be cured by Cymbals , Drums , Cornets and Trumpets ; because the Antients thought so . Yet for the same truths sake I account my self bound to justify the old Astronomers in the causes by them assigned of the several shapes of the Moon , as depending upon its mutuatious light , the proportion in which it is received , and the positions from which it offers its self to our view ; all concerning the Earth in the shapes of its lucid parts , save in its Eclipsses sometimes when it is at the full , being the product merely of ignorance and want of observation . I am not of opinion with many , that there is but only one fountain of light , which is the sun ; to which by imaginary refractions , and reflections , and strange labyrinthaean windings they would referre all other lights ; sending the most glorious of the celestial Bodies a borrowing to this fountain ; while evidently in these inferiour Regions , in the mineral , vegetable and animal Kingdoms , &c. not to speak of the caelestiall flames , several special fountains of light have been , and are frequently observed , though neither so full , nor durable , and perpetual as those above . However we cannot but confesse the Sun to be the Fountain of the principal Lunar light ; as another more faint light discernable in all parts of its body at whatsoever age , so it be out of the Combustion of the Beams of the Sun , which lye betwixt us and the Sun , or the Beams in vicinity to them , cannot be denyed to be innate unto it . And the roundness of the Moons and Suns bodies , being evident to the Eye in every positure and revolution , and apparent in Solar and Lunar Eclipses , besides several other demonstrations of their rotundity ; it follows from hence by necessary consequence that the Moons body cannot be guilded all over , at the same time , with such luminous beams as it borrows from the Sun : seeing in any two sphaeres , in whatsoever position , the one without the other , there is still a certain part of the surface of the one , unto which without penetrating its body from no point of the other can be drawn a straight line , as is easy to demonstrate . And the magnitude of the bodies of these two Stars , being confusedly unaequal the one unto the other , and the Suns the larger ; it follows in like manner by the same necessity , that though all the Moon cannot be at once enlightened by the borrow'd Solar light , yet at all times , more than half of the Moons sphaeral surface , is so enlightened ; except in those cases when the interposition of the earth , or other opake bodies , obstructs the solar radiations from falling upon it . For if a lesser , and a greater sphaere be put and adapted into an Isoscelary Cone , whose Axe is perpendicular to the circular Base at its Center , the Lines in which the surface of the Cone toucheth the surfaces of the sphaeres , shall be two Circles less than the respective greatest Circles , each of its own Sphaers as is not hard to demonstrate . And it is as apparent , that the Isorrhopical center of that part of the Moons surface , which is so solarly enlightened , is still the point directly obverted to the Sun ; thorow which point a straight line drawn between the centers of these two Stars passeth . So as the enlightened part of the Moon being still towards the Sun , no wonder , if in their conjunction the Moon cannot be seen at all ; as chiefly because of its combustion , so also because the enlightened side of it , is turned away from us towards the Sun : that though , by descending into deep pits , Stars above the Horizon may be seen at Noon day , yet the Moon in this case cannot by such helps be in like manner seen , its dark side being towards us , and the most that our Eye can at any time at one view see of the Moons surface , being ever less then the half of it , as is demonstrable . Upon the same grounds , at the Opposition , i. e. full Moon , the enlightened part of the Moon as it is towards the Sun , so it is towards us also , from whence follows , that all , that we can then see of the Moon , is enlightened , and that much more of it is enlightened , than it can be possible for us to see . In the Quadratures , whether of increase , or decrease , the state and positure of the enlightened , and unenlightened parts of the Moon , in respect of the Sun and us , offer themselves in a less entire , divided , middle manner : to wit , the parts of the Moons surface obverted unto us are but , as it were , half obverted to the Sun , and the parts of the Moons surface obverted to the Sun are but , as it were , half obverted to us : so as what is obverted to us in the Quadratures is , as it were , half enlightened , and half unenlightned and at other not Cardinal times , the nearer that the Moon is to the full , so much the greater part of the Moons surface obverted to us , is by the Sun enlightened : and the nearer the Moon is to its Change , whether past , or to come , so much the lesser part doth the Sun enlighten of the Moons surface obverted to us . And that these things are really so , may be from hence confirmed : at whatsoever . Age of the Moons crescency , or decrescency , if you observe its luminous parts seen by us , however horned , or bunched , the Sun is still on the luminous side of the Moon . Now the cause , why the Moons luminous parts appear plain and flat , rather than bearing out , like a Sphaeral surface , or a portion of a Sphaeral surface , is because the inequality of the visual beams , between the Eye and the several luminous points , is not so proportionate as to be discernable by our ordinary sight : for without such inequality , to be discerned in the visual beams , neither sense , nor reason can conceive true Idea's of a spheral surface . And upon these Hypotheses and principles all phaenomena's concerning the Moons shapes , as to magnitude , proportion , continuance , situation , alteration , alternation , being perpetually and accurately solved ; the Novelty which would dethrone this doctrine so apparent , so rational and unconvincible of the Antients , as it is unworthy the acceptance of the considerate and judicious , so it cannot but be unmeet for them to impose and obtrude upon others ; to omit the grosse inconsistency involved in it , which I shall in my next at large unfold , if these things fall short of giving Satisfaction . The third Answer . That there are fresh watersprings at the bottoms of the most antient seas . Whether Mercury by frequent transhaping it self , and often reduction loose not somwhat of its powers and virtues ? That the Doctrine and being of the four Elements , as unmixed bodies by their mixture making up all other bodies , is not unquestionable . In the four Elements may be allowed to be the general and most common lodges of the Worlds first Elements ▪ but themselves at the most can but be allowed to be only secondary Elements . How nature may so ballance the first or second Elements by some special Symbolical properties among them , as to elude all the endeavours which art can possibly make for the bringing of the first Elements to view and light . That the number of the four Elements and of their properties or qualities singly or in Conjugations ascribed to them seemeth insufficient to vest them in the right of first Elements ; upon the knowledge of whose natures , all Physical phaenomena should be capable of explication . That the antients seem to have allowed a greater number of first Elements . A conjecture what the antients might rationally at first design at their first introducing the Doctrine of the four Elements . SIR . THat fresh water springs lye at the bottom of the seas , both frequent , and with flashing issues ; is to me upon several observations , not undiligently made , as absolutely certain , as to you it seems impossible : and this I judge not only in the seas , which have made inchroachments by inundation upon the antient bounders of lands , which before were plenteously up and down watered with springs ; but as well , there being the like reason , in those seas , which are able to plead the highest and most antient praescription , and cannot be any other wayes chargeable , then in their dayly fluxes and refluxes , with the least new invading of the earths bosome , and of those wells of coldboiling-natural nectar , with which it is usually there stored . And why should natures opening a vein of freshwater into the sea , seem such a sea monster when at land we ordinarily meet with divers springs , of different virtues and originals , meeting at after together in the same channel ; from their concourse and mixture conceiving secret virtues , manifest alterations , and special properties , as strange to the illiterate and unexperienced , and generally wondered at by the most , as the boiling heat appearing presently in the suddenly mixt Oyles of Tartar and Vitriol , though cold , when poured together . I shall not urge , that some , would have the seas , proportionately to their depth , fresh at the bottom . I only move , if this be not more easy , to be assented to , then what is dayly seen , and therefore not to be questioned in point of truth , that the sea fishes &c. Though continually living in that briny pickle remain still however fresh : many times the sea-fowle , that most-what fly but about it , sometimes swim in the surface of it , senting and tasting much stronger of the sea , than the fish that live deep and constant in it . But Experience being the grand Umpiress in the Question , in assurance of its convictiveness , I forbear at present . For your reducing of Mercury after all operations of fire , whether actual , or potential upon it , I have no reason to cherish suspitions of the truth of such performances : but that reduction shall be so perfect , as to give back the Mercury as absolute in all virtues , as it was , or could at first be delivered , will not be easily consented to , by those that know that fire burns the chief wing upon which in Amalgames Mercury carryes along with it Gold : and the force of fire upon it , is in the nature of a rape robbing it of that virgin treasure , to which the noble mettal is so sequacious ; which once lost , can never be restored again to the defloured Mercury : as in all volatiles that which is of nimblest wing flyes first , and the highest spirit first : and when an impregnation is to be made by fire the work of Philosophy is judged chiefly to lye in the governing , of the firing , that , like the Sun , it may give enlivening heat , and not become , as a destroying Element . The reason , why so few are acquainted with the excellency and praerogative of this pure Mercury , is because generally it is a fire-burnt Mercury , which is at first delivered to us . I omit that in a thousand instances , after Art has separated the natural union of parts , though it may again unite them , yet that re-union will in many points fall short of the first natural union . But why does it seem so monstrous to you , to call in Question the existence of the four Elements , it being a doctrine , which in all Ages has been attended with doubts ? if you think you can shew as Air , and Earth and water , yet what shew can you make of Elemental fire ? And since the dissolution of the Orbes , there being no Concave of the Moon , what region is designed and intended for it ? I presume both Hearths , and Altars , are too low , to be the proper Sphaere of this high Element . And upon the whole , as little can be said for any of the other three as for this : the State of the Question and controversie being rightly understood . For it is not fire that is denied , or Earth , or Ayr , or water , but all as Elemental . How great a share and proportion these have in making up this part of the worlds systeme , is too evident to sense to be called in Question : many leagues of Earth , or sea , answering to each single degree : but that these four are the first uncompounded compounding bodies , of which all others by their mixtion consist , and are made ; seems , from hence , to follow by a very sickly consequence . Not without solid consideration , and sufficient cause , did the Antients honour the Earth with the style of the All-feeding-Earth : what innumerable vegetables and Animals spring , live and grow in its bosome , not to touch at the inestimable treasures lodged in its bowels ? Others , and of the worlds sages , with honours not unequal , assign unto the water not only Beauty's birth , but the Rise and original of all things : and every moment convinceth the use and necessity of Air &c. These are Arguments of their universal use , concern and excellency , but do not prove their Elementalness , no more then that one Tree is the Element of another , because the one is engrafted into the other , or that the mother is the Element of the child , while it lives annexed unto her in the womb . That in these are the general and most common Lodges of the worlds Elements , from which each nature may furnish it self with what is convenient for its being , nutrition and growth , may easily be consented unto : but that these are the very Elements unmixed and uncompounded , will be an Herculean task to make forth by any Argument , or experience , so long as each in its region appears replenished with all variety of Beings . What a numerous diversity of Earths are to be found in the Earth , of diverse colours , weights , virtues ; some healing , some scouring , some binding , some Alexipharmical , besides chalkes , and Marles , and several clayes , sands and gravels , noble quarries , rich mines , coals , bitumes , marcasites , salts , minerals and metals ? so in water , all coagulable vapours and exhalations meet condensed with the alluvion and dissolution of various salts and other minerals , together with manifold subterraneous Oyles and spirits ; whence the wonderful difference of their weights , sents , colours , tasts , consistence and operations . In like manner the Air , what is it but an uncertain , unconstant , randome composition of all sorts of fumes and vapours , according to the nature and position of the Atomes dispersed in it sometimes clear , sometimes cloudy , sometimes healthful , sometimes pestilent , sometimes delighting , at other times offending the senses ? And as difficult will it be to find and shew any uncompounded Fire . But you will say , that though these be not Elemental Earth , Fire , Aire and Water , it hinders not but there may be such Beings and bodies ; I answer , I have no abhorrency against the opinion , if so by any practice , or in any dissolution these Elements could but be shewn , and their sufficiency to explain the phaenomena of nature : but those parts , which , generally in dissolutions : are offered to be accepted for these Elements , appear nothing lesse , and , beyond all dispute , very distant from uncompounded natures ; and the analogous parts in several dissolutions , as different one from another , as one of the Elements can be from another Element ; which is repugnant to the nature of first Elements ; as is usually and truly urged against salts , sulphures and Mercuries to put by their claim in first Elementarinesse , in the mixtion of bodies : Viz. that in several dissolutions , the analogous parts answer not in the least one to another , except it be in some very general , and external conformity ; but one is sowr , another sweet , another sharp , another faelid , another fragrant , thus expanding into all manner of variety , wherein should be nothing but the pure simplicity of a first Element . In a good sense , and with fair Explications , I have been ever ready to acknowledge their interest as secondary Elements , as a doctrine consentaneons to the Sacred Traditions of Theology ; or as before , as the principal Lodges of the first Elements : but neither that which fils the regions , nor that which remains after their dissolution of mixed bodies , could ever yet to me seem capable of the denomination of first Elements . And possibly it may be one of natures mysteries never to permit us to see the first Elements naked so curiously ballancing them in their connexions , that all attempts of Art , for their discovery , shall be eluded : so any Artifice to resolve and anatomize a natural body into its first principles , grounded upon the fixedness and volatility of the parts , is eluded , if first , or second Elements of the same fixednes , or volatility be connexed : so if grounded upon dissolubleness in a certain Menstrue , it is eluded by connexing several first , or second Elements aequally dissoluble in that , or the like Menstrue : so corrosious by separatories , fumigating , anointing , cementing are all eluded as to the bolting forth of the first Elements , if they meet with several first , or other Elements aequally passible in those operations . And the very number of the Elements has not seldom rendered them unto me very suspitious , that they could not be first Elements . For by what fair Argument shal the Quaternion of them be demonstrated ? if , as is usual , we argue from qualities , whether singular , or in symbolismes , I see not how this number can be maintained : more qualities , and more conjugations of them , ought by the same reason to prove a far greater number of Elements And alas , how vainly light do they render themselves , that , by four conjugations of disputable qualities , seek to solve all the phaenomena which are in the world ; of the Loadstones pointing northward , its drawing untoucht steel , the Load-touched steels drawing of other steel , the bleeding of the slain at the presence of the Murtherer , the moving of an untouched Lute-string being Unison , or in a strong consonancy string that is moved , the sinking of persons drowned the first dayes , and then floating to the top at after , they have layd soaking so long in the water , the Cramp fishes astonishing the Fishers hand at the long distance of line and Angle , the strange Ebbings and flowings of particular seas and springs , and a thousand other ? Upon the old principles , how lame is the doctrine of solidness and fluidness , of opacity and transparency , in bodies sometimes of the same solidnes , sometimes of the same fluidnes , besides a million of other instances , whose resolution mateth the doctrine of the four Elements ? However mis-understand me not , as if I denied Elements , or first Elements : these must either be allowed , or no mixtion ; of which we have lucide examples in every corner of the world : for it was a Golden-rule in the school , which now I am opposing , that the same , or like , as so , working upon the same , or like , as so , cannot make any alteration : that I suppose I have good reason not to be forward to embrace the new received opinion , so much cherished by some persons of Eminency and parts , that there is only one Element of all things licked into several external shapes and forms . But this controversy not concerning your judgment , it were trouble now to pursue an impertinent . The rest I suppose , any where defensible , save at Stagira ; where Fire must burn , Air poyson , Earth bury , and water drown , whatsoever shall be suspected in , or alleadged against the Traditions of the imperial Philosopher . However my thoughts are still comported to yield up themselves to that doctrine upon the first clear and experimental demonstration of it ; if any such might be hoped . In the interim I want not fair footsteppings in the Antients to induce me to think , that when they make Bodies to be composed of that which is hot , and that which is cold , of that which is dry and of that which is moyst ; they mean nothing less then these four bodies , or rather vast Amassements , vulgarly now known by the name of the four Elements : but they rather intend , the true Elements of nature , it may be seldom , or never seen alone ; in which , such qualities , or properties are specially eminent : and they are so far from restraining natural compositions to the at present received Quaternary of Elements , that constantly at the same breath they hint many other : adjoyning in their recitals of natural mixtions , temperaments , and compositions , to that which it hot , cold , moyst , dry , Elements endowed with several other properties , as that which is salt , that which is sowr , that which is bitter , that which is sharp , that which is sweet &c. and the extremities and distempers intolerable unto nature , whether in general the Animal nature , or more especially the Humane nature , are made to be , when such Elements sever from their mixture , and go apart by themselves to violating , and breaking up that sweet proportionate composition and harmony , which is so friendly and grateful unto nature . As the Pyrotechnists analyse bodies , upon the consideration of several differences and contrarieties which are in their compositive parts , as that some will abide the fire , others not ; some be wrought upon by such dissolvents , or corroders , others not : so the Antients to reduce all inanimate things to four heads , may have insisted on several contrarieties , paving the way to such a doctrine : Viz. that such bodies are either firmly solid , or else fluid : and those that are fluid , are such , either in a grosse corpulent matter , or in fine exhalations : and those exhalations , either apt to conceive a flame , and burn , or else of a nature , thereunto indisposed . And according to such a distribution , many various bodies fall aptly enough under the same head of Amassment : and all inanimals in the world may be easily reducible to some one of these four heads . But then these four heads are not particular first Elements , uncompounded , and so constitutive of things in mixtion ; but general notions , unto which the inanimals of this lower part of the universe , are aptly reducible . Favour these Conjectures , which obtrude nothing , only labour what they can to justify the methods of the Antients . Send back my instruments and the last transmitted Problemes with your first convenience . The Fourth Answer . Concerning the seams of the Skull , and the number of the seams by which the Skullbones are joined one unto another , over and besides the three principal proper and true seams . That without contradiction , variety may be admitted both in the number and order of such seams . That neither abstruct nor concrete Mathematicks are wholly exempt from a liablenes to such varieties . That the pre-eminence of right-side parts is no way natural in such as twin but only at pleasure . SIR . THe learned men were riper for controversy , than became the gravity of their profession , or else upon the Point , which you have transmitted to me , held by each with so little real , though a manifest nominal difference , it had not been easy to have occasioned the hot language contained in your report . Though the one make but five pairs of seams , by which the Temple bones are joyned to the wedge bone , and also to the two Crown bones , and those ( besides the three principal seams ) to the forehead bone , or bones , and to the Nowl bone ; and the other , contrary to the general doctrine of the Anatomick School , asserts that there are six ; and both make their appeal to Autopsy and the Skeleton ; I see not wherein either is disabled to maintain his Assertion , as both agreable to truth and justifiable upon the view : only not without some rational ground for the difference , Viz. either hath , as I suppose , his different method , upon which he insists in making up the account of the seams . For the number will differ according to the ground by which you will distinguish and make out the unity of each seam : as also according as the seams are accounted singly , or by pairs ; from which last manner of accounting may arise also a third different number of them , though still without any change in the thing and object . Not being privy to the terms upon which this controversy was between them managed ; this Reconciliation , though unquestionably true , and pertinent to the Question , as by you in general proposed , may however possibly be inpertinent to it , as by them stated and defended : though I understand not upon what other terms the Assertions of both can be capable of justification : and I am not willing to think otherwise , between persons , so eminently learned . It cannot be denied but in these nicer things observed in the head , and distinguished usually by numbers , as the seams , and holes of the scull , there has not wanted some seeming diversity and obscurity : while it has been thought , that merely at the pleasure of Authors and of those that sit in the Anatomical chair , sometimes one thing , at other times another , and not constantly the same thing , is made to give the order , unity , integrity and distinction of seams . So the Nowlebones connexion with the Crown bone , and Temple bone of the same side , is generally construed to be two seams , and of two diverse kinds ; the one true , the other mendous , or defective : though so fair be the continuance of the one seam unto the other , that the one is usually known by the name of an Additament unto the other : and yet in other seams diversity of bones doth not , with all , make multiplicity of seams ; as in the Lepidoidal , or scaleseam where the Templebone is joyned to the Crown-bone and to the wedge-bone by a future , generally accounted but for one : so the connexion of the inner process of the forehead bone , to four several bones of the upper chapp , is by most accounted but for one common seam . The like , or worse perplexities occurre sometimes in the account of the holes in the head ; while some of the holes , which are common to several bones are accounted in each bone : others , in like manner common only in one of the bones , whence many times the number of the holes pertinent to each bone is left confused , and imperfect . For the reverence I bear unto the great Artists , in whom these things may be ordinarily observed ; I am not willing to impute them any otherwise then to their great intentnesse upon matter and things ; by which they seem overborn into a certain negligence of names and appellations . And those whose study is rather to be Anatomists , then so esteemed , and draw their Institutes and observations from the Body , more then out of Books , will easily consent with me that in this whole Doctrine , of the seams , and holes of the head , names and numbers are of less moment , so there be a clear understanding of the things themselves . So none , who has truly made use of his own Eyes can deny some parts , or sides of the true seams of the skull to be mendous , and some parts , or sides of some of the mendous to be in a sort true : that in several of them the distinction of true from mendous , and sutures from harmonyes , seems to be oft more matter of name imposed at pleasure , without clear and sufficient ground for real and peremptory distinction . Things thus standing , in the contest you mention ; how easy is it to make , on the same side , the seams , by which the Temple bone and wedge bone are joyned one to another , and ( as before ) to the Nowl bone , Crown bone and Forehead bone , to be at pleasure , either five in number , or if you please six ; For the one , or the other number follows , according as you shall take the connexion of the Temple-bone with a Crown-bone and the wedge-bone , to be one seams as it is most usually accounted ; or else to be two ; for which , being the connexions of two and two several bones , there wants not , as appears , some fair and probable ground . And thus though I would not charge with falsity , that whose truth is from real grounds so plainly defensible , howbeit somewhat varying from the ordinary methods , and systems of Authors ; yet I judge it not meet we be too forward , by reason of our more clear insight into things , in altering , slighting and rejecting the Terms , names , distinctions and methods , which have , time out of mind , been in continual use with learned men . For names , that were first coyned for distinction and instruction , if they should be dayly and hourly changed , would be sure to introduce confusion . And though in Names and numbers the Antients have used somewhat of authority , they have notwithstanding , in the same subject , fairly exercised their reason . So , with a very little allowance , this whole doctrine of the sutures , has been cast by them into a Mould methodical enough : the sum whereof in few may be this . The sutures of the head either concern not , or else concern the bones of the upper chap : those which concern not the Bones of the upper chap , are either largely toothed sutures , Viz. the Crown suture , the Dart suture , and the Lambda suture ; which may also receive another ground of distinction from their concerning the two Crown-bones connexion one with the other , or with the Forehead bones and the Noul-bone : or otherwise ; other sutures , not concerning the bones of the upper chap , are not so fairly not deeply , sometimes scarce at all , at least not so manifestly dented , or not in the same manner ; as the Lepidoidal connexting the Temple-bone to the Crown-bone and to the wedge-bone ; the connexion between the Crown-bone and wedge-bone ; the connexion between the Noul-bone and Temple-bone , commonly called the Additament of the Lambdoidal ; the connexion between the Nouls additament and the wedge-bone ; and the connexion between the Fore-head-bone and the wedge-bone : which may also receive another ground of distinction from their concerning the connexion of the Temple-bone and wedge-bone one with the other and with the Noul-bone , Crown-bones , and Forehead-bone . So the sutures , which concern the bones of the upper chap , either concern some one , or more of them in common with some of the aforementioned bones ▪ or else they concern , the bones of the upper chap alone , as connexed mutually amongst themselves . The sutures which concern some one , or more of the bones of the upper chap , in common with some of the aforementioned , make connexion only with some of these , Viz. the Temple-bone , wedge-bone , or Fore-head bone ; for the Crown-bones and Noul-bone are no where connexed to the bones of the upper chap : And they are particularly these ; Viz. the connexion of the outer processe of the Fore-head bone , with the inner processe of the first bone of the upper chap : the connexion of the first bone of the upper chap with the wedge bone : the connexion of the inner processe of the Forehead-bone with the fifth , fourth , second and third bones of the upper chap , being in the order recited , connexed from within outwards : the connexion of the outer , or yoke processe of the first bone of the upper chap , with the yoke processe of the Temple bone , in the middle of the yoke bone : which yoke bone is not a distinct and several bone , but made up of two processes of two several bones : and the last is the connexion between part of the upper , part of the dissepiment and the wedge-bone , Lastly the seams which concern the bones of the upper chap only among themselves are the connexion of the first and fourth bone , the connexion of the second bone with the third and fourth , the connexion of the third and fourth bones , the connexion of the fourth and fifth bones , the connexion between the two fifth bones , the connexion of the fourth and sixth bones , the connexion between the two sixth bones , the connexion of the other part of the upper part of the dissepiment with the fifth bones , the connexion of the lower part , of the dissepiment in the Plough-share bone with the sixth , i. e. the palat bones and some small part of the fourth bones . In all which , if somewhat at pleasure , they have used authority in the numeral order of the bones , and in the account and order of the seams , it is no more than is freely allowed to each Artist in his Art , so long as the Authority they use , neither bears , nor creats any repugnancy to the subject matter . And so even in abstract Mathematicks , somethings are determined , not by necessity , because they can be no otherwise , but by long usage and authority , because they may conveniently be as is determined . So Arithmetical numerations , which are every where received and taught in Decuple proportion ; with as much facility and Mathematical accurateness might be instituted in undecuple proportion ; and then the usual Probes , should not be by casting away of nines but of tens ; or in sexage cuple proportion ; and then the Probes should be by casting away of fifty nines : or non cuple proportion , and then the Probes should be by casting away of eights . And the like instances might be given in Geometry ; and in several , if not most parts of Concrete Mathematicks . So in ordering the Account of the Brain ventricles , of the sides of the same bones , and sometimes of the branchings of sinews , veins , Arteries , other vessels , and the like ; custome , and authority , commonly gives praecedency to the parts , cavities , or branchings , posited on the right side ; though without offence unto Truth , all Accounts might as exquisitely be compleated in a quite contrary order . But though these things might be , and as well , as what is ; yet what is , being as accurate , as what otherwise might be , it is sufficient to know that these things might be otherwise methodized , without renouncing the Antients method . I have , you see , too high an Opinion of the persons concerned , to imagine their difference could arise from , some peculiarities in unusual skulls ; in which it is not uncommon to find great difference in the numbers of bones , seams and holes , not only under diversity of Age and sex , which , is so common , it is not otherwise to be expected ; but as well when no such causes can be alleadged , for the diversity : nay , many times in the main and principal , commonly called True seams we do not ever find a constant regularity and uniformity . But of those things , which seldome are , we are not to maintain Controversy , as if they were the way of nature . This , Sir , I have written not to Inform , but confirm your judgement ; which I know so well versed in the Syntaxe of this our humane body , that it cannot dissent from what is . The Fifth Answer . That immense volatility may consist with immense ponderousness . That tincturs may be altered by maturation without any addition , Whether the appearing and motion of comets may be before their appearance predicted . That no such particular predictions can be made concerning the meteors