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,
see how it glows! This is the glorious lime-light, which rivals the
voltaic-light, and which is almost equal to sunlight. I have here a piece
of carbon or charcoal, which will burn and give us light exactly in the
same manner as if it were burnt as part of a candle. The heat that is in
the flame of a candle decomposes the vapour of the wax, and sets free the