142 FRAGMENTS OF SCIENCE 



The theorist takes his conceptions from the world of 

 fact, and refines and alters them to suit his needs. The 

 sensation of sound was known to be produced by aerial 

 waves impinging on the auditory nerve. Air being a 

 thing that could be felt, and its vibrations, by suitable 

 treatment, made manifest to the eye, there was here a 

 physical basis for the "scientific imagination 1 ' to build 

 upon. Both Hooke and Huyghens built upon it with 

 effect. By the illustrious astronomer last named the con- 

 ception of waves was definitely transplanted from its ter- 

 restrial birthplace to a universal medium whose undula- 

 tions could only be intellectually discerned. Huyghens 

 did not establish the undulatory theory, but he took the 

 first firm step toward establishing it. Laying this theory 

 at the root of the phenomena of light, he went a good way 

 toward showing that these phenomena are the necessary 

 outgrowth of the conception. 



By analysis and synthesis Newton proved the white 

 light of the sun to be a skein of many colors. The cause 

 of color was a question which immediately occupied his 

 thoughts; and here, as in pther cases, he freely resorted 

 to hypothesis. He saw, with his mind's eye, his luminif- 

 erous corpuscles crossing the bodily eye, and imparting 

 successive shocks to the retina behind. To differences of 

 "bigness" in the light-awakening molecules Newton as- 

 cribed the different color-sensations. In the undulatory 

 theory we are also confronted with the question of color; 

 and here again, to inform and guide us, we have the anal- 

 ogy of sound. Aerial waves of different lengths, or peri- 

 ods, produce notes of different pitch; and to differences 

 of wave-length in that mysterious medium, the all-pervad- 

 ing ether, differences of color are ascribed. Hooke had 



