An Appendix, Written by Way of Letter to the Publisher; Being an Answer to SomeObjections, Made by Several Persons, to the Precedent DiscourseSource: Philosophical Transactions (1665-1678), Vol. 1 (1665 - 1666), pp. 281-289Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/101508 .

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(' 8i) For wh'ich, thi's conrideration of the Common Center of Grav'ity

of the Earth and Moon , -is fo proper a rep5edy ( efpecially if it fhall be founid precifely to anfwer thiofe Phicnomena , which I have not Excami'ned, but am very apt to believe) that it is fo far from being, wilth me, ani Obje6tion againft it, that it is one of the reafons,which triake mue inclintable to introduce it.

1 muLft before I leave this, add one Confideratioii jnorc,0 That If we fhi ll uponi thecfe Conlfiderationis thinik it reafoniable, thius to coinfider thle commnon Center ofrGravity of the Earth and kfoon; it may as well be thloughlt reafoniable, that thec like Con'- fide ration ihould be hiad of 'upiter anid hiis four &atd1lztei,which accordinigto the Complicatioti of their feveral motiotns, will fomewhar chanige the pofition of Iupiter)2S to thlat. Common cen- ter of Gravity of all the fe Bodies; whichi yet, becauf7c of 'their fmallnefs, may chianice to be fo little., as thiat, at this diftanice, the chanige of .this apparenit place may not be difcernable. And what is laid of yupiter, is in the l;ke maln rer to be uinderftood of Saturne anid his Sate//er, difcovcred by Hagei : o0 l thefe Sate/liter are to their Principals, as fo maany Moonis to the Earthi. Anld I do very well rememiber, in the Lette'rs forecited, Mr. Horroc&kr expreffetlh fome fuchi little 'inequalities inl &aturne: mnotion, of which he could not imagine whiat gccounit to gives as if (to ufe his Expreffioni) thl's crabbed old Saiturn had defpi- fed his et.2 W,hich, for oughit I know , mighit well enioughi- have been accounted for.) if at that time the satelles of Saturn had been d ifcovered, and that M r.H-orroc4f had thloughit of Lizch a m4otion as the Common Center of Gravity of saturn anld his Compa. niSf:,to be confiderable,as to the guiiding of his motion.

You hiave now, in obedienice to your Commands, ani Ac. count of my thoughts, as to this matter, though yet immature and unpolifhied: -.What ufe you will pleafe to make of them) I [hall leave to- your prudenrce,&c.

A4n A P) P E N D I X, rwritten by wa,yof Letter to the Publiflier; Being an Aniwer to fome Objtflie 'W. made byjiever4l Perfonr., to the preedent Di/eourfe.

IReceived yours ; and am very wepll contented, that objeFli- ons bemade gaini fmyypotbelis concerining Tyd: en

Pp 2 pro.

(' 8i) For wh'ich, thi's conrideration of the Common Center of Grav'ity

of the Earth and Moon , -is fo proper a rep5edy ( efpecially if it fhall be founid precifely to anfwer thiofe Phicnomena , which I have not Excami'ned, but am very apt to believe) that it is fo far from being, wilth me, ani Obje6tion againft it, that it is one of the reafons,which triake mue inclintable to introduce it.

1 muLft before I leave this, add one Confideratioii jnorc,0 That If we fhi ll uponi thecfe Conlfiderationis thinik it reafoniable, thius to coinfider thle commnon Center ofrGravity of the Earth and kfoon; it may as well be thloughlt reafoniable, that thec like Con'- fide ration ihould be hiad of 'upiter anid hiis four &atd1lztei,which accordinigto the Complicatioti of their feveral motiotns, will fomewhar chanige the pofition of Iupiter)2S to thlat. Common cen- ter of Gravity of all the fe Bodies; whichi yet, becauf7c of 'their fmallnefs, may chianice to be fo little., as thiat, at this diftanice, the chanige of .this apparenit place may not be difcernable. And what is laid of yupiter, is in the l;ke maln rer to be uinderftood of Saturne anid his Sate//er, difcovcred by Hagei : o0 l thefe Sate/liter are to their Principals, as fo maany Moonis to the Earthi. Anld I do very well rememiber, in the Lette'rs forecited, Mr. Horroc&kr expreffetlh fome fuchi little 'inequalities inl &aturne: mnotion, of which he could not imagine whiat gccounit to gives as if (to ufe his Expreffioni) thl's crabbed old Saiturn had defpi- fed his et.2 W,hich, for oughit I know , mighit well enioughi- have been accounted for.) if at that time the satelles of Saturn had been d ifcovered, and that M r.H-orroc4f had thloughit of Lizch a m4otion as the Common Center of Gravity of saturn anld his Compa. niSf:,to be confiderable,as to the guiiding of his motion.

