14 THE ROYAL SOCIETY OF CANADA 
follows that the amount of active deposit obtainable at any selected 
point should pass through a maximum value if exposures were made 
as the pressure was lowered. It is evident too from the interpretation 
given that the pressure corresponding to the maximum deposit at a 
selected point should be the lower the farther the point under observation 
on the plates was taken from the salt. 
100, 
TET ee 
is 
Fee 
REED 
à 
pose cones 
a 
se 
es” "en = 
Activity. 10.Min A Arrer. EXPOSURE. Ararean Scare 

ata HR HE Hi 
ét = HH 
Q  H0. “200. “300. 400. 500. 600. 700 800 
Pressure.in.Mms. 
In considering these experiments it can be readily seen that the 
law observed by Kennedy, viz.:— 
Pix, =a constant 
throws some additional light on the manner in which the active deposit 
particles become positively charged. 
Let P denote the concentration of the emanation between the 
plates and K, its coefficient of diffusion. Taking the axis of x along 
