has been swept out, what comes away will be no longer combustible: It is
already burned. How burned? Why, burned thus:--In the middle of the flame,
where the wick is, there is this combustible vapour; on the outside of the
flame is the air which we shall find necessary for the burning of the
candle; between the two, intense chemical action takes place, whereby the
air and the fuel act upon each other, and at the very same time that we
obtain light the vapour inside is destroyed. If you examine where the heat
of a candle is, you will find it very curiously arranged. Suppose I take
this candle, and hold a piece of paper close upon the flame, where is the
heat of that flame? Do you not see that it is _not_ in the inside? It is
in a ring, exactly in the place where I told you the chemical action was;
and even in my irregular mode of making the experiment, if there is not
too much disturbance, there will always be a ring. This is a good
experiment for you to make at home. Take a strip of paper, have the air in
the room quiet, and put the piece of paper right across the middle of the
flame (I must not talk while I make the experiment), and you will find
that it is burnt in two places, and that it is not burnt, or very little
so, in the middle; and when you have tried the experiment once or twice,
so as to make it nicely, you will be very interested to see where the heat
is, and to find that it is where the air and the fuel come together.

This is most important for us as we proceed with our subject. 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, shewing 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