THE PATH OF EVOLUTION 



to the Chair of Optics at Cambridge. Having thus 

 every facility for his labors, he devoted himself to ob- 

 servations without number, and formed therefrom a 

 complete doctrine of the fundamental properties of 

 light, which he classified and arranged from his ex- 

 perience and experiments only, without any admix- 

 ture of hypothesis a novelty as unheard of as were 

 the new properties he disclosed. It was not until 

 1675 that he communicated to the Royal Society his 

 conjectures upon the nature of light, prefacing his re- 

 marks with : " To me the subject is unimportant, since 

 my discoveries are matters of fact, and for their ex- 

 istence independent of any hypothesis ; " but added : 

 " I believe I have seen that the heads of many of the 

 greatest savants run strongly towards hypotheses ; I 

 will say, therefore, what I am led to regard as the 

 most probable, should I be obliged to adopt one." 

 He then proceeded to describe, nearly as Descartes 

 had done, the probable existence of the imperceptible 

 Ether, in which and by which light is transmitted. 

 Newton thought that light was composed of hetero- 

 geneous particles, different from the ether itself, which 

 were emitted in all directions from a luminous body 

 with an excessive swiftness, agitating the ether, caus- 

 ing undulations therein, by which the movements of 

 the said particles, as well as the ether waves them- 

 selves, might be accelerated or retarded. The in- 



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