touching his Theory of Light and Colours. 215 



be, as it were, the succus nutritius of the earth, or primary 

 substance, out of whieh things generable grow; instead of 

 this you may write, that that spirit may be condensed in fer- 

 menting or burning bodies, or otherwise coagulated in the 

 pores of the earth and water into some kind of humid active 

 matter, for the continual use of nature, adhering to the sides 

 of those pores after the manner that vapours condense on the 

 sides of a vessel. 



In the same paragraph there is, I think, a parenthesis, in 

 which I mention volatile salt-petre; pray strike out that pa- 

 renthesis, lest it should give offence to somebody. 



Also where I relate the experiment of little papers made to 

 move curiously with a glass rubbed, I would have all that 

 struck out which follows, about trying the experiment of leaf- 

 gold, nq.ob 3omi£a I 



Sir, I am interrupted by a visit, and must in haste break off. 



Yours, 



January 25, 1675-6. Isaac Newton. 



^mJiuq is>jl.a t fcura I Amdi I I 



Letter from Newton to Boyle. 



aaorfi bfiii I li bna :uo^ Jnsa I J&dvsr riliw oiadj JSoagqcp o; 



oa n ; Honoured Sir, ^nildl otl quq. 



I have so long deferred to send you my thoughts about the 

 physical qualities we speak of, that did I not esteem myself 

 obliged by promise, I think I should be ashamed to send them 

 at all. The truth is, my notions about things of this kind are 

 so indigested, that I am not well satisfied myself in them ; and 

 what I am not satisfied in, I can scarce esteem fit to be com- 

 municated to others ; especially in natural philosophy, where 

 there is no end of fancying. But because I am indebted to 

 you, and yesterday met with a friend, Mr. Maulyverer, who 

 told me he was going to London, and intended to give you 

 the trouble of a visit, 1 could not forbear to take the oppor- 

 tunity of conveying this to you by him. 



It being only an explication of qualities which you desire of 

 me, I shall set down my apprehensions in the form of suppo- 

 sitions as follows. And first, I suppose, that there is diffused 

 through all places an aetherial substance, capable of contrac- 

 tion and dilatation, strongly elastic, and, in a word, much like 

 air in all respects, but far more subtile. 



2. I suppose this aether pervades all gross bodies, but yet 

 so as to stand rarer in their pores than in free spaces, and so 

 much the rarer, as their pores are less ; and this I suppose 

 (with others) to be the cause why light incident on those bo- 

 dies is refracted towards the perpendicular; why too well- 

 polished metals cohere in a receiver exhausted of air ; why $ 



