physical matter, it cannot be heaped up where it is required in
unlimited quantities.

All this changed directly man succeeded in producing energy
electro-magnetically by the mere rotation of material masses, and in
using the water-power of the earth - itself ultimately derived from the
cosmic energies of the sun - for driving his dynamos. Not only is the
source of energy thus tapped practically inexhaustible, but the
machines produce it without consuming on their own account, apart from
wear and tear, and so make possible the almost limitless accumulation
of power in one place. For electricity is distinguished from all other
power-supplying natural forces, living or otherwise, precisely in this,
that it can be concentrated spatially with the aid of a physical
carrier whose material bulk is insignificant compared with the energy
supplied.

Through this property of electricity it has been possible for man to
extend the range of his activity in all directions, far and near. So
the balance between production and consumption, which in previous ages
was more or less adequately maintained by natural conditions, has been
entirely destroyed, and a major social-economic problem created.

In yet another way, and through quite another of its properties,
electricity plays an important part in modern life. Not only does it
compete with the human will; it also makes possible automatically
intelligent operations quite beyond anything man can do on his own.
There are innumerable examples of this in modern electrical technology;
we need mention here only the photo-electric cell and the many devices
into which it enters.