is puzzled, right at the outset, with the meaning of my title, _The
Diving Bell_. It is plain enough to Uncle Frank, and possibly it is to
you; but it may not be; so I will tell you what a diving bell is, and
then, probably, you can guess the reason why I have given this name to
the following pages.

If you will take a common glass tumbler, and plunge it into water,
with the mouth downwards, you will find that very little water will
rise into the tumbler. You can satisfy yourself better about this
matter, if, in the first place, you lay a cork upon the surface of the
water, and then put the tumbler over it.

Did you ever try the experiment? Try it now, if you never have done
so, and if you have any doubt on the subject.

You might suppose, that the cork would be carried down far below the
surface of the water. But it is not so. The upper side of the cork,
after you have pressed the tumbler down so low that the upper end of
it is even below the surface of the water--the upper side of the cork
is not wet at all.

"And what is the reason of this, Uncle Frank?"

I will tell you. There is air in the tumbler, when you plunge it into
the water. The air stays in the vessel, so that there is no room for
the water.

"Oh, yes, sir; I see how that is. But I see that a little water finds
its way into the tumbler, every time I try the experiment. How is
that?"