You hiave now, in obedienice to your Commands, ani Ac. count of my thoughts, as to this matter, though yet immature and unpolifhied: -.What ufe you will pleafe to make of them) I [hall leave to- your prudenrce,&c.

A4n A P) P E N D I X, rwritten by wa,yof Letter to the Publiflier; Being an Aniwer to fome Objtflie 'W. made byjiever4l Perfonr., to the preedent Di/eourfe.

IReceived yours ; and am very wepll contented, that objeFli- ons bemade gaini fmyypotbelis concerining Tyd: en

Pp 2 pro.

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propofed' but- as a conje&ture to be examitledT 1; and, uponi th-at: Examin'ation, re&bfied,~ if there be occafion;. or r-ejedec&, if A.;. will not hold water..

x.To the firft.. objedbion-of thofe you-mentioon; Th at it dp. pearf not bow two Bodies, that have,P no tye, ca-n hbave. one common Cem. ter of Grav-ity: that is (for fo I anderftand the initendment of t-he objeation ) can a2t or be a6bed inYthe. famne manner, as i-f they weie c onne6ted-: I .ihali onely anfverl, lhat it is-harder o fhiew Hlow they have, than That they h3ave it. That the Load- ilone and Iron have fomewliat equivralent to a Tye; though we fee i't iot., yet by the effe6ts we know. And it would be eafy to fhew,that two Load- ftones,at once applyed,in differentt pofitions, to the fame Needle, at fomie conivenient diffance ; willI draw. irj,,not to point direa-ly:, to.either of theti, but to fome poinit betwe-en both;~ which 'poi-nt is, as to thofec two, the c-orn man. Center of AtiuraR~zon; and it is-the fam-e,as if fome one Load- fbone were in that po'int. Yet hiave thefe two Load. itones no connexion or tye, though- a common 'Center of V-irtue accord- in-g to which thney joyntly, a6tb. And- as to the prefent cafe, Howr the Earth-and Moon are conne6ted; I wi'll'not now un. der'take to fhew- ( nor, is. it- neceffary to my purpofe ;..) but, That there is fomew hat, that. doth connca tthem, (as much as what

conn6ts he Lad.fone,and-the Ironi, whi'ch it-draws,,) is p2 fk doubt to thofe, wh~o allow them, to be carryed about by the Sun, as one Aggyregzate or Body, whofe part's keep a refpe2iva pofit ion to one anouther: Like as7fit"er with.hisfioar Satellites., a.nd -Satw~n.withbhis one. Some, Tye therei~s)that m2kes th'ofe Satellitesrattend their Lords, anidmove in aBody; though we do not S*e t-hat- Ty-e, nor Hear the,Words- of Command,. And lo here.

.2. ',TO the fecond obje&ion;i That,- at. Chat4 am and It's thiA Tb4mes, tkt Ammnal Spring.-tyder,iapen about the .Xquirnexes;J- not (ai thA~, Hypothelri dotk~fiippo/e el/wer to have been obferved )-about

tk~ be,gini`g !ofFebruary andNovember..- If their m'eaningr be,that Annual High Ty-des,- d-o then happen, and then onely.: If this prove true, it- will cafe me of half my work. For it i-s then eafi-~ ly anfwered, that it depends upon the o)b1iqntityoftI.e Zvdiack~; th'e parts of the Mquino061ai anfwe ri-ng to equal parts of the

Zdiack,

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(283) ,odiack, being neer the Solftitial points greateft, and near the

