MEMOIR VII.] STUDIES IN THE DIFFRACTION SPECTRUM. 



of light as determined by the experiments of Foucault, 

 the number of vibrations made by the ether in the for- 

 mer of these radiations is 754 millions of millions in one 

 second, and the number in the latter case is 392 millions 

 of millions in one second. 



Or, to quote measures which are perhaps more familiar, 

 and numbers as given by Herschel, though not so exact 

 as those of Angstrom, the number of undulations con- 

 tained in one English inch at the extreme violet end is 

 59,750, and the number of vibrations executed in one 

 second is 727,000,000,000,000. The number of undu- 

 lations in one English inch at the extreme red end is 

 37,640, the number of vibrations executed there in one 

 second being 458,000,000,000,000. The velocity of light 

 used in these computations is 192,000 miles per second, 

 that used in the preceding paragraph, 186,000. 



Knowing the rate at which light moves in a second, 

 and the wave-length of any particular color, it is easy to 

 compute the number of vibrations made by the ether 

 in one second for the production of that color. This 

 is obtained by dividing the distance that light passes 

 over in one second by the wave-length of the color in 

 question. 



The numbers we thus obtain give us an idea of the 

 scale of space and time upon which Nature carries for- 

 ward her works among the particles of matter. They 

 also indicate to us the amazing activity of those portions 

 of the brain which execute motions in accordance with 

 those scales. 



The distribution of the colored spaces in the diffrac- 

 tion spectrum is not the same as in the prismatic. In 

 the former the yellow space, which is the most luminous 

 radiation, is in the middle of the spectrum, and is not 

 crowded down or compressed towards the red end, as in 



