Page:Popular Science Monthly Volume 40.djvu/414

398 pressures. The chemical combination made use of is the oxidation of hydrogen. Hydrogen is easily obtained, rapidly, in great quantities, and pure, and oxygen for burning it is already prepared in the atmosphere. Our bird, like the birds of Nature, therefore draws a considerable part of its food from the atmosphere. The detonating mixture is regulated at will, but it is nearly twenty-five parts of hydrogen to seventy-five parts of atmospheric air, while the inflammation of it is produced by electricity, as in gas machines. In the small model (Fig. 1) the generator of explosions is a revolver barrel (D), armed with twelve cartridges, the charge of which has been carefully determined; to make the catches perform and the barrel turn, the bird must be left to itself, while the cock is kept raised simply by the weight of the apparatus. To start the machine, it is suspended by a cord fixed at the end of a crane (Fig. 3), while the pendulum thus composed



is withdrawn from the vertical and held by a second cord against the foot of the crane. Two candles, one movable (A) and the other fixed (B), placed in the verticals of the points of attachment, are intended to burn the two cords.

When we burn the first cord with the candle A, the bird, like Foucault's pendulum, begins an oscillation. It goes, describing the arc of a circle, from the position 1 to the position 2, reaching there with a horizontal velocity, when the candle B is applied and burns the suspending cord. The hammer is released and falls, the cartridge explodes, the tube vibrates strongly, and the wings falling sweep the air vigorously; at the same time the bird abandons its first horizontal position, and with its inclined tail takes on a slight movement of ascension (position 3). Thus the disengaged gases escape into the atmosphere, in the inverse direction of the