observations show that during the early stages
of flight, before speed is acquired, they depend
on the undulating movement of the wings, and
some of them acquire the initial motion by flapping.
When speed is finally attained it is difficult
for the eye to note the motion of the wings.

SOARING BIRDS MOVE SWIFTLY.--Now, the first
observation is, that soaring birds are swiftly-
moving creatures. As they sail overhead
majestically they seem to be moving slowly. But
distance is deceptive. The soaring bird travels
at great speeds, and this in itself should be sufficient
to enable us to cease wondering, when it is
remembered that swift translation decreases
weight, so that this factor does not, under those
conditions, operate against flight.

MUSCULAR ENERGY EXERTED BY SOARING BIRDS.
--It is not conceivable that the mere will of the
bird would impel it forwardly, without it exerted
some muscular energy to keep up its speed. The
distance at which the bird performs this wonderful
evolution is at such heights from the observer
that the eye cannot detect a movement.

WINGS NOT MOTIONLESS.--While the wings appear
to be absolutely motionless, it is more reasonable
to assume that a slight sinuous movement,
or a rocking motion is constantly kept up, which