which are in the Atmosphear of the earth , nor of the first appearances of such Comets as are supposed to have their Original from new amassements of Cometical matter in other Atmospheares ; though after their first appearance , upon some observations accurately made , somewhat , though nothing so peremptorily as in other cases , may be predicted , relating to their future motion . That it is not impossible , but concerning Comets which are permanent bodies , and not new amassements , predictions may be made long before , of their future appearances and motion . SIR . I Take your satisfaction , upon my last proposed , clear , and doubtless Experiments , now since by you proved and approved , as a fair acknowledgment of that Truth , which however to me upon its former evidences needed no farther confirmation : Viz. that so different are the genuine notions and qualities of fixednes and gravity , that immense volatility may and is ordinarily consistent with an immense specifick ponderousness ; arising not from the moles and quantity of the bodies under consideration , but rather from their natures and kinds . That what in your first velitation you assumed as absurdly grosse , inconsistent , and impossible ; is now , upon your own acknowledgments , most easily and obviously demonstrable by experience . No less certainly is to be acknowledged , in what you propose for the tingeing of metalline bodies , only by ordering and attending them in the management of their maturations , without the addition either of body , or spirit , as being all the time of this operation under the sure seal . Could I perswade my self it should not be resented as a grand unkindnes , to be silent in what you call for my thoughts in , in the close of yours ; Viz. Whether prognosticks at certainty , such as are of Eclipses , of Coitions , oppositions , motions of other Starrs , whether , I say , such prognosticks and of like certainty , may not also be made of Comets , of their Appearances , common impediments removed , and of their motions ; I should , if it might be , herein , lay Harpocrates finger upon my lip , and seal them up into a pertinacions silence . Not but I am desirous to know , and willing to search after truth : only I fear me , these are secrets of nature , by their peculiar mysteriousnes , sinking themselves so low into the pit of obscurity , that the stock of observations and disquisitions about them , which the world as yet hath , is not able to raise them so high , and place them so near day , as to be within humane reach and discovery . What I now offer is a Caesarean birth of the mind , not brought forth by me , but cut out of the womb by your importunity : if it want shape , licking and lineaments , accept it as an unripe Abort , and either hatch it to perfection in your Thigh , or give it a little dust to cover it . I take by way of praesumption , that in this Quaery and Question you mean not by Comets , any of those more usual , less permanent is regularly moved Meteors , bred ▪ gathered , fired , and burning in the Atmosphaere of our Earth ; after their Appearance , there cannot be much certainty of their Motion , though sometimes there may be conjectures probable enough , and in the Event by observation justifyed , when the fuel , or fovent matter of such Meteors , is manifestly , upon what account soever , known to be only , or most copiously situate and disposed some one particular way : but of the generation and first appearance of such Meteors , particularly the moment when , and the point , or exact place where , they shall appear , much less of certainty , in such pronosticks is to be expected ; there being so much variety , contingency , and uncertainty , in the causes and meeting together of those causes , which contribute to their production . And though there are , and have been many praedictions in general , and Rules of praedicting Astrologically , or Physiologically , from the seasons of the year , the temperature , and distemper of seasons &c. Concerning such meteors in general ; yet in a matter so unallyed unto certainty , replenished with all manner of casualties , to promote , or retard such productions , I have not known any offer peremptory Pronosticks of the kind of the meteor , its shape , magnitude , duration , motion , with absolute determinations of its time and places , at any time beforehand . The quality and condition of the subject matter , making it as impossible to bolt out scientifical and oracularly certain predictions of such meteors , as it is , a year before , to prove , or shew that in such an hour , and in such a quarter , shall be a Rainbow , so colour'd , so continued , or discontinued and of such limited dimensions : or that , such a moment , from such a point of such an Azymuth , shall a devolant Star spring forth , which , in its fall , shall run obliquely thorow such and such Azymuths , and expire at such an height above the Horison ; or that such an hour , in such a Longitude and Latitude , shall in such Altitudet and positions , and of such dimensions , be seen by day four Suns , or by night three Moons . To lay aside therefore the consideration of these , as supposed impertinent to our present purpose ; what may judiciously be concluded upon your Questions concerning those other Comets , which lye without the compasse of this Earths Atmospaere ? If there be not two sorts of such celestial Comets ; there are at least two several and very different Hypotheses and notions under which they are considered by Artists : and Artists of equal worth and fame , order their reasonings , some upon the one supposition , some upon the other : Viz. Some , as if Comets were new made bodies , amassed , and gathered in some of the superior Atmosphaeres ; many of which are , not without fair reason , supposed to be in those vastly remote aethereal regions : others , as if Comets were coaeval to , and neither less permanent , nor more new , then the rest of the Stars ; only seldome seen , and when seen , soon passing again out of sight , by reason of the Line , upon which their Center is moved : and nothing as yet appears hindering the truth of the possibility and consistency of both these Opinions ; leaving it especially indifferent in the later Hypothesis , to call such stars at pleasure by the name , either of Comets , or New-stars , or rather seldome appearing Stars . Comets upon the first supposition , seem not to want some affinity with several , especially of the more eminent , meteors of our Atmosphaere : yet allowing a vast difference between them in place , proportion , duration , motion , and the like circumstantials . And as our Globe , though in its self large , is but a minute thing , compared with many of the caelestial Bodies ; that the vast error of the Earths semidiameter , by taking the Earth for a small point , many times in Astronomical , Gnomonical , and other operations , creates not by consequence any perceiveable Errour : so it is not unlike , but the Atmosphaere of our Globe is vastly disproportionable to the Atmosphaeres of many of those heavenly lights : which may in a sort be gathered also , from the small power , which our Atmosphaere has in the pressures which it makes upon moist and liquid bodies : as also from the common vastnes of cometical bodies , frequently accepted as much larger then all both our globe and its Atmosphaere , and therefore requiring a proportionately immense place both for their being and motions . And that such huge dimensions are not groundlesly attributed to the cometical bodies , is rendered undoubted from the glorious and glaring light , with which eminently above most of other Stars , they dazle , to admiration , the minds and Eyes of mortals at so great distance , that some times little , or no Parallax can be observed in them . As to these therefore to solve the Questions , unto which you have tasked me ; I cannot but judge it improbable , with any assurance to make praedictions before hand , that in such limited moments of futurity , shall appear such Comets , as are to be at after amassed , gathered , formed , and embodied in the Atmosphaeres , which are above : if seeming no more wilde to give heed and credit to the superstitious Auguries and soothsayings of the Antients , then the most subtle reasonings upon which such predictions can be made , in a subject of this nature . Yet though their first emerging and appearance cannot upon any calculation be foretold ; however at after they have a while appeared , and some , though not very many , curious observations have been made of the changes of place , and other circumstances , which they make in their several appearances , at such and such exalt distances of time ; it is fairly enough probable , that often , by an ingenious prognostick , the course of such a Comet may be nearly traced , and set down before hand , as to way and speed , only with this limitation , if the substance of the Comet do not first vanish , or dissolve , or by reason of its instant dissolution divert from , hasten , or retard its course : upon which score of their dissolubleness , and therefore their ere long to be expected dissolution , no prognosticks , upon them and their course , can be so absolute and peremptory , as those which may be made concerning such Comets , as are properly couched under the second supposition . And the grounds why most what in these Comets of the first constitution , or supposition , from past observations , a fair conjecture may be made of their future course notwithstanding their new production and amassement in Atmosphaeres , are chiefly hereupon founded : that such cometical bodies , as they are demonstrably vast , and manifestly , and by their nature dissoluble , so their dissolution is not observed very momentaneous , but most what more , leisurely by degrees and in time ; in short , they flame forth of a sudden , but expire gradually ; so as to be able , for a while , to retain the impressions of regular motion , whether communicated from somewhat in the Center of the same Atmosphaere , or from the confluent efficacy of several Agents all contributing constantly , each according to its nature , to the Comets alone , or its and its Atmosphaeres motion , whether by aequilibration , pulsion , traction , pressure , manifest , or secret ; or else inwardly wrought into the very substance and nature of the Comet : especially the Comets place being in those lofty aethereal regions , where are perpetual circumgyrations and every motion that is observable , the more accurately it is observed , it is found the more regular . And if it be urged here-against that the motion of Comets seldome , or never answers the motion of any other Starre , but commonly has a cross trajecting motion , whereby it moves asloope , athwart , transversely , or obliquely , varying from the usual , formerly observed motions . As this cannot be denyed , so it doth not at all infringe the possible regularity of such motions , which are observed to be most what in the same plain , though oddly posited : and that there are many and , diverse such undreamt of motions in the Heavens , constant and regular , of which save by some such , or late discoveries , no hint hath as yet bin made forth unto us , may in as good reason be allowed , as that vast number of Stars in the skyes acknowledged , of which , without the Telescop , 't is impossible to have any discerning . And if we grant that in respect of its peculiar Atmosphaere , the motion of a Comet solely considered as in it , be not so strictly regular ; yet the regular circumgyration of the Atmosphaere , in which the Comet is carryed , in respect of the Universe , cannot but with those that Cant upon that Hypothesis , enforce the Confession of a great degree of regularity in the Comets motion : and that Comets , in what part of the Heavens soever appearing , move in some conformity with other celestial bodyes , notwithstanding the contrariety or diversity of their proper , or peculiar motions from the rest , is , beyond all dispute , evident from their dayly moving , with the rest , from East to West . The manner of making observations , calculating to know the place , the distance , speed of such a Comet , and when it is at nearest , or remotest in its course from us , is no other then in Comets of the second supposition . And from this whole discourse is manifest ; the Hypotheses , upon which Calculations are to be made , in order to such praedictions , cannot be particularly in these Comets known before hand , but in several such Comets may be very different ; and are to be found out by curious , and diligent Observations ; which , in each respective Comet , must be accurate , and at least four in number : and I think predictions pretended from three observations , are over hasty , and , at best , can but be conjectural ; nay , in some cases , from four ; as if you be unsatisfyed , I shall be ready , by demonstrative instances , to remove your doubt . But if of these Comets any should be found , to wander , so as the motion of its Center cannot possibly be reduced any thing nigh unto the same plane , or regularity in change of Planes , or that the motion of its Center , in the same , or several Planes , describe not a Line regular , or near unto a regularity , it is not probably easy to make predictions at any certainty of truth , of the future course and motion of such Comets . Concerning Comets of the later kind , or Hypothesis ; possibly it is more easy to answer your Queries in them , then effectually without a world of time , sagacity and diligence to accomplish and attain the purport of those Answers . That the motion of such Comets of the second sort , being not truly new , but rather seldom appearing , and soon disappearing Cometical Stars ; that , I say the motion of such , is not without some regularity , though it may not be concluded without long observations and frequent experiences of their motion had , which in such seldom appearing , and soon again disappearing Stars is difficult enough to attain to ; yet if we consider the steady , unbiassed course , held by most , if not all the rest of the permanent Stars without deviation , though in different periods and with many different latitudes and declinations , and great diversity of motions , it cannot be less then mightily probable , nothing in sense , reason , or experience appearing as yet able to demonstrate the contrary , but that a fair , celestial regularity may rationally be expected in those their perpetual motions , whether their Centers be carryed in the same Plane , or in a continual change , and alterations of Planes . And in diverse respects in some , if not all of them , as in most other Stars , the same Center may be said to move regularly and perpetually in the same Plane , and also without elenchtical contradiction to move regularly with an incessant change of Planes : so the motion of any Planet , or other Starr , whose motion we are versed in , taken concretely and with complication of that mundane , or general circumvolution , which with all the rest it hath from East by South to West , though it be regular , yet it is not without a continual shifting of the Planets , or Stars center from plane to plane : whereas the proper motion of the same Planet , or Starr considered abstractly and severed from the general circumvolution it hath with the celestial universe , as it is regular , so it may keep the center of the planet , or Star constant in the same plane . And the Course , appearance , and returns of such cometical Stars will be of much more easy calculation , if their motions , in the regularity , propriety and peculiarity of them , be any wayes reducible , as is abovesaid , unto the same plane ; of which plane by observations is to be decided , whether it pass thorough the center of the Aequator and universe ; and if the center of the universe lye out of it , what is the perpendicular from the Center unto the plane ; and in the plane , what regular figure , or journey is described by the motion of the Comets center , and what are the Diameters or Axis of such figures , or centers of such motions in that plane : in the easiest , and plainest of all which cases , four observations are at least re-requisite : but where the regularity of the Comets motion , being irreducible to the same plane , is in a continual shifting from plane to plane , there many more observations may scarce be enough , to clear up the regularity of the Comets motion , sufficiently for easy calculation : and when a sufficient number of exquisite observations have been made , the calculation , as it will hardly be so accurate , so it will scarce be so easy , as in other cases - The observations , in all cases and suppositions , are to make discovery of the exact place of the Comets center at the moment of the observations , Viz. of its longitude , latitude and altitude not in respect of Azymuthal arches , but in right lines drawn between their center and the center of the universe . And the more exquisite the observations are , they make way for clearer calculations ; upon which may be founded so much the more assured predictions . To answer therefore your Queries in relation to these Comets of the second sort , or supposition ; I think it not impossible , but in time predictions may , it may be many Ages beforehand , be made of the Appearing , or rather Re-appearing of such Comets : according as , in the regularity of their motion , they come nearer or are removed Farther off from us . So I remember a person of Quality in the North , with an high measure of Assurance reported to me , that one of the late Comets appearance and Emerging , was by a certain Genoese praedicted at least two years before the Emersion and appearing of it : which if so , is to be referred , I doubt not , to the principle and method , above insisted on . According to which , after different intervals of years , several Comets may appear , one after another , and sometimes several such Comets may appear all at once : and yet there is no clear necessity of the constant re-appearing of the same Comet , in the same Horizon , still at after equal spaces of time . And if the Emerging of such Comets may be praedicted before their Appearance ; upon the same principles , the line of their motion , the casting of their Train , and their future recess , may as well be praedicted , whether before , or after their first appearance : as also when , and where shall be their Accelerations and retardations in motion ; especially , considering the advantage hereunto accruing , from their nearness to , or distance from the Eye of the spectator : not that this makes inequality , or inequability to be , but rather only to appear , in their motion . Upon the same accounts , the dayly rising , setting , and Southing of Comets may be calculated : as also what parallel , or spiral it describes : and how much it gains dayly in its proper motion : as also its place , as to longitude , latitude , altitude , above any limited Horizon , at any limite moment : what constellations it shall pass thorough : and in what Aspect it shall be posited to any Planet , or other Star : so of conjunctions , oppositions , quadratures , combustions , Eclipses , and many such like affections , in common incident to Comets with other Stars , there may as clear predictions be made : as also when it disappears , not for its remotenesse from us , but as other Stars dayly , because of the Suns propinquity to it , and our view , the times of its not being seen by reason of the circumfusion of the greater light of the Sun , being manifestly calculable ; though of other obscurations by clouds , and such like impediments and interpositions , no artificial prognostick can be made . So in the first Approaches , or last recesses of Comets , by falling into such circumfusions of solar light , the first appearance of the Comet will be later then otherwise , and in the other case , its appearing cease sooner then might be expected : and predictions are accordingly to be ordered . If I have been unusually long beyond the proportion of a Letter , suppose it to be the long Train peculiar to such Cometical , full-lighted , obscure-natured Stars , as you are now Quaering about . And not to dismisse you without a Task ; it were a noble disquisition clearly to unfold , what it is in these Cometical Stars , alone , or also in their circumfused Atmospheres , that enables the Sun , more especially to affix such glorious , long luminous Tayls unto them more then to other Stars , whether constant , or new , or rarely appearing Stars ; which in whatsoever position to the Sun , are still seen without any such long , beamy , luminous Trains . But I commit this and those other Queries about the salts of the highest volatiles to your serious leisure . The sixth Answer . That the motion of the Celestial bodies about their particular axes , is not a satisfactory proof of their Copornican Systeme . That Comets though supposed to be nearest to the Earth , when they are in opposition to the Sun , yet do not thereby prove the Earths motion . I See that neither the currency of Doctrines , nor the course of time , are able to beat off from you your old Philosophical genius . You can swallow nothing upon the mere Tradition of others , nor yet upon their reasons , till first examined , concocted , and digested in your own . Your doubts seem not causeless which you move upon that point ; whether the motion of the Celestial bodies turning themselves about , upon their own Axes , may be allowed for a just proof of the Copernican systeme . It is a golden and noble branch of intellectual Justice , so far as is possible , mathematically and to a punctillio , to clear and set forth the bounders of Truth : yet as your modesty delivers your judgement , I doubt not , by way of doubt ; so I desire you read my Answer , as writ only in the same Dialect ; that I , in like manner , may not appear a rash Judger , of what it seems has been concluded by men of great parts and learning . The Artfullness of the Instruments , and diligence of the Observers that , from several marks in several Stars , have noted this their circumvolution , I love and honour : and am apt to conjecture , the like motions may in future be discovered in other Stars , in which they have not as yet been noted : and shall be ready to improve the Observation in all inferences authorized and recommended unto us by the necessity of their consequence . But as things , at first glance , commonly offer a fuller raye then they hold in constant ; so I suspect the glimmering probability of the Earths motion according to the Copernican Hypothesis , upon the first discovery of this circumgyration of Stars about their own Axes , will , upon farther consideration and deliberation , grow still more faint . There being very few Hypotheses , with which ( to give it a short name ) this circumaxal motion of the Stars is expressely inconsistent ; it not being impossible , if all things else would consist and cohaere , but such a motion might be accomplished in the Hypothesis of Orbes and Sphaeres , so the Star were but unfixed and set lax and free to move according to its nature in its own orb , by a motion discharged , different and distinct from the motion of its orb : So in the old Hypothesis , while they affixed and bound the Starre unto its proper Epicycle , yet in its larger Orb they allowed it to be therein carryed sometimes progressively , sometimes retrogradely , and sometimes stationarily , according to the motion of the Epicycle , or Episphaere in the larger sphaere . And without any sense as yet , that it deserves a blush , I willingly profess , I want the Lyncean eyes and judgment , from such a circumaxall moving of Stars , to deduce the Suns , or Earths central , either rest , or motion : especially the vast distance , at which these bodyes are distant one from another , being on all hands yielded ; which if it do not necessarily , altogether amort , and abolish the powers , which one of these bodyes may possibly have upon the others , yet till such their powers over one another in this point of motion be fairly proved , it leaves it easily manifest , that any of these bodyes may be moved according to its own peculiar nature , without laying , by so long a reach , laws of necessity upon other Bodyes , at so great a distance , for their motion . As for example the bodyes A. and B. either of the same general , or special nature ; they being severed and severally placed at competent distance one from another ; both , or either may be at rest , or in motion , neither inferring upon the other the analogy either of its rest , or motion , or to be suspected so to doe , till it be pregnantly either so observed , or proved : Viz. That either has upon the other , even at distance , such a strong and efficacions power· And if the stress of the ratiocination hang upon this ; that otherwise there would not be a conformity between the motions of the Earth , the Sun , Saturn , Jupiter , &c. to my apprehension , nothing is more easy , then not only to turn the edge , but break the back and overturn the foundation of such an Argument . For first the motions , or unmovednes of these bodyes , is not to be made conform unto our retired thoughts , and speculations in a close study , or to the motions , which we have observed , and justly concluded certain in other noble Bodyes in the world ; but they are rather by all ingenions Arts and instruments , to be each by its self particularly observed , how in Truth they are , and so to be accepted and acknowledged in their appropriate sciences . And what greater necessity is there of making the Sun , or the Earth in rest and motion to be conform to Saturn , Jupiter , &c. then to be conform to them in shape , magnitude , respective distances , which on no hand is ascerted , but for the impossibility , and demonstrablenes thereof by observation , rather the contrary ? And why should there not be as great a necessity for them to be conform in rest and motion , to the Stars passing generally under the notion and title of Fixed , which has never yet been offered , because it is cl●●● it cannot be defended ? And what less necessity is there , why they should not conform in the celerity and nimbleness of their motion , as well as the form , kind and manner of it ? And what greater necessity for conformity of motion in Stars , then in Animals , in which some creep , some fly , some go upon feet , some swim ; neither in their supposed and called Elements can any such necessity of the same kind of motion be observed , though in the same Element . Upon the same way , method and force of reasoning , when Jacob is at the Dancing , or Fencing Schools in Oxford , Joga must be Galliarding or Brandishing it at the like Schools in Salamanca . Every stone has not in it the mysteryes of the Magnet , and several Jewels have their several splendours , virtues and properties : so several Stars considering their several situations , shapes , magnitudes , distances and diversities of nature , cannot but in rest and motion each have something proper and peculiar : at least may not without cause be suspected to have otherwise , till it be possible by some medium to evince the contrary . And as the Copernican Systeme receives not much confirmation from the praecedent circumaxal motion of Stars ; so that Comets are nearest the Earth when opposite to the Sun ; with what greater strength doth it , as others urge , prove the Earths motion ? wherein is requisite that the Hypothesis it self , be confirmed by frequent Observation in several Comets , before it be allowed as general ; that as by way of Induction may be inferred , that every Comet when it is nearest to the Earth , is then opposite to the Sun , and when this is allowed and fairly proved , there is no necessity by which it follows , or can be inferred from hence , that the Earth hath its annual Revolutions about the Sun : all that is in the allowed , and supposedly proved Hypothesis , being many ways accomplishable , and as easily and clearly , the Sun moving about the Earth , as the Earth moving about the Sun , in which I doubt not your judgment . The Second SECTION of PHILOSOPHICAL ANSWERS . CONTEINING QUERIES Relating to the Angle of Contact . LONDON , Printed by T. L. for Nathaniel Brooke , at the Angel in Cornhil near the Royal Exchange . 1670. To the right reverend Father in God , Seth Lord Bishop of Salisbury . To the right reverend Father in God Lord Bishop of Chester . My Lords . ALthough I know , the raw , untrained Reader , upon this last Answer above the rest , will be sure to pronounce his , Quis leget haec ? and to bestow upon it , no other fate then thuris & scrombrorum ; judging all things impertinent , that lye not in the dirty troden way ; or cold , which his torpid dullness is unable , at least too slothfull to strike any fire out of ; and every thing to be destitute of a kernel , which is too hard for his delicate Gum to crack the shell of : however , I fear not the rendering my self faulty beyond Apology , in laying this Answer , above all the rest divulged in this present manual , at your Lordships feet . The singular happines of both your Lordships in your studies , drawing in by way of divertisement , what multitudes of others study seriously and purposely for , and yet miss of , having made veneration to wait upon your judgment , and your minds so seemingly fruitful , in multitudes of as new as ingenious inventions ; hath too well acquainted your Lordships , with the Scufflings which have been in former ages , and between men of the clearest judgments , and most excellent parts , about these minute angles of contact ; being , by general confession , small beyond all proportion with rectilinearies ; and by others only denyed to be minute , because they think they have no quantity at all . Like as in solar Atomes , when myriades of them are before us , we cannot be peremptory in asserting a full sight of any one of them . And however I may have missed the Corinth I first hoysed sayl for , I know when retiring from your higher-region'd speculations you are pleased to make unto your selves a Platonick divertisement , upon a deigned perusall of this scrole to a friend , I doubt not but your Lordships will justify the essay , and allow that by such sallyes , a firm comprehension may at last be attained of the mercurial niceness of this question , which hath so oft eluded the grasp of those wits , who have formerly thought they have had it so firm and sure . My Lords , I know the admirable quality , and mighty merits of the persons that think and have thought otherwise , then I have delivered my thoughts here ; however I should have dealt faithlesly with my friend , if I should have returned him answer contrary to my judgment . And as I have been morally true to him , so what right , or injury I have herein done unto Philosophical truths in this nice , and hitherto inexplicable subtilty , none can better decide then your Lordships ; at whose feet it is left , by Your Lordships Servant . W. M. The Seventh Answer . Concerning angles of contact . That recto-convexe angles of contact are truly angles according to the definition of plane angles . That recto-convexe angles of contact are not destitute of quantity . How many wayes one quantity may be greater then another , what kind of homogeneity it is that is requisite for proportionalls . That angles have figuration as well as quantity . That in angles is observable a homogeneity or heterogeneity which is Mathematical , and also a homogeneity or heterogeneity which is not Mathematical , nor any way concerning their quantity , but only their figuration , &c. Of several special properties of magnitudes and angles . How some angles are Constituted by the concrescency and annexion of several parts and angles which are heterogeneal each to other . Whether like angles in unequal circles , and in loke segments of circles be always Equal ? That all Equal angles are not like . That all like angles are not Equal . THough I cannot consent unto your thoughts about the Angle of Contact , I should be angry with my own rashness , should I be forward to blame your late speculations thereabout ; seeing so many noble and sprightly wits , and such as have deserved the honour of Europe , siding with you . Especially I honour your thorow-conversation in the learned persons works , whom I perceive you so largely to have gleaned after : you could not have plowed in these hard grounds with a more worthy Assistant . But knowing it is not Complement you expect in Philosophy but Reason ; I shall in as short , as the matter will bear , and as plainly as I can , summe up the grounds , why I as yet remain so farre dissatisfyed , that I cannot without injustice to my own judgment , desert the generous and learned dissenters from your Opinion : or cease to averre Angles of Contact to be true quantities , equal ; or unequal one to another , though the highest multiplex of the greatest citradiametral Angle of Contact , be never able to exhaust , or equalize the least right-lined part of the most acute right-lined Angle . And that we may not mistake each other about the State of the Controversy ; and to be shorter , and more clear in the insuing discourse ; we shall first set down the definitions of certain termes , about which I suppose there will be no difference between us . As. 1 st . ( Our discourse extending no further then to plain Angles ) that by a Right-lined angle , we understand a plane angle contained under two concurring sides , or lines , which are two right-lines not posited directly the one in the production of the other , nor parallel the one to the other . As in fig. 1. the Angle B AC is a right-lined angle contained under the two right lines BA and CA ; BA and CA not being so posited at A as to make one right line : nor can they be parallel because of their rectitude and concurrence . 2 ly . That by a crooked-lined Angle , we understand a plane Angle , contained under two concurring sides , or lines , which are two crooked lines ; as in the fig. 2.3 4. the Angle B AC is a crooked lined angle contained under the two Crooked lines B A and C A. 3 ly . That by a crooked lined angle of concaves , or a Concavo-concave angle , we understand a plane angle contained under two concurring crooked lines ; both which crooked lines obvert at the Angle first of all inwards , the concave side of their Curvature , towards the angle under then contained . So in fig. 4. the angle B AC is a crooked-lined angle of Concaves , or a Concavo-concave angle , contained under the two crooked lines BA and C A both which obvert the Concave side of their curvature towards the angle under then contained . 