Active Deposits of Radium, Thorium, and Actinium. 607 
The above results then go to confirm the view held by 
Rutherford already referred to, that the active deposit 
particles which are directed to the anode have a negative 
-charge. 
Fig. 3. 
Pressure in cms. 
The activity of the cathode being much larger than the anode, the 
scale in fig. 3 for the cathode is one third that for the anode and neutral 
pole. 
It has been suggested by Rutherford *, in explanation of 
his results with thorium emanation, that the decrease in 
activity of the cathode as the pressure is reduced is due to a 
decreasing number of collisions between the active deposit 
particles and the gaseous molecules with which they are 
mixed. 
At the moment of expulsion of an a. particle from the 
emanation atom, the residue, i. e. the active deposit particle, 
acquires a velocity in the opposite direction, which, though 
* ' Kadioactivity/ p, 319. 
