purpose of giving out light. When we use oil, or gas, or candle, for the
purpose of illumination, their fitness all depends upon these different
kinds of combustion.
There are such curious conditions of flame, that it requires some
cleverness and nicety of discrimination to distinguish the kinds of
combustion one from another. For instance, here is a powder which is very
combustible, consisting, as you see, of separate little particles. It is
called _lycopodium_[7], and each of these particles can produce a vapour,
and produce its own flame; but, to see them burning, you would imagine it
was all one flame. I will now set fire to a quantity, and you will see the
effect. We saw a cloud of flame, apparently in one body; but that rushing
noise [referring to the sound produced by the burning] was a proof that
the combustion was not a continuous or regular one. This is the lightning
of the pantomimes, and a very good imitation. [The experiment was twice
repeated by blowing lycopodium from a glass tube through a spirit-flame.]
This is not an example of combustion like that of the filings I have been
speaking of, to which we must now return.
Suppose I take a candle, and examine that part of it which appears
brightest to our eyes. Why, there I get these black particles, which
already you have seen many times evolved from the flame, and which I am
now about to evolve in a different way. I will take this candle and clear
away the gutterage, which occurs by reason of the currents of air; and if
I now arrange a glass tube so as just to dip into this luminous part, as
in our first experiment, only higher, you see the result. In place of
having the same white vapour that you had before, you will now have a
black vapour. There it goes, as black as ink. It is certainly very
different from the white vapour; and when we put a light to it, we shall
find that it does not burn, but that it puts the light out. Well, these
particles, as I said before, are just the smoke of the candle; and this
brings to mind that old employment which Dean Swift recommended to
servants for their amusement, namely, writing on the ceiling of a room
with a candle. But what is that black substance? Why, it is the same
carbon which exists in the candle. How comes it out of the candle? It
evidently existed in the candle, or else we should not have had it here.
And now I want you to follow me in this explanation. You would hardly
think that all those substances which fly about London, in the form of
soots and blacks, are the very beauty and life of the flame, and which are
burned in it as those iron filings were burned here. Here is a piece of
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