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
wire gauze, which will not let the flame go through it; and I think you
will see, almost immediately, that when I bring it low enough to touch
that part of the flame which is otherwise so bright, that it quells and
quenches it at once, and allows a volume of smoke to rise up.

I want you now to follow me in this point,--that whenever a substance
burns, as the iron filings burnt in the flame of gunpowder, without
assuming the vaporous state (whether it becomes liquid or remains solid),
it becomes exceedingly luminous. I have here taken three or four examples
apart from the candle, on purpose to illustrate this point to you; because
what I have to say is applicable to all substances, whether they burn or
whether they do not burn,--that they are exceedingly bright if they retain
their solid state, and that it is to this presence of solid particles in
the candle-flame that it owes its brilliancy.