182 Mr. W. C. Dampier Whetham. [May 30, 



(3 X 10~~ u ) of the C.G.S. electrostatic unit of quantity. Other 

 estimates of the amount of this remarkable unit of electricity have 

 since been made, and do not materially differ from the above. Here, 

 then, we have all the machinery required. The motions which go on 

 actively within chemical atoms can scarcely fail to wave about these 

 electrons which are so closely associated with them ; and we know 

 that the waving about of such of these charges of electricity as 

 for the time happen to be undisguised, must generate in the 

 ether exactly such electro-magnetic waves as those revealed to us in 

 the spectra of gases (see ' Transactions of the Royal Dublin Society,' 

 vol. 4 (1891), p. 583). 



V. "On the Velocities of the Ions." By W. C. DAMPIER 

 WHETHAM, M.A., Fellow of Trinity College, Cambridge. 

 Communicated by Professor J. J. THOMSON, F.R.S. Re- 

 ceived May 2. 1895. 



(Abstract.) 



In a previous communication to the Royal Society (' Phil. Trans.,' 

 184, (1893), A. p. 337), I have described a method of experimentally 

 determining the velocities of the ions during electrolysis, by observa- 

 tions on the phenomena which occur when a current of electricity 

 is passed across the junction of two salt solutions, one at least of 

 which is coloured. 



The results obtained agreed, within the limits of experimental 

 error, with the numbers deduced by Professor F. Kohlrausch from 

 measurements of the conductivities. The method is, however, 

 seriously restricted by the conditions necessary for its success. The 

 two solutions must be of different densities, of different colours, and 

 of nearly equal conductivities at equivalent concentrations. 



In order to extend the method, I have used solid solutions in agar- 

 agar jelly, tracing the motion of the ion by the formation of a precipi- 

 tate. Jelly solutions were employed by Dr. Oliver Lodge, but, although 

 he got a good result for hydrogen with phenol-phthallein as an indicator, 

 when he tried to measure the velocity of barium and strontium by 

 watching the formation of precipitates, the experiments were not very 

 successful. This was probably due to the fact that, when a pre- 

 cipitate forms, it removes some of the electrolyte from solution, and 

 so increases the specific resistance and the local potential-gradient. 

 In order to eliminate this disturbing cause, instead of setting up two 

 solutions which completely precipitate each other, like barium 

 chloride and sodium sulphate, use was made of barium chloride and 

 sodium chloride, just enough sodium sulphate being added to the 

 latter to enable the motion of the barium ions to be traced by the 



