The flight of a shoal of flying-fish as they shoot forth from the dark green wave in a glittering throng, gleaming brightly in the sunshine, is a charming sight. But these fish can scarcely be classed with the creatures of the air, because true flight, that is the manipulation of the wings, is lacking. They are mentioned because they represent, like the kite, the first step toward that true flight which all other creatures in the air possess. They are capable of moving through the air from 500 to 600 feet, and as much as 20 feet above the water. The fish first acquires initial velocity by a preliminary rush through the water, when it throws itself suddenly into the air, and, at the same moment, spreads out, kite-like, at a slight inclination upwards, its extraordinarily large pectoral fins. It keeps up the great speed until its momentum is exhausted, when the same performance is repeated. The fact in favor of mechanical flight is certainly incontrovertible that less surface and less power is required and flight maintained the longest, in proportion to heavier bodies. It must be convincing, therefore, that it is possible for man to apply the laws of flight to industrial purposes in the same manner as he has been able, in these days, to apply all the other grand physical laws that he has taken the trouble to study and fathom. The law of surface and force reigns in the most absolute and exact manner over all flying animals. It does not stop here. Nature, whose laws are general and universal, has not created this one only for the restricted compass of the winged animate beings. The law which sustains on the water the leaf and the straw is the same for the gigantic Great Eastern; and the mechanical law of the forces which drives the wheelbarrow also conducts on its iron line the locomotive and its endless train. XVII.--MECHANICAL PRACTICABILITY OF ARTIFICIAL FLIGHT. Living beings have been, in every age, compared to machines, but it is only in the present day that the bearing and justice of this comparison are fully comprehensible. Modern engineers have created machines which execute more difficult and various operations than animate beings are capable of; yet it is always from nature first that man has to draw his inspirations. Of the different functions of animal mechanism, that of locomotion is certainly one of the most important and interesting; and as we have brought this art on land and water, by successfully imitating the natural movements of walking and swimming, to quite a high state of perfection, the next great problem, equally possible, because flight is a natural movement, remains to be solved. Of course, as different as the wheel of the locomotive is from the limb of the quadruped, and the screw of a steamship from the fin of a fish, so will the coming flying machine differ from the construction of bird, bat or insect.