et y formeront le globe terrestre s'il y en a assez pour cela, supposé que la terre ne fut pas encore. C'est donc en cela que consiste vraisemblablement la pesanteur des corps: laquelle on peut dire, que c'est l'effort que fait la matière fluide, qui tourne circulairement autour du centre de la terre en tous sens, à s'éloigner de ce centre, et à pousser en sa place les corps qui ne suivent pas ce mouvement.

P. 159. J'ai supposé.. que la pesanteur est la même au dedans de la Terre qu'à sa surface, ce qui me paroit fort vraisemblable. . .

Monsieur Newton. . trouve ... que la figure de la terre diffère bien plus de la sphérique, . . . . . aussi bien je ne suis pas d'accord d'un principe qu'il suppose dans ce calcul et ailleurs, qui est, que toutes les petites parties, qu'on peut imaginer dans deux ou plusieurs différens corps s'attirent ou tendent à s'approcher mutuellement. Ce que je ne sçaurois admettre, parceque je crois voir clairement, que la cause d'une telle attraction n'est point explicable par aucun principe de mécanique, ni des règles du mouvement. Comme je ne suis pas persuadé non plus de la nécessité de l'attraction mutuelle des corps entiers; ayant fait voir que, quand il n'y auroit point de terre, les corps ne laisseroient pas, par ce qu'on appelle leur pesanteur, de tendre vers un centre.

No. XIX.

FIRST COMMUNICATION OF THE PRINCIPIA TO THE ROYAL SOCIETY P.

1.

Newtonus principales de motu planetarum proposi

P From an original paper of Newton, belonging to the Earl of Macclesfield.

tiones anno 1683 Londinum misit cum philosophis communicandas. Anno 1686 Principia Mathematica ad Regiam Societatem misit ut in lucem emitteretur; et liber anno proximo prodiit, et epitome ejus anno sequente 1688 in Actis Lipsiensibus impressa est, et anno tandem 1689 Leibnitius selecta Newtoni inventa de lineis opticis, de resistentia mediorum, deque motibus planetarum novis verbis et novis calculis differentialibus ornavit, et pro suis in lucem statim emitti curavit, affirmans quod librum Newtoni nondum viderat. Qua licentia concessa, author omnis inventis suis facile privari possit. Sic et inventa Moutoni sibi asserere conatus est, quia hæc invenerat priusquam Moutoni librum viderat. Sed Newtoni librum prius consulere debuisset quam scripta sua de iisdem ederet, idque ne et Newtono injurius esset auferendo inventa ejus, et lectori molestus repetendo quæ Newtonus antea dixerat. Dum tantopere festinaret scripta sua edere non veritati consuluit, non scientiis, non lectoribus, sed sibi soli. Inventa Newtoni sibi arrogare festinabat. Et ex erroribus ejus manifestum est, insuper, quod methodum fluxionum in fluxionibus secundis nondum probe intellexerat. Calculum illum in fluxionibus primis jam ab anno 1677 exercuerat. Inventis Newtoni jam anno 1688 et 1681 excitatus est, ut methodum eandem in fluxionibus secundis exerceret, sed primo conamine multipliciter erravit, et erroribus patefecit se nec propositiones Newtonianas invenisse, nec methodum qua Newtonus easdem invenerat.

2.

Anno 1684 Newtonus propositiones principales earum, quæ in Philosophiæ Principiis Mathematicis habentur, cum Societate Regia communicare cœpit, annoque 1686 liber ille MS. ad Societatem Regiam missus

