Sgcrion III., 1901. [27] Trans R. 8 C: 
V.— Discharge of Electricity from Glowing Platinum. 
By E. Rurmerrorp, M.A., D.Sc., 
Macdonald Professor of Physics, McGill University, Montreal. 
(Read May 23, 1901.) 
The fact that glowing bodies discharge positive and negative elec- 
tricity with unequal facilities, has been shown by many observers. The 
most detailed examination of this subject has been made by Elster and 
Geitel! They found that when a platinum wire was heated to a bright 
red heat, in an atmosphere of air or oxygen at low pressure, a cold metal 
plate in its neighbourhood discharged negative electricity more readily 
than positive. If, however, a thin platinum wire or carbon filament is 
heated in an atmosphere of hydrogen at low pressure, the cold plate 
discharges positive electricity more readily than negative. 
The object of the present investigation was to test the validity of 
certain results obtained from a theoretical consideration of the conduc- 
tivity of gases when the ionization was confined mainly to the surface of 
one electrode. A very simple means of obtaining strong surface ioniza- 
tion is to heat a platinum wire to a red heat by an electric current and 
this method has been employed in the course of the investigation. An 
account of the theory is given in a recent paper’ by the author, in order 
to explain the differences observed in the value of the current through 
ionized gases when the electric field was reversed. When these investi- 
gations were in progress, C. D. Child published a paper (Phys. Review, 
Feb. and March, 1901), in which a similar theory was worked out and 
applied to determine the velocity of ions drawn from flame and from a 
carbon arc. 
À brief account of the theory will first be given and then a com- 
parison between the theoretical and experimental results. 
Let A (Fig. 1) be a platinum plate, the surface of which is to be 
a source of ionization; B, a metal plate placed parallel to it and ata 
distance. The plate A is connected to one pole of a battery of small 
accumulators, the other pole of which is to earth. The plate B is con- 
nected to earth through a sensitive galvanometer. Let v be the P.D. 
between A and B. 
Suppose the plate A charged positively. When the plate A is heated 
to a red heat, a current is observed to pass through the galvanometer, 
In order to produce this current. positive ions, produced either from the 


1 Wied. Annal., 37 and 38. 
2 Phil. Mag., Aug., 1901. 
