our when heated), and then heat it, you see the camphor
gas burning on the under side of the gauze, but the camphor gas on the
upper side is not fired (Fig. 33). Plenty of camphor gas is being given
off, but the flame of the burning camphor on the under side is not high
enough to set fire to the camphor gas on the upper side, owing to the
conducting power of the metal between the flame and the upper gas.
There is one other experiment I should like to show you. Upon this
piece of metal gauze I have piled up a small heap of gunpowder. I will
place a spirit-lamp underneath the gunpowder, as you see I am now doing,
and I don't suppose the gunpowder will catch fire. I see the sulphur of
the gunpowder at the present moment volatilizing, but the flame, cooled
by the action of the metal, is not hot enough to set fire to the
gunpowder.

[Illustration: Fig. 32.]

[Illustration: Fig. 33.]

I showed you the steel and flint lamp--if I may call it a lamp--used by
coal-miners at the time of Davy (Fig. 22). Davy set to work to invent a
more satisfactory lamp than that, and the result of his experiments was
the beautiful miner's lamp which I have here (Fig. 34). I regard this
lamp with considerable affection, because I have been down many a
coal-mine with it. This is the coal-miner's safety-lamp. The
old-fashioned form of it that I have here has been much improved, but it
illustrates the principle as well as, if not better than, more elaborate
varieties. It is simply an oil flame covered with a gauze shade, exactly
like that gauze with which I have been experimenting. I will allow a jet
of coal gas to play upon this lamp, but the gas, as you see, does not
catch fire. You will notice the oil flame in the lamp elongates in a
curious manner. The flame of the lamp cooled by the gauze is not hot
enough to set fire to the coal gas, but the appearance of the flame
warns the miner, and tells him when there is danger. And that is the
explanation of the beautiful miner's safety-lamp invented by Sir Humphry
Davy.

[Illustration: Fig. 34.]

Now let me once more put this fact clearly before you, that whether it
is the gas flame or our farthing rushlight, whether it is our lamp or
our lucifer match, if we have a flame we must have a gas to burn, and
having a gas, we must heat it to, and maintain it at, a certain
temperature. We have now reached a point where our tinder-box has
presented us with flame. A flame is indeed the consummated wor