on: Fig. 27.]

Let us take another step forward in the story of our tinder-box. Having
produced a red-hot spark and set fire to my tinder, I want you to see
what I do next. I set to work to blow upon my lighted tinder. You
remember, by the bye, that Latin motto of our school-books--_al[)e]re
flammam_, nourish the flame. When I blow on the tinder my object is to
nourish the flame. Here is a pair of common kitchen bellows (Fig. 25);
when the fire is low the cook blows the fire to make it burn up. What is
the object of this blowing operation? It is to supply a larger quantity
of atmospheric oxygen to the almost lifeless fire than it would
otherwise obtain. Oxygen is the spark's nourishment and life, and the
more it gets the better it thrives. Oxygen is an extremely active agent
in nourishing flame. If, for instance, I take a little piece of carbon
and merely set fire to one small corner of it, and then introduce it
into this jar of oxygen, see how brilliantly it burns; you notice how
rapidly the carbon is becoming consumed (Fig. 26). In the tinder-box I
blow on the tinder to supply a larger amount of oxygen to my spark. A
thing to burn under ordinary conditions must have oxygen, and the more
oxygen it gets the better it burns. It does not follow that the supply
of oxygen to a burning body must necessarily come directly from the air.
Here, for instance, I have a squib. I will fire it and put it under
water (Fig. 27). You see it goes on burning whether it is in the water
or out of it, because one of the materials of which the squib is
composed supplies the oxygen. The oxygen is actually locked up inside
the squib. When then I blow upon my tinder, my object is to supply more
oxygen to it than it would get under ordinary conditions. And, as you
see, the more I blow, within certain limits, the more the spark
spreads, until now the whole of my tinder has become red-hot. But my
time is gone, and we must leave the rest of our story for the next
lecture.

LECTURE III.

Recall for a few minutes the facts I brought before you in my last
lecture. The first point we discussed was the preparation of the tinder.
I explained to you that tinder was nothing more than carbon in a
finely-divided state. The second point was, that I had to strike the
steel with the flint in such manner that a minute particle of the iron
should be detached; the force used in knocking it off being sufficient
to make the small particle of iron red-hot. Th