point
about that. It is by what is called capillary attraction that the fuel
is conveyed to the part where combustion goes on, and is deposited
there, not in a careless way, but very beautifully in the very midst of
the centre of action which takes place around it.

_II.--The Brightness of the Candle_

Air is absolutely necessary for combustion; and, what is more, I must
have you understand that _fresh_ air is necessary, or else we should be
imperfect in our reasoning and our experiments. Here is a jar of air. I
place it over a candle, and it burns very nicely in it at first, showing
that what I have said about it is true; but there will soon be a change.
See how the flame is drawing upwards, presently fading, and at last
going out. And going out, why? Not because it wants air merely, for the
jar is as full now as it was before, but it wants pure, fresh air. The
jar is full of air, partly changed, partly not changed; but it does not
contain sufficient of the fresh air for combustion.

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 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.
It evidently existed in the candle, or else we should not have had it
here. 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. 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, it quells and quenches it at once, and allows a volume of
smoke to rise up.

Whenever a substance burns without assuming the vaporous state--whether
it becomes liquid or remains solid--it becomes exceedingly luminous.
What I 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 when heated, and that it is to this presence of solid
particles in the candle-flame that it owes its brilliancy.

I have here a piece of carbon, or charcoal, which will burn and give us
light exactly in the same manner as