[Illustration: FIG. 1.]
Here is a curious experiment in equilibrium (Fig. 1), which is easily
done. Two forks are stuck into a cork, and the cork is placed on the
brim of the neck of a bottle. The forks and the cork form a whole, of
which the centre of gravity is fixed over the point of support. We can
bend the bottle--empty it even, if it contains fluid--without the little
construction over its mouth being in the least disturbed from its
balance. The vertical line of the centre of gravity passes through the
point of support, and the forks move with the cork, which serves as
their support, thus forming a movable structure, but much more stable
than one is inclined to suppose. This curious experiment is often
performed by conjurers, who inform their audience that they will
undertake to empty the bottle without disturbing the cork.
[Illustration: FIG. 2.]
If a woodcock has been served for dinner, or any other bird with a long
beak, take off the head at the extreme end of the neck; then split a
cork so that you can insert into it the neck of the bird, which must be
tightly clipped to keep it in place; two forks are then, fixed into the
cork exactly as in the preceding example, and into the bottom of the
cork a pin is inserted. This little contrivance is next placed on a
piece of money, which has been put on the opening of the neck of the
bottle, and when it is fairly balanced we make it spin round by pushing
one of the forks as rapidly as we please, but as much as possible
without any jerk. We then see the two forks, and the cork surmounted by
the woodcock's head, turning on the slender pivot of a pin (Fig. 2).
Nothing can be more comical than to witness the long beak of the bird
turning round and round, successively facing all the company assembled
round the table, sometimes with a little oscillation, which gives it an
almost life-like appearance.