[ruTHERFoRD] DISCHARGE OF ELECTRICITY FROM PLATINUM 31 
According to the simple theory already considered, the current 
should reach a maximum and remain constant with further increase of 
temperature of the platinum plate. In the experimental case, however, 
the gas through which the ions move has its temperature increased with 
that of the platinum plate. As the ions increase in velocity with increase 
of temperature of the gas, and the current through the gas is directly 
proportional to the velocity of the ions, we should expect the current to 
increase rapidly to a certain point and then more slowly with increase of 
temperature of the platinum plate. This is the case for a distance of 
2 cms. and less. For distances of 3 to 8 ems., however, the current 
reaches a maximum and then steadily diminishes with rise of tem per- 
ature. 
Experiments, now in progress, point to the conclusion that the 
diminution of the current is due to some very slow moving carriers, 
which are produced in the gas at a high temperature. It can be 
theoretically shown that the presence of a small number of slow moving 
charged carriers may produce a large diminution of the current. A 
simple experiment serves to show this. The current between two plates 
was observed when the platinum was at a red heat. On blowing some 
tobacco smoke between the plates, the current momentarily fell to less 
than half its value. Some of the ions in their passage between the plates 
gave up their charge to the particles of the tobacco smoke. In con- 
Sequence of their size these moved very slowly compared with the ions 
and caused a falling off of the current. 
The results obtained for different distances and voltages receive a 
general explanation if we suppose that the number of these large carriers 
increase with the temperature and voltage, but not: so rapidly as the 
current carried by the ions which increases approximately as the square 
of the voltage. For a distance of 2 cms. and under, the increase of 
current due to increase of the velocity of the ions more than com pensates 
for the presence of the large carriers. 
VARIATION OF THE CURRENT WITH VOLTAGE. 
The current through the platinum plate was kept approximately 
constant at 100 amperes. This corresponds to the maximum current 
through the gas for the distance of 3 cms. and above. 
The current was found to vary approximately as the square of the 
P. D. between the plates. 
Distance between platinum and copper plates, 2 cms. 1 mm. of 
scale, 3°51 10-” amperes, 
