102 THE ROYAL SOCIETY OF CANADA 
who has worked out the case for a homogeneous distribution of radio- 
active matter throughout an infinite depth. With a slight change in 
notation, the result is there obtained in the form 
oOo —T2 
_ 2 Qk — 
Dh €, v dv, 
K 
1 
where à 
n == number of ions produced per second per c.c. 
Q—2-7 xX 1-4 X 10-12 grammes 
k= 034 X 2-7 
k — 3-1 X 10° 
À — -000044 
If we write Ns = Q and h— © in (10), and notice that f( ©) —0, 
we have 
HEART ÉTEND SUR oe (12) 
The integral co —dZ res 
v e du 
7 e ; dv = og pe oF (dz), so that 
1 rz 
(12) agrees with the results obtained by Eve. 
By means of (10) we may compare the effect of surface layers of 
radioactive matter of different depths in their influence on the gradient 
of intensity of penetrating radiation. If we take the intensity at the 
surface z = o as unity, we have to calculate the fraction 
JC) — fe + kh) 
1 — f( kh) 
for various values of zandh. It is more convenient in the use of tables 
to calculate the above fraction for various values of Az and xh. Then, 
by employing the values of À and « given in Eve’s paper, we can find 
the corresponding values of zandh. In the following table a few values 
of the gradient due to layers of different thicknesses are given. The 
height above the earth’s surface (z) is expressed in metres, the thickness 
of the layer of radioactive matter (h) is expressed in centimetres and 
the intensity of the earth’s surface is in each case taken as unity. 
