"From the locomotive to the aeromotive!" shouted the noisiest of all,
who had turned on the trumpet of publicity to awaken the Old and New
Worlds.

Nothing, in fact, is better established, by experiment and
calculation, than that the air is highly resistant. A circumference
of only a yard in diameter in the shape of a parachute can not only
impede descent in air, but can render it isochronous. That is a fact.

It is equally well known that when the speed is great the work of the
weight varies in almost inverse ratio to the square of the speed, and
therefore becomes almost insignificant.

It is also known that as the weight of a flying animal increases, the
less is the proportional increase in the surface beaten by the wings
in order to sustain it, although the motion of the wings becomes
slower.

A flying machine must therefore be constructed to take advantage of
these natural laws, to imitate the bird, "that admirable type of
aerial locomotion," according to Dr. Marcy, of the Institute of
France.

In short the contrivances likely to solve the problem are of three
kinds:--

1. Helicopters or spiralifers, which are simply screws with vertical
axes.

2. Ornithopters, machines which endeavour to reproduce the natural