THE POPULAR SCIENCE MONTHLY. 



pressures. The chemical combination made use of is the oxida- 

 tion of hydrogen. Hydrogen is easily obtained, rai:»idly, in great 

 quantities, and pure, and oxygen for burning it is already pre- 

 pared in the atmosphere. Our bird, like the birds of Nature, there- 

 fore 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 ex- 

 plosions 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 



Fig. 3. — Arraitgements fob starting the Bird. 



is withdrawn from the vertical and held by a second cord against 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 attach- 

 ment, 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 ajiplied and burns 

 the suspending cord. The hammer is released and falls, the car- 

 tridge 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 ittito the atmosphere, in the inverse direction of the move- 



