164 Bcyk, Grimaldi t Gregory > &c. [Book III. 



piter's fatcllites. About the fame time Mr. Boyle 

 made ,his experiments on colours. He proved that 

 jfnow {lid not affect the eye by a native, but reflected 

 light, a circumftance which, however, at this day, we 

 ihould fcarcely believe was ever neceffary 10 be proved 

 by experiment. By admitting alfo a ray of light into 

 a dark room, and letting it fall on a fheet of paper, he 

 tiemonftrated, that white reflected much more light 

 than any other colour \ and to prove that white bodies 

 reflect the rays outwards, he adds, that common burn- 

 ing-glaiTes will not, for a long while, burn or difcolour 

 white paper j on the contrary, a concave mirror of 

 black marble did not reflect the rays of the fun with 

 near fo much power as a common concave mirror. 

 The fame effect was verified by a tile, one half of the 

 lurface of which was white, and the other black. 



Some experiments were made about this time on 

 the difference of the refractive powers of bodies ; and 

 the firft advance to the great difcoveries by means of 

 the prifm was made by Grimaldi, who obferved, that 

 a beam of the fun's light, tranfmitted through a prifir, 

 inftead of appearing round on the oppofite wall, exhi- 

 bited an oblong image of the fun. Towards the clofe 

 of this century the reflecting telefcope was invented by 

 our countryman James Gregory. 



The reader will foon perceive how very imperfect 

 all the preceding difcoveries were in comparifon with 

 thofe of Sir I. Newton. Before his time, little or no- 

 thing was 'known concerning colours; even the remark 

 of Grimaldi refpecting the oblong figure of the fun, 

 made by tranfmitting the rays through a prifm, was 

 unknown to our great philofopher, having been pub- 

 Jifhed only the year before. This, however, it appears, 

 was the firft circumftance which directed the attention 

 of Newton to the inveftigation of the theory of co- 

 lours. 