4 ly . That by a crooked-lined angle of Convexes , or a Convexo-convexe angle , we understand a plane angle , contained under two concurring crooked-lines ; both which crooked-lines obvert at the angle first of all inwards , the Convexe sides of their Curvature towards the angle , under them contained . So in fig. 2. the angle BAC . is a crooked-lined angle of convexes , or a Convexo-convexe angle , contained under the two crooked-lines BA and CA , both which obvert the convexe sides of their curvature , first of all inwards , towards the Angle under them contained . 5 ly . That by a concavo-convexe angle we understand a plane angle , contained under two concurring crooked lines ; the one of which , at the angle first of all , obverts the convexe side of its curvature inwards towards the contained angle , the other the concave side of its curvature . So in fig. the 3 d. the angle BAC is a concave-convexe , or a convexo-concave crooked-lined angle , contained under the two crooked lines BA and CA , whereof the one BA obverts the convexe side of its curvature towards the contained angle , but the other CA obverts the concave side of its curvature towards the same contained angle . 6 ly . That by a mixed lined angle , we understand a plane angle , contained under two concurring lines ; whereof the one is a right line , the other a crooked line . So in fig. 5 th . 6 th . the angle BAC is a mixed-lined angle , contained under the right line CA. and the crooked line B A. 7 ly . That by a Recto-concave angle , we understand a plane angle , contained under two concurring lines ; whereof the one is a right line , the other a crooked line , having the concave side of its curvature obverted towards the contained angle , so in fig. 5. The angle B.A.C. is drawn a recto-concave angle , being contained under the right line C.A. and the crooked line B. obverting the concave side of its curvature towards the contained angle . 8 ly . That by a recto-convexe angle , we understand a plane angle , contained under two concurring lines ; whereof the one is a right line , the other a crooked line , having the convexe side of its curvature obverted towards the angle contained , so in fig. 6 th . the angle BAC . is drawn a recto-convexe angle , being contained under the right line CA. and the crooked line BA . obverting the convexe side of its curvature towards the contained angle . 9 ly . That by an Angle of contact we understand a plane angle , contained under two concurring lines ; which two lines are neither one and the same line produced , nor yet in their present positure and inclination can possibly cut one another , how farr soever either , or both of them be produced . So in fig. 7 th . and fig. 8 th . the angle B AC . being an angle of contact , if in either figure the crookd-line BA , be produced beyond the point of contact A , unto D , and in fig , 7 th . the crooked-line CA , in figure 8 th . the right line CA. be produced beyond the point of contact A unto E ; in neither the line C AE can fal into the production of the line BAD , nor in either shall the line C AE cut the line B AD. And 10 ly . From the figuration , positure and properties of the sides of such angles of contact ; that by a recto-convexe angle of contact , we understand a plane angle being recto-convexe , as above defined , and being also an angle of contact . So in fig. 8 th . if in the recto-convexe angle BAC , the right line C A touch and cut not the convexe arch B A the angle BAC is a recto-convexe angle of contact . 11 ly . That , by a recto-concave angle of contact we understand a plane angle of contact , which is also recto-concave , as above defined . As in fig. the 8 th . if in the recto-concave angle EAB the right line EA touch and cut not the concave arch BA , the angle EAB is a recto-concave angle of contact . 12. That by a concavo-convexe angle of contact we understand a plane angle of Contact , being also concavo-convexe , as above defined . So in fig. 12 th . if R AH being a concavo-convexe angle , the arch RA touch and cut not the arch H A then the angle R AH is a concavo-convexe angle of Contact . 13. That by a Citra-diametral-concavo-convexe angle of Contact , we understand a plane concavo-convexe angle of Contact , both whose conteining Arches lie on the same side of the right line tangent , which toucheth both the arches in the same point of Contact , As in fig. 12 th . the concavo-convexe angle of Contact H AR , having both Arches H A and R A lying on the same side of the right line tangent B A , which toucheth both the Arches in the same point A , the concavo-convexe angle of Contact H AR is citradiametral . 14. That by an ultra-diametral concavo-convexe angle of Contact , we understand a plane angle of contact being concavo-convexe , and having the one arch on the one side of the diameter passing thorow the Contact point , and beyond the right line tangent which toucheth the Arches in the same point ; but having the other arch on the other side of that diameter , and on the other side of the right line tangent . So in fig. 12 th . the two Circles F AH and ADK touching in the point A , and AK being their common diameter and AB being a right line tangent to both , the concavo-convexe angle of Contact DAH is ultra-diametral . 15. That by a mixed crooked lined angle , we understand a plane angle contain'd under two concurring crooked lines , of such several curvatures that it is impossible for them to be coapted from the angular point the one unto the other , or the one , or its production to be coapted to the other , or its production , at and from the angular point , by any circumduction whatsoever , so in fig. 9.10.11 . the angle B AC , being a mixed crooked lined angle , AB as being of a different curvature from AC , can no way possibly be coapted by any circumduction to AC from the angular point A : and if B A be produced to D and CA to E the crooked-line AB , because of its different curvature can neither be coapted to the crooked line AC nor to its production AE : nor the crooked line AC to the crooked line AB , nor to its production AD , by any circumduction upon the angular point whatsoever . 16. That by the isoclitical sides of an Angle , we understand two such lines , whether right , or crooked , containing a plane angle , as according to their present site and positure , without inversion when crooked , moving by the sides nearer one to another , will by such motion at last come to be coincident with and coapted exactly the one unto the other : and that by an isoclitical angle we understand a plane angle , contained under such isoclitical sides . So every right lined angle is manifestly isoclitical ; and its sides are isoclitical , the sides by such motion on the angular point one towards another being manifestly coincidible and coaptable So also in fig. 3d. if in the concavo-convexe crooked lined angle BAC . the crooked-lined side B A by moving upon the angular point A towards the other crooked lined side CA , will at last coapt and become coincident with the crooked lined side C A then are B A and C A isoclitical sides and the angle B AC anisoclitical angle . 17. That by the anisoclitical sides of an angle we understand two such lines , whether the one right & the other crooked , or else both crooked , and whether both of the same or different curvatures , containing a plane angle , so as according to their present site and positure , without inversion of either when crooked , by moving the sides nearer one another , by the continuance of such motion they can never be brought to be coincident with , and coapted exactly the one unto the other and that by an anisoclitical angle , we understand a plane angle contained under such anisoclitical sides . So all crooked lined angles of concaves , though having sides of like curvature , all crooked lined angles of convexes , though having sides of like curvature , all concavo-convexe angles , whose sides are of different curvatures , all mixed lined angles , whether recto-convexes , or recto-concaves , all mixed crooked lined angles whatsoever , are all of them manifestly anisoclitical angles , and their sides anisoclitical . So in fig. 4 th . though AB and AC . be supposed to be of uniform answering and equal curvatures , and likewise in fig. 2 d. though AB and AC again supposed to be of uniform , answering and equal curvatures , and in fig. 3 d. fig , 5 , 6 , 9 , 10 , 11. supposing AB and AC not to be of uniform , answering and equal curvatures , by moving the sides AB & AC in that their present fire & positure upon the angular point A , without the inversion of either , when both are crooked , to bring the sides nearer the one to the other , it is manifest that by the continuance of such motion they can never be brought to a coincidence with , and to be coapted exactly the one unto the other , and such also are all angles of Contact whatsoever , as in fig. 7 , 8 , 11. AB & AC are as uncoincidable and uncoaptable as in the former , except only ultradiametral , concavo-convexe angles of Contact , which are of equal and answering curvatures . 18. That by an Angle of curvature , or coincidence we understand a plane angle , contained by any two parts of a crooked line at the point of their concurrences any where to be imagined , or taken in crooked-lines . So in the 7 th . fig. let BAD be the circumference of a Circle , Parabola , Hyperbola , Ellipsis &c. At the mean point A , the sides BA and AD contain an Angle of Curvature , or coincidence . 19. That by autoclitical curvature , and so by an autoclitical crooked line , we understand such a crooked line , as passing from the angular point of a right lined angle , between the two sides , by the inclination of its curvature , keepeth the convexe side of its curvature , constantly obverted to one of the sides , and the concave side of its curvature constantly obverted to the other . As in fig. 17. in the right lined angle BAC , the crooked line AEF keeping its convexity constantly obverted to the side AB , and its concavity to the side AC , or so much of it as is intercepted between the intersection at F and the angular point at A the crooked line AEF is autoclitical , i. e. the convexity is all on one side , and the concavity all on the other . 20. That by antanaclitical curvature and so by an antanaclitical curve line , we understand such a crooked line , as passing from the angular point of a right-lined angle , between the two sides , by the inclination of its curvature , hath the convexe part of its curvature , sometimes towards the one side of the right lined angle , and sometimes towards the other side of the right lined angle , i. e. the convexeness and the concaveness are not constantly on the same several sides . As in fig. 17. in the right lined angle BAC , the crooked line AGH obverting the convexity at G towards AB , and at H towards AC is antanaclitical . These definitions praemised , to give now the true State of the controversy ; let there be , as in fig. 12. two equall Circles AHH and ADK touching in the point A : and let AG be the Semidiameter of the circle ADK : and AB be a right line tangent touching both the Circles in the point A : and let AEL be a greater circle then either , touching both the former , and also the right line tangent in the point A : and from the point A draw the right line AC at pleasure , cutting the circle ADK in the point D , and the circle AEL in the point E : now therefore whereas you say that the Recto-convexe angles of Contact BAE and B AF are not unequal , and that neither of them is quantitative ; and that the crooked-lines E A , DA , HA are coincident , Sc. so as to make no Angle with the right line AB , or one with another ; and that the right-lined right angle B AG is equal to the mixt-lined , i. e. Recto-concave angles of the Semicircles E AG and D AG severally , and that those angles of the Semicircles E AG and D AG are equal the one unto the other ; and that the mixed lined Recto-convexe angle F AG is severally equal to all , or any of the former ; and that there is no heterogeneity amongst plane angles , but that they are all of them of the same sort , and homogeneal and undevideable into parts specifically different , distinct and heterogeneal in respect of one another , and the whole ; and that to any mixt , or crooked lined angle whatsoever that is quantitative it is not impossible to give an equal right lined angle : I acknowledge for all these things you have disputed very subtilly ; yet I must with a clear and free judgment own and declare a dissent from you in them all , for the reasons to be alleadged in the insuing Discourse . To clear all which , nothing can be of higher consequence in this Question , then truly to understand the nature of an Angle , what an Angle is , what is an Angle , and what is not . And to exclude the consideration of Angles herein unconcerned ; they are plane angles i. e. such as are contained by lines , which lye wholly , and both in the same plane , the disquisition of whose nature we are now about . And such is the affinity , which the inclination of one line hath to another in the same plane , with the nature of an Angle , that without it a plane angle cannot be defined , or conceived . For where there is rectitude and voidness of inclination , as in a right line and its production , there never was justly suspected to be any thing latent of an angular nature ; nor between parallels , for want of mutual inclination . But yet the inclination of line upon line in the same plane , is not sufficient to make up the nature of an Angle : for in the same plane one line may have inclination to another , and yet they never meet , nor have in their infinite regular production any possibility of ever meeting ; as the circumference of an Ellipsis , or circle to a right line lying wholly without them , without either Section , or Contact ; or the Asymptotes in conjugate Sections , which though ever making a closer appropinquation to the circumferences of the conjugate figures , yet infinitely produced , never attain a concurrency . And though by possibility the inclined lines might meet , yet if they do not , an Angle is not constituted : only there is possibility of an Angle when being produced they shall meet . So as to make up the nature of an Angle two lines must be inclined one to another , and also concurre , or meet to contain on their parts a certain space , or part of the plane between their productions from their point of concurrence , or their angular point . And this being the general , and proper nature of a plane angle ; as it is manifest , that in a right line there is no Angle , so it is dubious what is to be judged of those curve , or crooked lines , whose curvature is either equall , uniform , or regular : Sc. whether in such lines there be not at every mean point an angularness , the lines still lying in the same positure . It is clear in a right line no mean point can be taken , at which the parts of the right line in their present position can be said to have any inclination one to another : that though the parts concurre , yet they want inclination : but in the circumferences of circles , Ellipses , Hyperbola's , Parabola's and such like curve , or crooked lines , being of equal uniform , or regular curvature , no point can be assigned at which the parts in their present position have not a special inclination one to another . So as , as before , inclination of lines and concurrency making up the nature of an angle ; it seems not reasonable to deny angularity at any point of such crooked lines , however their curvature be either uniform , equal , or regular . But I know it will be said that such crooked lines of equal , uniform & regular curvature are but one line , and therefore , by the definition of an angle , cannot contain an angle ; which requires two lines to its constitution . To which I answer , that in like manner , two concurring right lines may be taken for one line continued though not in its rectitude , and then the consideration of angularity between them is excluded : however by reason of the inflexion and inclination at the point of incurvation , there is an aptitude in that one produced line , there to fall , and distinguish it self into two , with inclination of one unto the other , and so to offer the constitutive nature of an angle : and so it is at every point of such crooked lines , whose curvature is equal , or uniform and regular ; being one , or more lines , according as by our conceptions they are continued , or distinguished And as a continued rectitude , such as is in right lines , is most inconsistent with the nature of an angle , so what should be judged more accepting of the nature of angularity , then curvature is , being thereunto contrariously opposite , and by all confest most what to be so , saving in the aforesaid cases when curvature is equal , uniform , or regular . But why should equality , uniformity , or regularity of curvatures , be so urged in the concern of angularity , by none of which is angularity either promoted , or hindered ? For there cannot be greater equality , uniformity , or regularity , then is to be found in Rectitude as well as angles , in right lines as well as Circles ; the things constitutive of the nature of an angle , being things quite different from them , Viz. inflexion or inclination and concurrence ; which are indifferently found in all curvatures equal and unequal , uniform , or not uniform , regular , or irregular : and besides are inseparable from them : curvature and a concurrent inflexion , or angularity being but as two notions of the same thing , considered as under several respects : Viz. curvature is the affection of a line considered as one : the same being angularity and inclination , when from any point of the curvature the same line is considered as two : so two concurrent right lines are said to be one crooked line : but when a right-lined angle is said to be contained by them , they are then considered as two from the point of their incurvation , or inclination : and equality , and uniformity , and regularity of curvature implying equality , uniformity and regularity of inflexion , or inclination , it is so far from concluding against angularity , that it inferrs it with an additament , Viz. of equal angularity , uniform angularity , and regular angularity ; as might be at large declared in the special properties of several crooked lined figures . And in several uniform , and regular crooked lined figures , there are some special points , offering even to view and sense a clear specimen of a more then ordinary angularity , without any such loud calling for the strong operations of the mind ; as the vertical points in conjugate figures , in parabola's , and the extream points of either axes , in ellipses , and the like , And in the definition of a plane angle , all the inclination , which is required in the concurring sides , is only , that their inclination be 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉 i. e. so as the sides make not one and the same right line , as it is generally understood : however so far are we from imposing upon any against their judgements , this special sort of angles , that we readily acknowledge , if the words 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉 , in the definition of a plane angle , be forced from the commonly received sense , of the sides not lying in the same right-line , to signify the non-coincidency of the production of the one side with the other , then according to that gloss upon the definition of plane angles , this whole sort of angles is to be rejected ; wherein every one is freely left to his own judgement ; the difference being a question and quarrel about words , more then matter , and not concerning the present controversy . However from the whole it out of Controversy appears , that recto-concave angles of Contact are true angles , contained under two inclined sides , concurring : also that ultradiametral concavo-convexe angles of Contact , whether less equal , or greater then two right right-lined angles are true angles , for the sides are inclined and concurr : of their concurrence can be no doubt : and that they are inclined must of necessity be yielded , seeing they neither lye in rectitude , nor which to some might be a causeless scruple , the one in the production of the other : so as their angularity is clear beyond all doubt : the inclination understood in the definition of an angle being generally any positure of one line with regard to another in the same plane , so as both neither fall in one right line , nor be situated parallel one to another , nor under such a manner of oblique extension , as may render their concurrence impossible : it is not only the oblique positure of one line in reference to another , as contradistinguished from perpendicularness in acute and obsuse inclinations : but such is the comprehensiveness of its sense , in the present acceptation , that every perpendicularness it self is taken for an inclination . So likewise it cannot reasonably be denyed but those special angles of Contact , which are the chief subject of this present controversy , I mean recto-convexe angles of Contact , are truly angles ; except either the inclination of their sides , or their concurrence could be called in question ; nothing else being requisite unto the nature , or comprized in the definition of an angle : and the like is to be judged of all other concavo-convexe and convexo-convexe angles of Contact . But you said that in the recto-convexe angle of Contact the right-line tangent and circumference make no angle , because the tangent is not inclined to the circumference , but coincident with it . What mystery of reason , or force of Argument should be in this deduction ? if you say it is coincidence , you mean by non-inclination ; I readily yield , where two lines , become coincident , their former angle is thereby extinct ; as thereby they come under the consideration but of one line : as when two right-lines , or two isoclitical crooked lines , are , one of each of them , so moved about the angular point , till the two lines become one . But where is any such coincidency between right-line tangents and circumferences ? or what possibility is there of any such coincidency : a crooked line and a right-line may no doubt be commensurate , or proportionable in length , but in position it is impossible : and if we imagine the tangent bowed to such a coincidence , then it is not any longer a tangent , or right-line , but a circumference . And though as you urge , a right-line circumduced about any middle point in the side of a regular polygone , at last becomes coincident with the side , and looses all inclination and angularity with the side ; what doth that concern , or how doth that prove the non-inclination of the tangent to the circumference ; your selves sometimes in every point , save only in the point of Contact acknowledging an inclination ; and as is else where hinted , in the point of Contact alone , and abstractedly , the inclination it self , which is the habitude of the concurring inclined sides , is not to be sought , but only the particular termination of their inclination there . But you will say , it is non-secancy which is meant by this coincidency : and what I pray is that more then the Lateran bells to the concern , or constitution of angles ? Are there not many regular curve lines produced , some infinitely without Section , in which especially the circumferences of circles , you are pleased sometimes every where to think you have cause to imagine an angle . It were meet to know the meaning of such odly connext terms , before reasonings upon them be regarded in questions of weight . That the Contact of the angular sides , is as different from coincidency , as from secancy , is most unquestionably apparent in angles of such sides , as are capable of all three , Viz. Contact , secancy , and coincidence . For example in fig. 16. let there be two Arches of equal Circles DAF and BAC . touching one another in the point A. If the arch DAF be circumduced about the point A as an unmoveable center ; at after an infinite succession of secancies , at last all will terminate in a manifest coincidency , and the arch AF be coincident with the arch AB , and the arch AD be coincident with the arch AC . So as secancy , Contact , and coincidency are distinguishable one from another with as much ease and cleareness , as an odde number from an even . But if it be urged , that you assert not a coincidency between the arch . D AF and the arch BAC , but only that GH being a right line and touching the arch B AC in the point A , that I say the right line GH and the arch BAC are coincident . The vanity of this may be evinced ; in that by the same reason it followes , that the right line GH must be coincident with the arch DAF , and so the arch DAF coincident with the arch B AC ; the contrary of which is above-shewn and confessed : and besides hereupon should two arches B AC and DAF being convexo-convexely posited , and the right line tangent GH be all coincident ; which I leave for others to say rather then my self . When a right line tangent and many crooked lines of different curvatures , all touch together in one and the same point , as in fig. 13 ; you say , though without the angular point of Contact the sides are variously divaricated one from another , yet in the point of Contact , they have not several inclinations , for you say they have no inclination at all . The truth is the angular point of its self is not capable of inclinations , nor for the indivisibility of its nature can by any possibility comprehend them : yet that lines concurring in one only point , and presently after receding each from the other , should not be inclined each to other in or at the point of their concurrency , whether it be by Contact , or Section , though in the case of Contacts the inclination be less , then can be expressed by the inclination of any right-line upon a right-line , is absolutely unconceiveable , there being no lineary coincidence , but only of one point between them . For as else where , in the same plane , neither of point to point , nor of point to line , nor of point to plane can be any inclination : but in the present case of plane angles , inclination must be of lines , and may be of them in the very point of concurrence ; or else from the point of concurrence they would not part several wayes : for it is their diverse inclination at that point , which makes their departure one from another when they depart from thence . And as even in the angular point of right-lined angles the lines have the same inclinations as else where , so in all other angles , save only such angles of Contact , as are less then the least right-lined angles , by drawing right-lined tangents to the arch , or arches at the angular point , is shewn in right-lines , either the very inclination of the sides , in , or rather at the angular point , or else the least right-lined inclination , which is greater , or the greatest right-lined inclination , which is less : for though they may differ much in their distance and divarication one from another , without the point of their concurrence ; in the point of their concurrence , without much absurdity , they may be said to be equally distant , i. e. not at all distant there one from another , for there they are not indeed at all distant any of them from the rest : yet it doth not hence any way follow , that in like manner it may be said of them without absurdity , that in the point of concurrence they have equal inclinations , i. e. no inclinations one to another : for though in the point of concurrence it is truth , they have no distance , yet it no wayes as may appear to those that will consider equally follows , that they should there have no inclination . Besides , that the urging of the coincidency of the sides in recto-convexe angles of Contact is most directly opposite to the nature and properties of the special lines under which such angles are contained . For , t is the special propertie of some lines that they can touch , but they can no way be-coincident ; as Arches of unequal and unlike curvature : and a right-line and a crooked line : some can be coincident , and can no way touch , as right lines : some can both ; as Arches of equal and answering curvature , which set concavo-convexely , and citradiametrally cannot touch , but will fall into a coincidence : but posited convexo-convexely , cannot be coincident , but may construct an angle of Contact . So as the chimaera of the coincidency of the sides in recto-convexe angles of Contact , if persisted in , is worth laughing at , and like his Philosophy who when every one was at his high Lavolta's , denyed the possibility of motion in the world : But to justify the non-inclination of the sides against the eye and reason , this horridly distorted Monster of their coincidency was introduced . Indeed if they be coincident they make no angle : But it will cramp the understanding of an Oedipus to declare how either a right-line , or a crooked-line , touching another crooked-line in one only point and no more , should ever be conceived , notwithstanding to be coincident with the production of the other crooked-line , whether the tangencie of the crooked-lines be concavo-convexe , or convexo-convexe , i. e. the one within the other , or else the one turned away from the other . But you 'll say , you assert coincidency only in the point of Contact . I answer , that 's frivolous , not to say ridiculous and impertinent ; for coincidency in the present question of angles is taken as opposed to inclination , which is an affection and propriety of the concurring sides of the angle , not only of the angular point taken by it self abstractedly . As inclination cannot be in a point , though it may be at a point , so a point cannot be said to be inclined unto a line , especially it self being in the same line : it may be said to hold such and such a distance from the line , when it is without it , but not to be inclined unto it . And if the being of the point of Contact , generally as a point of the one side , in the tangent line , as in the other side , whether right , or crooked , make a coincidency destroying inclination ; then all inclinations and angles whatsoever are destroy'd ; and every where will be a coincidency , for that is common to every angle to have the angular point still common to both sides : and the secant angles might as well be said coincident , as the tangent angles , For what you say , that it is tangency as opposed to secancy , that you mean by coincidency ; I answer the glosse is improper and besides the anvil and tangency undenied , but in this case impertinently by you alleadged , till it be proved that tangency in one only point , and no more , doth quite annul and destroy the inclination of the lines , though on both sides of the Contact clearly receding the one from the other : till which be done happiness to my friend and no longer . I might adde that it is Touching which is only mentioned in the definition of plane angles ; but I shall dispatch all by setting the case before you in this Diagramme in fig. 12. if the right line BA touch the arch LA in the point A and the right-line LB be so drawn as to touch the arch LA in the point L , here now is a plane on every side bounded by two right-lines , Viz. BL and BA and one crooked-line , Viz. the arch LA. That LBA is an angle will not be doubted : and because the three lines perfectly bound in and limit a plane on all sides ; the Arch LA can neither be coincident with the right line LB , nor with the right-line AB , and in the angle LAB , the lines LA and BA ; and in the angle ALB , the lines LA and BL concurring without coincidency , and without lying in the same right-line , or the one , so much as , in the production of the other ; inclination , and so the true nature of an angle , cannot be denyed them ; according to the most severe limitations and hardest glosses , that can with any reason be deduced from the definition of a plane angle . And to make all clear let a Paper , or other plane be cut in the form of the mixed-lined Triangle ALB and the wildness of questioning the angularity of the two recto-convexe angles of contact LAB and BLA will be clear to all persons both rude and learned . I take it therefore for granted ; that , all suspicion of coincidency and non-inclination , in whatsoever pertinent sense , of Contact-angle sides , being evicted and sent of the scene , all recto-convexe angles of Contact are truly angles . To passe now unto another of your Thesis's in which you peremptorily conclude Recto-convexe angles of Contact to be devoyd of all quantitativeness ; when I urge their quantitativeness , I mean not that they can at pleasure be devided into parts in any given and limited proportion , or by a mathematical homogeneity holding any proportion with the Angle of Contact devided ; only that from the angular point between the sides of the least Recto-convexe angle of Contact infinite other lines may be drawn , dividing the angle , though heterogeneally . And certainly its being an angle of Contact cannot in the least prejudice its quantitativeness : for it is most apparent that a convexo-convexe angle of Contact contained under Arches of equal curvature , may be divided into two mixed-lined , i. e. recto-convexe angles of Contact , which hold proportion of equality one with another , and each of them is in subduple proportion to the convexo-convexe angle of Contact , which was divided : and infinite numbers of Contact-angles of several sorts may be adjoyned one unto another , distinct in their situation , without drowning and extinguishing one another and each lying without the other : which is not true of indivisibles when they are adjoyned to , and touch one another . Besides the recto-concave angle of Contact is greater then the greatest right-lined angle , at the angular point of Contact having a manifest inclination of the sides ; for concurring , they neither are one right-line , nor one crooked-line . Moreover ultra-diametral concavo-convexe Angles of Contact may be equal to two right right-lined angles , or greater sometimes : As in fig. 12. if the two Circles