Aquinodtial points leaft of all. But befide this annual Vicfi- tude of the Equinoxes,not to fay, of the 4. Cardinal Points ( which my-Hypothefis doth allow and afert; ) I believe it will be found,. that there is anather Annual vicijffjtde anfwering to the Suns A,ogtcum and Perigceum. And that the greateft Tydes ofall,wil! be found to be upon a refult of thefetwo caufes Co. operating: which(as doth the Inequality of Natural dayes, de- pendirg on thefe fame caufes ) will light nearer the times, I mention. To what is faid to be obfervedat Chatham and in the Thames, contrary to that I allege as obferved in Ilumrney marb : 1 muft at prefent i^twv, and refer to a melias. inquirendMm. If thofe who objed this contrary obfervation, fhall, after this no- tice, find; upon new Obfervations heedfully taken, that the Spring-tydes in February and November, are not fo high, as thofa in March and September; I fhall then think the objection very confiderable. But It do very well remember, that I have feen in Nevember, very high Tydes. at London, as well as in Futmney MaarfJ. And, the time is not yet to far paft, but that itmay be remembered ( by your felf or others then in London) whether in November laft when the Tydes were fo high at Dover, at Deal, at Margate, and all along the Coaff from thence to- Fumney Marlh, as to do in Tome of thofe places much hurt, (and,ini Ho- land, much more ;) whether, I'fay, there were not alfo at the fame time, at London ( upon the Thames ) very high Tydes, But a good Diary ofthe Height and time both of High-water; and Low-water,. for a year or two together, even at Chatham, or Greenwich; but rather at fome place in the openSea, or at t.e Lands end in Cornwral, or on the Weft part s f Irtland ,;or at St. Hellene or the Bermodas,, &c. woild do.moreto the refolving of this ptint than any verbal difcourfe without it.

3. To the third QbjeCtion, Thbt fuppofng'izh Earth and rMon to move about a Common center of gravity ; if that the highbet TdeJ be at the New-moon,when the moon beinxg marefi to the Sun,the Earth is farthef frf omit, and itcompound'motion.at t/frifteft; and thatt the Tydes abate as the Earth approachetb nearer; till it ctos into the, fnptofed Circle ef her Annual mltion: It mat e demanded, whSd they not flill abate as the Earthb comef yet a marrt rt t nt ai.ndte.

Irvf j^e

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(Z84) /wfte~ of its compound motionfJlillfiackem ? And fio, wrhv hav~e wve

not -Spring tide at the New~ Moon (whpenj the motion is fwiftejl ) and Neap.tidesf at Full Mloo* (whpen the motioan is floroeji ) but Spring tides at both ? The- anfwer ( if obferved ) is already given Iif my Hy. pothejFs it. feif.. Becaufe the effeaf is indiff:rently to follow, ei- thier uipon-a fu-ddaini Accel'eration , or a f-uddain Retardation. (.Li-ke as a loofe thing, lyi'ng on a movinig body j if the body be thruft fuddainly forward, that loofe thing is caft back, or ra- thier left behind, not having yet obtainied an equal i'mpetu with that of the body onwhich it lyes; but if froppe d., or notably rntarded, that loofe incumbent is thrown forward, by its for. rm-erly contra6fted impetufc not yet qualified or accomnodate-d to the Ilownefs of the- Body, on which. it lyes. ) Now both of thefe happeninag, thec,one 4f the -Ne-_w M-oon, the other at the Full Moon, do caufe h~iggh Tides at both.

4. To the fourth Obje6bion, That the b(gheft Tydes are not at 411/lacesr, about the New Moon and Fu47 Mooin - and particularly, thbat, in /vime places of .the Eafi Indies., the Hivhe,/I Tydes a re at thet QOaqdraturex: I muift firft atofwer i'n g'en,eral '~ That as to the p ar- ticular varieties .of Tydes in feveral parts of the Worldj, I can- tnot pretend to give a fatisfa6ftory account., for want of a coin- petent Hiftory of Tydes, C&c. Becau-fe ( as is inti mated,in what I wrote in the general) the various pofitions of Chanels, Bays, Promontories, Gulfs, Sh.allows, Currents, Trade-winids, &-c. muft needs make an innumearable variety of Accidents in par-* ticular places, of which no fatisfa&or~ account is to be given f rom the! general Hypotheftr ( though never fo true.) without a -due confideration o-f all tho fe. Which is a task too great for me to undertake, 'being fo ill furniflibed with materials for it. And then as to the particular inftance of fome places in the- Eaft Indies, wher'e th'e higheft Tydes are at the. Q~,adratxres: fuppofe, it may be chiefly intended of thofe about Cambai'a and Pe,gu. At which' places, befide that they are, fi'tuate at the inmoft parts of Vait Bayes). or Gulfs. (as. they are c-alled)

