Our readers are well aware that the above question has been answered, theoretically, in the affirmative many times; but it has never been practically answered except in the negative. We mean, of course, an artificial flying machine capable of performing flight independent of ordinary winds and currents, so that under most common circumstances it can be trusted to perform its work as ships do now, and have done for centuries. Man has made himself master of the treacherous sea, can he not also penetrate the aerial depths and control his motions in that element ? Much as has been said, written, and done in the elucidation of this subject, it is astonishing how little has been to the purpose. The inventions which have from time to time been made and tried only to demonstrate their utter absurdity, have been for the most part constructed in apparent ignorance of the true principles involved; and those who have criticised these inventions and ridiculed them have shown, in a majority of instances, almost as much ignorance as those whose work they have condemned. Notwithstanding the failures which have uniformly attended the attempts to construct a useful flying machine, and the emphatic negative given by a large number of scientific writers to the question which heads our article, the belief in the ultimate accomplishment of flight by means of human devices has never lacked adherents among the learned and the unlearned. The organization of the Aeronautical Society, which gave its first exhibition at London last June, is an evidence that the belief is gaining rather than losing ground. Let us, then, examine the merits of this question. The report of the above society contains some curious matter in the description of the engines exhibited. Steam en gines have usually been considered as quite inapplicable to any possible flying machine, on account of the high relation their weight bears to their power. But what are we to say of an engine weighing only sixte.en lbs., and being able to work to one-horse power ? The council of the society voted their 100 prize to Mr. Stringfellow for an engine of this description; and whether or not it ever becomes the motive power for flight, it would seem, from its ingenuity, to be well worth the reward. The cylinder, the report tells us, is 2 inches in diameter, stroke 3 inches, and works with a boiler pressure of 100 lbs. to the square inch; the engine working 300 revolutions per minute. The time of getting up the steam was noted; in three minutes after lighting the fire the pressure was 30 lbs.; in five minutes, 50 lbs.; and in seven minutes there was the full working pressure of 100 lbs. When started, the engine had a fair amount of duty to perform in driving two four-bladed screw propellers, 3 feet in diameter, at 300 revolutions a minute. The data for calculating the power are taken as follows : Area of piston, 3 inches; pressure in cylinder, 80 lbs. per square inch; length of stroke, 3 inches; velocity of piston, 150 feet per minute; 3 X 80 X 150 = 36,000 footpounds. This makes rather more than one-horse power (which is reckoned at 33,000 foot-pounds). The weight of the engine and boiler was only 13 lbs., and it is probably.the lightest steam engine that has ever been constructed. The engine, boiler, car, and propeller together were afterwards weighed, but without water and fuel, and were found toi6 16 lbs. This engine seems to demonstrate thepossibility of making engines light and powerful enough for purposes of flight The American wild goose frequently weighs more than this entire machine, boiler, propeller, and all; and the power exerted by this bird in flight, must be vastly less than that per, formed by the engine, according to the report referred to. Borelli assumed that a goose exerts in flight a force of 400-horse power, an estimate so wild and extravagant that it is simply ridiculous. Dr. Fox, of Scarborough, has translated an instructive paper written by M. de Lucy, of Paris, On the Flight of Birds, of Bats, and of Insects, in reference to the subject of aerial locomotion; in which it is stated, as the result of numerous investigations, that in flying animals the extent of winged surface is always in inverse ratio to th-e weight of the creature. He compares gnats, dragon-flies large and small, ladybirds, daddy-longlegs, bees, marsh-flies, drones, cockchafers, stag-beetles, and rhinoceros-beetles together, and arrives at the following highly interesting and unexpected results. The gnat, which weighs 460 times less than the stag-beetle, has 14 times more of (proportional) surface. The ladybird weighs 150 times less than the stag-beetle, and possesses 5 times more of surface, etc.; and it is the same with birds. The sparrow weighs about 10 times less than the pigeon, and has twice as much surface. The pigeon weighs about 8 times less than the stork, and has twice as much surface. The sparrow weighs 339 times less than the Australian crane, and possesses 7 times more surface. If we now compare the insects and the birds, the, gradation will become even more striking. The gnat, for example, weighs 97,000 times less than the pigeon, and has 40 times more surface; it weighs three million times less than the Australian crane, and possesses 140 times more surface. Coulomb calculated that in order to support a man it would be necessary to have a surface 12,789 feet and 2 inches in length, by 191 feet and 10 inches in breadth, but it has been since ascertained that a man can descend quite easily from a great elevation, with a supporting surface of 29 square yards, 8 square feet, and 14 square inches. This superfices reduced to a square gives the length of a side 53 linear yards, nearly. The length of supporting beams from the center needs therefore to be only about 275 yards, provided their own weight is not taken into account. Precisely here comes in the first difficulty. These arms or beams necessary to sustain a web of silk or other texture, must have strength, rigidity, and lightness. When man can make a structure as strong; as rigid, as elastic, as light in proportion to bulk as a goose quill, the problem of flight will be nearly solved. Compensation for want of power in the muscles of the chest may be made by calling into play those of the thighs and legs as well as the arms, by means of suitable appliances. What is now required, is a material combining greatest strength with least weight. We know of no such material now available for the purpose. We therefore conclude that until such materials are discovered man will not fly. To use the words of one of the sages of a shop in which many of our youthful days were spent, flying is, at present, theoretically practicable, but practically impracticable.”