wire gauze, which will not let the flame go through it; and I think you
will see, almost immediately, that when I bring it low enough to touch
that part of the flame which is otherwise so bright, that it quells and
quenches it at once, and allows a volume of smoke to rise up.
I want you now to follow me in this point, that whenever a substance
burns, as the iron filings burnt in the flame of gunpowder, without
assuming the vaporous state (whether it becomes liquid or remains solid),
it becomes exceedingly luminous. I have here taken three or four examples
apart from the candle, on purpose to illustrate this point to you; because
what I have to say is applicable to all substances, whether they burn or
whether they do not burn, that they are exceedingly bright if they retain
their solid state, and that it is to this presence of solid particles in
the candle-flame that it owes its brilliancy.
Here is a platinum-wire, a body which does not change by heat. If I heat
it in this flame, see how exceedingly luminous it becomes. I will make the
flame dim, for the purpose of giving a little light only, and yet you will
see that the heat which it can give to that platinum-wire, though far less
than the heat it has itself, is able to raise the platinum-wire to a far
higher state of effulgence. This flame has carbon in it; but I will take
one that has no carbon in it. There is a material, a kind of fuel a
vapour, or gas, whichever you like to call it in that vessel, and it has
no solid particles in it; so I take that because it is an example of flame
itself burning without any solid matter whatever; and if I now put this
solid substance in it, you see what an intense heat it has, and how
brightly it causes the solid body to glow. This is the pipe through which
we convey this particular gas, which we call hydrogen, and which you shall
know all about next time we meet. And here is a substance called oxygen,
by means of which this hydrogen can burn; and although we produce, by
their mixture, far greater heat[8] than you can obtain from the candle,
yet there is very little light. If, however, I take a solid substance, and
put that into it, we produce an intense light If I take a piece of lime, a
substance which will not burn, and which will not vaporise by the heat
(and because it does not vaporise, remains solid, and remains heated), you
will soon observe what happens as to its glowing. I have here a most
intense heat, produced by the burning of hydrogen in contact with the
oxygen; but there is as yet very little light not for want of heat, but
for want of particles which can retain their solid state; but when I hold
this piece of lime in the flame of the hydrogen as it burns in the oxygen,
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