tion, and there is the white substance into which it burns.
And so, if I take that flame of hydrogen as the representative of a
candle, and shew you a substance like zinc burning in the flame, you will
see that it was merely during the action of combustion that this substance
glowed--while it was kept hot; and if I take a flame of hydrogen, and put
this white substance from the zinc into it, look how beautifully it glows,
and just because it is a solid substance.

I will now take such a flame as I had a moment since, and set free from it
the particles of carbon. Here is some camphine, which will burn with a
smoke; but if I send these particles of smoke through this pipe into the
hydrogen flame, you will see they will burn and become luminous, because
we heat them a second time. There they are. Those are the particles of
carbon re-ignited a second time. They are those particles which you can
easily see by holding a piece of paper behind them, and which, whilst they
are in the flame, are ignited by the heat produced, and, when so ignited,
produce this brightness. When the particles are not separated, you get no
brightness. The flame of coal-gas owes its brightness to the separation,
during combustion, of these particles of carbon, which are equally in that
as in a candle. I can very quickly alter that arrangement. Here, for
instance, is a bright flame of gas. Supposing I add so much air to the
flame as to cause it all to burn before those particles are set free, I
shall not have this brightness; and I can do that in this way:--If I place
over the jet this wire-gauze cap, as you see, and then light the gas over
it, it burns with a non-luminous flame, owing to its having plenty of air
mixed with it before it burns; and if I raise the gauze, you see it does
not burn below[10]. There is plenty of carbon in the gas; but, because the
atmosphere can get to it, and mix with it before it burns, you see how
pale and blue the flame is. And if I blow upon a bright gas-flame, so as
to consume all this carbon before it gets heated to the glowing point, it
will also burn blue: [The Lecturer illustrated his remarks by blowing on
the gas-light.] The only reason why I have not the same bright light when
I thus blow upon the flame is, that the carbon meets with sufficient air
to burn it before it gets separated in the flame in a free state. The
difference is solely due to the solid particles not being separated before
the gas is burnt.

You