The ionization Produced by the impact of Solid 

 Bodies in Air. 



By Kerr Grant, M.Sc, and G. E. M. Jauncey, B.Sc. 

 [Read April 11, 1912.] 



Introduction. 



This paper contains an account of experimental investi- 

 gations made by the authors on the phenomenon of the 

 ionization which accompanies the impact of solid bodies in 

 air. 



The magnitude of the effect and of the total charge on 

 the air, and the dependence of these magnitudes upon the 

 nature of the surfaces of the impinging bodies and upon the 

 energy of impact, as well as the character of the ions pro- 

 duced, have been more or less fully determined. 



Two different methods of investigation have been em- 

 ployed, impact being produced in the one by a rifle bullet 

 striking a metal target, and in the other by allowing a stream 

 of shot or similar material to fall upon a plate. 



The paper is divided into three sections : — The first con- 

 taining a brief historical review ; the second a description of 

 the methods and results of the experiments ; the third a brief 

 summary and discussion of the results. The second section 

 is divided into two subdivisions — the first relating to experi- 

 ments made with the air-gun, the second to those made with 

 the stream of falling shot or beads. 



I. Historical Review. 



In 1892 Lenard discovered that the air at the foot of a 

 waterfall was powerfully electrified-, and showed by experi- 

 ment that this was due to the splashing of the water on the 

 rocks and consequent rupture of the water surface. 



This effect and other allied phenomena have since been 

 studied in detail by many observers and shown to occur with 

 many different liquids and solutions ; but so far as we can 

 find the corresponding effect for solids has not been observed, 

 much less studied. 



The first observations of this effect were made in Sep- 

 tember, 1910, for the case of a leaden bullet striking an 

 iron target. The air in the vicinity of the target was examined 

 in the usual way by means of an insulated electrode of brass 

 wire connected to an electrometer, an electric field being 



