419 
ELECTRIC DISCHARGES 
IN GASES AT LOW PliESSURES. 
F/]0.1/!I Cordon D/ox/de 
VI. Sparh Potentials ivith (Jiffcrent Electrodes. 
It has no^v Ijeen shown, using brass electrodes of constant size, that, for discharges 
in a uniform field, in any gas, the values oi the spark potentials are determined 
solely hy the product of the pressure of the gas and the distance between the 
electrodes. From this result it appeared that If the size or material of the electrodes 
did not affect the results, the spark potentials were dependent only n])on the quantity 
of the gas per unit cross section between the electrodes. 
In order to determine this point, the brass electrodes wliicii had been used up to 
this time were replaced in turn by electrodes of iron, zinc and aluminium, of exactly 
the same size. The results of the experiments showed that there was no variation 
in the difierent sets of readings, and it was evident that there was not the slightest 
efiect produced in any case by a change in the material of wliich the electrodes 
were made. 
In order to see if the size of the electrodes afiected the values of the spark 
potentials for the different pressures, provided the discharge took place in a uniform 
field, a reduction was made in the surface of the electrodes exposed to the gas. 
This was done by replacing the ebonite rings C, C, fig. I, which had an inner 
diameter of 3 centims., by others whose inner diameter was but 1 centim. By this 
device the areas of the electrodes exposed to the gas were reduced to about of 
their value in the early experiments, and the condition that the discliarge could 
only take place In a uniform field still held. Using this apj)aratus with air, no 
difterence could be observed in the values of the discharge potentials corresponding 
to the different pressures, and It was therefore certain that the value of the spark 
potential was in no way influenced by the size of the electrodes. 
It is therefore clearly established that the only factors aftecting the spark 
potentials are pressure and the distance between the electrodes, and hence Baschen’s 
3 H 2 
