The question is whether these men are not working on wrong lines, and whether their utmost endeavours and those of their successors will ever produce anything more than a very semi-successful craft. Their efforts appear foredoomed to failure. As Sir Hiram Maxim has observed, a balloon by its very nature is light and fragile, it is a mere bubble. If it were possible to construct a motor to develop 100 horse-power for every pound of its weight, it would still be impossible to navigate a balloon against a wind of more than a certain strength. The mere energy of the motor would crush the gas-bag against the pressure of the wind, deform it, and render it unmanageable. Balloons therefore must be at the mercy of the wind, and obliged to submit to it under conditions not always in accordance with the wish of the aeronaut. Sir Hiram in condemning the airship was ready with a substitute. On looking round on the patterns of Nature, he concluded that, inasmuch as all things that fly are heavier than air, the problem of aërial navigation must be solved by a machine whose natural tendency is to fall to the ground, and which can be sustained only by the exertion of great force. Its very weight would enable it to withstand, at least to a far greater extent than the airship, the varying currents of the air. The lifting principle must be analogous to that by which a kite is suspended. A kite is prevented from rising beyond a certain height by a string, and the pressure of the wind working against it at an angle tends to lift it, like a soft wedge continuously driven under it. In practice it makes no difference whether the kite be stationary in a wind or towed rapidly through a dead calm; the wedge-like action of the air remains the same. Maxim decided upon constructing what was practically a huge compound kite driven by very powerful motors. But before setting to work on the machine itself he made some useful experiments to determine the necessary size of his kites or aeroplanes, and the force requisite to move them.