FAH and ADK be equal and touch in the point A , and AK be diameter : and AR be another Arch falling beyond the diameter AK and beyond the right line tangent AB : it is manifest that the concavo-convexe ultra-diametral angle of Contact DAH is as to the recesse of the sides equal to two right-lined angles : for the recto-concave angle of Contact BAH is equal to two right right-lined angles , deducting the recto-convexe angle of Contact HAS : and the recto-convexe angle of Contact BAD is equal to the recto-convexe angle of contact H AS ; therefore the ultradiametral concavo-convexe angle of Contact D AH is equal to two right right-lined angles : and therefore the ultra-diametral concavo-convexe angle of Contact D AR is greater then two right right-lined angles . And then , what greater Monster is discoverable in the doctrine of the quantitativeness of the recto-convexe angle of Contact ? it is demonstrated that between the right-line tangent and the Arch which it toucheth , no right-line can passe : i. e. the recto-convexe angle of Contact is less then the least right-lined angle : but why should hence be inferred that the recto-convexe angle of Contact hath no true quantity ? you will say , because a right-lined angle is infinitely divisible into less and less parts , and therefore must at last be less then the recto-convexe angle of Contact , if the recto-convexe angle of Contact be a true angle , having truth of quantity . I answer , after all possible divisions of a right-lined angle into parts of its owne kind , I mean such as are made by right lines , the least part is still a right-lined angle ; then which the recto-convexe angle of Contact is most fairly demonstrated to be ever less : i. e. the inclination of its sides is eve● less : and the convexe arch will still at the angle fall within : so as truly from thence may be inferred , that the recto-convexe angle of Contact can never be either a right-lined angle , or equal to it , or greater than a right-lin'd angle : but that therefore it is no angle , and hath no true quantity at all , because it hath not the quantity of a right-lined angle , is a wild and perverse inference , and else-where disproved . And why should the quantitativeness of the recto-convexe angle of Contact be called in question , because it is demonstrated less then the least right-lined angle ? If between the right-lined tangent and the arch a right-line could be drawn , then you would confesse the quantitativeness of it as undeniable : and why doth not the passing of a thousand crooked-lines from the angular point , between the sides of the recto-convexe angle of Contact , as well prove its quantity and divisibility , as the passing of one right-line between them could : there being equal force of proof from the one , as from the other ? And when a right-line & two equal Circles , all three touch in the same point ; there are two equal recto-convexe angles of Contact adjacent the one continuedly to the other , and situate the one without the other : which in indivisibles is impossible . And when the question is of the quantity of angles , what is it we enquire , but only , what is the inclination of the sides , especially at the angular point ? And in recto-convexe angles of Contact , the answer is ; there is no inclination at all as of a right-line to a right-line , but only as of a crooked-line to a right-line : that it were wildness to say ; because in recto-convexe angles of Contact , there cannot be the inclination of a right-line to a right-line , that therefore the sides meeting and parting one from another , and not lying both in a right-line , do make no inclination one to another . And seeing the convexo-convexe angle of Contact contained under two Arches of equal curvature is dividable into two equal parts by a common right-line tangent to them both ; angle of Contact , and of both the recto-convexe angles of Contact , clearly appears ; though the quantitativenes of every one of them be demonstrable to be less then the quantity of any the least right-lined angle whatsoever : because right-lines cannot contain a less angle then is agreable to the inclinations they possibly can have one to another : whereas in crooked lines generally , these are the constant properties of curvature ; though the angles of coincidence , or curvature , as we for method , brevity and distinction sake named them , may be very unequal one to another , according to the degrees of the inflexion , inclination and curvature ; yet constantly the angle on the concave side , from any point of the curvature manifestly if it be equal , uniform and regular , is still greater then any the greatest acute , right , or obtuse right-lined angle : and the angle between the convexe arch and a right-line tangent , at the same point , is constantly less then any right-lined angle : and yet either may be made still infinitely less , or greater , the recto-convexe angle of Contact still remaining less then the least right-lined angle , and the angle of curvature , or coincidence greater still then the greatest right-lined angle : which is as much as to say , that in curvatures the difference between the angle of curvature and two right right lined angles , cannot be a right-lined angle ; as in truth it cannot , nor is in reason so to be expected , but of necessity it must be a mixed-lined , Sc. a recto-convexe angle : and is the recto-convexe angle of Contact at the same point . And that a recto-convexe angle of Contact , by no multiplicity can equal , or exceed a right-lined angle ; doth not disprove either its angular nature , or its quantitativeness , both which are otherwise cleared , but it is rather a confirmation of the heterogeneal difference , which is between the angles of the one sort and the other . And in my judgement there needed no greater argument of the quantitativeness of recto-convexe angles of Contact , then the absurdity following upon the contrary doctrine ; that the angle of a semi-Circle , and a right right-lined angle are equal , Viz. The whole and a part , the one being a mixed-lined and the other a right-lined angle ; and in the indeavour of coaptation , and being coapted on one side , the other side all the way falls within , or without the other , so as both the sides of the one angle are impossible to be coapted to both the sides of the other , but will both still lye within both the sides of the other . And the angles of semi-Circles must either be confessed unequal in unequal Circles , or the curvature of unequal circumferences , be manifestly against the truth asserted to be equal . And if still they be averred to be equal , its desired their equality should be demonstrated , and the way of admeasuring their equality shown . But you will say , if recto-convexe angles of Contact be quantitative , why can they not exhaust any other angle whatsoever contained under the very same sides ; for possibly you will urge , that we should not question the homogeneity between such angles ? To this I answer , without examining what homogeneity may in other respects be between them ; that a quantitative and mathematical homogeneity can with no reason between them be imagined : because the difference which is between them is a right-lined angle , to which all angles of Contact whatsoever are heterogeneal ; and your self will not assert any mathematical homogeneity , or at least proportionablenes which as to this purpose is all one between any recto-convexe angle of Contact and a right-lined angle . As in fig. 18. let KAB be a recto-convexe angle of Contact , and KAF another recto-convexe angle under the very same sides : and let AD be a right-line tangent upon the arch AF : therefore the recto-convexe angles of Contact D AF and KAB being equall , the right-lined angle KAD is the difference of the recto-convexe angle of Contact KAB and the other recto-convexe angle KAF under the divarication of the very same sides . So as it is impossible to divide this , or any other angle whatsoever , which is not isoclitical , to divide , I say , all of it into any numbers at pleasure given of parts , which shall be homogeneal all of them one unto another : for how many soever be homogeneal , the angle of Contact , or that which is taken out of it , or that unto which it adhaeres , will have and make heterogeneity . And if you say , how can recto-convexe angles of Contact be said to be parts of such concrete and composite angles , if unable by any multiplicity to exhaust the composite angle ? omitting the answer that parts are sometimes essential and of the definition , and yet by no multiplicity can equalize the whole ; as four angles in the definition of a Tetragone , and a foot line in the definition of a foot Cube : I answer chiefly , that where the integral is heterogeneal as here , and made up , and properly and naturally resoluble into several heterogeneal parts , and connot be divided into any numbers at pleasure of parts all homogeneal , there some parts may never be able by any multiplicity to equalize the whole , or some other heterogeneal parts . And elss-where that under the same coaptable sides may be angles different in their ultimate kind in some further respects , though not without proportionableness in this instance , is most apparent among right-lined angles , by comparing a right right-lined angle , and an acute right-lined angle , and an obtuse right-lined angle together ; which all receive their specifick differences from the specifick differences of their inclinations : in right right-lined angles the inclination being no more one way then the other , no more from the angle side , then to the angle side , Sc. perpendicular : in acute angles the inclination being to the angle side : and in obtuse angles the inclination being more especially from the angle side . And yet though we defend the quantitativeness of recto-convexe angles of contact we are equally obliged to assert their improportionableness to right-lined angles : nor will there be any difficulty in answering that suggession you cast , though in anothers name ; that a recto-convexe angle of Contact is in proportion less then a right lined angle , as being both homogeneal ; and that by the multiplicity of the recto-convexe angle of Contact , an angle may be made equal to a right lined angle , or greater , only by changing its kind , Sc. into a right-lined angle : Viz. in the same manner , as an acute right-lined angle , being less then a right , or any obtuse right-lined angle , by its multiplicity may with change of its sort and kind become equal , or greater then a right , or any given obtuse right-lined angle . To which may be answered , omitting what kind of distinction it is which is between acute , right and obtuse right-lined angles , as not pertinent to the present controversy ; it would be well done to shew what multiplex of any recto-convexe angle of Contact , is equal to what right-lined angle , that so a right-lined angle might , upon that proportion , be formed equal to , or less then the recto-convexe angle of Contact ; contrary to what has been clearly demonstrated , and is generally by all consented to in Geometry . Though acute and right right-lined angles are less then any obtuse whatsoever that are right-lined ; however they hold proportion one with another : but recto-convexe angles of Contact cannot be demonstrated to hold any proportion with any right-lined angle , but clearly the contrary . And as by the divarications of the sides of an acute right-lined angle is made a Genesis of a right and infinite obtuse right-lined angle : there cannot so by the divarication of the sides of a recto-convexe angle of Contact be effected any Genesis of right-lined angles , but only of recto-convexe mixt-lined angles , whose sides concurre by way of section ; and between which and the recto-convexe angle of Contact is no proportion , as there is between the divaricated acute right-lined angle and the other right-lined angles created from that divaricacation . The reason of which is clear , for that the recto-convexe angle of Contact being demonstrated of it self to be less then any right-lined angle whatsoever , by the divarication of the sides of it , there are continually greater and greater right-lined angles added to it , so creating an improportionality between the one , and the other . The comparison made between Cyphers and angles of Contact , to draw the one , as well as the other into the notion of nullities , is unhappy enough : for single and several Cyphers are not greater , or less in power one then another ( though they may make other figures to be so ) as the angles of Contact are , and may be made larger , or lesser , and many of them one without or within another , contiguously and continuously conjoyned together , with enlargement , or diminution of their angularity ; which is impossible in indivisibles , and unappliable to , and unintelligible of , mere nullities . That your Lemma is without exception , and without proof might have been admitted : Viz. That two quantities by the ordinate application , or motion of a line , or plane , increasing , or decreasing proportionably , whether by a proportionality in the same , or different powers , when the ordinate application , or motion attains the end , and bounding term of the one quantity , it at the same moment reacheth & hath attained the bounding term of the other , and when it hath passed the one it hath passed the other . But the objection against the quantitativeness of the recto-convexe angle of Contact , which you would hereupon found , hath no reason to expect the like allowance . You say , the right-lined right angle at the point of Contact contained under the right-line tangent , and the diameter of a Circle , equally with the circumference intercepted , increaseth , or decreaseth by the motion of the diameter upon the point of Contact , as a Center ; which is true and acknowledged : and whereas you say , that therefore when the diameter leaves nothing at all of the circumference in its circumvolution about , un-run over , but attains the last bounder and termination of it , in the point of Contact , then as the circumference is quite exhausted and vanished , so is the angle too : this also we acknowledge to be undeniable . But whereas when the diameter is come so near the right-line tangent in its circumvolution upon the angular point of Contact , as to intercept nothing at all of the circumference between them , you then imagine still an angle remaining , which you say , is either the recto-convexe angle of Contact , or not less then it ; you herein forget the force of your own manifestly true lemma , which you took so much pains to prove ; except against Geometrical demonstration you could discover a possibility of dividing a recto-convexe angle of Contact by a right-line : for it is out of doubt and in Geometry , as above demonstrated , that when the diameter in such circumvolution intercepts nothing of the circumference between its self and the right-line tangent , the diameter is then coincident , and the same right-line with the right-line tangent ; and of the former angle therefore , hath lest nothing at all , because of the coincidency of the two right-lines , whose parts can in that positure have no inclination one unto another : and therefore there is not so much as the least angle of Contact , or any other angle whatsoever , left after this circumvolution : so as the whole Argumentation is a long arrow out of a strong Bow , but quite besides the mark . It is a seeming weighty objection that which is urged out of opticks , and the usage in that science , to demonstrate in conical figures , the angles of incidence and reflexion to be equal , only with respect to the right-line tangent , touching the figure in the point of incidence and reflexion , without special respect to the curvature in the conical section . But hereto without wrong , either to truth , nature , or that noble science , may be upon good grounds answered . 1. That opticks is not pure Geometry , and obstructed stereometry , and mathematicks ; wherein quantities , mensurations , and proportions are considered merely as in themselves without relation to matter , and the uses to which in other faculties they are applicable : but in opticks , is an improvement of what in nature may be observed about luminous and visual beams , and luminous mediums and objects , by mathematical demonstration and assistance . Now 2 ly . Nature doth not tye it self in its wayes so strictly to an indivisible , absolute , vertical punctilio , that if it cannot reach , without impediments , that mathematical exquisitenes , it will not act at all . If heavy things on the clive side of an hill cannot descend in a direct line towards the Center , however they will seek it in the nearest oblique line possibly they can , so long as the motion brings them nearer : all animals are not formed in the same mould , or with equal strength of Body , or vigour of spirit . So as in these optical instances , the brave Authors sell not in the least short of their task , when they had demonstrated the most equal right-lined angles which nature could cast it self into , in the alledged cases , Viz. angles of incidence and reflexion equal , if compared with a right-line tangent at their point . For as elsewhere , they are but very few points in most conical sections , where , by a right-line , their angularity can be divided into equal parts : nature therefore when it cannot attain its prime and general design , which is a perfection and absoluteness in its work , it doth not therefore slugge and do nothing , but seeks to approach its first design as near as possible : and that is in making with right-lined beams equal angles respectively to the right-line tangents at the points concerned ; which angles so formed at those points with respect unto the right-line tangents , are as is elsewhere shewn , either the least of the greater right-lined angles , or the greatest of the less right-lined angles : that in such curvatures with great judgement the quality of the angles of incidence and reflexion , in beams passing by right-lines , as affected for their directness and shortness , and as near as possible endeavoured by nature , is in demonstration referred to examination at the right-line tangents of the same points ; an absolute equality by right-lines to be made , being most what impossible , and that demonstrably in such curvatures : so as causeless was the exception which was made against the demonstrations of the noble Perspectivists : nor stood , either they , or nature in need of that improper , lame solution and help , by making recto-convexe angles of Contact to be neither angles , nor quantitative . The truth of the angularity and quantitaveness of recto-convexe angles of Contact thus asserted ; however , the rest of the things in this controversy cannot be determined without a clear understanding of what homogenealness it is that is requisite for proportionals , and which is mentioned in the definition of proportion . To bring our selves unto the right understanding of which , know there are three wayes whereby one thing may be said to be greater then another . 1 st . Improportionably , and by the whole kind ; as in heterogeneals : in which sometime the least of the one is still , beyond all proportion , greater then the greatest of the other : as the least surface is greater then any line ; for a longer line may be drawn in the least surface , then any the longest line , that can possibly be given : and so the least body is improportionably , and heterogeneally , and by the whole kind greater then any surface : for by the dividing , or altering the figuration of the least body , it may be made , by its perimetry , to exceed the quantity of the greatest surface , that possibly can be given : so a point , or a circle of a foot diameter , is said to be less then the whole world ; which is to be understood , as by the whole kind , and without proportionableness . And so I doubt not , but it will be confessed , that the least recto-convexe angle of Contact , is greater then the greatest acute , right or obtuse right-lined angle : and the least right-lined angle , then the greatest recto-convexe angle of Contact . 2 ly . One thing is greater then another infinitely , or , if you please , indefinitely : so an infinitely , or indefinitely inlarged line , is longer then any given line , without limitation , and so consequenely without proportion . Or , 3 ly . One thing is greater then another , rateably and according to the proportion , which they hold at the same standard , whereby they are after the same manner measured , in the same kind in which they are compared . So one lenght , or line is longer then another , according to such a proportion of length when both are measured as lengths at the same standard upon an indefinite line ; and this , whether the lengths , or lines be , one , both , all , neither , or none of them directly , or indirectly posited , in right , or crooked lines ; and whether the one be a depth , and the other a height , or another a breadth , or a fourth a periphery . So one number is greater then another number , according to such a proportion : and , though it is well known to be determined in Philosophy , that numbers are of different kinds , yet for the proportion they hold one to another in their common nature , there cannot be denied unto them the truth of a mathematical and analogical homogenealness . And as things are said to be several wayes one greater then another ; so homogeneity wants not its several acceptations . What homogeneity is , is not at all any where expressely defined in the mathematicks ; but we are left at large , rationally to collect , what is by that Term in those faculties to be understood . The most usual acceptation of the word homogeneity in Philosophy is to compare any divisible being with the parts into which it may be divided : those things being said to be homogeneal , which cannot be separatingly divided into parts of any other name , or nature then the whole is : as the least separable part of water is said to be water ; of wine , wine : and the least separable part of a line , a line : and those things are said heterogeneal , which by possibility may be separatingly divided otherwise ; Viz. into parts of different name and nature from the whole . All which , as appears , hath its dependance upon the similar , or dissimilar natures of the whole and parts . So all solids , surfaces , lines , and plane angles may be said to be homogeneal ; for by dividing and separating them part from part , every part of the solid is a solid , of the surface a surface , of the line a line , and of the plane angle a plane angle : and by taking number in a large sense , every part of a number may be said to be a number . But then if you descend lower in numbers and angles , even and odde numbers , &c. and right-lined and mixed-lined and crooked-lined angles will scarce be able to defend their homogeneity at this touch : for Even numbers may be divided into parts that are odde : and a right-lined plane angle may be severed into parts whereof the one may be a recto-concave angle of a semi-Circle , the other a recto-convexe angle of Contact ; of which last mentioned severed part you say , it is no angle , and therefore it must be heterogeneal : and we assert it heterogeneal , because it is improportionable , and its quantity not mensurable after the same manner , that the quantity of right-lined angles is measured . And with reference to the same acceptation , two distinct beings , being compared together , as to homogeneity and heterogeneity , they are then said to be homogeneal , when both having the same name and nature , the one may be the severed part of the other , or both together the severed parts of an integral of the same both name and nature . So all solids are homogeneal : all surfaces : all lines : all plane angles and all numbers whatsoever . But sometimes also in an abusive acceptation , the agreeing , or disagreeing of things in some general , or special kind and nature , passeth for a certain kind of homogeneity or heterogeneity among them : so bodies and surfaces and lines in respect of their common agreeing in quantity , continuity , longitude , latitude and profundity , are partly homogeneal , partly heterogeneal : so numbers in respect of their general quantitativeness , parity , imparity , symmetry and a symmetry &c. Are partly homogeneal , partly heterogeneal ; and so solid , sphaerical , and plane angles , and all their several kinds are partly homogeneal , and partly heterogeneal . So as from any of the former acceptations it is no way possible to determine what is that mathematical homogeneity which is every where hinted unto us in the definitions of proportion ; for the bolting forth of which we shall be constrained of necessity to betake our selves to another course , in the quest of which , it is not likely but we shall meet with some abstruseness and difficulty . To make therefore an Essay ; proportion being the habitude of the compared magnitudes according to quantity , it is an homogeneity in quantity which is only herein required ; not an homogeneity in substance , quality , site , or other kinds and manners of being : for heterogeneity in any of those other respects , as substance , quality , site , or other kinds of being , doth not hinder , but they may notwithstanding be one proportionable to another , if any quantitative homogeneity be to be found amongst them . So the heterogeneity of figure and figuration , which is between a Circle , pentagone , square , triangle , surface of a pyramide , &c. Hinders not , but they may be compared and hold proportion in respect of their Area's and superficial contents ; wherein they retain a quantitative homogeneity : and those of them which are meerly bounded planes , also have a homogeneity in respect of their perimetries , or the like quantities which they hold in common . So crookednes and rectitude are different kinds of positure , and make an heterogeneity in situation ; yet a right line and a crooked-line , hold still a quantitative homogeneity , in respect of their longitude and extension . So the different positures of the surfaces in a sphaere , and in a cone , and in a plane , hindereth not their analogy in Area and quantity . But further to pursue this diquisition ; though it be homogeneity in quantity , which is herein understood yet it is not the being quantities , or magnitudes in general that doth make up , or can compleat the homogeneity hinted in the definition of proportion : for then lines , and bodies , and numbers , and surfaces , being all of them magnitudes and quantities , there should be a proportionablenes between lines and bodies , bodies and surfaces , surfaces and numbers ; which in such a general-homogeneity it were vanity to look for . In like manner , though plane , sphaerical and solid angles be all angles , yet I think there are very few , that because of that their general homogeneity will expect a proportionablenes amongst them . Besides as little necessity is there of restraining this homogeneity of magnitudes , unto their very last , and in every respect , ultimate kinds : except you will understand it to be in respect of some indefinite , most pure abstracted quantity , in which the compared magnitudes are to be each of them measured . For though some referr all numbers unto quantity , distinguishing them into several kinds , not only from their parities and imparities , with all their variations thereupon , but making every number to be of a different kind , receiving its specification from the last unite ; as some also referr unto quantity all lines , which they distinguish into several kinds , & the like specifick distinctions are made by others of surfaces and bodies : yet between proportionals , for their homogeneity , is not , we confesse , in this sense required , that both magnitudes be of the very same ultimate kind : for hyperbolar , parabolar , elliptical , circular arches , and right-lines are homogeneal in length , extension , and as lines , so holding analogy , though in respect of rectitude and curvature , and their several kinds of curvature they be heterogeneal . So all numbers , even , odde , commensurable , or incommensurable , however , as above is said , heterogeneal , yet as multitudes and numbers in general , and the accounts how oft an unite and its parts is posited , or how far in account is proceeded , whether retrogradely or progressively from an unite ; so , all numbers are homogeneal , holding mutual analogy one to another . So notwithstanding the distinction between acute , right , and obtuse , right-lined angles , all truth and exquisitenes of proportion , as the measure of their quantitative relation , is most apparent amongst them . Which again doth further shew unto us what and how great is the difficulty of limiting the homogeneity expressed in the definition of proportion ; so as neither to set it uselesly too high , nor sink it lower then is necessary for proportionality . For right right-lined angles are proportionate , one to another , but there can be amongst them no proportion of inequality : and no given acute right-lined angle can have so small a proportion to any acute right-lined angle , as it may have and hath to a right right-lined angle , or to any obtuse right-lined angle : and though all even numbers hold analogy and proportion one to another , yet even numbers are not capable of all diversities of proportion ; as in uneven numbers , duple and subduple proportions are impossible : nay numbers in general , I mean unbroken and integral numbers , are not capable of all kinds of analogy ; as particularly not of such proportions as are asymmetral . But not to be nice in my thoughts to my friend , I never in this point and question understood any other thing to be meant by homogeneity in the definition of proportion , then a mensurablenes of the quantities of two , or more magnitudes in the same indefinite quantity for kind , as the measure of their quantity and of the quantity of all their homogeneals , the mensuration therein still being according to that same kind of quantity of which the indefinite quantity is . And so proportion is the rate and habitude , which the rateable magnitudes hold mutually one to the other in respect of the same way of measuring their quantities , or in respect of the same kind of indefinite quantity in which their quantities are measured . And upon this gloss as the true and genuine meaning of this mathematical homogeneity , I ever understood that postulate to be founded in which is required and granted , so to multiply any given quantity , as to exceed any other given quantity whatsoever of the same kind . For if that mensurablenes in the same indefinite quantity , as a measure , and according to that same kind of quantity of which the indefinite measure is , were not the very thing designed by mathematical homogeneity , the matter of the Postulat were not fit to be granted without proof : for it is because they are measured in the same indefinite quantity for kind , and according to the same kind of quantity , i. e. they have the very same way of measuring in the same indefinite quantity ( which is their homogeneity , by necessity of consequence creating a proportionablenes between them ) that the less by multiplying may be made greater then the greater , and the greater by a continual cutting off still more then half may be made less then the less . And though hereby homogeneity and proportionablenes be not made to be the very same thing , however in the mathematicks , where the physical natures of things are not inquired into , the one by a necessary consequence doth immediately flow from and is annexed unto the other ; and because of their necessary connexion , in usual speech and acceptation , the one may be allowed to be taken for the other . And when in the definition of proportion , proportion is said to be the mutual habitude of magnitudes of the same kind according to quantity , or if you please multiplicity ; the meaning is no other , but that proportion is the mutual habitude of magnitudes , which have their mensuration after the same manner , according to quantity , or multiplicity ; taking the word multiplicity in a large sense : i. e. according to the quantity and multiplicity , which they have each to other in the same indefinite quantity and measure , upon which they are in the same manner and according to the same kind of quantity measured . However in natural Philosophy for very weighty reasons homogeneity and proportionablenes are to be acknowledged of very distant and different natures . So I presume in Mathematicks it would be taken for a solaecisme to say a body and a line were homogeneals and of the same kind , because all separable parts of each agree in their being all of them continuous quantities ; though in the Physiological school that they do concenter and meet in the same general nature is not deniable ; and so they may carry a seeming shadow of homogeneity , so far as homogeneity may be abusively wrested to denote any such common agreement in a general notion and nature . So it would be a solaecisme in Mathematicks to say , that a solid angle , a sphaerical angle and a plane angle were all homogeneal , because they are all angles and every separable part of each is an angle : but to pro●e Mathematical homogeneity , the mensurablenes of the quantity of the compared magnitudes in the same indefinite quantity , or measure for kind , and according to the same kind of quantity with the indefinite measure is to be made out : for that all are quantities , or all angles , makes them not in the mathematical school homogeneal ; except by reason of this mensurability of the quantity of both in the same indefinite quantity , or measure , according to the same kind of quantity , the less by multiplying can be made greater then the greater , and the greater by dividing less then the less . And indeed this is the true homogeneity , not denoting a general conveniency in their natures in respect of some abstracted notion , but rather a special identity by reason of their mensurablenes in the same substrate kind of quantity and measure , only with difference , or proportionablenes of magnitude between both the wholes , and all the least , or greatest , proper , i. e. homogeneal parts of each : as if one be a line , so is the other , and the greatest and