it is able to pick out ascending air currents.

THEORIES ABOUT FLIGHT OF BIRDS.--Then we
are offered the theory that the bird has an instinct
which tells it just how to balance in the
air when its wings are once set in motion.
Frequently, what is taken for instinct, is something
entirely different.

It has been assumed, for instance, that a cyclist
making a turn at a rapid speed, and a bird flying
around a circle will throw the upper part of the
body inwardly to counteract the centrifugal force
which tends to throw it outwardly.

Experiments with the monorail car, which is
equipped with a gyroscope to hold it in a vertical
position, show that when the car approaches a
curve the car will lean inwardly, exactly the same
as a bird, or a cyclist, and when a straight stretch
is reached, it will again straighten up.

INSTINCT.--Now, either the car, so equipped
possesses instinct, or there must be a principle
in the laws of nature which produces the similarity
of action.

In like manner there must be some principle
that is entirely independent of the form of matter,
or its arrangement, which enables the bird