thousands of millions of years. It is in radium and its offspring
that we see most clearly the constitution of matter.

A gramme (less than 15 1/2 grains) of radium contains-- we will
economise our space--4x10 (superscript)21 atoms. This tiny mass
is, by its discharge, parting with its substance at the rate of
one atom per second for every 10,000,000,000 atoms; in other
words, the "indestructible" atom has, in this case, a term of
life not exceeding 2500 years. In the discharge from the radium
three elements have been distinguished. The first consists of
atoms of the gas helium, which are hurled off at between 10,000
and 20,000 miles a second. The third element (in the order of
classification) consists of waves analogous to the Rontgen rays.
But the second element is a stream of electrons, which are
expelled from the atom at the appalling speed of about 100,000
miles a second. Professor Le Bon has calculated that it would
take 340,000 barrels of powder to discharge a bullet at that
speed. But we shall see more presently of the enormous energy
displayed within the little system of the atom. We may add that
after its first transformation the radium passes, much more
quickly, through a further series of changes. The frontiers of
the atomic systems were breaking down.

The next step was for students (notably Soddy and Rutherford) to
find that radio-activity, or spontaneous discharge out of the
atomic systems, was not confined to radium. Not only are other
rare metals conspicuously active, but it is found that such
familiar surfaces as damp cellars, rain, snow, etc., emit a
lesser discharge. The value of the new material thus provided for
the student of physics may be shown by one illustration. Sir J.