[RUTHERFORD] DISCHARGE OF ELECTRICITY FROM PLATINUM 33 
VARIATION OF THE CURRENT WITH DISTANCE BETWEEN THE PLATES. 
From the theory, the current between the plates for a given P. D. 
should vary inversely as the cube of the distance between them. This 
relation is, however, widely departed from in the experimental case. 
The following table shows the way in which the current, for a tem- 
perature corresponding to about 100 amperes, varies with the distance 
between the plates for a P. D. of 624 volts. 




Distance d in cms. Current 1. CCI 
2 18,800 150,000 
3 2,690 72,600 
4 835 53,400 
5 296 37,000 
6 156 33,700 


The above values were taken from observations at different times 
and are only approximate. 
The current thus falls off more rapidly than the inverse cube of the 
distance. The value 7 d° should be equal if the ionic velocities are con- 
stant for different distances between plates. Later experiments have 
shown that, in consequence of the air being heated near platinum plate, 
the velocity of the carrier is greater near the platinum plate and dimin- 
ishes as we proceed from the plate. The variation of velocity of the ions 
with temperature is sufficient to account for the inequalities in the values 
given in the above table. 
The results obtained on the variation of the current with the voltage 
and the variation with distance between the plates are thus in general 
agreement with the theory of ionization, taking into account the disturb- 
ances due to the experimental conditions, 
Experiments are now in progress to determine the velocity of the 
ions for different distances between the plates by a direct method and to 
compare the values thus obtained with those calculated by aid of the 
theory described in the beginning of this paper. 
Sec. III, 1901. 3. 
