[MCLENNAN] DIFFUSION OF ACTINIUM EMANATION 19 
aly 
From this yp” =e 
—— y C 
—- Ave *pi ewhere Aye. 7 
or y= Se € D 
Now from the form of the function constituting the right hand 
member of this equation we see that y vanishes both for very high 
and for very low values of p. It follows then on re-substituting for y 
that the product of aq is given by 
where q is the rate at which the emanation leaves the salt and @ is the 
proportionality factor between the concentration of the emanation 
and the concentration of the active deposit particles produced from it, 
which are or become positively charged. 
It is evident then from (5) that the law discovered by Kennedy 
for the distribution of the active deposit leads to the conclusion that 
either one or other of the magnitudes @ and q, or perhaps both, is a 
function of the pressure. 
Some interesting information which could be used in testing the 
result given in (5) might readily be obtained by confining the actinium 
salt and the emanation liberated from it at different pressures in a 
small chamber constructed in such a way that a negatively charged 
electrode inserted in it would have access to all the emanation during 
an exposure. 
Such an arrangement, however, would possess one defect. Accord- 
ing to the conclusions we have reached the active deposit particles 
which get positively charged would grow fewer and fewer as the pres- 
sure in the chamber was lowered and the quantity of the deposit which 
would reach the negatively charged electrode through the agency 
of the directive action of its field would then become less and less with 
decreasing pressures. On the other hand, as the pressure was decreased 
the active deposit particles which were uncharged, would reach the 
bounding surface of the chamber including the surface of the negatively 
charged electrode either by projection or diffusion in ever increasing 
amounts, and so unless the negatively charged electrode had a surface 
