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 flight of birds.
3.

Aeroplanes, which are merely inclined planes like kites, but towed or driven by screws.
Each of these systems has had and still has it partisans obstinately resolved to give way in not the slightest particular.

However, Robur, for many reasons, had rejected the two first.
The ornithopter, or mechanical bird, offers certain advantages, no doubt.