Mr Newton’s letter upon <s>the<\s> his receipt of Mons<sup>r<\sup> Huyens’s Book de Motu Pendulorum together with <s>his<\s> some considerations upon it; as also an Answer to the same M. Huyens’s letter of june 10.1673; In w<sup>ch<\sup> Answer y <s>e<\sup> he further explains his New Theory of Light and Colors, and particularly y<s>t<\s> of whiteness , etc. Entred LB 6.152 Or. Trans: 96.) I received yo<sup>r<\sup> letters w<sup>th<\sup> M. Hugens kind present w<sup>ch<\sup> I have viewed w<sup>th<\sup> great satisfaction, finding it full of very subtile & usefull speculations worthy of y<sup>e<\sup> Author. I am glad y<sup>t<\sup> we are to expect another discours of y<sup>e<\sup> vis centrifuga, which speculation may prove of good use in natu rall Philosophy & Astronomy as well as mechanicks. Thus for instance if the reason why the same side of y<sup>e<\sup> moon is ever towards y<sup>e<\sup> earth be y<sup>e<\sup> great er conatus of y<sup>e<\sup> other side to recede from it; it will follow (upon supposi tion of y<sup>e<\sup> Earths motion about y<sup>e<\sup> Sun) that y<sup>e<\sup> greatest distance of y<sup>e<\sup> Sun from y<sup>e<\sup> earth is to y<sup>e<\sup> greatest distance of y<sup>e<\sup> Moon from y<sup>e<\sup> earth, not greater then 10000 to 56 & therefore the parallax of y<sup>e<\sup> Sun not less then 56/10000 of y<sup>e<\sup> Parallax of y<sup>e<\sup> moon: Because were the sun’s distance less in proportion to y<sup>t<\sup> of y<sup>e<\sup> moon, she would have a greater conatus from y<sup>e<\sup> sun then from y<sup>e<\sup> earth. I thought also sometime that y<sup>e<\sup> moons libration might depend upon other conatus from y<sup>e<\sup> Sun & Earth compared together, till I apprehended a better cause. In y<sup>e<\sup> Demonstration of y<sup>e<\sup> 8<sup>th</sup> Proposition, De descensu gravium, there seems to be an illegitimate supposition, namely y<sup>t<\sup> y<sup>e<\sup> flexures at B & C do not hinder y<sup>e<\sup> motion of y<sup>e<\sup> descending body. For in reality they will hinder it, so y<sup>t<\sup> a body w<sup>ch<\sup> descends from A shall not acquire so great velocity when arrived to D as one w<sup>ch<\sup> descends from E. If this supposition be made becaus a body descending by a curve line meets with no such opposition, & this Proposition is laid down in order to y<sup>e<\sup> contem plation of motion in curve lines: then it shoud have been shown that though rectilinear features do hinder, yet y<sup>e<\sup> infinitely little flexures which are in curves, though infinite in number, do not at all hinder the motion. The rectifying curve lines by that way w<sup>ch<\sup> M. Hugens calls evo lution, I have been sometimes considering also, & have met with a way of resolving it w<sup>ch<\sup> seems more ready & free from y<sup>e<\sup> trouble of calculation than that of M. Hugens. If he please I will send it him. The Problem also is capable of being improved by being propounded thus more generally. “Curvas invenire quotascunque quarum longitudines cum propositae alicujus Curvae longitudine, vel cum area ejus ad datam lineam applicata, com parari possunt.” <s>(Mr Newtons answer to ye foregoing letter further explaining his Theory of Light and Colors, and particularly y<sup>t<\sup> of Whiteness, together wth his continued hopes of perfecting Telescopes by Reflections rather than Refractions.<\s> M, Hugens hath shown how <u>White <\u> may be produced out of two uncompounded colours , I will tell him why he can conclude nothing from <u>that <\u>; my meaning was, that such a White, (were there any such,) would have different properties from the White, wch I had respect to, when I described my Theory, that is, from y<sup>e<\sup> white <u>of<\u> y<sup>e<\sup> Sun’s immediate light, <u>of<\u> y<sup>e<\sup> ordinary objects of the senses, & <u>of<\u> all white Phaenomena that have hitherto faln under my ob servation. And those different properties would evince it to be of a diffe rent constitution: Insomuch that such a production of white would be so
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Manuscript details
 Author
 Isaac Newton
 Reference
 EL/N1/47
 Series
 EL
 Date
 1673
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Isaac Newton to Henry Oldenburg, 1673. From The Royal Society, EL/N1/47
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