ce of potato, for instance,
or an apple, and take the tube and cut out a pellet, as I have now done,
and push it to one end. I have made that end tight; and now I take another
piece and put it in: it will confine the air that is within the tube
perfectly and completely for our purpose; and I shall now find it
absolutely impossible by any force of mine to drive that little pellet
close up to the other. It cannot be done. I may press the air to a certain
extent, but if I go on pressing, long before it comes to the second, the
confined air will drive the front one out with a force something like that
of gunpowder; for gunpowder is in part dependent upon the same action that
you see here exemplified.

I saw the other day an experiment which pleased me much, as I thought it
would serve our purpose here. (I ought to have held my tongue for four or
five minutes before beginning this experiment, because it depends upon my
lungs for success.) By the proper application of air I expect to be able
to drive this egg out of one cup into the other by the force of my breath;
but if I fail, it is in a good cause; and I do not promise success,
because I have been talking more than I ought to do to make the experiment
succeed.

[The Lecturer here tried the experiment, and succeeded in blowing the egg
from one egg-cup to the other.]

You see that the air which I blow goes downwards between the egg and the
cup, and makes a blast under the egg, and is thus able to lift a heavy
thing--for a full egg is a very heavy thing for air to lift. If you want
to make the experiment, you had better boil the egg quite hard first, and
then you may very safely try to blow it from one cup to the other, with a
little care.

I have now kept you long enough upon this property of the weight of the
air, but there is another thing I should like to mention. You saw the way
in which, in this popgun, I was able to drive the second piece of potato
half or two-thirds of an inch before the first piece started, by virtue of
the elasticity of the air--just as I pressed into the copper bottle the
particles of air by means of the pump. Now, this depends upon a wonderful
property in the air, namely, its elasticity; and I should like to give you
a good illustration of this. If I take anything that confines the air
properly, as this membrane, which also is able to contract and expand so
as to give us a measure of the elasticity of the air, and confine in this
bladder a ce