This was first demonstrated by Borelli, an eminent Italian mathematician and philosopher, who lived in a fertile age of discovery, and was thoroughly acquainted with the true principles of mechanics and pneumatics. He showed, by accurate calculation, the prodigious force, which in birds must be exerted and maintained by the pectoral muscles, with which the all-wise Creator has supplied them, and, by applying the same principles to the structure of the human frame, he proved how extremely disproportionate was the strength of the corresponding muscles in man. In fact, the man who should attempt to fly like a bird would be guilty of greater folly and ignorant presumption than the little infant who should endeavour to perform the feats of a gladiator! It is well for man in all things to attain, if possible, to a knowledge of what certainly lies beyond his powers, for such knowledge prevents the waste and misdirection of energies, as well as saving from disappointment and other evil results. But many of those enthusiasts, who have attempted at various periods of the world's history to fly, did not fall into the error which we have attempted to point out. On the contrary, they went intelligently to work; their only aim being modestly to fly _somewhat_ after the manner of a bird, but they all failed; nevertheless one philosopher, of modern times, stoutly continued to assert the opinion that there is no impossibility in man being able to fly _apparently_, though not really, like a bird. He did not hold that man could ever fly as high, or as far, or as fast, or in any degree as easily, as a bird. All that he ventured to say was, that he might perhaps fly _somewhat like one_. As the plan of this philosopher is rather curious, we shall detail it. It is well known that balloons, filled with appropriate gas, will rise. Big balloons and little ones are equally uppish in their tendencies. It is also known that rotundity of form is not essential to the successful rising of a balloon. "Well, then," says this philosopher, "what is to prevent a man making two balloons, flattish, and in the form of wings, which, instead of flying away with him, as ordinary balloons would infallibly do, should be so proportioned to his size and weight as that they would not do more than raise him an inch or so off the ground, and so keep him stotting and bobbing lightly about, something like the bright thin india-rubber balls with which children are wont to play now-a-days?