air cannot get in because the water by its capillary attraction round the
edge keeps it out.

I think this will give you a correct notion of what you may call the
materiality of the air; and when I tell you that the box holds a pound of
it, and this room more than a ton, you will begin to think that air is
something very serious. I will make another experiment, to convince you of
this positive resistance. There is that beautiful experiment of the
popgun, made so well and so easily, you know, out of a quill, or a tube,
or anything of that kind,--where we take a slice 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.