Isaac Newton to Henry Oldenburg

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                                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.

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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Isaac Newton
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Isaac Newton to Henry Oldenburg, 1673. From The Royal Society, EL/N1/47



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