least proper , i. e. homogeneal or homometral parts of each are lines and proportionable to either . For , if besides the mensurablenes of the quantity of the compared magnitudes in the same indefinite quantity , or measure , be not also added that condition , that in that indefinite quantity , or measure they are also mensurable according to the same quantity for kind , of which the indefinite measure is , and so consequently proportionable one to another ; by nothing will it yet be determinable , whether all angles be not homogeneal : for in every angle , though of several kinds , every part of each angle is an angle : nor will it be determinable , whether all continuous quantities be not homogeneal ; for every part even of heterogeneal continuous quantities is a continuous quantity : nor will it be determinable whether all numbers be not homogeneal ; for that all numbers are of the same kind will be found a doctrine of very hard digestion any where save in the mathematick school : yet according to this explication of mathematical homogeneity , notwithstanding the diversity of their kinds in other philosophical considerations , they have in them a clear mathematical homogeneity : and even an unite , which in other parts of Philosophy is not passable for a number , will fall also within the verge of the same homogeneity ; as will also all the parts of an unite , whether commensurable , or incommensurable . And this explication of mathematical homogeneity will be allowed its due right and justification more easily , by those who note how the main matter and design of mathematical definitions is but exegetical to clear up what is meant by the terms in those sciences used : for what other occasion could there be in the Mathematicks to intermeddle with homogeneity , but to explain the noble points of proportion and proportionality . And yet though in mathematicks there be such a grand affinity between the proportionablenes and homogeneity of magnitudes and in common use and spee●h the one may be put for the other , yet as above the notions are easily distinguishable by the understanding : Viz. two , or more magnitudes are said homogeneal chiefly in respect of the same way of measuring them , or in respect of the same kind of indefinite quantity in which they are both mensurable : but they are said proportionable in respect of the mutual habitude and quantitative relation which is between themselves upon such their mensuration , in the same way , or according to the same kind of quantity . So all finite lines are homogeneal , as mensurable in the same indefinite line ; but that one finite line is double to another is the habitude of the one to the other declared upon that mensuration . That upon the whole matter mathematical homogeneity doth not insist only upon identity in kind at large , or restrain unto identity in kind at all points , and in every respect and consideration ; but it is identity in quantity and therein particularly in the manner of the mensuration of their quantities , in which the homogeneity of magnitudes is chiefly lodged : and that is that which I ever understood in those words ( according to quantity , or if you please , rather quotuplicity ) which are in the definition of propo●tion , viz. quantity and quotuplicity in the same way of measuring . And if you urge here , according to this account I must conclude all incommensurables to be heterogeneal ; I answer , not in the least : for though they may have no common measure , which can by possibility exactly measure both or all , yet there may be a common indefinite measure , in which each may exactly measure forth its own quantity . As for example in fig. 24. Let A and B be incommensurable lines , and DC . an indefinite line , beginning at D , and on the part of C infinitely produced : from the point D in the line DC take the line DE equal to the line A : and also in the line DC take the line DF equal to the line B. here in the line DC as a common indefinite measure of their homogeneity , the two lines A and B , though incommensurable , have measured forth themselves by the lines DE and DF. So in fig. 1. upon A the angular point of the right-lined angle BAC , as Center , draw the Arch dfe cutting the line AB in the point d , and the line AC in the point f , and the right-line Ae in the point e , so as the Arch df be incommensurable to the Arch fe . Here the two right-lined angles d Af and f Ae are incommensurable , yet have a common way of measuring their quantity and proportion , Viz. by Arches of Circles drawn upon the angular point , as center , intercepted respectively between the sides : as by the Arch dfe , the one being in that Arch measured by the Arch , df , the other by the Arch fe . So as by mathematical homogeneity is understood an homometricalnes , or autometricalnes with the necessary consequent of a rateablenes therein , without any necessity of symmetricalnes between themselves at all . For still , if in homogeneity besides homometricalnes in the same indefinite quantity be not also included , that the mensuration of both be according to the same kind of quantity , of which the indefinite quantity , in which they are measured , is ; a point and a line may measure themselves in an indefinite line , and a line and a surface may measure themselves in an indefinite surface , and a surface and a solid may measure themselves in an indefinite solid . But true mathematical homogeneity is when two , or more quantities being mensurable in the same indefinite quantity , or measure , and according to the kind of the indefinite quantity are by consequence rateably , i. e. proportionably and homometrically equal , or the one bigger then the other , not the one infinitely bigger than the other , as an infinite line is longer then a finite line , for between such it is acknowledged there is no proportion nor mathematical homogeneity ; nor the one bigger then the other by the whole kind , as every solid is bigger then any surface , and every right-lined angle then any recto-convexe angle of Contact : and proportion is the rate , or quantity of their mutual habitude in that their homogeneity , or homometricalnes : i. e. proportion is the rate , quantity , or account of their proportionality . And applying our minds rightly to conceive of homogeneity as mathematical ; of necessity such , and no other can be the notion of it , thereby making two quantities to be rateably , i. e. proportionably equal , or the one bigger then the other , and according to their capacity and possibility in any rate and proportion so to be constituted and set out . For the genuine well known notion of homogeneity in general , what is it but that all and each of the proper , i. e. homogeneal parts , and the whole , fall under the same Denomination and nature , as if one be a line , all the rest to be lines , if one be water , or stone , or oyle , &c. all the rest of the parts and the whole to be so also ? And in the mathematicks what is said properly and homogeneally to be a part of any magnitude , but only such lesser magnitudes separable from it as are able to measure out , i. e. by their multiple to exhaust the first magnitude ? For a surface is not said to be an homogeneally proper part of a solid : nor a line of a surface . And by such measuring forth of the integral magnitude by its homogeneally proper , i. e. exhausting parts , is not understood the symmetry of the parts , and whole , for the whole and its true homogeneal parts , may be incommensurable ; but that which is understood is the true mathematical homogeneity of the whole and the parts in respect of their common way of measuring , and the proportionality , which is thereupon lodged between them So as by laying these undeniable remarks together , mathematical homogeneity in respect of the same integral magnitude , is that every part thereof being proper , i. e. mensurable in the same indefinite measure according to the special kind of its quantity , and therefore able to exhaust the whole , be all of them only in respect of their quantitativenes , not their figuration , or other respects , of the same nature and denomination , and any proportion whatsoever ( according to the capacity of such kind of quantities ) possible to be constituted amongst them . And by consequence several magnitudes are then said to be mathematically homogeneal , when being the one able to exhaust the other , & so in proportion one unto another , both and all the proper parts of each , all of them , as being of the same nature fal● under the same quantitative denomination . And here it is worth our noting , how some magnitudes are so homogeneal , that they cannot be separatingly divided into parts , or magnitudes which are heterogeneal ; but all the parts into which they are separatingly divided will still be homogeneal , both one with another and with the whole : So a line can no way be separatingly divided into parts which are magnitudes , but each is a line homogeneal to the whole and to all parts whatsoever of whatsoever other line : neither can a body and surface be separatingly divided , but into bodies and surfaces ; each of whose parts are still able to exhaust the whole and are thereunto proportionable . But such an absolute homogeneity is not in all other magnitudes , especially in heterogeneally concrete magnitudes , but that the whole may be divideable into parts separable one from another , which yet are heterogeneal : as in the present case of angles a right right-lined angle is divideable into a recto-convexe angle of Contact , and the recto-concave angle of the semi Circle ; which are separable one from another , and therefore truly parts ; yet neither of them is homogeneal to the whole , nor one of them unto the other : for neither can the whole right right-lined angle , nor the recto-concave angle of the semi Circle ever be exhausted by any number whatsoever of such heterogeneal parts , as is the recto-convexe angle of Contact : nor ever any equality , or other proportion can possibly be shewn between the right right-lined angle , and the recto-concave angle of the semi Circle , because there is no way possible in which their quantities can be proportionably mensurable . For not without very good reason unto all magnitudes are to be allowed their special properties ; as to all positures and figuration , theirs . To angles these things are peculiar , being otherwise in other magnitudes : Viz. in angles which are truly and on all hands confessedly homogeneal , you cannot to any given angle , set forth another of the same kind in any given proportion at pleasure : for every right-lined angle by a necessity of nature , must be less then two right right-lined angles : and in a plane all the angularity at any point cannot exceed what the circumjacent space , or plane is capable of ; which is only four right right-lined angles . That as number cannot be infinitely divided without fraction ; so angularity cannot at pleasure at the same point , in the same plane , be inlarged : whereas some other quantities have both infinite divisibility and infinite multiplicability . So another property of the magnitude of angles is , that it may not only in notion and speculation , but in truth and severingly , be divided into parts either able , or unable to exhaust the whole : as when a right right-lined angle is divided into the recto-concave angle of a semi Circle , and a recto-convexe angle of Contact : you may sever them the one from the other : and angularity is equally , if not much more apparent in the recto-convexe angle of Contact , then in the recto-concave angle of the semi Circle ; yet the one of them is demonstrated and confessed unable ever to exhaust the right right-lined angle , the other not . A further property of the magnitude of angles is , that sometimes the same part , which hath already been severed from it , cannot exactly and immediately again by its equal be severed from it on the same side , though the remaining angle be by the whole kind greater . So after a recto-convexe angle of Contact is taken out of a right right-lined angle , there cannot again immediately on the same side , be severed from the remaining angle another angle equal to the recto-convexe angle of Contact , which was before severed from it . If it can , let it be performed . Also the divisibility which is in the magnitude of all Angles , though boundles and infinite , in some however , leaves the dividing of the Angle into two equal parts , impossible : as notwithstanding the perpetual divisibility of lines , the side and diameter of a square are left incommensurable . So some other angles may be divided into two equal parts , but it is impossible to divide them into three equal parts : as convexo-convexe angles of Contact , with infinite other convexo-convexe angles and concavo-concave angles being contained under equal , uniform and answerable Arches . To consigne this point , the principal thing we have laboured herein to dilucidate , & as we doubt not have effected is , that mathematical homogenealness is not an homogeneity of all the parts whatsoever , that are in the magnitudes , which are homogeneal in respect of some special way of measuring their quantities ; or an undivideableness of such homogeneal magnitudes into parts otherwise heterogeneal according to which acceptation the word is chiefly taken in other parts of Philosophy : for there is no right-lined angle whatsoever , nor any other angle whatsoever , but as is up and down herein shewn may be separatingly divided into heterogeneal parts : but mathematical homogeneity is homogeneity in the way of measuring the quantity of the compared magnitudes , Sc. in the same indefinite measure and quantity , and according to the kind of the indefinite measure , and which thereupon follows , a proportionality between them , in respect of their common way of measuring : and of this mathematical homogeneity , fair foot-steppings are to be found every where in the deducing of those demonstrations which concern proportions and proportionals . That , such magnitudes as have no common way of measuring their quantity , as weights and measures , are heterogeneal : or if they have a common way of measuring in which they may measure themselves , but therein do not measure themselves according to the same kind of quantity with the indefinite measure , and so want proportionality , yet notwithstanding they are heterogeneal : as all recto-convexe angles of Contact , all recto-concave angles of semi Circles , all recto-convexe angles of semi Circles , all acute , or right right-lined angles , these may all measure themselves , and in what order their sides fall within , or without in any obtuse right-lined angle whatsoever : yet because this their homometry is only of the situation , or order , in which the sides part from the angular point , but not of their quantity in an indefinite measure and according to the denomination of the same quantitative measure , so as to lodge a proportionality between the magnitudes so compared together in their common way of measuring ; they are not , nor can thereby be vindicated from their otherwise innate mathematical heterogeneity : which concerning some of them is confessed on all hands and is without the verge of the controversy . And as follows , angles are of a concrete nature , having in them something quantitative and something not quantitative : whereas that which is to be the indefinite measure of homogeneal quantities is to be considered abstractly as quantity without heterogeneal concretion : so it is the circumference of a Circle that measures all right-lined angles . And when all plane angles are said to be homogeneal , it is not in respect of a common indefinite quantity by which they are all measured , which the recto-convexe angles of Contact doe sufficiently evince , but as is manifest it is only because of the position and situation of the sides in the same plane ; which homogeneity is of no concern unto quantity , nor by any necessity can thereupon infer the consequent of proportionableness . But to proceed ; as is said , besides the former mathematical and quantitative homogeneity and heterogeneity there is also an extramathematical and extra-quantitative homogenealnes and heterogenealnes in angles every where observable in their shapes , figures , positure of their sides , such like schematismes and other respects . In general as is above hinted , every part of a plane angle is a plane angle , even the recto-convexe angle of Contact , however you deny it to be an angle and quantitative : but then this is not a mathematical homogeneity , but only in respect of a certain figuration , in respect of the positure and situation of the surface in which those angles are ; shewing how all plane angles from the greatest to the least , agree in that particular of their general figuration , Viz. of having their containing sides to lye still in the same plane ; whereby they distinguish themselves from all other superficial angles , which are heterepipedal , whose containing lines , or sides lye in several planes : such as are all sorts of sphaerical , cylindrical and conical surface-angles . But if ever a mathematical and quantitative homogeneity be proved among all plane angles , you that know that it is not my use to start from my word , shall hereby rest assured , upon the first summons I will give up this cause . And we are not to think strange , that a figuration is asserted to be in angles ; for if we seriously consider , wee shall find there is shape and figure in angles , as well as quantity ; as lines , and surfaces , and bodies have their figurations , the positure of their parts , their shapes and forms , as well as their quantities and magnitudes : in each , their figuration being manifest ; Viz. in lines , in respect of their lineary positure : in surfaces , in respect of their superficial positure : in bodies in respect of their solid positure : and in the casting of each of their schematismes quantity is involved , as length , breadth , depth , Viz. their quantities , and the quantities which are compounded of several , or all of them together . And here by the figuration which we assert in angles , we cannot be thought to mean that any right-lined figure can be compleated , perfectly to bound up a plane on all sides , by one angle ; it being beyond the power of two : and three , being the least number of angles , requisite so to constitute and perfectly limite out a right-lined plane figure . And though some plane figures are perfected , and perfectly bounded , without any such angles as are contained by sides concurring by way either of section , or Contact , as namly all Circles and Ellipses ; yet the angularity of curve coincidence is every where found , or at pleasure assignable in the bounders of such figures . But our meaning is , a plane angle , though most what it do not by the continuation and production of its sides , perfectly bound in and limit out a certain plane and space on evry side , however being the mutual habitude of concurring lines , it gives an imperfect figuration to the plane and space on its part . And as a bounded plane cannot be without some kind of plane figure , so a limited angle ever implies in it an imperfect figuration of some sort , or other . For figuration is the consectary of material finiteness and limitation in the position of lengths , breadths , depths , surfaces and solidities ; that every angle having its limits and bounds cannot be thereof destitute . And if the name of figures be so frequently given to hyperbola's , parabola's , and the like , which neither do , nor ever can by any possible production perfectly bound in their planes ; what reason is there then why angles should be denied an imperfect interest in the name . Besides as a plane in its own general nature at large doth not denote any special plane figure ; but the rise of figures , I mean plane figures , is from the bounding of the plane : so it is in angles , as they by the mutual habitude of their concurring sides give imperfect limits and bounds unto the space and plane , so they therein make an imperfect figuration . That in angles something of form and figure is to be noted as well as magnitude . And one line cannot concurre with and be inclined upon another , but an imperfect figuration will arise from that their mutual inclination . And the same two angles may have the inclination , i. e. the recesse of their respective sides one from another equal , though there be no analogy between the figurations of the angles , or the shapes in the which the sides are inclined in the one and in the other . For by reason that in angles form and figure are to be observed as well as quantity ; crooked-lined and right-lined angles may be equal in some particular quantity , yet other-wise not of the same kind : they having equality in some magnitude , but being distinct in the manner of their forming , figuration and constitution : as equality may be between a square and a triangle , though figures altogether different in kind . And in respect of such their figurations , plane angles receive distinction , either from the diverse manners in which their containing sides do concurre , or else from the diverse natures , and figurations of the lines under which they are contained , or , which is tantamount from the diversity of the inclinations and inflexions , or rather inclinablenesses and imflexiblenesses by which they are inclined each to other , or from several of these grounds of distinction taken together . Plane angles from the different manner of their sides concurring , may aptly be thus distinguished , Viz. into angles , whose sides concurre by way of section ; or else that have their sides concurring only by way of touch in some single singular point without mutual section ; or else their concurrence is in curvature , where , after the meeting of their sides in the angular point , the sides do not in their productions depart one from another , neither by way of touch , nor section ; but become , the production of the one side coincident with the other side ; so as this kind of angles may aptly be called angles of coincidency , or angles of curvature : and in these lies the genuine Ratio and true account of the curvature . From the diverse figuration of the lines , under which a plane angle is contained , very many differences of angles may arise , according to the various distinctions , of which lines themselves are capable , I mean such lines , as fall not without the capacity and comprehensivenes of the same plane : as that some are helicoidal , some parabolar , some elliptitical , &c. But as of lines , so hence of angles , the chief and primary distinctions are especially these , Viz. that plane angles are either right-lined angles , contained under two inclined right-lines ; or not right-lined angles . Not right-lined angles , are either mixed lined angles ; contained under one right-line , and one crooked-line : or crooked-lined angles contained under two crooked-lined sides . And from the several kinds of special , or ordinary curvatures , as Circular , elliptical , hyperbolar , &c. The mixt-lined , and crooked-lined angles , are capable of many farther and more particular distinctions ; but especially from the site of the convexeness , or concaveness of the lines to , or from the angle side : though all such secondary distinctions rising from these two last mentioned heads , are as properly and pertinently referable to the other ground of distinguishing plane angles , taken from the differences which may be in the inclinations of the one containing side to the other . For a vast difference is in the inclination of a crooked-line , by obverting the concave , or convexe side to any other line . So the constituting a circular , or elliptical arch &c. For one side , makes a vast difference in the inclinations , because of the difference in their curvatures . Also another principal distinction of angles from their sides , may be into angles , whose sides are coaptable , and by possibility may be coincident one with another : or else such as have between them no possibility of coaptation and coincidence . Of the former sort are all right-lined angles , and all concavo-convexe angles contained by Arches of equal homogeneal , uniform , regular , or answering curvatures : of the later sort are all other ; whether mixt lined angles , or crooked-lined angles ; whether they be mixed crooked-lined angles , or unmixt crooked-lined angles . And consequently thereupon , besides the numerous distinctions of angles in respect of their different inclinations , such as above mentioned ; one is more eminently material above the rest , that the inclination of the sides , is sometimes with an equability all along their production ; though imagined to be infinitely extended , in such lines as by possibility may with reason be imagined so to be : and sometimes there is nothing of equability to be found in the inclination of the several parts of each side to the other ; though it may be one of the sides be a right-line , or an Arch of most equal , uniform , regular and homogeneal curvature . And this equability and inequability of the inclination of the sides , strangely alters the properties of angles . As in right-lined angles , for the equability of the inclination of the sides , no parts of the one side are more inclined then the rest unto the other side : and so in concavo-convexe angles of equal curvatures , no parts of the one Arch are more inclined then the rest unto the other ; but the one Arch is all along inclined unto the other , as at the angular point ; and the inclination , which the one bears unto the other at the angular point , is obviously expressable as to the quantity of the recesses , which they make one from another , by the inclination of a right-line to a right-line , except when the inclination of the Arches is equal to , or greater then two right right-lined angles . And in such crooked-lined angles , whose sides have equability of inclination , the points , which from the angular point are at equal distances along the Arches , are also absolutely at equal distance from the angular point , along the chords : and right-lined tangents at any two such homologal points , where ever taken , alwayes meet and contain a right-lined angle , equal as to the quantities of the recesses of the sides , to the crooked-lined angle contained by the two Arches ; as is obvious to demonstrate , especially in circular Arches . And the right-lined angle contained under the two right-lined tangents touching at the two homologal and answering points , which is equal to the isoclitical crooked-lined angle , if the two right-lined tangents occurre on that side of the right-line connecting the homologal points on which the isoclitical angle falls , then it is the angle contained by the two right-lined tangents into whose space part of the space comprized between the two Arches at first falls , which is equal to the crooked-lined isoclitical angle : but if they occurre on the other side of the right-line connecting the two homologal points , i. e. aversely from the crooked-line isoclitical angle , then it is the complement of such an angle , which is equal to the crooked-line isoclitical angle : but if the two right-lined tangents occurre in one of the homologal points , the angles either way contained under the two right line tangents are equal , viz. right right-lined angles ; either of them making forth what is herein asserted . As in fig : 19. under the two circular isoclitical arches bda and acn let there be constituted the isoclitical angle bac ; and let the right-line ag touch the Arch acn in the point a : and let the right-line af touch the Arch adb in the point a : so making the right-lined angle fag equal to the isoclitical concavo-convexe angle bac . Then take in the Arch adb any point at pleasure , Viz. the point d : and draw the chord ad . Then in the Arch acn take the Arch ac subtended by the chord ac equal to the chord ad . Therefore because of the isocliticalness of the circular Arches the two points d and c are two homologal , i. e. answering points the one in the one Arch , the other in the other , Viz. the point d in the Arch adb and the point c in the Arch acn . Then draw the right-line dc connecting the two homologal points d and c. Also draw the right-line de touching the arch adb in the point d ; and the right-line ce touching the Arch acn in the point c. And let de and ce the two right-line tangents be produced till they meet in the point e ; which in this figure is on that side of the right-line dc on which the concavo-convexe angle cab lyeth . I say therefore that the right-lined angle dec contained under the two right-lined tangents de and ce touching the Arches respectively at the homologal points d and c is equal to the right-lined angle fag , contained under the two right-line tangents fa and ga touching the Arches respectively at a the angular point of the isoclitical concavo-convexe angle . For the right-lined tangent fa cutting de the other right-lined tangent of the same Arch adb in the point h ; and the right-lined tangent de of the Arch adb cutting the chord ac in the point k ; upon this construction the right-line da is equal to the right-line ac ; and the right-line tangent dh is equal to the right-line tangent ha : therefore the right-lined angle adh is equal to the right-lined angle dah and so to the right-lined angles ace and cag severally . And therefore the right-lined angle ahe being equal to the two right-lined angles hda and dah taken together , and the right-lined angle hda being equal to the right-lined angle cag ; the right-lined angle ahe is equal to the two right-lined angles cag and dah taken together . Therefore that which maketh each equal to two right right-lined angles ; the two right-lined angles hka and hak taken together are equal to the two right-lined angles hak and dal taken together . Therefore the right-lined angle hka is equal to the right-lined angle dal . Therefore the right-lined angle cke is equal to the right-lined angle dal . And therefore that which makes either equal to two right right-lined angles , the two right-lined angles kce and kec together taken are equal to the right-lined angle dag , which is equal to the two right-lined angles dac and cag taken together : and the right-lined angle cag is equal to the right-lined angle kce : therefore the right-lined angle kec is equal to the right-lined angle dac : therefore because the right-lined angles dah and cag are equal ; also the right-lined angle kec S c. dec is equal to the right-lined angle hag S c. fag , which was to be demonstrated . But if the two right-lined tangents de and ce as in fig. 20. do not occurre towards the concavo-convexe angle bac , but on the other side of the right-line dc in the point e ; then is the right lined angle dec contained under the two right line tangents de and ce touching at the homologal points d and c , not equal to the concavo-convexe isoclitical angle bac , or the right lined angle , equal unto it , fag , but to its complement unto two right right-lined angles , Viz. unto the right lined angle fal ; the right line la being the production of the right line ga . For as before by construction , the right line chords da and ca to the homologal points d and c are equal : and the right line fa cutting the right line de produced in the point h , the right lines dh and ah being two right lines tangents of the same Circle adb , occurring , are equal . And let the right line ac produced , occurre with the right line de produced , in the point k. As appears ; the right lined angles adh , dah and cag , as before , are equal ; and the right lined angle ahe is equal to two right right lined angles , all but the two right lined angles hda and had that is , all but the two right lined angles cag and had . Therefore the right lined angle ahe being equal to the two right lined angles hka and kah ; the two right lined angles hka and kah are equal to two right right lined angles all but the two right lined angles cag and had . Therefore two right right-lined angles are equal to the four right lined angles cag and had and hka and kah . Therefore out of equals taking equals , the right lined angle hka , which is the right lined angle cke is equal to the right lined angle dal . Therefore what on either side remains to make up two right right lined angles on either part ; the two right lined angles kce and kec are together equal to the right lined angle dag , which is equal to the two right lined angles dac and cag taken together . And producing the right line ec till it cut the right line ag in the point g ; the right lined angles cag and acg and kce are equal . Therefore the right lined angle kec is equal to the right lined angle dac . And because the right-lined angle dah and cag are equal , therefore adding the common angle fac , the two right lined angles dac and hag are equal . And therefore the right lined angle kec is equal to the right lined angle hag . And therefore their complements unto two right right lined angles , Viz. the two right lined angles dec and hal are equal ; which was to be demonstrated . So in fig. 22. if the right line tangent de passe directly unto the other homologal point c , as it doth when the isoclitical concavo-convexe angle is equal to a right right lined angle , and the homologal points d and c are taken at quadrantal or other distances from the angular point ; then most manifestly the right-lined angles dcg and fag are equal , being under the two and two respective right lined tangents ; and between the angles and their complements unto two right right lined angles is no difference , as appears by what is in the former demonstrations . So in fig. 23. if the homologal points d and c be so taken , that the chords da and ca be the diameters : then producing the right line tangent ce till it occurre with the other right line tangent de in the point e , and with the other right-line tangent fa in the point f ; the right lined angles cfa and fag are equal . And in the trapezium def a the two right lined angles eda and daf are each of them a right right-lined angle , therefore the right-lined angle dec is the complement of the right lined angle efa unto two right right-lined angles , i. e. it is the complement of the angle fag unto two right right lined angles ; which was to be demonstrated . And like demonstrations may be formed upon every other case . But where the