the hae afo ailIn'raghts of fome hundred miles within Land;- which wheni the Tydes are o'ut, dolye (in a manner) quite dry:- And mlay therefore very well be fuppofed 'to parti. cipate the effe&l of the Menftrual Tydes many dayes after the

cauf&

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(295) catire of them happens i'n the open Sea, upon a i'ke ground as in Straigzhts and niarrow Channiels the Diurnall Tydes happeni fomechour,slaterEthan in the Ocean., And alike-accouncumuft be given of particular accidents in other places, from the par. ticular fituation of thofe places, as Baysr, Chanels, Currents,&c.

y.To the 5. Obje6tion, That the Spring-Tydes happen not, witb us, jufi at the Fullan Change u or three daers after. I (hould with the more con'fidence attempt an Anfwer, were I 'certain , whether it b'e fo in the peSasoroly in our Channels.For the Anfwers will not. be the fame in both cafes. If onely 'in our Channels,where the Tydes find a large in.-draughr; but not in the Op)en Se;as: we muff feek the reatbn of it from th-e-particular pofition of thefe placesk. But if it -be fo gene- r-alliy in the wide Open Seas: We muift theiir feek:a reafoll Of 'it from the general Hypothefis. IAnd, till 1 know:t'he matter of F-aa, I kniow not well, whichi to offer at;- left whilft I1 attempt to falve onejI fhiould fall foul-of the other. I kniow that Mar- riners ufe to fpeak of Spri'nogTydes at the New and. Full of -the Moon;J- though I have H[llhad a fufpition that it mighlt be fome dkies after, a s w ell in.the -open Seas,- as in our n'arrower Chan- nels;,V (anid therefore I h-ave chofen to fay, i'n nmy Papers, A4bout the New anid Full, rather than At the New and Full; aind even when I do fay At, I inten'd it in that laxer fenfe in which 1 fup. pofe the Mlarrjiners are to be underfto'od ; for Neer that time: Of which fufpi'ti'on you -wi'll find fome intimati6ns even in my firft Papers:.9 But this though I can-admit; yet,becaufe I was not fure of it, I durft not builc upon it. .1The truth is, 'the Flux and Rteflux of water i'n a vefTel by reafoni of the joggiing of it;though it-follow thereupon Yet is,for the-moft part difcerinable f ome tim after. For thr muff, upon that jog,be fome time for Motion, before the Accumul 'tion can have made a Tyde. And ft, I do not know but that we muff allow it i'n all the Periods;For

as theme~~jrual High Tyde,ino (at leaft with 'us) ilfm Dai'es- after the F4ull and Changes -Co is the Diurnal High water., about-as many Hours after th6 Moons commi'ng -to South; 1 mean,At Sea.. for in Chanels-i't varies to all Hours,according as they are neerer orfurther-from theopen Sea:) And the Ann'u'al Iiigh-Tydes- of November and Februa'ry;- fomaewhat -later Than

(what

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(2S6) (what -I conj'e&ure to be from the fame caufes) t'he greateft In-w equalities of the natural Days, happe'ni'ng in January and Ode10 tier. But this though I can admir,yet i(ti'll I am l'ure of the mat- ter of Fad) I domiot build upon. And fince.it hath hitherto bteen the -cuftome to fpeak with that Jaxnefs of expreflion;- ~Af- -figniuig the times of -New-moon, Full.mooD and Quadratures, with the Moons comming to South, for', what is iieer th'ofe times:- I did not think my felf obliged in my coiijedural Hy. pothefis-(while itt i's yet but a Candidate ) to fpeak more niicely. tIf thet. Hypothefis for the mainie of it be -found Rational~ t he N icte of -it are to be adjufted, in time, from particular Ob- fervation.

