16 THE EVOLUTION OF LIFE 
all the more real and forcible by modern investiga- 
tions concerning radium—in which a spontaneous 
disintegration seems to be constantly occurring in 
some of its highly complex atoms. Like changes 
are known to occur in thorium, uranium, and actinium, 
and will probably be met with in other elements. 
The astounding discovery made in 1901 by 
Professor and Madame Curie that radium main- 
tained itself at a temperature nearly 3° F. above 
that of the surrounding atmosphere, was first 
explained by Professor Rutherford and F. Soddy as 
due to a spontaneous disintegration of the radium 
atom, and the bombarding of its substance by the 
corpuscles and a/pha rays thus liberated—acting as 
minute projectiles and moving with inconceivable 
rapidity. They showed also that among the pro- 
ducts of disintegration there were, in an ‘‘emana- 
tion,’ atoms of a density comparable with those of 
hydrogen and helium. 
Subsequently Sir William Ramsay, in conjunction 
with F. Soddy, collected this gas, or emanation, 
evolved from salts of radium, and, writing on 
this subject, the former investigator says!: ‘We 
showed that this gas, presumably of high density, 
disintegrates in its turn, and that perhaps 7 per 
cent. of it changes into hellum. What becomes of 
the remaining 93 per cent. 1s as yet undecided ; still 
‘some hint may be gained from the fact that a 
constant ratio exists between the amount of helium 
obtainable from a mineral and the weight of lead 
which it contains. It may be that lead forms the 
1 The Atheneum, March Io, 1906, p. 301. 
