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. 
\Read 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. 
