touching his Theory of Light and Colours. 187 



that reflected ; and added that I had not tried this experi- 

 ment, but thought he was not unacquainted with notions of 

 this kind. To which he replied, that the notion was new, 

 and he would, the first opportunity, try the experiment I pro- 

 pounded. But, upon reviewing the papers I send you, I 

 found it there set down for tried, which makes me recollect 

 that about the time I was writing those papers, I had occa- 

 sionally observed in an air-pump here, at Christ's College, 

 that I could not perceive the reflexion of the inside of the 

 glass diminished in drawing out the air. This I thought fit 

 to mention, lest my former forgetfulness, through having long 

 laid aside my thoughts on these things, should make me seem 

 to have set down for certain what I never tried. 



Sir, I had formerly purposed never to write any hypothesis 

 of light and colours, fearing it might be a means to engage 

 me in vain disputes; but 1 hope a declared resolution to an- 

 swer nothing that looks like a controversy (unless possibly at 

 my own time upon some other by-occasion) may defend me 

 from that fear. And therefore considering that such an hy- 

 pothesis would much illustrate the papers I promised to send 

 you, and having a little time this last week to spare, I have not 

 scrupled to describe one so far as I could on a sudden recol- 

 lect my thoughts about it, not concerning myself whether it 

 be thought probable or improbable, so it do but render the 

 papers I send you, and others sent formerly, more intelligible. 

 You may see, by the scratching and interlining, it was done 

 in haste, and I have not had time to get it transcribed, which 

 makes me say I reserve the liberty of adding or altering it, 

 and desire that you would return those and the other papers 

 when you have done with them. I doubt there is too much 

 to be read at one time, but you will soon know how to order 

 that. At the end of the hypothesis you'll see a paragraph 

 to be inserted, as is there directed. I should have added 

 another or two, but I had not time, but such as it is, I hope 

 you will accept it. 



Sir, I am, 



Your humble Servant, 

 (Signed) I. Newton. 





Mr. I. Newton's Letter sent to H. O.* 

 An Hypothesis explaining the Properties of Light discoursed 

 of in my several papers. 

 Sir, 

 In my answer to Mr. Hook you may remember I had 



* Registry Book of the Royal Society, vol. v., from 1675 to 1679. 



02 