est. . . . . . Proximo anno prodiit liber Newtoni, et anno sequente epitome ejus in Actis Lipsiensibus impressa est. Qua lecta, D. Leibnitius epistolam de lineis opticis, schediasma de resistentia medii et motu projectorum gravium in medio resistente, et tentamen de motuum cœlestium causis composuit et in Actis Lipsiensibus anni 1689 imprimi curavit, prætendens, quod ipse quoque præcipuas Newtoni his de rebus propositiones invenisset, et quod librum Newtoni nondum vidisset. Qua licentia concessa, autores quilibet inventis suis facile privari possunt. Quamprimum liber Newtoni lucem vidit, exemplar ejus Domino Fatio datum est ut ad Leibnitium mitteretur. Viderat Leibnitius epitomen ejus in Actis Leipsicis. Per commercium epistolicum, quod cum viris doctis habebat, cognoscere posset propositiones cujuscunque generis in libro illo descriptas. In scriptis illis nihil invenit novi. Newtoniana tantum descripsit suo more ac describendo nonnunquam. . . .

No. XX.

EXTRACT FROM NEWTON'S HYPOTHESIS OF LIGHT".

That there is an ethereal medium, much of the same constitution with air, but far rarer, subtiler, and more strongly elastic.... Perhaps the whole frame of nature may be nothing but various contextures of some certain ethereal spirits or vapours, condensed as it were by precipitation, much after the manner that vapours are condensed into water, or exhalations into

n From Birch's Hist. of Royal Soc. vol. iii. p. 249–251.

grosser substances, though not so easily condensible...

The elastic effluvia seem to instruct us that there is something, of an ethereal nature, condensed in bodies. I have sometimes laid upon a table a round piece of glass, about two inches broad, set in a brass ring, so that the glass might be about one eighth or one sixth of an inch from the table, and the air between them being inclosed on all sides by the ring; then rubbing a pretty while the glass briskly with some rough and raking stuff, till some very little fragments of very thin paper, laid on the table under the glass, began to be attracted and move nimbly to and fro; after I had done rubbing the glass, the papers would continue a pretty while in various motions. . . . Now, whence all these irregular motions should spring, I cannot imagine, unless from some kind of subtile matter, lying condensed in the glass, and rarefied by rubbing as water is rarefied into vapour by heat, and in that rarefaction diffused through the space round the glass to a great distance, and made to move and circulate variously, and accordingly to actuate the papers, till it return into the glass again and be recondensed there. And . . . so may the gravitating attraction of the earth be caused by the continual condensation of some other such like ethereal spirit, not of the main body of phlegmatic ether, but of something very thinly and subtilely diffused through it, perhaps of an unctuous or gummy, tenacious, and springy nature, and bearing much of the same relation to ether, which the vital aereal spirit, requisite for the conservation of flame and vital motions, does to air. For, if such an ethereal spirit may be condensed in fermenting or burning bodies, or otherwise coagulated in the pores of the earth and water, into some kind of humid active matter, for the continual uses of nature, adhering

to the sides of those pores, after the manner that vapours condense on the sides of a vessel; the vast body of the earth, which may be every where to the very centre in perpetual working, may continually condense so much of this spirit, as to cause it from above to descend with great celerity for a supply; in which descent it may bear down with it the bodies it pervades, with force proportional to the superficies of all their parts it acts upon; nature making a circulation by the slow ascent of as much matter out of the bowels of the earth in an aereal form, which for a time constitutes the atmosphere; but being continually buoyed up by a new air, exhalations and vapours rising underneath, at length, (some part of the vapours which return in rain excepted,) vanishes again into the ethereal spaces, and there perhaps in time relents, and is attenuated into its first principle: for nature is a perpetual worker, generating fluids out of solids, and solids out of fluids, fixed things out of volatile, and volatile out of fixed, subtile out of gross, and gross out of subtile; some things to ascend, and make the upper terrestrial juices, rivers, and atmosphere; and by consequence others to descend for a requital to the former.

The passage then immediately follows, which is quoted by Newton in App. VI. p. 33, 4.

No. XXI.

HALLEY'S REVIEW OF THE PRINCIPIA°.

Philosophie Naturalis Principia Mathematica, autore Is. Newton Trin. Coll. Cantab. Soc. Matheo From the Phil. Trans. vol. xvi. p. 291.