x] RADIO-ACTIVE PROCESSES 339 
amount of energy, on the same principle that a detonator is 
necessary to start some explosives. It has been shown that the 
number of atoms of any radio-active product which break up per 
second is always proportional to the number present. This law 
of change does not throw any light on the question, for it would 
be expected equally on either hypothesis. It has not been found 
possible to alter the rate of change of any product by the appli- 
cation of any known physical or chemical forces, unless possibly it 
is assumed that the force of gravitation which is not under our 
control may influence in some way the stability of the radio-atoms. 
It has been suggested by J. J. Thomson! that the rate of dis- 
integration of radium may be influenced by its own radiations. 
This, at first sight, appears very probable, for a small mass of pure 
radium compound is subjected to an intense bombardment by the 
radiations arising from it, and the radiations are of such a character 
that they might be expected to produce a breaking up of the 
atoms of matter which they traverse. If this is the case the 
radio-activity of a given quantity of radium should be a function 
of its concentration, and should be greater in the solid state than 
when disseminated through a large mass of matter. 
I have recently tried an experiment to see if this were the 
case. Two glass tubes were taken, in one of which was placed a 
few milligrams of pure radium bromide in a state of radio-active 
equilibrium, and in the other a solution of barium chloride. The 
two tubes were connected near the top by a short cross tube and 
the open ends sealed off. The activity of the radium in the solid 
state was tested immediately after its mtroduction by placing it 
in a definite position near an electroscope made of thin metal of 
the type shown in Fig. 11. The increased rate of discharge of the 
electroscope was observed. ‘This rate of discharge was due to the 
8 and y rays from the radium. By placing a lead plate 6 mms. 
in thickness between the radium and the electroscope, the rate of 
discharge observed was then due to the y rays alone. By slightly 
tilting the apparatus, the barium solution flowed into the radium 
tube and dissolved the radium. The tube was well shaken so as 
to distribute the radium uniformly throughout the solution. No 
appreciable change of the activity measured by the y rays was 
1 Nature, April 30, p. 601, 1903. 
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