ELECTRON EMISSION FROM GLOWING SOLIDS. 
283 
ting and with continuous current heating, were repeated. The temperature of the 
filament was then raised by lessening the resistance in the transformer circuit. A 
corresponding alteration was made in the battery circuit, and measurements of the 
thermionic emission and the temperature of the filament were made on both circuits. 
The observations were repeated at gradually increasing temperatures up to about 
2050° C., after which the temperature was gradually lowered again, the measurements 
being repeated at frequent intervals. In this way three series of measurements of 
the thermionic current at different temperatures were obtained, with the filament 
heated (l) by an alternating current; (2) by a continuous current in one direction ; 
Points marked # are for heating by alternating current. 
Points marked © are for one direction of continuous current. 
Points marked x are for reverse direction of continuous current. 
(3) by a continuous current flowing in the opposite direction through the filament. 
The values of these thermionic currents were plotted against the corresponding 
temperatures, and it was found that for temperatures up to about 1750° 0. the points 
all fell fairly well upon one curve, but that at temperatures much higher than this 
they separated out into three curves ; the curve corresponding to tire alternating 
heating current falling between the two curves corresponding to the different 
directions of the continuous current. A set of curves obtained with one of the 
filaments experimented on is given in fig. 1. In this the thermionic currents for the 
2 o 2 
