84 Mr. McClung on the Lffect of Temperature on the 
of one volt between the quadrants when the needle was 
charged to 120 volts. The other electrode E was connected 
through a large liquid resistance R to one pole of a battery 
of accumulators, while the other pole was to earth. 
Now if the gas between two insulated electrodes be ionized 
by a constant source of ionization, and if to one of these 
electrodes a steady voltage be applied sufficiently large to 
extract all the ions from the gas before they have time to 
recombine, the other electrode will charge up at a rate pro- 
portional to the number of ions produced in the gas per 
second. The rate at which this electrode charges up will 
therefore be a measure of the amount of ionization produced 
in the given volume of gas per second. The deflexion of 
the electrometer-needle per second, which is proportional to. 
the rate at which H’ charges up, will be proportional to the 
amount of ionization produced in the gas, and will therefore 
be a measure of the amount of ionization. 
To measure the ionization at different temperatures of the 
gas the following method was adopted. ‘The rays were 
started and allowed to pass into the cylinder for an interval 
of five or ten seconds, so that the ionization might reach a 
steady state. During this interval the electrode H’ and the 
quadrants of the electrometer were connected to earth. At 
the end of this time the quadrants connected to H’ were 
insulated, by a key worked at a distance by means of a cord, 
and were allowed to charge up for a given number of seconds, 
and at the end of the given time the rays were stopped and 
the deflexion of the electrometer-needle observed. Several 
readings like this were observed at the ordinary temperature 
of the room and the mean of these readings taken. The 
cylinder and inclosed air were then heated up to a given 
temperature, and when the temperature became steady the 
deflexions were observed as before. This having been 
done the air was once again heated to a still higher tem- 
perature and the deflexions again observed. ‘I’his was done 
tor several temperatures up to the highest one investigated. 
The amount of ionization at the different temperatures could 
thus be compared by comparing the deflexions obtained at 
these temperatures. 
Instead of starting the series of readings at the lower 
temperature and gradually heating the air up to the higher 
temperatures, the order of procedure was in some cases 
reversed, and the air was heated up to the highest tempera- 
ture to start with, and the deflexion corresponding to the 
ionization observed. ‘The gas was then gradually cooled 
down from point to point, observations being taken at each 
temperature. Similar results were obtained in both cases. 
