[MCLENNAN] DIFFUSION OF ACTINIUM EMANATION 15 
a line midway between the plates and perpendicular to the salt, it 
dP 
follows that — K, —— is the rate at which the emanation crosses a 
dx. 
square centimetre taken perpendicular to the axis. From this it can 
2 
ake 
ation increases per cc. at a distance x from the salt. 

be readily seen that K, - represents the rate at which the eman- 
If now X, is the decay constant of the emanation \,P will denote 
the rate at which the emanation in each cubic centimetre is being 
transformed into the active deposit product, and therefore for equi 
brium we have 

Ege 
Ks 7 A PI0r 
od te le 
dx? 5 
<i ere J Nee 
ai 1 Ke 
OF P == C +C, e 
if now when x —o, P= P, and when x = infinity, P— © 
we have C,—0 
and GERS 
\ TR 
or PAPE Ka 
Again, if q be the rate at which the emanation is leaving the salt 
per sq. em., we have 
Ge when x = 0 

