3d, The great rapidity with which wings, especially insect wings, are made to vibrate, and the difficulty experienced in analysing their movements.
4th, The great weight of all flying things when compared with a corresponding volume of air.
5th, The discovery of the balloon, which has retarded the science of aërostation, by misleading men’s minds and causing them to look for a solution of the problem by the aid of a machine lighter than the air, and which has no analogue in nature.
Flight has been unusually unfortunate in its votaries. It has been cultivated, on the one hand, by profound thinkers, especially mathematicians, who have worked out innumerable theorems, but have never submitted them to the test of experiment; and on the other, by uneducated charlatans who, despising the abstractions of science, have made the most ridiculous attempts at a practical solution of the problem.
Flight, as the matter stands at present, may be divided into two principal varieties which represent two great sects or schools—
1st, The Balloonists, or those who advocate the employment of a machine specifically lighter than the air.
2d, Those who believe that weight is necessary to flight. The second school may be subdivided into
(a) Those who advocate the employment of rigid inclined planes driven forward in a straight line, or revolving planes (aërial screws); and
(b) Such as trust for elevation and propulsion to the vertical flapping of wings.