1898.] Fall of Potential at the Electrodes, etc. 25 



The results of the investigations described in this paper may 

 be summarized as follows : — 



I. During conduction through a gas under the influence of 

 Rontgen rays, convection currents are produced in the gas which 

 in general move towards the electrodes. 



II. The convection currents are caused by the motion of the 

 free charges existing in the gas. 



III. The rapid fall of potential near to the electrodes during 

 the conduction exists within the first -^ mm. from the surface. 



IV. The electric force acting upon the electrodes is increased 

 by exposing the gas to Rontgen rays. 



I desire, in conclusion, to express my thanks to Prof. J. J. 

 Thomson for many valuable suggestions during the course of the 

 investigation. 



Cavendish Labobatoey. 



(7) On Velocity of Solidification. By Hakold A. Wilson, B.Sc. 

 (Lond. and Vic), 1851 Exhibition Scholar. 



When solidification is started in a supercooled liquid such as 

 phenol then rays of solid grow in the liquid with a definite velocity 

 depending on the temperature of the liquid and on its purity. 

 This velocity has been determined for a number of substances at 

 various temperatures*. 



The connection between the velocity and the supercooling for 

 most of the substances investigated can be represented by a curve 

 of the following general form. 



Supercooling 

 Fig. 1. 



When the supercooling is very small the velocity increases 

 very slowly with the supercooling. As the supercooling is in- 

 creased the velocity increases more rapidly at first but then again 

 more slowly and is then constant over a considerable range of 

 temperature. When the supercooling is very great the velocity 

 becomes very small and may even fall to zero. 



* See papers by Friedlander and G. Tarnmann, Zeitschrift P. C. xxiv. p. 152, 

 1897, and xxm. p. 326, 1897. 



