required to maintain a Current in a Gas. vou 
above table was 603 volts. The battery was connected to 
the electrodes in series with a resistance of 10,000 ohms and 
a voltmeter having a resistance of 38,000 ohms. With this 
external resistance (48,000 ohms) the voltmeter gave a 
steady deflexion slightly over 200 volts, when the potential 
of the battery was 603 volts. The fall of potential along the 
10,000 oa resistance was over 52°5 volts, so that w hen the 
current (,45 ampere q.p.) was flowing, the difference of 
potential between the electrodes in the. gas was less than 
351 volts. When the circuit was broken for an instant and 
a potential of 601 volts applied, no effect was produced, the 
_ gas in fact insulated ; but when the potential of the battery 
was raised to 603 volts the spark appeared again and the 
same current ;4, ampere passed through the gas. It was 
found possible to adjust the current to any smaller value by 
increasing the external resistance. The potential-difference 
at the electrodes required to maintain the smaller currents 
was greater than 351 volts, and for very small currents a 
difference of potential between the electrodes of 603 volts 
was required. 
When the pressure was reduced to that which corresponds 
to the minimum sparking potential, it was found that the 
potential required to maintain a discharge did not differ much 
from the minimum sparking potential. 
According to the theory the potential of 603 volts is 
required to maintain a current in a uniform field. When the 
current increases, a charge, as has been explained, accumulates 
in the neighbourhood of the negative electrode, and when the 
cathode fall of potential is fully developed the potential 
required to maintain the current is about 340 volts. The 
theory leads to the conclusion that the field of force changes 
gradually as the current increases, from a uniform distri- 
bution of force to one in which there is considerable 
polarization at the negative electrode which approaches to 
the value of the minimum sparking potential. 
Some preliminary experiments on the field of force between 
two parallel plate electrodes have confirmed these con- 
clusions. 
Over a large range of values of the current there is a change 
in the potential- -difference between the electrodes and in the 
field of force corresponding to changes in the intensity of the 
current. As the current is increased, the total fall of potential 
between the electrodes diminishes, and the intensity of the 
force increases at first in the neighbourhood of the negative 
electrode, and subsequently a similar but smaller effect appears 
3H 2 
