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.
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