Vv] RATE OF EMISSION OF ENERGY 163 
Curve A shows the variation of the heat emission of the radium 
and curve B of the emanation. The sum total of the rate of heat 
emission of the radium and the emanation together, was at any 
time found to be equal to that of the original radium. The maxi- 
mum heating effect of the tube containing the emanation from 30 
milligrams of radium bromide was 1:26 gram-calories per hour. 
The emanation together with the secondary products which arise 
from it, obtained from one gram of radium, would thus give out 42 
gram-calories per hour. The emanation stored up in the radium 
is thus responsible for more than two-thirds of the heat emission 
from radium. 
After removal of the emanation from radium, the activity, 
measured by the a rays, decays in the course of a few hours to a 
minimum of about 25°/, and then increases to its original value 
after about a month’s interval. At the same time, the apparent 
activity of the emanation in a closed vessel increases to a maximum 
in the course of a few hours and then decays with time according 
to an exponential law, falling to half value in about four days. The 
gradual decay of the activity of the radium, after removal of the 
emanation, is due to the decay of the “excited activity” on the 
radium itself. The increase of the apparent activity of the emana- 
tion is due to the production of “excited activity” on the walls of 
the containing vessel. The variation in heat emission of the radium 
and the emanation in both cases is approximately proportional to 
the activity measured by the a rays. It is not proportional to the 
activity measured by the @ or ¥ rays, for the intensity of the 8 
and ¥ rays falls nearly to zero when the @ radiation of the radium 
is at the minimum of 25 per cent. These results are thus 
in accordance with the view that the heat emission of radium 
accompanies the expulsion of @ particles, and is approximately 
proportional to the number expelled. 
107. Source of the energy. On the theory of atomic dis- 
integration advanced in section 87, this heat 1s derived, not from 
external sources, but from the internal energy of the radium atom. 
The atom is supposed to be a complex system consisting of charged 
parts in very rapid motion, and, in consequence, contains a large 
11—2 
