﻿386 Prof. H. A. McTaggart on the Electrification 



would be necessary to take into consideration the variation 

 of the mean free path of an electron with its velocity of 

 agitation, and the large reduction of the energy of an electron 

 when ionization by collision takes place. 



These points in connexion with the motion of electrons in 

 gases have not been taken into consideration by Lenard, and 

 it does not appear that his formula is more correct than 

 others which have been proposed. 



Yours faithfully, 



3rd May, 1922. JOHN S. ToWNSEND. 



XXXVIII. On the Electrification at the Boundary between a 

 Liquid and a Gas. By Professor H. A. McTaggart, M.A., 



University of Toronto *. 



MANY years ago, in the course of some experiments on 

 the effect of an electric current on the motion of small 

 particles in a liquid, Quincke {Ann. d. Phys. cxiii. p. 513, 

 1861) observed that small gas-bubbles in water moved as 

 though negatively charged. Although a good deal of atten- 

 tion has been paid to the movement of solid and of liquid 

 particles in such cases, very little effort has been devoted to 

 the study of small spheres of gas suspended in a liquid — one 

 obvious reason being the difficulty of controlling them while 

 under observation. A systematic examination of their elec- 

 trical properties ought, however, to yield further information 

 as to the physics — and chemistry too — of surface layers. 



Before the war experiments in this field were begun by 

 the author in the Cavendish Laboratory under Sir J. J. 

 Thomson, and some results were obtained. Measurements 

 were made ^Phil. Mag. Feb. 1914, p. 297) of the velocity, 

 under a fall of potential, of small spheres of air in distilled 

 water and their electrical charges were estimated. The 

 effects on the charge of the addition of minute amounts of 

 various inorganic electrolytes were studied. Results were 

 obtained (Phil. Mag. Sept. 1914, p. 367) showing how the 

 charge varies with the presence in the water of certain 

 alcohols and organic acids, and a parallel was shown to exist 

 between the variation of the electric charge and the surface 

 tension. 



The present paper deals with some further experiments 

 carried out in the University of Toronto, and describes the 

 variation observed in the electric charge on small spheres 



* Communicated by Professor J. C. McLennan, F.R.S. 