Having thus gi'ven you fome Aufwers to the Obje%dtons you~ fignifie to hate been mad e by feveral perfons to myHypothefis, and that in the fame o'rder your Plaper prefents them to mn-.: I fhall nextt gi've you fomae account of the two Book-r, whiclh yoP advifed mrfe to confult j fo far as feems necefTary to this bufi- nefs :Whicb,upon your intimati'oDI have fince perufed,though be'fore I hiad not.

And firft,as to-that of Ifaac Yo.Ffutr, De motu Marium &J en :err~m;?iThough. I do nor concur with him in hi's Hyp'othefis; That all the Great motions of the Seas,&c. fbiould arife onely from/fa fImalla warmi'ng of the water as to raife it.(where moft of' all) net a Foot in perpendicular, (as in his i 2th Chapter;) Or th:It there is no other connexion betw'eeni the Moons motion, and the Tydes menfmirl period, than a cafiial Syncbronzfm (which feems -to be the do6trine of his ir6th and 18ehb Chapters5) Befide ma- nly other tbir~gs in his Philofoplhy, which I cannot allow .: Yet I am wellI enough pleafed with what is Hiftorical in it,' of the matter of Fadt- Efpecially if I may be fecu're,that he is therein accurate and candid, not wrefting the PbxenoMnena to -his own purpofe. But I fitid nothing in it,which doth induce mc to vary fom my.H iyothtfis. For, granting his Hi ftoricals to be all

frue;- the- account of the con ftant Current of the Sea Weft- ward, and of che conftan t -Eaftern Blafts., &c. within the Tra.

pic, is much more plaufibly , and (I fuppofe) truly tendered by Galilxo oloig fvrice, from theE~arrh-sDiuernal motion: (wh'ichi, neare the 1Eiuator. defcribing a greater Circle, thani necar'er the

Polef,

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@287) Polef, miakes the. C"urrenit to be there more coiufpicuous and fwift, and, confequently, the Eddy, or recurrent moti'on,nne7ar.- er the Poles,where this is,mnore remifs:) than cani eafily be ren- dered by fo fmnall a Tumor,. as hie f uppof'eth. Not to adde i that his account of the Progreffive motioon,which he fanifieth to fol- low upon 'this Ttimnefadion, and by Acceleration~ to grow to fo great a height near the Shoar ( as in Chiap. 13. and '4 )i a Notion,which feemis to mie too extravaga.nt to be falved by a- niy laws of Statickf . And that of the Moons motion oniely Syni- chronizing with the Tydes, cafually, withiout any Pb.yfca(con- liexion; cani very hiardly afen't to. For it can hardly be imagined, that aniy fLichi conftanlt Synch)roui/iine fiould be in

Nature bu hr,either the one is the caufe of the other,,o both depenid upon fomcComimon caufe.And where we fee fo fair a foundationi for a PI;y/ical conne6tion. I am nlot prone to a- fcribe it to an Inidepeindent Synichro'nifin. In fum ; His Hliftory doth well enoughi agree with mny Hypothefis; and I think) the. Phxnomena are miuchi better falved by mine, than his.

And then as to Gafenduf,in hit difcouirfe De' --flu Mfarif;I finid himi, af ter the relatinig of many other Opinions concerning, the Cauife ofir,incliningo that of.Ga1ihro, fcribing it to thece~ ration & Retardation of th,e- Ea,,r1ths motion.compounded of the Annual and Diurnal;- And moreover attem ptinlg to give an ac- counit of the Alfen /rual Periods- from the Earthis carrying the Mooni abouIt it felf,as-yupiter doth hiis SateAi'ites; whiich togethler with them is carryed about by the Sunm, as one Aggregate;- (and that the Earth with ifs Moon is to be fuppofed in like manticr to be carried about by thie Sur,, as one Aggregate,1 caninot be rea- fo-inably dloubted, by tlhofe who entcertain the Copernican ffy)po- thelt?s, anid do allow thc faml'e of 7uP'iter anid hlis Satellites.) Buit though he would hthus have- the EP,arth anid Moor' looke-d uponi as two parts ofrlie fan'ie nmcwed A ggregate, yet he doth ftill fup- pofe ( as Gatileo hlad done before% him) that thie line of the Mean Motion of this Ag!gregate (or, as he calls, motust iequabi. Eri et veluti medius) is deftcribed by the Ctnterof thle Earth (about which Center he fuippofeth bothl its own revolutioni to be made, and an Epicy'cle defcribeod by the-Moon's motioii ;) not by ano- ther Point,diftin,ft from theCenters of both,about which,as thec

