, while it is a well-known matter of record
that both arc and incandescent lights were invented long before
Faraday's time, yet it was not until a source of electricity was
invented, superior both in economy and convenience to the voltaic
battery, that either of these lights became commercial possibilities.
Such an electric source was given to the world by Faraday through his
invention of the dynamo-electric machine, and it was not until this
machine was sufficiently developed and improved that commercial electric
lighting became possible. The energy of burning coal, through the
steam-engine, working the dynamo, is far cheaper and more efficient for
producing electricity than the consumption of metals through the
voltaic pile.

It is characteristic of the modesty of Faraday that when, in
after-life, he heard inventors speaking of their electric lights, he
refrained from claiming the electric light as his own, although, without
the machine he taught the world how to construct, commercial lighting
would have been an impossibility.

The marvellous activity in the electric arts and sciences, which
followed as a natural result of Faraday giving to the world in the
dynamo-electric machine a cheap electric source, naturally leads to the
inquiry as to whether at a somewhat later day a yet greater revolution
may not follow the production of a still cheaper electric source. In
point of fact such a discovery is by no means an impossibility. When a
dynamo-electric machine is caused to produce an electric current by the
intervention of a steam-engine, the transformation of energy which takes
place from the energy of the coal to electric energy is an extremely
wasteful one. Could some practical method be discovered by means of
which the burning of coal liberates electric energy, instead of heat
energy, an electric source would be discovered that would far exceed in
economy the best dynamo in existence. With such a discovery what the
results would be no one can say; this much is certain, that it would,
among other things, relegate the steam-engine to the scrap-heap, and
solve the problem of aerial navigation.

What is justly regarded as one of the greatest achievements of modern
times is the electrical transmission of power over comparatively great
distances. At some cheap source of energy, say, at a waterfall, a
water-wheel is employed to drive a dynamo or generator, thus converting
mechanical energy into electrical energy. This e