Take a small cork and ask some one to blow it into a fairly large
sized, ordinary bottle that has a neck.
This seems to be quite an easy matter. The one who tries it will
probably blow as hard as possible upon the little cork; but, instead
of going into the bottle, as expected, it will simply fall down. The
harder the puffs or blows, the more obstinate the cork will appear to
be; and even if the effect of blowing gently be tried, it will be of
no use; the cork will not go into the bottle, much to the amusement
of those who are watching. The reason why the cork will not go in is
this: The bottle being already full of air, when the cork is blown,
more air will be forced into the bottle, and consequently the air
inside will be greatly compressed and will simply force the cork back.
The following is a simple way of overcoming the difficulty: Instead
of trying to force the cork through the compressed air in the bottle,
just the contrary should be tried, that is, some of the air should
be sucked out of the bottle; this being done, the bottle will become
partly emptied, and when the outside air rushes in to fill up the
empty space, it will carry the cork with it to the bottom of the
bottle.
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