78 THE ROYAL SOCIETY OF CANADA 
calculate from my determinations the heating effects due to the g and ¥ 
rays from a curie of radium C, making the assumption that the energy 
expended in ionization is a measure of their heating effects when ab- 
sorbed. 
Total Ions | 
Rays. per Second. | Calories/hour. 
| ae 
ics tastes foun Patil hoe Se ede al 244 X 10" | 103-6 
PRE el ANE ae ets nf X 10] 2-0 (6) 
MN nr San RS ET ENS 0 PONT ae 10-2 10") | 4-4 
| a 
110-0 
Thus, the 8 and y rays together contribute 6 per cent. of the total 
heat, and the y rays alone 4 per cent.* This result agrees well with 
the measurements of Rutherford and Barnes, who obtained an increase 
of about two calories an hour, when about one-half to one-third of the 
y rays were absorbed in a lead cylinder. 
The energy required to make an ion may be calculated from any 
of the above relations and the results must, of course, be concordant. 
The value obtained is 5-2 x 10“ergs perion. If the work required 
to produce an ion is e’/r, where r is the radius of a molecule, it follows 
that the radius of a molecule is 0-46X10% cm., a result of the right 
order, but apparently somewhat small. Townsend has found that the 
minimum energy required to make an ion is 2-5X10™ ergs. 
If the old view of the y rays is examined, which supposed that the 
expulsion of a g particle caused an electro-magnetic pulse with uniform 
distribution of energy near a spherical shell, some remarkable results 
follow. The work of Wulff on the penetration radiation on the Eiffel 
Tower proves that the y rays from radium and thorium in the earth 
reach a height of 300 metres, and ionize there. This paper shows that 
the mean range of a y-ray disturbance is 250 metres. It has already 
been pointed out that Townsend found the minimum energy required to 
make an ion is 2-5X10™! ergs, and such an ion may be produced by 
y rays at 300 m. from the radioactive source. If A is the area of the 
cross section of a molecule, we have over a surface A at distance 250 m. 
from the centre at least 2-5X10 ergs. Therefore, over surface A at 
1 cm. from the source there must be an energy 2-510 X (25000)?, 
or -0156 ergs. 
* Rutherford, “ Radioactivity,’ p. 200, has calculated the energy ratio for v 
and B particles, as 83 for a # particle with velocity 1-5 X 10°. 
t+ Phys. Zeit., 15th Sept., 1910. 
