I 



THE 

 LONDON, EDINBURGH, and DUBLIN- 

 PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



MA Y 1911. 



LXVI. On the Discharge from an Electrified Point. By 

 A. M. Tyndall, M.Sc. (Bristol), B.Sc. (LoncL), Lecturer 

 in Physics in the University of Bristol*. 



[Plate V.] 



SOME experiments, chiefly on (1) the pressure of the 

 Electric Windf, and (2) the field in the neighbourhood 

 of a discharging point J, led Prof. A. P. Chattock and the 

 author to adopt certain theories as to the nature of point dis- 

 charge which at the time were capable of explaining most of the 

 results obtained. The author has since extended the experi- 

 ments, and has obtained results which are to a certain extent 

 at variance with these theories. It seems desirable, therefore, 

 to review the situation in the light of the more recent 

 experimental facts. 



The theories of point discharge originally suggested may 

 be briefly summarized thus : — 



Suppose that a point P is gradually charged with electricity; 

 the field near its surface is at first unable to do more than 

 clear away the few initially present ions in its neighbourhood 

 as fast as they are formed. But as soon as it is strong 

 enough to impart to the positives among them sufficient 

 energy to enable these to ionize fresh molecules in their turn, 



* Communicated by the Author. 



t Chattock and Tyndall, Phil. Mag-. [6] xix. p. 449 (1910). 



% Chattock and Tyndall, Phil. Mag. [6] xx. p. "277 (1910). 



Phil Mag. S. 6. Vol. 21. No. 125. May 1911. 2 Q 



