and the feathers are extremely light, compared
with their sustaining powers.

THE HELICOPTER MOTION.--The helicopter, or
helix-wing, is a form of flying machine which depends
on revolving screws to maintain it in the
air. Many propellers are now made, six feet in
length, which have a pull of from 400 to 500
pounds. If these are placed on vertically-disposed
shafts they would exert a like power to
raise a machine from the earth.

Obviously, it is difficult to equip such a machine
with planes for sustaining it in flight, after it is
once in the air, and unless such means are provided
the propellers themselves must be the
mechanism to propel it horizontally.

This means a change of direction of the shafts
which support the propellers, and the construction
is necessarily more complicated than if they
were held within non-changeable bearings.

This principle, however, affords a safer means
of navigating than the orthopter type, because
the blades of such an instrument can be forced
through the air with infinitely greater speed than
beating wings, and it devolves on the inventor to
devise some form of apparatus which will permit
the change of pull from a vertical to a horizontal