I o i Mifcellanea Curio fa. 



fuccemVely pafs through the hole in it, that I 

 might obferve to what places on the Wall the 

 fecond Prifm Would refract them. And 1 faw by 

 the Variation of thofe places, that the Light, 

 tending to that end of the Image, towards which 

 the Refraction of the firft Prifm was made, did, 

 in the fecond Prifm, fufier a Refraction confider- 

 ably greater than the Light tending to the other 

 end. And fo the true caufe of the length of 

 that Image was detected to be no other, than that 

 Light conflfts of B^ays differently refrangible^ which, 

 without any refpect to a difference in their, inci- 

 dence, were, according to their degrees of Refran- 

 gibiiity, tranfmitted towards divers parts of the 

 Wall 



When I underftood this, I left off my aforefaid 

 Glafs Works ; for I faw, that the perfection of 

 Telefcopes was hitherto limited, not fo much for 

 want of Glaffes truly figur'd, according to the 

 prefer ipt ions of Optic k Authors ( which all Men 

 have hitherto imagin'd), as becaufe that Light it 

 lelf is a Heterogeneous mixture of differently refran- 

 gible Hays, So that, were a Glafs fo exactly fi- 

 gured, fo as to collect any one fort of Rays into 

 one Point, it could not collect thofe alfb into the 

 fame Point, which having the fame Incidence 

 upon the fame Medium, are apt to fufFer a diffe- 

 rent Refraction, Nay, I wonder'd, that feeing 

 the difference of Refrangibiiity was fo great, as I 

 found it, Telefcopes (hould arrive to that per- 

 fection they are now at. For, meafuring the 

 Refractions in one of my Prifms, I found, that, 

 fuppofing the common Sine of Incidence upon 

 one of its plains, was forty four Parts, the Sine 

 of Refraction of the utmoft Rays on the red end 

 of the Colours, made out of the Glafs into the 

 Air, would be fixty eight part?, and the Sine of 



Refraction 



