x] RADIO-ACTIVE PROCESSES 317 
atoms of the radio-elements, the parts composing the atoms more 
distant from the centre might be able to escape from the central 
attraction and thus give rise to the radiation of energy observed. 
In December 1901, Becquerel! put forward the followmg hypo- 
thesis, which he stated had served him as a guide in his investi- 
gations. According to the view of J. J. Thomson, radio-active 
matter consists of negatively and positively charged particles. The 
former have a mass about 1/1000 of the mass of the hydrogen 
atom, while the latter have a mass about one thousand times 
greater than the negative particle. The negatively charged par- 
ticles (the 8 rays) would be projected with great velocity, but 
the larger positive particles would have much lower velocity and 
would form as a sort of gas (the emanation) which would deposit 
itself on the surface of bodies. This in turn would subdivide 
giving rise to rays (excited activity). 
In a paper communicated to the Royal Society in June 1900, 
Rutherford and McClung? showed that the energy, radiated in 
the form of ionizing rays into the gas, was 3000 gram-calories per 
year for radium of activity 100,000 times that of uranium. Taking 
the latest estimate 1,500,000 of the activity of a pure radium com- 
pound, this would correspond to an emission of energy into the 
- gas in the form of a rays of about 45,000 gram-calories per gram 
per year. The suggestion was put forward that this energy might 
be derived from a re-grouping of the constituents of the atom of 
the radio-elements, and it was pointed out that the possible energy 
to be derived from a greater concentration of the components of 
the atom was large compared with that given out in molecular 
reactions. 
In the original papers’ giving an account of the discovery of the 
emanation of thorium and the excited radio-activity produced by 
it, the writer took the view that both of these manifestations were 
due to radio-active material. The emanation behaved like a gas, 
while the matter which caused excited activity attached itself to 
solids and could be dissolved in some acids but not in others. In 
conjunction with Miss Brooks, it was shown that the radium 
emanation diffused through air like a gas of heavy molecular 
1 C. R. 133, p. 979, 1901. 2 Phil. Trans. A, p. 25, 1901. 
3 Phil. Mag. Jan. and Feb. 1900. 
