unchangeable condition before the combustion; but afterwards it is in the
form of gas, which it is very difficult (though we have succeeded) to
produce in a solid or a liquid state.
Now, I must take you to a very interesting part of our subject to the
relation between the combustion of a candle and that living kind of
combustion which goes on within us. In every one of us there is a living
process of combustion going on very similar to that of a candle; and I
must try to make that plain to you. For it is not merely true in a
poetical sense the relation of the life of man to a taper; and if you
will follow, I think I can make this clear. In order to make the relation
very plain, I have devised a little apparatus which we can soon build up
before you. Here is a board and a groove cut in it, and I can close the
groove at the top part by a little cover. I can then continue the groove
as a channel by a glass tube at each end, there being a free passage
through the whole. Suppose I take a taper or candle (we can now be liberal
in our use of the word candle, since we understand what it means), and
place it in one of the tubes; it will go on, you see, burning very well.
You observe that the air which feeds the flame passes down the tube at one
end, then goes along the horizontal tube, and ascends the tube at the
other end in which the taper is placed.
[Illustration: Fig. 32]
If I stop the aperture through which the air enters, I stop combustion, as
you perceive. I stop the supply of air, and consequently the candle goes
out. But, now, what will you think of this fact? In a former experiment I
shewed you the air going from one burning candle to a second candle. If I
took the air proceeding from another candle, and sent it down by a
complicated arrangement into this tube, I should put this burning candle
out. But what will you say when I tell you that my breath will put out
that candle? I do not mean by blowing at all, but simply that the nature
of my breath is such that a candle cannot burn in it. I will now hold my
mouth over the aperture, and without blowing the flame in any way, let no
air enter the tube but what comes from my mouth. You see the result. I did
not blow the candle out. I merely let the air which I expired pass into
the aperture, and the result was that the light went out for want of
oxygen, and for no other reason. Something or other namely, my lungs had
taken away the oxygen from the air, and there was no more to supply the
combustion of the candle. It is, I think, very pretty to see the time it
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