pound; and I have calculated the weight of the air in this room, you
would hardly imagine it, but it is above a ton. So rapidly do the weights
rise up, and so important is the presence of the atmosphere, and of the
oxygen and the nitrogen in it, and the use it performs in conveying things
to and fro from place to place, and carrying bad vapours to places where
they will do good instead of harm.
Having given you that little illustration with respect to the weight of
the air, let me shew you certain consequences of it. You have a right to
them, because you would not understand so much without it. Do you remember
this kind of experiment? Have you ever seen it? Suppose I take a pump
somewhat similar to the one I had a little while ago to force air into the
bottle, and suppose I place it in such a manner that by certain
arrangements I can apply my hand to it: my hand moves about in the air so
easily that it seems to feel nothing, and I can hardly get velocity enough
by any motion of my own in the atmosphere to make sure that there is much
resistance to it.
[Illustration: Fig. 27.]
But, when I put my hand here [on the air-pump receiver, which was
afterwards exhausted], you see what happens. Why is my hand fastened to
this place, and why am I able to pull this pump about? And see! how is it
that I can hardly get my hand away? Why is this? It is the weight of the
air the weight of the air that is above. I have another experiment here,
which I think will explain to you more about it. When the air is pumped
from underneath the bladder which is stretched over this glass, you will
see the effect in another shape: the top is quite flat at present, but I
will make a very little motion with the pump, and now look at it see how
it has gone down, see how it is bent in. You will see the bladder go in
more and more, until at last I expect it will be driven in and broken by
the force of the atmosphere pressing upon it.
[Illustration: Fig. 28.]
[The bladder at last broke with a loud report.] Now, that was done
entirely by the weight of the air pressing on it, and you can easily
understand how that is. The particles that are piled up in the atmosphere
stand upon each other, as these five cubes do. You can easily conceive
that four of these five cubes are resting upon the bottom one, and if I
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