The whole material universe is supposed to be embedded in a vast medium
called the ether. It is true that the notion of the ether has been
abandoned by some modern physicists, but, whether or not it is
ultimately dispensed with, the conception of the ether has entered so
deeply into the scientific mind that the science of physics cannot be
understood unless we know something about the properties attributed to
the ether. The ether was invented to explain the phenomena of light, and
to account for the flow of energy across empty space. Light takes time
to travel. We see the sun at any moment by the light that left it 8
minutes before. It has taken that 8 minutes for the light from the
sun to travel that 93,000,000 miles odd which separates it from our
earth. Besides the fact that light takes time to travel, it can be shown
that light travels in the form of waves. We know that sound travels in
waves; sound consists of waves in the air, or water or wood or whatever
medium we hear it through. If an electric bell be put in a glass jar and
the air be pumped out of the jar, the sound of the bell becomes feebler
and feebler until, when enough air has been taken out, we do not 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._