isoclitical arches are not circular the demonstrations must vary according to the propriety of every several curvature , notwithstanding its equability and isocliticalness . But to return , in angles contained by sides whose inclination each to other is without any such equability , ( except only in unmixt crooked-lined anisoclitical angles ) the account of the homologal points along the chords and along the arches is still different : but in none of them do the right line tangents from the two and two homologal points , still in their meeting make the two same angles which are made by the two right lined tangents at the angular point ; nor can any right line angle expresse the inclination , which the sides have each to other at the angular point . Hence is manifest how the same angle may from several of the grounds of distinction here proposed be referable to several heads , or kinds . So right lined angles as isoclitical , have alwayes equability of inclination ; and the concurrence of their sides is alwayes by way of section and cannot be by Contact , or coincidency . So mixed lined angles being anisoclitical have always inequability in the inclination of their sides ; and their concurrence may be either by Contact , or Section , but never by coincidence . And in crooked lined angles , their sides may have either equability , or inequability of inclination : and accordingly the concurrence of the sides may be by section , or Contact ; and with , or without possibility of coincidence Sc. Isoclitical crooked-lines , but they must be posited convexo-convexely , or anisoclitical crooked-lines posited whether convexo-convexely , or concavo-convexely , or a right-line and a crooked line , any two of these may touch without cutting , and so the angular sides have inclination tangent and not secant , So isoclitical concavo-convexe angles may have sides circumducted to coincidence : but the same sides posited concavo-concavely , or convexo-convexely become anisoclitical in the circumduction , one in respect of the other ; yet either is isoclitical sometimes and in some cases with the production of the other . From these things though distinguishing angles into their several kinds , only with respect to the diversity of their figuration , may however more abundantly appear how unmanageable a task they take upon themselves , who to exclude recto-convexe angles of Contact from being angles , and from quantitaveness , would force all plane angles to be of the same kind , allowing no specifick difference possible among them . Not here to pursue what other diversities in kind may be observed among angles ; how can the inclination of a crooked-line upon a right-line differ less then in kind from the inclination of a right-line upon a right-line ? For as a right-line and a crooked-line agree as lenghts and in lineariness and are therein mathematically homogeneal , but as right and crooked differ in kind and have therein heterogeneal figuration ; the crookedness of the crooked-line having no analogy to the rectitude of the right-line , nor the rectitude of the right line any proportionableness unto the curvature of the crooked-line ; so the inclination of a crooked line upon a right line , and of a right line upon a right line they agree in the common nature of inclination , and the one may be greater and the other less as the respective sides fall within , or without : but this relation of greater , or less is without any proportionableness , and only by the whole kind , depending upon the passing of the respective sides , the one within , or without the other . For these two inclinations differ so far in kind that neither the curvature of the mixt lined inclination hath any thing in it conform , or proportionable to the rectitude of the right-lined inclination , nor the rectitude of the right-lined inclination to the curvature of the mixt lined inclination . In a word , so different is the inclinableness of a crooked line upon a right line , from the inclinableness of a right line upon a right line , that it is impossible for the one ever to be either equal , or any way determinately proportionable unto the other : because the coaptation of a right line as a right line , to a crooked-line , as a crooked Iine is against the properties of their figurations , kinds and natures . And for what reason should there be lesser difference between a crooked-lined inclination and a right lined inclination , then there is between a crooked-line and a right line ? Yet all this their distinctness concerns only an heterogeneity in their figuration and not at all , or not primarily their quantities . The argument , if they be angles , or plane angles , they are homogeneal and of the same kind , is of no more force then this consequence ; if they be quantities , or continuous magnitudes , they are homogeneal and of the same kind . And they that deny all heterogeneity in angles , because they are all angles ; will find it an hard task upon the same ground to maintain an analogous homogeneity , or any other considerable homogeneity , between right lined angles and sphaerical angles , or any other angles , made by planes cutting the heterepipedal surfaces of solids , and especially solid angles , of what sort soever . And to yield that all plane angles are homogeneal ; for it is true : and the most absolute , proper and genuine homogeneity is among plane angles : i. e. no part of a plane angle can be any other then a plane angle , how great , or little soever , and whether proportionable , or improportionable one to another , i. e. whether mathematically homogeneal , or heterogeneal : yet if we seriously consider what is this homogeneity which is among plane angles , that all their parts are plane angles , it is not as is said any quantitative , or mathematical homogeneity , the contrary of which is plentifully demonstrated in Geometry to be possible ; nor any such homogeneity in respect of the manner of their positure and figuration , as to exclude all farther distinguishableness in respect of figuration ; but only denotes that in every plane angle , and in every part of every plane angle , the sides lye still in the same plane : which homogeneity , as is plain , excludes neither heterogeneity , in respect of figuration , nor in respect of proportion and identity in the way of measuring their quantities . To the objection that in fig. 12. the recto-convexe angle of Contact BAF can be added to the right right-lined angle BAG , so making the outer angle of a semi Circle F AG ; or taken out of it , Sc. the recto-convexe angle of Contact BAD out of the same right right-lined angle BAG , so making the inner angle of a semi Circle GAD : and that therefore the recto-convexe angles of Contact F AB and B AD and the right right-lined angle BAG , and the two angles of the semi Circle GAD , and FAG , are all of them homogeneal and of the same kind ; I answer . First what need is there of such endeavours , for you to prove their homogeneity , it being Geometrically demonstrated and confessed that there is no analogy , or proportion between them ; I mean between the recto-convexe angles of Contact and either the right right lined angle , or either of the angles of the semi Circles ? And according to your opinion that which is added or taken out is said to be nothing . But especially its thought strange , why there should be such doubting , that heterogeneals can be added and laid up together as into one repository ; it being with as easy connexion performable , as is usual in the addition of incommensurables and specious quantities of which it is not known , whether they be homogeneal , or heterogeneal . And out of an heterogeneal sum , as a store-house , why cannot some of the heterogeneals be subducted , the rest remaining ? and what is more usual then the adding of heterogeneal figures one unto another ? and subducting out of a given figure some other figure , which is quite heterogeneal to the first given figure ? So to adde together numbers , and measures , and weights ? the sum of which may be divided , multiplyed , increased , or lessened , notwithstanding its heterogeneity . As supposing A B , C , D , all heterogeneal , as is usual in analyticks , the half , or third part , or any proportionable part of this heterogeneal sum may be given : and any one of the heterogeneal magnitudes subducted , the rest remaining : or a fifth heterogeneal magnitude added to the former sum : or any Algorythme , ever speciously , sometimes compleatly and absolutely thereupon performed . Besides upon geometrical demonstration and your own confession , all recto-convexe , convexo-convexe and citradiametral concavo-convexe angles of Contact must necessarily by your own principles be allowed to be absolutely heterogeneal to all right-lined angles whatsoever ; your self acknowledging that neither in equality , nor in any kind of multiplicity , or submultiplicity is any proportionableness possible amongst them . And where between angles a mathematical homogeneity is confessed and allowed , yet heterogeneity in respect of their Schematismes and figurations is undeniable . The things therefore constituting and distinguishing plane angles in respect of their figuration are , as above , their sides , their inclinations , or rather inclineablenesses , and their concurrence . That when two angles have all these in the same respective kinds , the angles are upon good reason in this sense concluded to be homogeneal : but when between two angles is an heterogeneity in any of these things , which are of the essence and constitution of an angle , those angles may justly be judged in this sense to be heterogeneal . And that such a specifick heterogeneity may be in each of these , may easily be declared as above . As first in lines which are the containing sides , how easy is it to discover such an heterogeneity ? For though a right line , and a crooked-line agree undeniably in the general nature of a line , and of length , and of extension , yet the rectitude of the one and the curvature of the other , are several kinds of positure , into which the length of the one , and of the other is disposed : that except , in contrarieties , we can see nothing but homogeneity , such an heterogeneity must needs be acknowledged between them . And whereas homogeneity , as to sides , inclination and concurrence , is required to the homogeneal figuration of angles ; the heterogeneity of the sides hinders the possibility of ever making them out to be such ; or that by any altering their divarication , keeping their present properties they can be coaptable . And that angles contained by heterogeneal sides may be equal , proves only the equality of the inclinations in either , but not the homogeneity of the figuration of the angles , or inclinations ; as the equality between a square and triangle in respect of their equal perimeters , area's , heights , bases , proves not in the least the homogeneity of their figures . And as right-lines and crooked-lines are heterogeneal , as above , not possibly to be coapted , with the precedent limitations ; So also are all curve lines , whose curvature is unequal and unlike , nay though it may be they be but several parts of the same line , or though the curvature of both , be every way , and every where equal and like , yet if the convexe and concave parts of the one be not alike posited as in the other , there will be a manifest heterogeneity in them , and an impossibility of coapting them , observing the limitations as above . And why doth the heterogeneity in the sides make heterogeneity in the angles , but because thereby is founded an heterogeneity in the inclinations , or rather in the inclinablenesses of the one side to the other ? For here , it is not the several degrees of the same kind of inclination that is intended ; for then all unequal right-lined angles should be altogether heterogeneal one to another : but it is a more then gradual , a specifick distinctness in their inclinablenesses , which we are now discovering to make the figuration of the angles more fairly and fully heterogeneal . And as inclination is the habitude of line to line , not being posited in the same right line , nor parallel , for even perpendiculars are in this sense here said to be inclined ; so , as above , from the heterogeneity of the lines will arise an heterogeneity of inclinations : and indeed for no other reasons do heterogeneal lines make heterogeneal angles , but because their inclinations are necessarily heterogeneal . And , as above , heterogeneal inclinations being respectively equal , as in some right lined and crooked lined angles , this doth not in the least annul the heterogeneity of their inclinations ; as a right line and a crooked line may be equal , yet as to the positure of their extension they are heterogeneal . And as heterogeneity of sides , or inclinations makes heterogeneity of angles , so likewise doth any heterogenealnes in the other point requisite to the nature of an angle ; which is the manner of the sides concurrence . And there are only three wayes in the concurrence of the sides of angles , according to which they can be heterogeneal one to another . For either the production of the one concurring side becomes coincident with the other concurring side , or else it departs from it on the same side on which it did occurre ; or else it departs from it on the contrary side to that on which it did occurre : all which are clearly not several degrees of the same manner of concurrence , but several kinds of concurrence : Viz. the one by way of Contact , the other by way of Section , and a third by way of curvature , or coincidence . That as these are diversified in angles , I mean from kind to kind , not from degree to degree , so there is thereby lodged in their figurations an heterogeneity , though in some mathematical respects , neither sides , nor inclinations can sometimes be denyed to be however homogeneal . So particularly angles of Contact in respect of their figuration must necessarily be acknowledged clear of another kind , then all other angles : because the inclination of their sides is tangent , concurring only in a punctual touch , whereas the inclination of the sides of all other angles is secant , and at the point of their concurrence by reason of their inclination they cut one another , or else they are coincident ; then which , what can make a more material difference in the inclination of the sides ? And as more especially relating to that so much urged analogy between right-lined angles and angles of Contact ; the inclination of the conteining sides in every angle of Contact is such as is impossible to be between the sides of any right-lined angle : for the sides of no right-lined angle can touch without cutting . And what more manifest and material difference can be in the inclinations made upon , or unto a right-line , then if in the one case a right-line be inclined unto it , and in the other a circumference , or other crooked-line ? Yet further to clear that differency of kind , which is between angles of Contact and other angles ; I think on all sides it will be judged unreasonable to make those angles of the same kind ; which have neither one common way of measuring , nor are coaptable , nor any way proportionable one to another , nor can any way by the contraction , or dilatation of their sides be made equal one to another ; and this we shall find to be the condition of many angles one in relation to another . However mis-understand me not , as if I made any commensurability a full mark of a full homogeneity : for as before crooked-lined and right-lined angles may be equal and of different kinds ; having their inclinations different in the kinds of their figurations , though equal in the recesses of the sides . And thus having at large deduced the grand difference which is between the mathematical heterogeneity of angles , and their heterogeneity in respect of their figurations , it will now be easy for us to extricate our selves out of all the difficulties with which former Disquisitions upon this subject have been involved . As first what is to be understood by the equality , which is asserted to be between right-lined , and isoclitical concavo-convexe angles . For it is out of controversy and on all hands yielded , that to any right-lined angle given may be given also a concavo-convexe isoclitical angle equal ; and that also , in a thousand varieties ; as is most manifest , in the circumferences of any two and two equal Circles , or any two and two equal Arches . And so in a converse manner ; to any isoclitical concavo-convexe angle given , whose sides make their recesse one from the other by an Arch less then a semi Circle , may be given an equal right-lined angle : although in the infinite number of right lined angles , it is impossible to find any more then one right-lined angle equal to the given concavo-convexe angle ; because in rectitude there can be no diversity , as there may and is in curvatures . Now in the above recited cases , why is equality between such different angles asserted possible ? and what is meant by their equality ? and whence , and how is the equality of them to be demonstrated ? Of necessity it must be founded upon some special method of measuring angles , or of somewhat which is in some , if not in all angles ; of which in common both these different sorts of angles are naturally and indifferently capable . And to be short , particular and plain ; all the mysteriousness of this their equality is founded upon this : that these two sorts of angles , right lined angles , and concavo-convexe angles of equal arches , they both have in common one special property , of which all other sorts of plane angles whatsoever are destitute . Viz. that each in their kind are isoclitical angles , and the sides in each are isoclitical , and in each angle the one side by the adduction , contraction , and drawing together of the sides will be coincident and coapted unto the other . And as the coincidence of right lines the one upon the other makes a right lined angle of Contact impossible , so the coincidence of isoclitical crooked-lines the one upon the other makes an isoclitical angle of Contact impossible , except only in an ultradiametral positure . And as the mensuration of right lined angles is by the Arches of Circles drawn upon the angular point intercepted between the two isoclitical sides , to shew how far they are departed from their coincidence ; so in isoclitical crooked lined angles , by the same way of mensuration an account may be taken of the departure , which each isoclitical side hath made from the other since their coincidence : and this is the point in which their equality consists and is accounted , and which founds the mathematical homogeneity which is between them . To instance in the case which is most manifest ; in fig. 18. from the angular point A , let the two arches ABC . and AFH of equall circles constitute and contain the isoclitical concavo-convexe angle CAF , and let the arches ABC and AFH be equall : then thorow the points C and H draw the two right-lines AD and AG. According to what is above delivered ; it is on all hands agreed , that the isoclitical concavo-convexe angle C AH is equal to the isoclitical right-lined angle CAH : as is copiously demonstrable from the equall arches of Circles drawn upon the angular point as center , cutting all the four lines : viz. the Arches comprized between the two isoclitical crooked-lines , are still equall to the respective arches comprized between the two isoclitical right-lines . For example in the chord AH take any where at pleasure the point I and from the center A draw the arch IB cutting the arch AFH in the point F and the right-line AEC in the point E and the arch ABC in the point B. The arch BF between the two isoclitical arches ABC and AFH is still equall to the arch EI intercepted between the two right-lines DA and GA. For the arches ABC and AFH being equall in equall circles , the right-lines AC and AH are equall : and also AE semidiameter is equall to AI semidiameter : and by the converse of the same ratiocination AB arch is equall to AF arch : so as in short by superposition , or adaptation the arch BE will appear to be equal to the arch FI : and therefore adding the common arch EF ; the arch BF intercepted between the two isoclitical crooked-lines ABC and AFH is equall to the respective arch EI intercepted between the two isoclitical right-lines : and this wheresoever the point I be taken in the right-line AH . So as by this common way of mensuration , common to both these sorts of angles , by reason of the isocliticalness , and the coaptability and coincidibleness of the sides in each , the one being an isoclitical concavo convexe angle is copiously demonstrated to be equal to the other being a right-lined angle . But now after what manner are we to understand this equality asserted between such right-lined and isoclitical concavo-convexe angles ? It is not an every way absolute equality which is between the angles , such as is between two equall squares , or two like and equall triangles , or any two regular and equall figures of the same kind or , to come nearer to the matter , it is not such as is between two equall right-lined angles , or between two equall , isoclitical , concavo-convexe angles , all whose four sides are all of them isoclitical each in respect of all the rest : but as things that are like each other , are like only in some things , and unlike it may be in many others ; such is the equality between any two such angles ; Viz. only a respective equality , such as is possible among heterogeneals , and inferring a necessity of some other respective inequalities . And such an equality may be between two mere heterogeneals ; they may be of equal length , and different breadth , or weight : so a Triangle , and a square and a Circle may be all equal , either in perimetry , or surface , but not in both ; so a right-lined angle , and an isoclitical concavo-convexe angle may be equal in respect of the recesses which the isoclitical sides make each from other and from their coincidence and coaptation , but in other respects they want not their manifest inequalities and heterogenealness . As a solid to a solid may have equal proportion that a line to a line , yet solids and lines are heterogeneal : so a crooked-line from a crooked-line may make equal recesses , as a right-line from a right-line , and yet in many other things much heterogenealness may be in the angles which they constitute . You will say wherein ? I answer in the rectitude and curvature of the containing sides . And in these different respects two isoclitical concavo-convexe angles may be both equal and unequal the one unto the other , Viz. equal in the recesses of the sides , but unequal in the curvatures of the sides : in the same manner as two figures may be equal in their perimetry , or superficial , or solid content , and yet be figures of different kinds under diverse inequalities : as the one a Rhombus , the other a square , the one a Cylinder , the other a Dode●aedron . So a thousand concavo-convexe isoclitical angles may be equal in respect of the recesses of the sides , yet each of a several kind : as a thousand figures different in kind may be equal in perimetry , height , base , superficial , or solid content . But you 'll say , what is the rectitude , or curvature of the containing sides to the nature of angularity ? I answer , they are of essential concern to the limiting and determining the nature of angles : angularity being the habitude of concurring lines each in respect of the other , as to their concurrence and inclination . And though the inclination of isoclitical crooked lines may be equal to the inclination of right-lines one upon another , in respect of the equal recesses and departures which the isoclitical lines make each from the other ; yet there still remains a vast inequality , dissimilitude , and unanalogableness between the angles and their inclinations , in respect of that little of figuration , without which neither can an angle be constituted , nor an inclination made : in a word the sides may make equal recesses , yet be unequal in their curvature , and unlike in their figuration : and neither by imagination , nor circumduction , nor any other operation can the one possibly be reduced , or coapted to the other , without setting the homologal points at improper and undue distances and positures one from another ; which shews a specifical difference between the two inclinablenesses of the one and the other : besides that a right-lined angle can continue its inclination between the sides infinitely , but many isoclitical concavo-convexe angles thereunto equal by the necessity of their curvature must terminate within a very little space : circumferences and several other arches , not being possible to be produced beyond their integrity ; so as some three given angles constituting a given triangle as to its angles , cannot , in like manner , constitute a triangle of any given magnitude ; which is otherwise in right-lined angles . And that the equality between isoclitical concavo-convexe and right-lined angles is not so absolute as to make them every way alike , equal , and of the same kind , may appear especially in this , which is elsewhere demonstrated ; Viz. that an ultradiametral concavo-convexe angle of Contact , being isoclitical , is alwayes equal to two right right-lined angles , which no one right lined-angle can be : and if it be anisoclitical of the larger , it is ever greater then two right right-lined angles can be , which is impossible also for one right-lined angle to be . And the difference between mathematical heterogeneity and the heterogeneity of angular figurations being as above discovered ; the nature as well of anisoclitical crooked-lined and mixt-lined secant angles will as clearly appear : Viz. that comparing them with right-lined angles they are compound and concrete angles constituted of right-lined angles and angles of Contact ; which are demonstrated every way heterogeneal : and such anisoclitical secant angles cannot be divided into any number at pleasure of parts homogeneal either mathematically , or in respect of their figuration , but of necessity some of them must be both wayes heterogeneal . This is manifest , because the fluxe , or circumduction of angles of Contact or of one of their conteining sides addes only a right-lined angle to them : after the same manner as the four right right-lined angles , which compleat the space in any plane , about any given point , may be exhausted by the circumduction of a crooked , concave , or convexe autoclitical , or antanaclitical line , as well as by the circumduction of a right-line . And that this ties not both angles to be of the same kind , may easily appear from the heterogeneity between lines and their fluxes , which are superficial ; or surfaces and their fluxes , which are solid . No wonder therefore if by the fluxe of an angle of contact , or of one of its sides , be created another kind of angle , holding no analogy with the former : the heterogeneity and improportionableness of right-lined angles and angles of Contact having been demonstrated . So upon the same ground we may be assisted to look into the special properties , considerable in the several kinds of angles peculiar unto some and incommunicable unto others , for example . In right lined angles , neither the greatest possible angle , nor the least possible angle can be given ; though all usually said to be within the compasse but of one kind . But to pursue the difference which is in angles ; angles of Contact , except such as are contained under lines of the same rectitude and curvature are every one of a several kind , either mathematically , or in respect of their figuration , or both . And except convexo-convexe angles of Contact of equal arches , which may be divided into two equal angles by common right-lined tangents ; all other angles of Contact are , every one , both the greatest , and least possible , of their special kind : and every angle of Contact contained under the convexe side of its arch , or arches , is the least possible under those sides ; which I suppose was the speculation unhappily missed by those learned men , who would have imposed upon the world , upon that their mistake , the dream of the coincidence of the sides in such angles . Again a right-line may be drawn dividing a convexo-convexe angle of Contact , whether it divide it equally , or unequally , but a right-line cannot be drawn dividing either of the recto-convexe angles of Contact into which the former was so divided ; whether the two recto-convexe angles of Contact be of the same , or different kinds : as is up and down demonstrated in Geometry . In citradiametral concavo-convexe angles of Contact , either the Arches are of unequal curvature , or which is tantamount , though they be of equal curvature , yet they touch not at homologal and answering points , being not all over of equal curvature ; which makes them notwithstanding the respective but not answering equality of their curvature to be anisoclitical . And between their Arches containing the angle of Contact , a right-line cannot be drawn ; but infinite crooked-lines in number may be drawn , bearing in like manner their convexity towards the concave which is inward , and their concavity towards the convexe of the other side , which is also inward . Concavo-convexe angles concurring by way of section , and having two right-line tangents drawn upon the Arches at the angular point are equal unto the right-lined angles contained under those right-lined tangents ; adding respectively to each right-lined angle one of the recto-convexe angles of Contact , and subducting out of it the other recto-convexe angle of Contact : and when those two recto-convexe angles of Contact are equal , as they are , when the sides are isoclitical , then the concavo-convexe angle is exactly equal to the right-lined angle : but when the two recto-convexe angles of Contact are unequal , as they are when the sides of the concavo-convexe angle are anisoclitical then the concavo-convexe angle and the right-lined angle are unequal . Concavo-concave angles concurring by way of section ( as all such ever do ; or by coincidence , and then one right-lined tangent gives the analysme of them , shewing the two recto-convexe angles of Contact , by which the angle of coincidence is less then two right right-lined angles ) are by two right-lined tangents at the angular point reduced into the right-lined angle ; which is the least of those right-lined angles that are greater then it , exceeding it only by two recto-convexe angles of Contact to be taken out of it . Convexo-convexe angles concurring by way of section are by two right-lined tangents at the angular point reduced into a right-lined angle ; unto which to make it equal to the convexo-convexe angle , are to be added two recto-convexe angles of Contact . And the right-lined angle is the greatest of all the right-lined angles that are less then the convexo-convexe angle . Recto-concave angles concurring by way of Contact are the greatest angles possible under those two sides . Recto-convexe angles concurring by way of Contact are the least angles possible under those two sides . If we compare recto-concave angles of Contact with right lined angles , they are less then two right right-lined angles by one only recto-convexe angle of Contact . And the least recto-concave angle of Contact is greater then the greatest right-lined angle whatsoever . Recto-concave angles concurring by way of section compared with right-lined angles which are constituted , i. e. compleated by the right-lined tangents drawn upon the Arches at the angular points ; are less than such respective right-lined angles by a recto-convexe angle of Contact . Recto-convexe angles concurring by way of section compared with right-lined angles which are constituted , i. e. compleated by right-line tangents drawn upon the Arches at the angular points ; are greater then such right-lined angles by a recto-convexe angle of Contact . Every angle of curvature , or coincidence , having a right-line tangent drawn upon the angular point , appears to be less then two right right-lined angles by two recto-convexe angles of Contact . The inclination of the sides without the angular point at any two respective , or other points , the one taken in the one side , the other in the other , is very nearly shewn , and as nearly as is possible in right-lines , by the right-line tangents of those respective points : but in mixed lined and mixed crooked-lined angles by several wayes of accounting , several points are made to answer one another , as by accounting by distance from the angular point , or by accounting by equalness of lines along the sides &c. Mixed lined angles of Contact , when they can be , and are , divided by a right-line , the parts are heterogeneal and unequal : and one of the unequal parts is a right-lined angle . Every recto-convexe , and convexo-convexe , or citradiametral concavo-convexe angle of Contact is the least possible under those sides . Rectilineary mensurableness in mixt lined , crooked-lined angles concurring by way of section , begins from the recto-convexe angle of Contact : as in right-lined angles from coincidence . A convexo-convexe angle of Contact , in respect of dividableness by right-lines is an angle made up only of heterogeneal parts , when it is a mixt-crooked-lined angle : but when it is an unmixt crooked-lined angle , it hath some parts which are homogeneal , Viz. two equal recto-convexe angles of contact , which are therein added the one unto the other . And those two equal recto-convexe angles of contact , as they are homogeneal , I mean of the same kind one with another , both mathematically and in respect of their figuration ; so mathematically they are homogeneal and of the same kind with the convexo-convexe angle which was divided ; but in respect of it , as to their figuration , they are heterogeneal and of another kind . The most simple angle may be divided into heterogeneal parts : i. e. the inclinableness of the one side to the dividing line both in respect of figuration and proportion may be specifically different from the inclinableness of the other side to the same dividing line : as a pentagone may be divided into a tetragone and a triangle , so a recto-convexe angle of Contact may be divided into two parts heterogeneal