1 66 Further Experiments of Newton. [Book III, 



degrees of refrangibility, according to which they were 

 transmitted through the prifm to the oppofite wall. 

 It was further evident from thefe experiments, that as 

 the rays of light differ in refrangibility, fo they alfo 

 differ in exhibiting particular colours, fome rays pro- 

 ducing the colour red, others that of yellow, blue, &c. 

 and of thefe different-coloured rays, feparated by means 

 of the p:ifm according to their different degrees of re- 

 frnngibility, the oblong figure on the wall was com- 

 pofed. But to relate the great variety of experiments, 

 by which he demonftrated thefe principles, or the ex- 

 tenfive application of them, would lead me too much 

 into detail; let it fuffice to lay, that he applied his 

 principles to the fatisfaftory explanation of the colours 

 of natural bodies, of the rainbow, and of moft of the 

 phenomena of nature, where light and colour are con- 

 cerned ; and that almoft every thing which we at pre- 

 fent know upon thefe fubjec~ts was laid open by his ex- 

 peri men rs. 



His oblervations on the different refractive powers 

 of different Jubilances are curious and profound ; but 

 chemiftry was at that period fcarcely in a ftate fuffi- 

 tiendy advanced to warrant all his conclufions. The 

 general refult is, that all bodies feem to have their re- 

 fractive powers proportional to their denfities, except- 

 ing fo far as they partake more or lefs of inflammable 

 or oily particles. 



The difcovery of the different refrangibility of the 

 component rays of light fuggefted defects in the con- 

 flrudlion of telefcopes, which were before unthought 

 of, and in the creative hand of a Newton led to fome 

 no lefs extraordinary improvements in them. It is 

 evident, that fince the rays of light are of different re- 

 frangibilities, the more refrangible will converge to a 

 focus much fooner than the lefs refrangible, confe- 



quently 



