Miftellanea Curiofa. 



A Letter of Mr. Ifaac Newton s 

 Profejfor of the Mathematicks in 

 the Vniverfity of Cambridge ; 

 containing his New Theory about 

 Light and Colours : Sent by 

 the Author to the Fublifher from 

 Cambridge, Feb. 6. 1674.; in 

 order to be communicated to the 

 Royal Society. 



s 1 



TO perform my late promife to you, I fliall 

 without further Ceremony acquaint you, 

 That in the beginning of the Year 1666 (at 

 which time I apply 'd my le!f to the grinding of 

 Optick-glaffes of other Figures than Spherical,) 

 I procur'd me a Triangular Glafs-Prifm, to try 

 therewith the 'celebrated Phenomena of Colours. 

 And in order thereto, having darkened my 

 Chamber, and made a fmall hole in my Win- 

 dow-fhuts, to let in a convenient quantity of the 

 Sun's Light, I plac'd my Prifm at his entrance, 

 that it might be thereby refracted to the oppo- 

 flte Wall. It was at Erft a very pleafing Diver- 

 tifement, to view the vivid and intenfe Colours 

 produced thereby ; but after a while applying my 

 (elf to confider them more circumfpe&y, I be-* 

 came furpriz'd to fee them in an oblong Form ; 

 which, according to the received Laws of Rare- 

 fra<ftion ? I expected fhould have bef n Circular. 



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