286 
Mr Richardson, On the Negative Radiation 
On the Negative Radiation from Hot Platinum. By O. W. 
Richardson, B.A., Coutts Trotter Student, Trinity College. 
[ Read 25 November 1901.] 
Ever since the original discovery by Messrs Elster and Geitel 1 
that the air in the neighbourhood of a hot metal discharged 
electricity, several physicists have investigated the laws of this 
phenomenon. Most of these investigations have been concerned 
with the effect in gases at pressures approximately atmospheric, 
when the charge on the gas may be either positive or negative, 
according to the gas used. Professor M c Clelland 2 , however, was 
able to show that platinum at high temperatures produced a 
negative charge in all surrounding gases. The effect was more 
marked the lower the pressure ; the discharge also increases very 
rapidly with the temperature of the wire, as the figures given 
by Professor M c Clelland indicate. The fact that the carriers of 
the negative electrification are charged particles was proved by 
Professor Thomson 3 , who showed that they were deflected by a 
magnetic field. 
The present investigation was undertaken with the idea that 
in the negative radiation at high temperatures the phenomenon of 
conductivity produced by metals took its simplest form. This 
idea seemed legitimate since only in this case is the conductivity 
to any extent independent of the surrounding gas. 
The following experiments were made to determine the 
saturation current from the wire at various temperatures, since 
this appeared to be the most fruitful method of attack. 
With regard to the theory of the phenomena, the results can 
best be explained on the corpuscular theory of conduction in 
metals. According to that view a metal is to be considered as a 
sponge-like structure of atoms and positive ions with negative 
ions or corpuscles moving freely throughout the mass. The mean 
free path of the corpuscles varies from about 10~ 4 cms. in the case 
of bismuth to 10 -6 cms. in the case of most other metals. It is 
thus of the same order as that of a molecule in air at atmospheric 
pressure. The time during which the corpuscles are colliding is 
1 Elster and Geitel, Wied. Ann. xvi. 1882, p. 193, and later papers. 
2 J. A. McClelland, Proc. Camb. Phil. Soc. x. 1900, p. 241. 
3 J. J. Thomson, Phil. Mag. xliv. 1897, p. 203. 
