Radioactivity and the Gravitational Field. (359 



be accompanied by a change in the apparent magnitude 

 of the force or! attraction between the body and other 

 bodies in its neighbourhood arising from surface tension. 

 In the analogous system of the aether, — an apparent change 

 in the gravitational force acting on a body would be 

 observed in the case of a body moving with accelerated 

 motion in the aether. 



In conclusion it should be remarked that there does 

 not seem to be anything suggested by the analogy which 

 we have been considering which is directly contrary to or 

 inconsistent with the principle of relativity. At the same 

 time it seems to encourage the view that it may yet be 

 possible to detect absolute motion of the Earth in aether 

 and that it may therefore also be possible to escape from 

 a principle involving so much indefiniteness with respect to 

 fundamental units. In one sense therefore this analogy 

 seems to present an avenue of escape from the principle 

 ■of relativity : for if the velocity of light is really a minimum 

 wave-velocity in aether, then in the apparent changes of 

 inertia of electrons as the velocity of light is approached 

 and in the behaviour of the pulses constituting X-rays, 

 we are beginning to be able to detect velocity relative 

 to aether. 



LXA T . Radioactivity and the Gravitational Field. By 

 Arthur H. Comptw, Ph.F)., National Research Fellow 

 in Physics *. 



IT is well known that in order to account for the age and 

 the present temperature of the earth, the average radio- 

 activity of its component minerals must fall off rapidly a few 

 miles below its surface. The high density of the radioactive 

 minerals, however, makes it appear probable that they should 

 occur more abundantly in the earth's interior than in the 

 surface crust. Thus it appears that substances which at the 

 earth's surface are radioactive may have practically no 

 radioactivity in the earth's interior. These considerations 

 suggest that the rate or energy of radioactive disintegration 

 may be a function of the intensity or potential of the 

 earth's gravitational field. This suggestion appears the 

 more plausible since both radioactivity and gravitation are 

 essential attributes of the atomic nucleus. 



Tt has recently been pointed out by A. Donnan t that 



* Communicated by Prof. Sir E. Rutheiford, F.R.S. 

 t A. Donnan, ' Nature,' Dec. 17, 1919. 