Q_ q common

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(2S8) c:ommon Ceniter of Gravity, as well that of the Earthi, as that of thie Meoon, are to defcribe feveral Epicycles. And, for that Reafon fails of givinig arty clear account of this menjirual Pe- riod. (And in like maniner, he propofeth the CoDfiderati'on as well of the Ea rt hs Apbeliwnu anid Perihelium, as of the £1uainc fi`b al anid Soyifltl Poinits, in order to the fin'dinlg a Reafoni of the A4nnual Viciflicudes; bLut doth nlotLfix upon any thinglf, inj whichi hiimr['elf can Acquiefce:. Anid the-refore leaves it i'n med'o as he founid it. )

It hiad been more, agreeable to th Lasof Statickr, ifh hia d, ( as I do,) fo con fidered the Earth and Mlioon as two parts of the fame movable, ( not. fo., as hie dothi, aliam rniCenitro etf/~ quienternprsvcife revolution~em axif, aliam remnotiufti-ac ve/ut ini cir6-um-

ferentia, buti,) fo, ais to mnake neither of them the Ceniter, but horth ouit of it', defcribinig- Epicycles about it: Like as, whlen a longr flick throw:11 Inl the Air, wholFe one end is lheavycr thani thec ot.her, is whiirled abouti, fo as that the End', whitch did firft fly foremoft , b~ecomes hili-ndoft ; the_ proper line of motioni of thlis whole Body is not that, whicha is deflcribed by eithe,r End', buti that, which is defcribed by a middle point between thiem;i about which poinit eachi end, in whirl'ing,defcribes an Epicycle And i'ndeed, in the prefent cafe, it is not the Epicycle defcribed by ithe Mooni, b-'ic that, defcribed by the Earthi, which gives thec M~fenfriral Viciffitud%es of motion to zhe Water;j wh'ich wouild, as to this,be the fame, i'f the Earthi [6 move, whether there wele any Moon t-o move or nolt ; nior would the Moonis Mlotioni, fup. pofmrg the Earthi t o hiold on it- owni courfe', any wh'it concern thle mo.1tion of the Water.

Bu1i [ti ow,(after all ouir Phyfical,or S*~tatical Confiderations)the cleare-ft Evidence for this Hypotheris (if it cani be had) will be from Celeftial Obfervatoions. As fior inftanice; (fee Fia75)Sp poling the Stin at 5; the E-1arthls pla-ce in its Ainnual Orb 'at T;- anid Marf (in oppoficioni to thie Sun,or near it) at MI: From whenice Marsf[hould appear in thle Zodiack at ~e and wi'll at Full mnoon- be feen there to be; the Moon, being at C and the Earth at c:- (and the like at the New-moorn) Butt if the Moon be in the' £lirftquiarterat A,and the Eauh aca;lr Marf will befken, notar

~,but at a; too flow:- A nd when the MAoon is atrE; anid thie Earth at b .bAfar-f will be- fcen at 9; ye-~o fow: till atthe Full,.

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(2 89) moon, the Moon at C, the Earth at c, MAors wii [be feen at a ,

its true place,as if the Earth were at T. But then,after the Fullt the Moon at D,the Earth ac d ; Matrs will be ccen, not at y, but ar'; too forward: and yet more, when the Moon (at the laft Q.arter ) is at E, the Earth at e, and Mars feen at I. If there- fore Mart (when in oppolition to the Sun) be found (all other allowances being made ) iomewhat too backward before the Full moon, and fomewhat coo forward after the Full-moon, (and moft of all,at the Quadratures: ) it will be the beft con- firmation of the Hypothelis. (The like may be fitted to Mars in other pofitions, mutatis mutandis j and fo for the other Pla- nets.)

