er substance[6], so that you may
trace its course; for with the spirit alone you could hardly see well
enough to have the opportunity of tracing its direction. By lighting this
spirit-of-wine, we have then a flame produced; and you observe that when
held in the air, it naturally goes upwards.

[Illustration: Fig. 5]

You understand now easily enough why flames go up under ordinary
circumstances--it is because of the draught of air by which the combustion
is formed. But now, by blowing the flame down, you see I am enabled to
make it go downwards into this little chimney--the direction of the
current being changed. Before we have concluded this course of lectures,
we shall shew you a lamp in which the flame goes up and the smoke goes
down, or the flame goes down and the smoke goes up. You see, then, that we
have the power in this way of varying the flame in different directions.

There are now some other points that I must bring before you. Many of the
flames you see here vary very much in their shape by the currents of air
blowing around them in different directions; but we can, if we like, make
flames so that they will look like fixtures, and we can photograph
them--indeed, we have to photograph them--so that they become fixed to us,
if we wish to find out everything concerning them. That, however, is not
the only thing I wish to mention. If I take a flame sufficiently large, it
does not keep that homogeneous, that uniform condition of shape, but it
breaks out with a power of life which is quite wonderful. I am about to
use another kind of fuel, but one which is truly and fairly a
representative of the wax or tallow of a candle. I have here a large ball
of cotton, which will serve as a wick. And, now that I have immersed it in
spirit and applied a light to it, in what way does it differ from an
ordinary candle? Why, it differs very much in one respect, that we have a
vivacity and power about it, a beauty and a life entirely different from
the light presented by a candle. You see those fine tongues of flame
rising up. You have the same general disposition of the mass of the flame
from below upwards; but, in addition to that, you have this remarkable
breaking out into tongues which you do not perceive in the case of a
candle. Now, why is this? I must explain it to you, because when you
understand that perfectly, you will be able to follow me better in what I
have to say hereafter. I suppose some here will have made for t