the one to the other , and to the first angle of Contact , both in respect of figuration and proportion : viz. into a new recto-convexe angle of Contact , and a concavo-convexe angle of Contact . Therefore no angle can be said homogeneal in that sense , as if it could not be divided into parts heterogeneal ; whether you please to understand it , in respect of mathematical homogeneity , or positure , and figuration , or what respect soever else that limits and distinguisheth plane angles one from another . And to give a brief and general account of the comparative admensuration of angles , as not being right-lined , yet by way of comparative admeasurement , they may in respect of their rectilineary parts be reduced and referred to those that are right-lined ; the containing sides not being right-lines , at the angular point draw right-line tangents touching the arch , or arches in the angular point ; and the right-lined angle contained by those right-lined tangents will be , as to the recesses of the sides at the angular point , either equall unto the first proposed angle , or the least right-lined angle greater then it , or the greatest right-lined angle lesser then it : or if two right-lined tangents cannot be thus placed at the angular point , either the first proposed angle was a mixt-lined angle of contact , said , if a recto convexe to be less , if a recto-concave to be greater then any right-lined angle ; or else it is a crooked-lined angle of contact , which if convexo-convexe , or concavo-convexe and citradiametral is less then any right-lined angle , but if concavo-convexe and ultradiametral , is greater then any right-lined angle , nay sometimes equall to , or greater then two right right-lined angles : or else it is an angle of coincidence , or curvature . All which is to be understood to shew the inclination of the sides at the angular point , as the chief for use in Geometry , but not necessarily else-where . So crooked-lined , or mixed lined angles are compared with right-lined angles by drawing at the angular point right-lines touching the Arches there , and comparing the crooked or mixed lined angle with the right-lined angle so constituted , respectively adding , or subducting the recto-convexe angles of Contact hereby created : and this , whether the Arches be isoclitical , or anisoclitical , or however posited . So all crooked , or mixed-lined angles concurring by way of section may have a right-lined angle given , which if it fall short of equality is either the least of the right-lined angles that are greater , or the greatest of the right-lined angles that are less then the first crooked-lined , or mixed lined angle . And so an analysme may be made of the greater angle into its heterogeneal parts ; and the crooked lined , or mixed-lined angle may be reduced unto , or compared with right-lined angles , only with the addition , or substraction of recto-convexe angles of Contact , being angles less than the least right-lined angle whatsoever . All angles have their inclinations compounded of the inclinations of the interjacent lines each to other in order : and of the inclinations of the sides to the lines next adjacent to them ; which composite inclination may be heterogeneal , as well as homogeneal in respect of the inclinations of which it is , or may be compounded . Equally arched convexo-convexe , or concavo-concave angles , may by a right-line be divided into equal parts mathematically homogeneal , but heterogeneal in respect of their figuration : but such angles cannot be divided into any more , or any other equal parts , for the reason immediately to be subjoyned . Heterogeneals taken together in several concretes proportionably , S c. each respectively in the same proportion , they hold exact proportion , concrete to concrete : as double cube and double line , are double , to single cube and single line , Viz. the concrete to the concrete : but set them out of the same respective proportions and the concretes are no way proportionable , or in analogy , concretely to be compared : as double cube and treble line , are in no proportion , to single cube , and single line . So double number , and double weight , and double measure , the whole concrete , is double , to single number , single weight and single measure : but setting them out of the same respective proportions ; double number , and double weight and treble measure , being alltogether concretely taken , are mathematically heterogeneal and improportionable to single number , single weight and single measure ; being in like manner concretely taken : because the heterogeneals in the one concrete ●old not the same respective proportions to the answering heterogeneals in the other . So convexo-convexe , or concavo-concave equally arched angles being secant , hold proportion when divided equally , as they may , by right-lines : but they are merely heterogeneal and without proportion , when divided by a right-line unequally . The ground of which is the heterogeneity of the parts , of which such concrete angles are made up when compared with angularity constituted by right-lines ; which heterogeneal parts , when the angle is divided equally in two by a right-line , are in the concretes , each respectively in the same proportion ; so making the concretes , though of heterogeneal parts , to be mathematically homogeneal and proportionable one unto the other : but when the angle is unequally divided ; in the two concretes the heterogeneal parts , of which they are made up , are not respectively in the same proportion ; for the recto-convexe angles of Contact , in the concrete angle , are divided equally , and the right-lined angle , which is in the concrete angle is divided unequally : so making the parts of the divided angle mathematically heterogeneal and improportionable ; because the compounding heterogeneal parts are not respectively according to the same proportion divided . The least possible angle under any two given incoincidible lines is the least angle of Contact which is possible under them . Recto-convexe , and citradiametral concavo-convexe angles of Contact as they are the least angles possible under their sides ; so they are indivisible into parts holding all each to other any thing of mathematical homogeneity , or proportionableness : Like unites they may be multiplyed to any proportion as whole numbers , and separately set : but cannot at pleasure be divided , nor at all into parts which are all of them mathematically homogeneal : nor can any number of them be at pleasure adjoyned one to another . So to any right-lined angle another may be imagined in any proportion , but sometimes it must be the composition of seseveral angles , and more then can stand at the space circumjacent about any one point . It not being possible for above four right right-lined angles to stand about the same point . As to a given point , other points may be given in any proportion , as whole numbers ; but they must not then be adjoyned one to another : but properly by the dividing of a point , farther proportions are not to be expected . So in such angles , though heterogeneal divisions be infinitely possible ; homogeneal , I mean mathematically , being impossible , are not , as above , to be expected . Two unequal anisoclitical angles contained under the same two anisoclitical sides , though in respect of their figuration , both are formed upon the same inclinableness of the sides one to another , yet they are mathematically heterogeneal : because being two concrete angles made up of heterogeneals , viz. of the angle , or angles of Contact and right-lined angles ; in the two concrete angles , the angles of Contact are in the proportion of equality , and the right-lined angles in the proportion of inequality : so as the concrete angles can have no proportion the one to the other . The half of the inclinableness of any arch upon its self , i. e. upon another arch like and equal , is still comprehended and contained under the inclinableness of a right-line upon the same arch : that though their figurations are ever heterogeneal , and their inclinations can never be equal , yet they may be mathematically homogeneal : as different numbers are alwayes unequal though ever proportionable . To no anisoclitical angle , whether of Contact , or concurring by way of section can any right-lined angle be made equal . And generally between isoclitical and anisoclitical angles equality is impossible . And when anisoclitical angles are compared with those that are isoclitical as greater , or lesser ; it is not to denote in both any mathematical homogeneity , and that so by possibility they are reducible to a true , compleat and analogous equality ; but the intent is only to declare , whether of them hath , or can have the containing side , or sides falling within , or without the other ; which is only from their inequality by the whole kind . So though anisoclitical angles may be greater , or less then a right-lined angle , yet between the one and the other there is neither common way of measuring , nor any proportion , though both of them be quantitative plane angles . There is no common way of measuring them , because of the anisocliticalness , and if there could be any proportion between them , then might a right-lined angle be given equal to such anisoclitical angles ; the contrary of which is otherwise clearly demonstrable . So as a thousand angles quantitative by conf●ssion and having right-lined angles lesser and greater then themselves , yet can have no right-lined angle equal to them . A right-lined angle cannot have its inclination at the angular point , much less all along the sides divided equally by a crooked-line , whether autoclitical , or antanaclitical , or of what curvature soever : though any such crooked-line may from any angle divide equally the plane bounded within a right-lined triangle : for if in fig. 17. BAC be a right-lined angle : I say , no crooked-line &c. can divide it at the angular point equally . If it be possible let it be divided into equal parts by the arch AGE whether autoclitical , as when it is conceived to be part of the arch AGEF , or antanaclitical , as when it is conceived to be part of the arch AGEHD . Then let the right-line AD divide equally the right-lined angle BAC . It is manifest , if the crooked-line AG never occurre with the right-line AD , that then it doth not divide the angle B AC equally ; for the right and crooked-lines cannot be coapted . Let therefore , if they do occurre , the place of their first meeting , or occurrence be at E. Therefore the arch AGE falleth within the angle BAD and therefore divides the whole angle BAC unequally , whether it be autoclitical , or antanaclitical . And by the same demonstration appears that it is as impossible for it to divide the inclination all along the sides equally . And though a crooked-line may divide any right-lined figure , because of its perfect bounds , from any angle into equal parts ; yet this no way evinceth any possibility of dividing a right-lined angle by a crooked line into equal parts : and though from any point of such a dividing crooked line , lines might be drawn making up a figure , whose parts divided by the crooked line from the angle are equal ; yet this is no more then is performable upon any point of any crooked line drawn between the sides of a right-lined angle at randome , whether the parts of the angle be homogeneal , or heterogeneal , equal , or unequal . Difference of curvature by a perpetual necessity infers difference of inclination , whether the curve line be inclined upon a right-line , or upon a curve line ; for still the one of the curve lines will fall within , or without the other . So let inclination upon a right-line be in a recto-concave angle of Contact , recto-convexe angle of Contact , recto-concave , or recto-convexe secant angles ; by no right-line can any of those inclinations be made upon the first right-line , nor by any other crooked-line : but still the lines will fall either within , or without ▪ And all angles of Contact under lines of different curvature and rectitude , as they are of ● thousand Mathematically and extra-quantitatively different kinds one from another , so they are 〈◊〉 manifestly distinct in kind from all right-lined angl●● whatsoever . And as every number is a different kind , in like manner as to positure and figuration is every line a distinct kind differing from all other not agreeing with it in rectitude and curvature ; whether the curvatures be homogeneal , i. e. every where equal , as in Circles , or heterogeneal , i. e. unequal in the several parts , as in ellipses , hyperbolas , parabolas , &c. And accordingly judgment is to be made of the sides under which angles are contain'd , and the angles contain'd under them : alter the kind of either side , and the kind of the angle is chang'd ; ever , in respect of figuration ; and most what , mathematically ; because the former inclinablenes of the sides is taken away , and a new kind of inclinablenes introduced between them . Hence appears ; no two recto-concaves , no two recto-convexes , no two concavo-convexes , no two convexo-convexes , being all angles of Contact can be equal , except their sides have the very same rectitude and curvature . In general , equality is not to be asserted between angles , except either for the mensurablenes of both in some common way of measuring , or at least because they can be so cast into a coaptation , as that either shall contain all the quantity which is in the other . And as he erred in squaring the superficial content of a circle , that in his quadrature left out a small lunular figure ; so neither can he be justifyed to have given one anisoclitical angle equal to another , who , as he must of necessity , takes in , or leaves out an angle , or some angles of contact which are in the one and not in the other . Particularly no mixed lined , nor mixed crooked lined angles whatsoever , whether secant , or of contact , can by any possibility , either by right-line , or crooked line be divided into equal parts , or angles , whether of the same , or of different , kinds . And in few , those angles , which cannot be divided into two equal parts cannot be divided into three , fower , five , or any other number of equal parts . The comparative admensurement , as above , of right-lined and not right-lined angles is as well of their heterogeneal inequality , when heterogeneal , as of their homogeneal equality and proportionablenes when homogeneal . All not right-lined angles comparatively admeasured , to right-lined angles , only with the addition , or only with the subduction of any angle , or angles of contact , are heterogeneal to all right-lined angles , as also , if when one angle of contact is to be added , and another subducted , the two angles of contact be unequal . And as is manifest , of several not right-lined angles , that is still the greater , whose comparative and relative admeasurement is made to the greater right-lined angle : and of those , whose comparative admeasurement is unto equal right lined angles , they are greater , or equal , or less according to the equality , or inequality , and comparing together of their angles of Contact ▪ And of concavo-concave angles the right-lined angle cannot be given , which is the greatest of those right-lined angles that are less then the concavo-concave angle : nor in convexo-convexe angles can be given a right-lined angle , which is the least of those right-lined angles which are greater then the convexo-convexe angle : nor in recto-concaves the greatest of the less : nor in recto-convexes the least of the greater : whereas in concavo-convexe angles , the right-lined angle to which the comparative admeasurement is made , may according to the case be either equal , as when the sides are isoclitical ; or the greatest right-lined angle that is less , as when the concave side is of less curvature ; or the least of the greater , as when the concave side is of greater curvature . From these things may appear how that objection is to be answered , in which you urge that there is a proportion between mixed lined angles , whose sides are seca●● , and right-lined angles , because the one by its multiple may exceed the other ; and that therefore an homogeneity , mathematically to be understood , is to be acknowledged amongst them . To this is answered that all anisoclitical angles whatsoever having their sides concurring by way of section when compared unto right-lined angles are heterogeneal compositions of angularity , i. e. cannot be divided into any number at pleasure of parts all equal ; but as is manifest , they in that their relative nature are concrete and composite angles , formed of right-lined angles by adding to them , or subducting from them mixed lined angles of Contact : so as the right-lined part of the secant anisoclitical angle , or any the least part of it hath true proportion with all right-lined angles ; and the whole being heterogeneal , yet hath a semblance of proportion with right-lined angles , because of those parts which it hath which are homogeneal with them ; but between the other heterogeneal part which is the mixt-lined angle of Contact , and right-lined angles , neither is , nor can be any proportion : and it is because of this part that it is not a true , but a seeming proportion only , which is between the whole concrete heterogeneal , composite anisoclitical angle , and right-lined angles : for if it were a true proportion and proportionablenes which were between them , it should then be possible to give a right-lined angle equal to such an anisoclitical secant angle ; which when done , I have no more to say , being well assured I am able to demonstrate the contrary upon whatsoever right-lined angle shall be offered under that notion . And whereas it is urged that a right-lined angle is , and may be equal to a mixed lined angle ; all their difference being only in this , that the sides of the one are more spread and divaricated then the other ; what is this else but to say , that they are equal , saying that the one is bigger then the other . For angles of Contact can divide angularity , or space equally , or unequally into more , or fewer parts : and they are not indivisible , because every one contains innumerably more in it : and by the definition of an angle , lines have a sufficient inclination to constitute an angle , if in the same plane , they lye not both in the same right-line . And to all other cases and objections of the like nature grounded upon them athematical heterogeneity of the parts , of which such special angles are constituted in respect of right-lined angles , like answers may be addressed . Though a right-lined angle cannot be divided into equal parts of the same kind mathematically , or in shape by a crooked-line , nor a mixed , or crooked-line angle by a right-line into parts of the same kind in respect of figuration ; yet some crooked lined angles may be divided into parts exactly equal of the same kind one with another , and with the whole mathematically by a right-line . For it is apparent , there may be between magnitudes a sufficient homogeneity for proportionablenes without excluding all further discriminableness between them : as between equal arched convexo-convexes , or concavo-concaves and their parts when they are equally divided . So between lines of all kinds , and numbers of all kinds , is proportionality . Yet still their proportionality is in respect of somewhat which is homogeneal in them . Viz. that they are all resoluble into parts that are homogeneal , or parts into which the rest are homogeneally resoluble , or after the same manner mensurable , as equal arched convexo-convexe angles into two equal recto-convexes : yet notwithstanding the proportionablenes between the convexo-convexes and the recto-convexes ; such an heterogeneity is in their figuration , that by no divarication of sides can they ever be made equal . And though the equal arched convexo-convexes and concavo concaves may be divided by a right-line into two equal parts ; by no lines whatsoever can they be divided into any more equal parts nor their recto-convexes by any line whatsoever into two equal parts ; such parts of such angles being more impossible to be given in Geometry , then the square roots of unsquare numbers , or cubicke roots of uncubical numbers are in Arithmeticke . As any two points , or any two indivisibles may have some few proportions amongst them , but no more : the latitude of proportionablenes being limited by the special natures and kinds of things : so between special kinds of numbers cannot be all proportions : nor between special lines all angles , or all proportions in all angles . Hence also we may clear the possibility of that speculation of the learned persons by you named , that in heterogeneals there may be a passing from greater to less , and from less to greater in a continuous manner without , ever passing thorow equality ; however you are pleased to bestow upon it a contemptuous smile , if not an hiss : Viz. that we should assert that mixed lined , or crooked lined angles can pass by the divarication of the same sides from being greater to be less then given angles , or contrarily by their contraction , and yet in that transit , never be equal . What is more obvious then to give instances of anisoclitical angles , less then a given isoclitical angle , and by divaricating and distending the sides of the anisoclitical angle , it may be made to exceed the first given isoclitical angle ; yet in all the way they could never be equal the one to the other ; the one being isoclitical , the other anisoclitical : coaptation and the passing of the sides from the angular point every where prove their inequality : and let those that assert their equality any way shew and admeasure it . And the sober understanding of those sayings , that such angles passe from less to greater without ever being equal , is not to assert any homogeneity , or proportion of any kind between them , or common way of measuring their quantity in and according to the same indefinite quantity , but only to shew how the sides may pass within and without each other ; but because of their anisocliticalnes and difference in respect of rectitude and curvatures , they can never be brought to be coincident . And why should this appear so monstrous , that transitions should be , in the sense abovesaid , made from greater to less , without passing thorow equality ? seeing it is most manifest that though a crooked-line circumducted about the angular point of a right-lined angle makes infinite divisions of the right-lined angle ; yet they are ever unequal , and never by possibility can be equal : though notwithstanding , the same crooked line may divide a crooked lined isoclitical angle equal to the given right-lined angle into equal parts ; which besides plentifully shews the heterogeneity which is between equal right-lined and crooked-lined isoclitical angles , notwithstanding their equality : yet by making up the right-lined angle into a compleately bounded figure , the crooked-line may divide the plane of it into equal isoepipedal and isorrhopical parts : as is more easy to demonstrate then that there should be any need to set it down . And it is not to be stranged at , that we assert a crooked-line can divide a right-lined triangle into equal parts , but not any of its right-lined angles : for the figuration of the one is compleat , and the production of the crooked-line , as well as of the lines containing the right-lined angle , in the triangle are limited ; all which are quite otherwise in mere angles , being in many kinds of angles and inclinations very alterable by the production of the lines . And if you will pertinaciously say that a crooked-line may divide equally a right-lined angle , shew their equality , and your way of admeasuring the equality of the parts : both coaptation of sides , in whose habitude the nature of angles chiefly consists , and also the way of measuring by interjected arches demonstrating and declaring the contrary : Nay sometimes in quantities among which there is true proportion , the special differences of their kinds may be the authour of little less . So commensurable quantities , being in their commensurability infinitely divisible , may be continually increased , or lessened by quantities vastly , less then any given quantity ; yet as they pass from less to greater never can hit equality with any the like quantities of the same general kind , being incommensurable . So in the present question , heterogeneity of sides makes an impossibility to coapt , though by straitning and divaricating they may fall within , or without , and so be less , or greater , but being impossible to coapt , and incapable of any other common way of measuring , equality cannot be conceived in them ; in which is praesupposed a common way of measuring to declare and prove their asserted proportion and equality . And in this whole matter what is more said then that the cutting inclination of a right-line upon a right-line , and of a right-line upon a crooked , or of a crooked-line upon two crooked-lines being all of different curvature , may any of them be greater , or less then one another heterogeneally , but can never be equal ; as to those that will consider , is most clearly manifest and necessary . And this is no more strange , then that odde numbers may be less , or greater then any even number , at least above two , yet by their constitutive nature , they can never be equal : and for the same reason magnitudes commensurable and incommensurable may be greater , and less then one another , and by a less quantity then any quantity that can be given ; yet , for the specialty of their natures , they can never be equal , remaining so distinct in their ultimate kind : and however they have many general things in which they agree , yet they are not accountable specially , but by several wayes and algorythmes . And as it is the binding up of numbers to the specifick properties of Evenness , or oddness , and of magnitudes to commensurability , or incommensurability , that makes equality between their kinds impossible ; so it is the incoaptablenes and want and impossibility of a common way of measuring , which is between the two and two sides of such heterogeneally unequal angles , keeping all along the properties of their inclination , that renders equality between their kinds impossible ; though either may sometimes truly and manifestly be greater or less then the other , however without proportion . For in heterogeneals may be a two fold inequality , either an inequality according to proportion , or an inequality without proportion : and though they be heterogeneals , if it be a true limited , determinate proportion of inequality which is between them , as between an odde number and an even , a commensurable magnitude and an incommensurable , they are then considered as some way , or according to something which is , homogeneal , not heterogeneal , in both : but if their inequality , though real and apparent be without any true and homogeneally determinable proportionablenes , as between right-lined and anisoclitical angles , then the consideration had of them is in their heterogeneity . So to the objection , that right-lined angles , and recto-convexe angles of Contact have proportion of greater and less , and are therefore homogeneal , if any quantitativenes be to be asserted in the recto-convexe angles of Contact ; and so of the rest : I answer , there is not a proportionable inequality between right-lined angles and recto-convexe angles of Contact , and the like ; but an inequality , which is improportionable : as when the Earth is said to be intruth greter then a point ; though in many particular hypotheses contrarily conceived , for the better observing and accounting several phaenomena , and the better accommodating of instruments for the making of observations . So in the genesis of quantities and figures , when one quantity hath its genesis by the fluxe , or motion of another , the quantity formed by that motion is greater then the quantity moved , though still without any proportion : so by the divaricating of the sides , by the motion of one of the sides , of a recto-convexe angle of Contact , is a genesis of recto-convexe angles of section ; and the recto-convexe angles of section are still greater then the recto-convexe angle of Contact , or it s respectively moved side : and all still without any proportion . And inequality without proportionality being so usually asserted , and familiar between mere heterogeneals , doth easily acquit it self from the reproach you charge it withal , of being a contradiction in the very terms ; for finite and infinite never were denyed to be unequal , yet never can be made out to be mathematically homogeneal and proportionable . For though all proportion is either of equality , or inequality ; that hinders not but an inequality in heterogeneals may be admitted , without an asserting of proportion between them . So as mathematical homogeneity is not proved by inequality , till proportionablenes be as well proved as inequality ▪ Of the same leaven is that strange kind of reasoning you use ; to any right-lined angle a crooked-lined angle may be made equal ( we confess a thousand several crooked-lined angles may be made equal to any one right-lined ) angle ) but you from thence inferre that therefore all crooked lined angles and right-lined angles are of the same kind ; without adding as well , that to any crooked-lined , or mixed lined angle , a right-lined angle also might be made equal ; which can never be done ; the contrary thereof being confessedly demonstrated in Geometry : or if any be so opinionated that it is either easy , or feasible , let them give a right-lined angle equal to an anisoclitical angle , whose sides concurre by way of section or to an ultradiametral convexo-concave angle of Contact : and trye whether the equality of the two angles be not disproveable . In the same manner inequality without proportion , is asserted between both the recto-concave and recto-convexe angles of the semi-circle , i. e. the inner and outer angles of the semi-circle , and a right , or any other right-lined angle ▪ But to return , from the concrete and composite nature of not right-lined angles , when compared with right-lined angles ; the enigmaticalnes of the proposition , that magnitudes of one sort may be greater , and less then a given magnitude of another , but never equal , becomes most clear and doubtles : as infinite solids may be given greater , or lesser then the heterogeneal concrete magnitude of a cube foot and a foot-line ; but never can any solid be given thereunto equal : so likewise infinite heterogeneal concrete magnitudes consisting each of solids with the accrescency , or annexion of a foot-line , may be given greater , or lesser then a cube elle ; but in such comparisons , never can the concretes of the heterogeneal magnitudes be equal , or in proportion to any solitary , single , one , of the heterogeneals . In like manner it manifestly appears what is to be thought of that often pretended equality between the two angles of a semi-circle and a right right-lined angle : for by coaptation and the goings forth of the lines from the angular point it appears otherwise . And how will they that assert their equality demonstrate it ? and by what way will they admeasure it ? for interjacent and intercepted arches of Circles drawn upon the angular point as center , can in these angles contribute nothing to the admeasuring of them : and coaptation makes against their equality : and is so farre from making a right right-lined angle to be the constant standard of all angles of semi-circles , that it manifestly shews the angles of greater semi-circles to be greater and of less , lesser . The objection , that unequal circles , semi circles , and segments of equal degrees , cannot be judged like and homologal figures , except all their respective angles be equal , as well as the sides homologal : this may be easily answered ; Viz. that it is like genesis that makes like figures , which in all right-lined figures makes the answering angles equal , and in all figures the sides to be homologal , and the difference of the homologal angles to be less then the least right-lined angle . In Circles the same genesis , by the circumduction of the semi-diameter about the Center , which makes the figures like , and the sides homologal , makes in unequal circles the curvatures , angles of coincidence , the angles of the semi circles , and of homologal segments , necessarily unequal . Or , then figures 〈◊〉 be judged like when in a concentrick 〈…〉 the perimeter , sides and lines of the 〈…〉 proportionable to those in the other , 〈…〉 or may be placed parallel , or 〈…〉 those in the one , to those in the other ▪ , 〈…〉 which in right-lined figures , t is true , th●●● alwayes follows equality between the answering angles , but not so in other lined figures . And because equality of angles in like right-lined figures is so much urged ; the difference of the case of angles in like right-lined and like crooked-lined figures may plainly appear in another remarke ; Viz. that in like right-lined figures , the sides of the answering angles may from the answering angular point be exactly coapted one to another ; which in unequal Circles , though never so like figures , is most apparently impossible : that it cannot but be unreasonable to expect as absolute a conformity between the answering angles in like crooked lined figures , as there is in like right-lined figures ; being so manifestly against both the eye and demonstration . And therefore like segments of Circles , are not defined by equality of angles contained between their arches and their chords ; but by the equality of the angles contained in them ; the one being certain , constant in all , and demonstrable ; the other in most cases , not only doubtful , but impossible . So the objection , from the asserted equality of alternate angles , made by a right-line cutting parallel circumferences ; is readily answered by denying the truth of what is presumed in the objection , as never by any demonstrated , or ever possibly demonstrable , Viz. that the alternate and vertically opposite angles , made by a right-line cutting parallel circumferences are equal . And the tyranny of forcing lines out of their natures and special properties , may appear in that very instance of compelling the parallelisme of curve lines to answer the consectaries and idioms of the parallelisme of right-lines : in which , to omit the alleadged instance , as by you unproved , and for good reasons by us to be denyed , a right-line tangent of the lesser concentrick Circle cuts the circumference of the greater , and infinite right-lines cutting the greater , neither cut , nor touch the lesser , which is repugnant to the nature of parallelisme in right lines . That that which is so much contended for , that a crooked-line and a right-line are homogeneal as to length and their general lineariness , was , or ought never to be denied , there being all possibility of equality , and truly proportionable inequality between them , what kind of curvature soever the crooked-lines bear : but that they are homogeneal as to the positure of their longitude ; the site and manner of their extension , hath unto me been alwayes unconceivable : whence the truths on both hands clearly follow , Viz. that an arch and a right-line may be equal and hold alwayes a true limited , exact proportion one to another , but the arch and it s chorde never can be equal , i. e. there never can be equality between a right-line and a crooked-line , both posited between the same two terminateing points , nor any analogy between the rectitude of the one and the curvature of the other . And the seeking to prove the equality of angles contain'd under homologal lines , the one curve , the other a right-line from your usual fancy of a regular polygone of infinite angles in every circle , is too wild to be perswasive : for though at any mean point in curve lines , the two parts of the curve-line may be conceived specially to meet as several parts and lines , and so to have inclination the one to the other , and so to constitute an angle ; which we call the angle of curvature and coincidence , not reasonably to be denyed by those , with whom it is so ordinary to make such suppositions , and especially such as can so usually against possibility imagine angles in a right-line remaining a right-line : yet that angles should be without sides , and a perimeter of any figure conceived at once to be all angular points and no lineary sides , clearly ●●●●stes the perimeter of the nature of a line : 〈◊〉 to me it seems far from the nature of a ●●●ular figure , that hath nothing but points ●●stead of lines to bound it : but which is most material ; that a number actually infinite should be so easily given , is hard to allow : and that indivisibles , as points , should be so adjacent 〈◊〉 to another , one without another , with●●● coincidence , identity and unity , is new ●●●●osophy , and not easily capable of any in 〈◊〉 defense . Therefore that argumentation 〈◊〉 , that such a regular polygone of in 〈◊〉 whether sides or angles is either a circle , 〈◊〉 inscribable in a circle , is too vain : for it can be neither , being nothing , because there neither is , nor can be any such thing : for if any such were allowed they must of necessity have equal and infinite perimeters ; which is too gross to be admitted in it self , and besides renders the whole matter unapplyable to Circles , which are acknowledged , to be some less then others . So as all discourses of a regular polygone of infinite angles , are discourses not only of a non-entity , but an absolute impossibility , which renders all suppositions thereof unjustifiable . And of the same fineness are those sayings , that the magnitude of an angle is not to be judged of from the divarication which the sides have without the angular point , or point of concurrence , but from the divarication which they have in the point of concurrence ; as if in an indivisible point they could have any divarication at all . But as if it were resolved that even this should be transcended in monstrosity , for the justifying of the equality of mixed lined angles contain'd by homologal sides in unequal Circles , by an instance from the coapting of unequal hexagones to the same line , as a common side in them all , divided equally by a perpendicular passing thorow the centers of all , a right-lined angle is strangely constituted either of three right-lines concurring , but not in the same point , or of two lines without any concurrence , or else the instance must be void of all pertinency to the question . So to all those objections seemingly founded upon that proposition , or postulate , that what is less then any positive quantity whatsoever is not any quantity at all , is justly answered ; that the proposition or postulate is most true and reasonable , and cannot by any of sound mind be denyed , or doubted : but no force of objection could be made out of that , if other things of a less veritable nature had not been taken in ; as in most of them the fancyed possibility of a regular polygone of infinite angles ; and frequently that a Circle is that regular polygone . But besides , though what is less then any positive quantity whatsoever be not any quantity at all ; yet this hinders not , but quantityes may be mathematically heterogeneal and improportionable one to another : so every surface is less then any solid : and angles of Contact are not less then any quantity whatsoever , for there is in the least of them an endles , unexhausted divisibility ; which how it can consist with a nonquantitativenes , let those that have a mind to be serious solemnely consider . To the objection that would prove , neither semi-circumference to contain an angle with the right-lined tangent of it in its extreem point , because the two semi circumferences contain no angle at that point , but are one regularly continued line , and the circumference and right-lined tangent are lines coincident , at least as to the point of Contact ; manifest and reasonable answers cannot be to seek out of what hath already been said . For first what hinders the reasonable conceiving of angularity at any point of a curve-line , where is both concurrence , inclination and divisibility , more then the notion of divisibility at any mean point of a right-line ? And not to doubt but a curve line may be conceived reasonably as one continued line , as well as two , or more , inclined and concurring right-lines ; yet that the right-line tangent and curve-line which it toucheth , should be said to be coincident lines , in such sense as to exclude angularity ; or that any two lines can be so coincident in one only point , as to exclude angularity , and the inflexion of one to , or from the other , except both lye in one and the same right-line ; hath , as elsewhere , been plainly and abundantly answered to . To the objection that the Area of a Circle is equal to a rect-angle under the semidiameter and semi circumference ; and that therefore the semidiameter in a Circle is perpendicular to the circumference in a Circle and makes at the circumference four equal right-angles ; is answered , that the whole objection is a manifest paralogisme . For it is not denyed but in the right-lined rect-angle under the semidiameter , and a right-line equal to the semi circumference , is presumed , and by the definition of a rect-angle inferred , that the angle under those two right-lines is a right right-lined angle : besides it is not denyed , but the diameter falls perpendicularly in the circle upon the circumference : and that the four angles made by the falling of the semidiameter upon the circumference differ from one another less than the least right-lined angle : however that cannot force the falling of the semidiameter perpendicularly upon the circumference into the properties of perpendicularness between right lines , which still divides the space at the angular point into four angles always , every way alike , and equal ; which in right lines perpendiculars upon curve lines in the same plane , is impossible to be , and therefore impossible ever to be demonstrated . It will not be unuseful here to enquire wherein the likeness and unlikeness of angles doth consist , and whether there be any such thing as likeness and unlikeness in angles , or whether the likeness , or unlikeness of figures be only in the similitude , or dissimilitude of the sides . And that by a circumspect consideration of the nature of mathematical similitude in other cases , we may be the better guided into the true and most rational notion of similitude in angles , let us remember what hath already been judged in this point , and what is herein confessed on all hands . First , in right lined figures , those figures are judged like , whose answering angles are equal , and the answering sides and other lines proportionable ; and if they be equal , they may be coapted , homologal side to homologal side , and answering angle to answering angle ; or whether they be equal , or unequal , all the sides and other answering lines of the one may be set , as from the same center , each at parallelisme , or coincidency with the answering sides , or lines of the other , so as in like right lined figures is proportionablenes ▪ in the answering sides , equality of the answering angles , coaptability of all the answering sides into either coincidence , or equidistance , and a proportionate distance of the answering angles , each from the other . But now the similitude of figuration which is in circles founded upon the like genesis of all circles is in the equidistance , or coincidence of their circumferences , when the center of the one is coapted to the center of the other ; and that equal angles from the center intercept proportionable parts of the circumferences , and that proportionable parts of the circumferences are connected by proportionable chords , and contain and sustain equal right lined angles . And the like speculations might be pursued in other figures both plane and solid . In a rational application of which to the disquisition of angles , it may be first enquired , whether there be any such thing as similitude & dissimilitude to be own'd or observ'd among angles ; and if so , how that similitude is to be understood ; and whether it be inconsistent with inequality in the answering angles . To clear all which we must know , that in unequal but like right lined figures , the homologal angles are always equal , being contained in both figures under right lines : but in unequal , and like mixed lined and crooked lined figures , the homologal mixed lined , or crooked lined angles , neither are , nor can be equal ; only their difference is ever less than the least right lined angle ; and their similitude hath never rationally yet by any been questioned but with good reason according to the following gloss is to be justified . The more clearly to demonstrate all which in Fig. 21. upon the common center A. draw two unequal Circles , Viz. HEG. the lesser , and BCD . the greater . Then from any point B. in the greater circle BCD . draw the right line BEAFK . thorough the common center A. cutting the circumference of the lesser circle HEG. in the point E. then take AF. equal to BE. and upon the center F. and semidiameter FE . draw another circle ECKD . equal to the greater circle CBD . Here on all hands is agreed , that the lesser circle HEG. and the greater circle CBD . are like figures , and that therefore the two mixed lined recto-concave angles ABD . and AEG . are like angles . And by the construction it is apparent that the two recto-concave angles ABD . and AED . are equal : and that the two recto-concave angles AEG . and AED . are unequal : and that the recto-concave angle AED . is greater than the recto-concave angle AEG . and in all like cases it is always so ; however the difference of the two angles must necessarily be less than any right lined angle , because all such citradiametral concavo-convexe angles of contact , as GED . are always less than any right lined angle ; as is consequent to what hath been demonstrated in Geometry , which was to be shewn . Whence we may clearly observe that similitude of Figures lies chiefly in the proportionality and like positure of homologal sides , in respect of parallelisme and coincidence , without imposing any other necessity for the equality of answering angles , then as it may consist with the proportionating and like positing of the homologal sides and lines . And such inequality of the answering angles , as is requisite to the proportionating and alike positing of the homologal sides and lines in like and unequal mixed , or crooked lined figures , is so far from being inconsistent with their figurative similitude , that they cannot without it , under inequality keep similitude in their figuration . And though the inequality , which is between angle and angle be less then that which is , or may be , between the Homologal sides and lines ; yet the inequality of the angles is more different , being an inequality without proportion , whereas the inequality of the homologal sides and lines is ever according to proportion . Upon the whole , it is not equality that generally makes angles to be like , for a right lined , and an Isoclitical concavo Convexe may be equal angles , but never can be like , nor were ever suspected to be so : but that which makes angles to be like is rather their being contained under homologal sides , posited so as to construct a like & homologal figuration . And this whole matter depends upon what I before hinted , Viz. the figuration of lines and angles ; Sc. rectitude , being one single , simple , figuration of lines incapable of any variety , like angles under right lines are always equal , and never can be unequal : but 〈◊〉 , being infinitely variable , those 〈…〉 are said to be like , i. e. homologal , ●hose construction is like , so as in like figure● upon a common center , to set homologal sides and lines proportionably equidistant , or coincident ; as circumferences of like though unequal circles , ellipses , &c. And so under a thousand inequalities such mixed and crooked lined angles may be like : as in Fig. 21. the recto-concave angles AEG . and AED . being unequal , are both like to the angle ABD . and so is every angle how different soever , if contained under a diameter and a circumference . And indeed the figuration of angles , being incompleat , and the length of their sides undetermined , neither parallelisme , nor coincidency , nor proportionality , nor homologal positure , can , when they are unequal , be conceived in their sides , without special relation to some compleat Figure and its Center : so the recto-concave angles AEG . and ABD in Fig. 21. are like , as conceived to be each contained respectively under a diameter and a circumference , and so upon a common center positable into parallelisme , coincidence and proportionableness , and all possible likeness and homologalness of figuration . In right-lined angles , where homologal and like angles are always equal ▪ for the same reason every angle equal to a right-lined angle , is not presently a like angle : 〈◊〉 a thousand equal angles , are all , ever , and to all purposes , unlike ; as two equal isoclitical right lined and crooked lined angles , because they can never be coapted to be answering angles , in like Figures , or to set their containing sides homologally , and in parallelisme , or coincidence . That equality of answering angles is not so of the essence of like Figures , as proportionality of sides , and answering lines , with their parallelisme , or coincidency : only from the propriety of like plane Figures , follows an equality in all like right-lined angles ; and in like curve lined Figures , that their inequality is ever less than the least right-lined angle . Hence therefore appears that from the similitude which is in unequal circles , the equality between angles of semi-circles & right right-lined angles is not effectually proved . And notwithstanding any thing in those arguments tendred and proved , every recto-concave angle contained under a concave arch of a circle and a right-line , which is perpendicular to the right line tangent of the arch at the angular point , is greater than any right-lined acute angle , and less than a right right-lined angle : and the recto-convexe angle contained under the convexe arch and the right lined tangent is less than any right lined angle whatsoever : and the other recto-convexe angle contained under the convexe arch and the right line , which is perpendicular to the right line tangent at the angular point , is greater than a right right-lined angle , and less than any obtuse right-lined angle whatsoever . And whereas you object that if , as in Fig. 12. the right line KG A. be the diameter of the circle K AD. and AB the right line tangent , then KAB is a right right lined angle : and the recto-convexe angle of contact DAB is no part of the right right lined angle KAB . that therefore the angle of the semicitcle KAD is still equal to a right right lined angle , because what is taken out of it was no part of it . I answer , the recto-convexe angle of contact DAB is indeed no proportionable part of the right right-lined angle KAB , but yet it is truly a part , though improportionable , and so mathematically heterogeneal : for if it had been no part at all , and nothing , then the angle of the semicircle KAD . ( nothing being taken out of the right right-lined angle KAB , but the recto-convexe angle of contact D AB , which is said by you to be nothing , and no angle ) it should ●●ill remain a right right-lined angle ; which is not by any asserted , the contrary being so manifest : besides that the separability of the recto-convexe angle D AB from the recto-concave angle KAD makes clear and certain , the truth of its being a part of the right-lined angle KAB . And likewise from what hath been before declared in our opening the nature of a plane angle may clearly appear , that we are not to understand that a plane angle is meerely the angular point , or meerely in the angular point , as contradistinguished from the containing sides , though it there terminate , or thence have its rise ; but angles are in the habitude of the concurring , containing and inclined sides : Viz. the habitude which they hold each to other all along their tendency unto the angular point , or their rise from thence , if we would have the full notion , inclination and figuration of an angle . For there is often a great inequality and vast imparity between the inclination , sometimes of one part of the containing side to the other containing side , and the inclination thereunto , of other parts of the same first containing side ; as may appear in all mixed lined , mixed crooked-lined and all other anisoclitical angles . And the nature of an angle consisting in inclination as well as in concurrence , though concurrence may be and is in a point , and inclination at a point , yet inclination must be in the lines and of the lines , and cannot be in a point separately . And methinks the nature of an angle , and its inclination , is scarcely so fully held forth , when the inclination of the two lineary sides containing it , as if the sides were not therein concerned , is ordered to be observed only in the angular point , and not out of it : because , as you say , though you urge it to the contrary , many times out of the angular point in the containing sides , no two points can be shewen in the one side , where it hath the same inclination unto the other . Certainly in an indivisible , such as is the angular point , if abstractly considered , it were vain to expect and impossible to observe any inclination : and no doubt as the magnitudes inclined are without the angular point , so is also the inclination : though as they terminate in the angular point , so doth the inclination . So the angle of a semi circle is not the common terme of the diameter and the semi circumference , excluding the diameter and the semicir-cumference for then in an abstracted point it should be possible to observe an inclination ; and a point being indivisible should be inclined unto its self ; which is not convenient to assert : but rather the angle of a semi circle is the inclination of the semi circumference to the diameter , terminated in the angular point , which is common to both . And whereas it is said that out of the angular point , no two points can be shewen in the diameter , at which the diameter is equally inclined to the semi circumference , nor in the semi circumference where it is equally inclined to the diameter ; all is allowed and averred as glosseably true , and this is that which makes the great difference between anisoclitical and isoclitical angles , and renders it so impossible to give an anisoclitical angle equal to an isoclitical angle . For in isoclitical angles the inclination of the sides , the one unto the other , is at all points the same without any variation ; as every where appears by the interjected arches of circles drawn upon the angular point as Center : but in anisoclitical angles , at every several point , the one containing side hath several and different inclinations to the other containing side : which is the cause that isoclitical angles may possibly and easily be given , sometimes greater , and sometimes lesser then anisoclitical angles , but never equal : because in the one the inclination of the containing sides still varieth , in the other not at all . And if the whole nature of an angle lye in the angular point , without extending the habitude of it farther into the production and figuration of the containing sides ; it will not only be necessary for us to yield unto you that recto-convexe angles of contact are not quantitative ; but besides both you and we , contrary to what we have alwayes hitherto judged , shall be constrained to acknowledge that there is no quantitativenes neither in crooked-lined , nor right-lined , nor any other angles whatsoewer , whether superficial , in one , or several plaines , or solid . And can any thing be more horrid then to say , the quantity of angles is not to be measured by the divarication of the sides at the angular point , but by their divarication in the angular point , where they have none at all ? But yet though it is thus evident , that the inclination of the sides at the angular point , may and frequently is much less or greater then the inclination of the same sides at other points ; which , as is above hinted , is not to be left out in the full , genuine and clear consideration of the nature of angles , their kinds , figurations and quantities : however the inclination of the sides at the angular point , is that which is most usually enquired after , and most useful to be searched and observed in Geometry ; for the discoveries which are from thence made of lines , how they fall coincidently , or within , or without others . To the objection that in fig. 12. the right-lined tangent AB and the arch AL make all one and the same equal inclination to the right-line secant AC in the common angular point A ; and that therefore the right-lined angle BAC under the right-lined secant AC and the right-line tangent AB is equal to the mixed-lined recto-concave angle EAL under the right-line secant AC and the arch AL ; I answer as before , inclination is not in the angular point abstractly considered without regard to the sides passing out of it , but inclination is the relative situation which the concurring sides have at the angular point : at least that is their inclination there : for a point to a line can have no inclination : it may have distance from the line , but cannot be inclined unto it , because of its indivisibility . And having already shewn the inclination of side to side to be of the essence , notion and nature of an angle ; a little may be reply enough to all those hypersceptical objections which are sounded upon the imagination of an angle in a right-line , or any inclination , or angularity imagined between a right line and a point , especially the point being in the right-line . And equality , or inequality of angles is not , nor can be judged of by the so abstractly considered angular point ; in which a thousand several sides of several and unequal angles may meet indifferently ; but the judgment of the magnitude and equality and inequality of angles is from the sides , and the order of the divarications , in which they passe , especially first of all , from the angular point . Besides how strangely is it taken for granted , without proving , th●● the right-line tangent AB and the arch AL are equally in the angular point A inclined unto the right-line secant AC ? If that could be once proved , the concern of it would turn the scales of the controversy : but demonstration is so clear to the contrary , that as without proof it is not fit to be admitted , so for the proof of it , I know nothing can be produced besides an utter despair of ever making it out . For if the congruency of the sides terminatively in the angular point , were sufficient to constitute equality in angles , it appears not how any angles meeting in the same or different angular points could be unequal : every point by reason of its indivisibility being incapable of inequality , as well as inclination . And if all such angles so constituted by the falling within , or without of the sides , shall be doubted and questioned whether they be true and quantitative angles , and whether the addition , or subduction of them be able to diversify other angles and their quantities ; all the pains of the Geometricians to prove the intracadency and extracadency of the angular sides from the same angular point , were vain and to no purpose ; the angles remaining altogether the same and equal , whether such angles of contact be added to them , or taken from them . But yet though the true , 〈◊〉 and genuine nature of an angle consist in the mutual habitude and inclination of the containing and concurring sides , it is not ever necessary to consider it with such a largenes in Geometry . The inclination which the sides bear mutually each to other at the angular point is out of doubt that which is of most constant necessity , highest concern and usefulnes in all angles to be observed . It is true in isoclitical angles , the inclination of the two containing sides being every where the same and equal , it is indifferently by Geometricians taken by a circle whose center is in the angular point , of what diameter soever thereunto applyable , and at what same distance soever from the angle , or at what same longitude soever from thence in the sides the points be , at which their inclination is observed by intercepted arches : and the same two points , terminating the intercepted arches at which their mutual inclination is observed , constantly offer themselves together , whether you take points at equal distance from the angular point , or intercepting in the sides equal longitudes between them and the same angular point But in anisoclitical angles ; the inclination of the anisoclitical sides varying still in the continuity of their production , if we use the former method of measuring the inclination of the sides by intercepted arches of a circle drawn upon the angular point as center ; in them therefore Geometricians concern themselves little further then to observe the mutual inclination of the sides at the very point of their angle : and not at any other points in the anisoclitical sides , save only the point of their concurrence ; because of the constant variation of their inclination , both in respect of such , and every other method and way of measuring , according to the continuity of their production . And by arches of circle drawn upon the angular point as center , it is impossible to measure the inclination of the anisoclitical lines at the point of their concurrence ; the only way therefore which remains unto Geometricians to measure such anisoclitical angles , i. e , the inclination of their sides at the point of their concurrence , is by observing the lines in what order they depart from the angular point : Viz. which line falls within , which without , and which is coincident with that unto which it is compared . So in fig. 12. if AHF and ADK be equal circles touching in the point A : and G the center , and AGK the diameter of the circle ADK : and AEL the arch of a greater circle touching both the former circles in the same point A and with its concave side at A respecting the center G , and with its convexe side at A respecting the circle HAF : also if AB be a right-line tangent touching all the three former circles in the point A , and the right-line ADEC cutt the circle ADK in the point ● , and the circle AEL in the point E : here the Geometrician demonstrates the angle K AB to be a right right lined angle , and that the arch AFH passeth out of the angular point A without and beyond the right-line tangent AB , and without the right right-lined angle K AB : and that the arch AEL passeth from the angular point A within , or on this side of the right-line tangent AB , and within the right right-lined angle KAB , but without the arch ADK , and without the angle of the semi circle KAD : and that the right-line ADEC passeth from the angular point A within the arch ADK , and within the angle of the semi circle K AD. And this is all which is intended in Geometry when recto-convexe and such like angles of contact are said to be less then the least right-lined angle : not that there is any proportion between any angles of contact and right-lined angles ; for there is none : but that the sides of any such angle of contact are coaptable , both of them within any the least right-lined angle . In like manner when one angle of contact is said to be greater or lesser then another ; it is not the intendment of the Geometrician to assert any proportionablenes between them , but only to set down in what order the inclined lines pass , each in respect of the rest , from the angular point , or point of concurrence : and how each is conseque●●ly more , or less inclined in that respect , to any one of the rest , though by the whole kind and without proportion , and without a common way of measuring their quantities in some indefinite quantity , according to the kind of the measuring , indefinite quantity ▪ the semblablenes of saying , one angle of contact is greater , or less then another being only in this , that when one side is coapted , the other falls within , or without ; or when neither sides can possibly be coapted , both fall within , or both fall without , so as the one is really greater , or less then the other , not in proportion , but by the whole kind and heterogeneally , as a two foot right-line is lesser then a four foot square , and a two foot right-line cannot be contained in an inch square , though in an inch square may be drawn a line ten thousand times longer , only out of rectitude . And to prove such an heterogeneal inequality , whether of the greater , or of the less between angles , is that which is frequently sufficient for many Geometrical purposes . Only two things now remain of all your objections and scrupulous quaeries . Viz. First , why in some quantities , between the homogeneals , to a given quantity you cannot give another in what proportion you please greater or less , The answer is clear out of the foregoing discourse : because some quantities have but a limited extensibility : and other quantities have but a limited divisibility . All proportions at pleasure with respect to any given quantity , are only assigneable in those homogeneals whose quantityes have both an unlimited extensibility and an unlimited divisibility ; either of which failing , though they cannot be , save in a limited proportion one to another , and to every given homogeneal , yet they cannot be in any proportion , at pleasure , to any given homogeneal . And 2ly . for your other Quaery ; whether this controversy about the recto-convexe angle of contact concern abstract Mathematicks , whose glory used to be that it was devoid of Controversy , locking forth and keeping out all unpeaceful bickerings with the diamond-key of doubtless demonstration ; or whether it concern concrete Mathematicks , which for its concretion unto matter cannot so well free its self from the intanglements of doubts and disputes ? and if it concern the more abstract part of the Mathematicks ; what was the first slip that drew so unworthy a disparagement upon that most noble piece of learning ? In the preceding discourse you may observe , I have been free and clear in my judgement concerning this ; that it is a controversy of the purer and more noble part of the Mathematicks : and therefore of the higher concern , that it be brought to a fair decision and irrefragable diremption : and that the first spark from whence all this heat afterward arose , was at first struck out of the dubiousnes and aequivocation of the word homogeneity , mentioned in certain Mathematical definitions and Postulates ; but of it self no where expressely defined in the Mathematicks ; except we shall take one of the Pustulates , for its definition cast into the form of a Postulate ; or as cryptically implying that definition and the postulate to be thereupon immediately formed : especially when they compared homogeneity in a mistaken sense , with some mathematical conclusions , which they had observed to be fairly demonstrated . Pardon this my zeal on the behalf of the old learned Romane professour . And if these papers seem long , remember yours were not short ; and the question hath long troubled the world : and in matters that are new , and scarce yet well understood , to inculcate once and again the same things , is not only justify'd as allowable , but judged expedient and in such cases necessary . If you please , let the whole passe for a fuse Comment upon this ; that in recto-convexe angles of contact is the inclination required for an angle by the definition of an angle ; and therefore they are angles and their sides not coincident : and they are angular parts of acknowledged angles separable from the remaining angular parts ; and there is an infinite divisibility in them , so as they must be quantitative : and yet it is demonstrated that they are improportionable to all right-lined angles ; therefore they are heterogeneal : which inference is the more necessary , when upon examination we find nothing so convenably to set forth unto us the nature of mathematical homogeneity , as the homometricalnes and the thence arising proportionablenes of the magnitudes , and of mathematical heterogeneity as their heterometricalnes and improportionablenes .