342 RADIO-ACTIVE PROCESSES 

is only 10-"* of that of the single pale moving with the same 
velocity in the same orbit. 
Results of this kind indicate that an atom consisting of a large 
number of revolving electrons may radiate energy extremely slowly, 
and yet, finally, this mimute but continuous drain of energy from 
the atom must result either in a rearrangement of its component 
parts into a new system, or of an expulsion of electrons or groups 
of electrons from the atom. 
A suggestion, due to J. J. Thomson', of a possible mechanism 
to account for the expulsion from the radio-atoms of an a particle, 
z.e. of a connected group of electrons, has recently been explained 
by Whetham? as follows :—“ The sub-atomic corpuscles, when their 
velocity is changing, must radiate ethereal waves. Their energy 
is thus gradually diminished ; and systems of revolving corpuscles, 
permanent while moving fast, may become unstable. As a simple 
example, six bodies at the corners of a plane hexagon under the 
influence of mutual forces may continue, while their velocity 
exceeds a certain limit, to revolve about a central pomt while 
keeping their relative positions. When there is no motion, how- 
ever, this arrangement is impossible, and the six bodies must place 
themselves, five at the corners of a pentagon and one at the centre. 
Thus, as the velocity falls to a certain value, a sudden and ex- 
plosive rearrangement occurs, durmg which, in the complex 
system constituting an atom, the ejection of parts of the system 
becomes possible.” 
207. Radio-activity and the heat of the sun and earth. 
It was pointed out by Mr Soddy and the writer? that the 
maintenance of the sun’s heat for long intervals of time did not 
present any fundamental difficulty if a process of disintegration, 
such as occurs in the radio-elements, were supposed to be taking 
place in the sun. In a letter to Nature (July 9, 1903) W. E 
Wilson showed that the presence of 3°6 grams of radium im each 
cubic metre of the sun’s mass was sufficient to account for the 
present rate of emission of energy by the sun. This calculation 
was based on the estimate of Curie and Laborde, that one gram 
1 Prof. Thomson’s paper has just appeared. Phil. Mag. March, 1904. 
2 Quarterly Review, p. 123, Jan. 1904. 3 Phil. Mag. May, 1903. 