But this proof, is of like nature as that of the Parallaxis of the Earths Annual Orb to prove the Copernican Hypothefis. If it can be obferved, it proves the Affirmative but ifit canlnoc be obferved,it doth not convince the Negative,but only proves that the Semidtameter of the Earths Epicycle is fo fmall as noc to make any difcernable Parallax. And indeed, I doubt, that will be the ifiue. For the Semidiameter of this Epicycle,being little more than the Semidiameter of tlhe Earth it felf, or about lj thereof (as is conjectured, in the Hypothe,s , from the Mag- nitudes and Diftances of the Earth and Moon compared;) aud there having not as yet been obferved any difcernable Parallax ofT3Aart i even in his neereft poficion to the Earth; it is very fulfpicious, that here it may prove fo too. And whether any of the other Planets will be more favourable in this point,l can- not fay.

ANIMA D VE kSI10 NS Of Dr. Wallis, upon Mr. Hobs's late Book, De Prinicipiis &

Ratiocinatione Geometrarum, Thefe were communicated by way of Lecter,written in Ox-

ford, July 24. x666. to an Acquaintance of the Author, as fol- lows : Since I law you laft, have read over Mr. Hob's Book Contra JGeometras(or De Princi'tj & Jtiocisnatione Geometraruamnwhich

you then {hewed me. A NAer Book of Oldmaster: Containing but a Repetiion of what he had before told us,more than once; and which hath been Anfwered lotng agoe.

In which, though there be Faults enough to offer ample mat- Q.q tcr

(2 89) moon, the Moon at C, the Earth at c, MAors wii [be feen at a ,

its true place,as if the Earth were at T. But then,after the Fullt the Moon at D,the Earth ac d ; Matrs will be ccen, not at y, but ar'; too forward: and yet more, when the Moon (at the laft Q.arter ) is at E, the Earth at e, and Mars feen at I. If there- fore Mart (when in oppolition to the Sun) be found (all other allowances being made ) iomewhat too backward before the Full moon, and fomewhat coo forward after the Full-moon, (and moft of all,at the Quadratures: ) it will be the beft con- firmation of the Hypothelis. (The like may be fitted to Mars in other pofitions, mutatis mutandis j and fo for the other Pla- nets.)

But this proof, is of like nature as that of the Parallaxis of the Earths Annual Orb to prove the Copernican Hypothefis. If it can be obferved, it proves the Affirmative but ifit canlnoc be obferved,it doth not convince the Negative,but only proves that the Semidtameter of the Earths Epicycle is fo fmall as noc to make any difcernable Parallax. And indeed, I doubt, that will be the ifiue. For the Semidiameter of this Epicycle,being little more than the Semidiameter of tlhe Earth it felf, or about lj thereof (as is conjectured, in the Hypothe,s , from the Mag- nitudes and Diftances of the Earth and Moon compared;) aud there having not as yet been obferved any difcernable Parallax ofT3Aart i even in his neereft poficion to the Earth; it is very fulfpicious, that here it may prove fo too. And whether any of the other Planets will be more favourable in this point,l can- not fay.

ANIMA D VE kSI10 NS Of Dr. Wallis, upon Mr. Hobs's late Book, De Prinicipiis &

Ratiocinatione Geometrarum, Thefe were communicated by way of Lecter,written in Ox-

ford, July 24. x666. to an Acquaintance of the Author, as fol- lows : Since I law you laft, have read over Mr. Hob's Book Contra JGeometras(or De Princi'tj & Jtiocisnatione Geometraruamnwhich

you then {hewed me. A NAer Book of Oldmaster: Containing but a Repetiion of what he had before told us,more than once; and which hath been Anfwered lotng agoe.

In which, though there be Faults enough to offer ample mat- Q.q tcr

This content downloaded from 195.78.108.141 on Wed, 14 May 2014 06:38:34 AMAll use subject to JSTOR Terms and Conditions