disappears, if burned properly, without the least trace of dirt in the
candlestick--and this is a very curious circumstance. In order, then, to
examine this candle carefully, I have arranged certain apparatus, the use
of which you will see as I go on. Here is a candle: I am about to put the
end of this glass tube into the middle of the flame--into that part which
old Hooker has represented in the diagram as being rather dark, and which
you can see at any time, if you will look at a candle carefully, without
blowing it about. We will examine this dark part first.

[Illustration: Fig. 7.]

Now, I take this bent glass tube, and introduce one end into that part of
the flame, and you see at once that something is coming from the flame,
out at the other end of the tube; and if I put a flask there, and leave it
for a little while, you will see that something from the middle part of
the flame is gradually drawn out, and goes through the tube and into that
flask, and there behaves very differently from what it does in the open
air. It not only escapes from the end of the tube, but falls down to the
bottom of the flask like a heavy substance, as indeed it is. We find that
this is the wax of the candle made into a vaporous fluid--not a gas. (You
must learn the difference between a gas and a vapour: a gas remains
permanent, a vapour is something that will condense.) If you blow out a
candle, you perceive a very nasty smell, resulting from the condensation
of this vapour. That is very different from what you have outside the
flame; and, in order to make that more clear to you, I am about to produce
and set fire to a larger portion of this vapour--for what we have in the
small way in a candle, to understand thoroughly, we must, as philosophers,
produce in a larger way, if needful, that we may examine the different
parts. And now Mr. Anderson will give me a source of heat, and I am about
to shew you what that vapour is. Here is some wax in a glass flask, and I