And what does this imply? It implies a great deal: for if all the energy
in the world became unavailable, the universe, as it now is, would cease
to be. It is possible that, by the constant interchange of heat
radiations, the whole universe is tending to some uniform temperature,
in which case, although all molecular motion would not have ceased, it
would have become unavailable. In this sense it may be said that the
universe is running down.
[Illustration: NIAGARA FALLS
The energy of this falling water is prodigious. It is used to generate
thousands of horse-power in great electrical installations. The power is
used to drive electric trams in cities 150 to 250 miles away.]
[Illustration: _Photo: Stephen Cribb._