MODERN CONCEPTIONS OF THE UNIVERSE. 65 
associated with electrical charges or, possibly, being nothing 
else but electrical charges. The variety of the elements can 
then be accounted for by variations in the number and 
arrangement of these component parts. Even if the component 
parts were merely electrical charges, the inertia and momentum 
of matter could be explained by the principles of electro- 
magnetism. 
§ 6. Radio-active Substances—It used to be thought that the 
molecules of all substances were absolutely incapable of any 
change, but now it has been found that some substances such 
as uranium, radium and thorium, which according to most 
tests behave as elements, suffer transformations into other 
forms which again appear to be elements. ‘This, of course, 
only strengthens the belief that all matter is only a single 
substance under a great variety of forms. The theory 
that molecules are built up of minute parts associated with 
electrical charges promises to account for these transformations 
and for the remarkable effects which are found to accompany 
them. 
Of the radio-active substances, radium is perhaps the most 
amazing. .As radium is being transformed into its child, the 
radio-active gas known as radium emanation, it emits vast 
numbers of positively electrified particles. In a single second 
one milligramme of radium emits about thirty millions of these 
particles, that is, one particle for each inhabitant of England. 
The activity of the radium decays because some of the radium 
ceases to be radium and becomes emanation, which in its turn 
suffers further transformations, but 1,800 years would pass 
before half the radium would be transformed. In spite of the 
excessive smallness of the emitted particles, Rutherford has 
found a way of observing an effect due to a single one. 
To say that these particles are emitted gives a very faint 
notion of the stupendous velocity with which they are shot out, 
for their velocity is about one-fifteenth of the speed of light or 
about ten thousand miles per second. Some of the other 
radio-active substances shoot out negatively charged particles 
whose speed rises, in some cases, to nearly the speed of light. 
The impact of these projectiles upon the surrounding matter 
produces heat and thus a radio-active substance, such as radium, 
maintains itself by self-bombardment at a temperature above 
that of its surroundings. In a single hour one gramme of 
radium produces enough heat to raise one gramme of water 
from the freezing to the boiling point. 
These experimental facts of radio-activity have given us 
