For consider our present methods of making artificial light; they are
both wasteful and ineffective.

We want a certain range of oscillation, between 7,000 and 4,000
billion vibrations per second; no other is useful to us, because no
other has any effect upon our retina; but we do not know how to
produce vibrations of this rate. We can produce a definite vibration
of one or two hundred or thousand per second; in other words, we can
excite a pure tone of definite pitch; and we can demand any desired
range of such tones continuously by means of bellows and a keyboard.
We can also (though the fact is less well known) excite momentarily
definite ethereal vibrations of some million per second, as I have
explained at length; but we do not at present seem to know how to
maintain this rate quite continuously. To get much faster rates of
vibration than this we have to fall back upon atoms. We know how to
make atoms vibrate; it is done by what we call "heating" the
substance, and if we could deal with individual atoms unhampered by
others, it is possible that we might get a pure and simple mode of
vibration from them. It is possible, but unlikely; for atoms, even
when isolated, have a multitude of modes of vibration special to
themselves, of which only a few are of practical use to us, and we do
not know how to excite some without also the others. However, we do
not at present even deal with individual atoms; we treat them crowded
together in a compact mass, so that their modes of vibration are
really infinite.

We take a lump of matter, say a carbon filament or a piece of
quicklime, and by raising its temperature we impress upon its atoms
higher and higher modes of vibration, not transmuting the lower into
the higher, but superposing the higher upon the lower, until at length
we get such rates of vibration as our retina is constructed for, and
we are satisfied. But how wasteful and indirect and empirical is the
process. We want a small range of rapid vibrations, and we know no
better than to make the whole series leading up to them. It is as
though, in order to sound some little shrill octave of pipes in an
organ, we are obliged to depress every key and every pedal, and to
blow a young hurricane.

I have purposely selected as examples the more perfect methods of
obtaining artificial light, wherein the waste radiation is only useless
and not noxious. But the old-fashioned plan was cruder even than this;
it consisted simpl