296 Mr McClelland, On the Action of 



On the Action of Incandescent Metals in producing Electric 

 Conductivity in Gases. By J. A. McClelland, M.A., Trinity 

 College ; Fellow of the Royal University of Ireland ; Professor 

 of Natural Philosophy in University College, Dublin. 



i 



[Bead 25 November 1901.] 



1. In this paper an account is given of some experiments on 

 the nature of the conductivity produced in gases by the action of 

 incandescent metals. The conductivity can be shown to be due 

 to ionisation produced by the hot metal, and in the paper some 

 properties of the carriers of the electricity are studied in air at 

 atmospheric and at lower pressures. 



A statement is first given of the results obtained when the gas 

 surrounding the incandescent wire is at atmospheric pressure; the 

 paper then deals with experiments in air at reduced pressures, 

 and here it may be mentioned that when the pressure is suffi- 

 ciently reduced many important changes occur in the phenomena 

 observed. 



Experiments with the Incandescent Wire in Air at 

 Atmospheric Pressure. 



2. Many of the results obtained with the incandescent plati- 

 num wire in air at atmospheric pressure have already been given 

 in a previous paper " On the Conductivity of Gases from an Arc 

 and from Incandescent Metals 1 ," and we shall merely mention 

 them here. 



It was shown that the conductivity produced by the incan- 

 descent wire is of the nature produced by the ionisation of a gas ; 

 the current varies with the E.M.F. in the usual way, and the gas 

 loses all its conductivity when passed between terminals kept at a 

 sufficiently great difference of potential. 



The gas taken from near the hot wire discharges a negatively 

 charged body but not a positively charged body if the wire is at a 

 dull red heat, in fact a negative charge is discharged if the wire 

 is only just luminous. The wire must be raised to a higher 

 temperature before the gas from it can discharge a positively 

 charged body. 



This shows that as the temperature of the wire is increased we 

 get in the gas from near it positive carriers before we get negative 



1 Proceedings of the Cambridge Philosophical Society, Vol. x. Pt. iv. 



