The question which I propose to consider in the following pages is a very old one, and one which is almost universally answered with a confident negative. It is this: “Can man imitate the flight of birds by means of a machine set in motion by his own muscular power?” For the sake of brevity, I will call this the problem of man-flight. As I have said, the great majority of people will answer at once, “No,” and will give as their reason the alleged fact that man has not enough power. The fact that a man can raise himself by means of a ladder seemed, however, to me to prove that he is possessed of sufficient power, the difficulty or impossibility of the problem lying in the difficulty or impossibility of constructing an apparatus which should be at the same time reasonably light, and yet take firm hold of the air. In considering this question, the first thing to be done was evidently to ascertain the power a man can exert.