ascending current; but, in order to give you a notion of the quantity of
matter which ascends in this way, I will make an experiment by which I
shall try to imprison some of the products of this combustion. For this
purpose I have here what boys call a fire-balloon. I use this fire-balloon
merely as a sort of measure of the result of the combustion we are
considering; and I am about to make a flame in such an easy and simple
manner as shall best serve my present purpose. This plate shall be the
"cup," we will so say, of the candle; this spirit shall be our fuel; and I
am about to place this chimney over it, because it is better for me to do
so than to let things proceed at random.

[Illustration: Fig. 10.]

Mr. Anderson will now light the fuel, and here at the top we shall get the
results of the combustion. What we get at the top of that tube is exactly
the same, generally speaking, as you get from the combustion of a candle;
but we do not get a luminous flame here, because we use a substance which
is feeble in carbon. I am about to put this balloon--not into action,
because that is not my object--but to shew you the effect which results
from the action of those products which arise from the candle, as they
arise here from the furnace. [The balloon was held over the chimney, when
it immediately commenced to fill.] You see how it is disposed to ascend;
but we must not let it up, because it might come in contact with those
upper gas-lights, and that would be very inconvenient. [The upper
gas-lights were turned out, at the request of the Lecturer, and the
balloon was allowed to ascend.] Does not that shew you what a large bulk
of matter is being evolved? Now, there is going through this tube [placing
a large glass tube over a candle] all the products of that candle, and you
will presently see that the tube will become quite opaque. Suppose I take
another candle, and place it under a jar, and then put a light on the