ese two
things together. I have a little mortar in which I will mix them. (Before
I go into these experiments, let me hope that none of you, by trying to
repeat them, for fun's sake, will do any harm. These things may all be
very properly used if you take care; but without that, much mischief will
be done.) Well, then, here is a little gunpowder, which I put at the
bottom of that little wooden vessel, and mix the iron filings up with it,
my object being to make the gunpowder set fire to the filings and burn
them in the air, and thereby shew the difference between substances
burning with flame and not with flame. Here is the mixture; and when I set
fire to it, you must watch the combustion, and you will see that it is of
two kinds. You will see the gunpowder burning with a flame, and the
filings thrown up. You will see them burning too, but without the
production of flame. They will each burn separately. [The Lecturer then
ignited the mixture.] There is the gunpowder, which burns with a flame;
and there are the filings--they burn with a different kind of combustion.
You see, then, these two great distinctions; and upon these differences
depend all the utility and all the beauty of flame which we use for the
purpose of giving out light. When we use oil, or gas, or candle, for the
purpose of illumination, their fitness all depends upon these different
kinds of combustion.

There are such curious conditions of flame, that it requires some
cleverness and nicety of discrimination to distinguish the kinds of
combustion one from another. For instance, here is a powder which is very
combustible, consisting, as you see, of separate little particles. It is
called _lycopodium_[7], and each of these particles can produce a vapour,
and produce its own flame; but, to see them burning, you would imagine it
was all one flame. I will now set fire to a quantity, and you will see the
effect. We saw a cloud of flame, apparently in one body; but that rushing
noise [referring to the sound produced by the burning] was a proof that
the combustion was not a continuous or regular one. This is the lightning
of the pantomimes, and a very good imitation. [The experiment was twice
repeated by blowing lycopodium from a glass tube through a spirit-flame.]
This is not an example of combustion like that of the filings I have been
speaking of, to which we must now return.

Suppose I take a candle, and examine that part of it which appears
brightest to o