218 Profs. E. Rutherford and H. T. Barnes on the 
Although the experimental results are not yet complete 
enough to settle definitely whether the heating effect of each 
of the products is proportional to its activity, measured by 
the a rays, the results, as far as they have gone, indicate 
that this is approximately the case. The heating effect is 
certainly directly connected with the radioactivity of radium, 
and the time-variation of the heating effect of each of the 
radioactive products is the same as the time-variation of the 
activity. This result shows that the heat emission of radium 
is an accompaniment of the successive changes occurring in 
radium. 
It still remains to be shown how much of the heat emission 
of radium is due to the kinetic energy of the a particles, and 
how much to the atomic systems from which they are ex- 
pelled. Ina mass of radium nearly all the « rays, emitted 
from it, are absorbed in the radium itself. The radium is 
thus subjected to an intense bombardment by the @ particles 
projected from its own mass. There is no doubt that a pro- 
portion of the heating effect of the radium is due to this self 
bombardment, but probably, also, a part is due to the energy 
emitted consequent upon the rearrangement of the com- 
ponents of the atoms from which the a particles are expelled. 
It is not to be expected that the division of heat between 
the two systems would be the same for each active product, 
and, in consequence, that the heating effect of each product 
should be accurately proportional to ils activity measured by 
the a rays. 
In the experiments made on the heating effect, the a rays, 
in all cases, were absorbed in the glass envelope, and thus 
added their heating effect to that given out by the systems 
from which they were expelled. A large proportion of the 
8 rays and practically all the y radiation escaped. It has, 
however, been shown* that, in all probability, the energy 
emitted in the form of 8 and y rays is only a small fraction 
of the energy emitted in the form of « rays. 
Amount of Heat from the /manation. 
It has been shown that the heating ettect from the emana- 
tion, together with that of the active product to which it gives 
rise, is equal to about 75 per cent. of the total heat emission 
of radium. Since 1 gram of radium emits heat at a rate of 
100 gram-calories per hour, the emanation from 1 gram 
of radium in a state of radioactive equilibrium, a few hours 
after its removal, radiates heat at the rate of 75 gram- 
calories per hour. Since the rate of heat emission at any 
* Rutherford and Grier, Phil. Mag. Sept. 1902. 
a 

