.194 POPULAR LECTURES AND ADDRESSES. 



metre, or at the rate of 40,000 to the centimetre, 

 or about two to the ether wave-length of blue 

 (F) light, 1 seems quite to negative the idea of 

 any such possibility of only five or six molecules 

 to the wave-length, even if we were not to declare 

 against it from theory and observation of the 

 reflection of light from polished surfaces. 



We must then find another explanation of dis- 

 pecsion ; and I believe there is another explanation 

 I believe that, while giving up Cauchy's un- 

 modified theory of dispersion, we shall find that 

 the same general principle is applicable, and that 

 by imagining each molecule to be loaded in a 

 certain definite way by elastic connection with 

 heavier matter each molecule of the ether to 

 have, in palpable transparent matter,, a small 

 fringe so to speak of particles, larger and larger 

 in their successive order, elastically connected with 

 it we shall have a rude mechanical explanation, 

 realisable by the notably easy addition of the 



1 Loschmidt, quoting from the Zollvereins department of the 

 London International Exhibition of 1862, p. 83, and from Harting 

 "On the Microscope, "p. 88 1, Sitzungsberichte derWiener Akademie 

 Math. Phys., 1865, vol. iii. 



