ot hear
the bell at all. Sound cannot travel in a vacuum. We continue to _see_
the bell, however, so that evidently light can travel in a vacuum. The
invisible medium through which the waves of light travel is the ether,
and this ether permeates all space _and all matter_. Between us and the
stars stretch vast regions empty of all matter. But we see the stars;
their light reaches us, even though it may take centuries to do so. We
conceive, then, that it is the universal ether which conveys that light.
All the energy which has reached the earth from the sun and which,
stored for ages in our coal-fields, is now used to propel our trains and
steamships, to heat and light our cities, to perform all the
multifarious tasks of modern life, was conveyed by the ether. Without
that universal carrier of energy we should have nothing but a stagnant,
lifeless world.

[Illustration: _Photo: Leadbeater._

AN ELECTRIC SPARK

An electric spark consists of a rush of electrons across the space
between the two terminals. A state of tension is established in the
ether by the electric charges, and when this tension passes a certain
limit the discharge takes place.]

[Illustration: _From "Scientific Ideas of To-day."_

AN ETHER DISTURBANCE AROUND AN ELECTRON CURRENT

In the left-hand photograph an electric current is passing through the
coil, thus producing a magnetic field and transforming the poker into a
magnet. The poker is then able to support a pair of scissors. As soon as
the electric current is broken off, as in the second photograph, the
ether disturbance ceases. The poker loses its magnetism, and the
scissors fall.]

We have said that light consists of waves. The ether may be considered
as resembling, in some respects, a jelly. It can transmit vibrations.
The waves of light are really excessively small ripples, measuring from
crest to crest. The distance from crest to crest of the ripples in a
pond is sometimes no more than an inch or two. This distance is
enormously great compared to the longest of the wave-lengths that
constitute light. We say the longest, for the waves of light differ in
length; the colour depends upon the length of the light. Red light has
the longest waves and violet the shortest. The longest waves, the waves
of deep-red light, are seven two hundred and fifty thousandths of an
inch in length (7/250,000 inch). This is nearly twice the length of
deep-violet light-waves, which are 1/67,000 inch. But light