am going to make it hot, as the inside of that candle-flame is hot, and
the matter about the wick is hot. [The Lecturer placed some wax in a glass
flask, and heated it over a lamp.] Now, I dare say that is hot enough for
me. You see that the wax I put in it has become fluid, and there is a
little smoke coming from it. We shall very soon have the vapour rising up.
I will make it still hotter, and now we get more of it, so that I can
actually pour the vapour out of the flask into that basin, and set it on
fire there. This, then, is exactly the same kind of vapour as we have in
the middle of the candle; and that you may be sure this is the case, let
us try whether we have not got here, in this flask, a real combustible
vapour out of the middle of the candle. [Taking the flask into which the
tube from the candle proceeded, and introducing a lighted taper.] See how
it burns. Now, this is the vapour from the middle of the candle, produced
by its own heat; and that is one of the first things you have to consider
with respect to the progress of the wax in the course of its combustion,
and as regards the changes it undergoes. I will arrange another tube
carefully in the flame, and I should not wonder if we were able, by a
little care, to get that vapour to pass through the tube to the other
extremity, where we will light it, and obtain absolutely the flame of the
candle at a place distant from it. Now, look at that. Is not that a very
pretty experiment? Talk about laying on gas--why, we can actually lay on a
candle! And you see from this that there are clearly two different kinds
of action--one the _production_ of the vapour, and the other the
_combustion_ of it--both of which take place in particular parts of the
candle.

[Illustration: Fig. 8]

I shall get no vapour from that part which is already burnt. If I raise
the tube (fig. 7) to the upper part of the flame, so soon as the vapour