1883.J 



on the Size of Atoms. 



203 



The numbers in the first two columns were determined by Dr. Hopkinson, 

 those ill the last three by Messrs. Gladstone and Dale. The index of refraction 

 of air tor light near the line E is 1 - 000294. 



say 10 in hard crown glass ; 8 in flint glass ; and in carbon disul- 

 phide actually not more than 4 molecules in the wave-length, if we 

 are to depend upon Cauchy's unmodified theory for the explanation 

 of dispersion. So large coarse-grainedness of ordinary transparent 

 bodies, solid or fluid, is quite untenable. Before I conclude, I intend 

 to show you, from the kinetic theory of gases, a superior limit to the 

 size of molecules, according to which, in glass or in water, there is 

 probably something like 600 molecules to the wave-length, and 

 almost certainly not feiver than 2, or 3, or 400. But even without 

 any such definite estimate of a superior limit to the size of molecules, 

 there are many reasons against the admission that it is probable or 

 possible there can be only four, or five, or six, to the wave-length. 

 The very drawing, by Nobert, of 4000 lines on a breadth of a milli- 

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

 ether wave-length of blue (F) light,* 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 dispersion. I believe 

 there is another explanation. I believe that, while giving up Cauchy's 

 unmodified 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 transj)arent 

 matter, a small fringe so to speak of particles, larger and larger in 



* Loschmidt, " quoting from the Zollvereins department of the London 

 International Exhibition of 1862, p. 83, and from Harting ' On the Microscope/ 

 p. 881," ' Sitzuugsberichte der Wiener Akademie Math. Pliys.,' 1865. Vol. iii. 



