ances disintegrate much
faster than others. Thus Uranium changes very slowly, taking
5,000,000,000 years to reach the same stage of disintegration that
Radium A reaches in 3 minutes. As the disintegration proceeds, the
substances become of lighter and lighter atomic weights. Thus Uranium
has an atomic weight of 238, whereas lead has an atomic weight of only
206. The breaking down of atoms is fully explained in the text.]

[Illustration: _Reproduced by permission from "The Interpretation of
Radium" (John Murray)._

SILK TASSEL ELECTRIFIED

The separate threads of the tassel, being each electrified with the same
kind of electricity, repel one another, and thus the tassel branches out
as in the photograph.]

[Illustration: SILK TASSEL DISCHARGED BY THE RAYS FROM RADIUM

When the radium rays, carrying an opposite electric charge to that on
the tassel, strikes the threads, the threads are neutralised, and hence
fall together again.]

[Illustration: A HUGE ELECTRIC SPARK

This is an actual photograph of an electric spark. It is leaping a
distance of about 10 feet, and is the discharge of a million volts. It
is a graphic illustration of the tremendous energy of electrons.]

[Illustration: _From "Scientific Ideas of To-day_."

ELECTRICAL ATTRACTION BETWEEN COMMON OBJECTS

Take an ordinary flower-vase well dried and energetically rub it with a
silk handkerchief. The vase which thus becomes electrified will attract
any light body, such as a feather, as shown in the above illustration.]

Such cells are now made of zinc and carbon, immersed in sal-ammoniac,
but the principle is the same. The flow of electricity is a flow of
electrons; though we ought to repeat that they do not flow in a body, as
molecules of water do. You may have seen boys place a row of bricks,
each standing on one end, in such order that the first, if it is pushed,
will knock over the second, the second the third, and so on to the last.
There is a flow of _movement_ all along the line, but each brick moves
only a short distance. So an electron merely passes to the next atom,
which sends on an electron to a third atom, and so on. In this case,
however, the movement from atom to atom is so rapid that the ripple of
movement, if we may call it so, may pass along at an enormous speed. We
have seen how swiftly electrons travel.

But how is this turned into power enough even to ring a bell? The actual
mechanical apparatus by which the energy of the electr