450 



SCIENTIFIC RECREATIONS. 



Rubber, and used by MM. Penaud and Hureau de Villeneuve, what were the 

 best shapes in which to reproduce the wings, in order to adapt them to a 

 large apparatus acting by compressed air. After several attempts, he decided 

 on the employment of long, narrpw wings. Wenham had previously proved 

 that a wing may be equally effectual whether it be narrow or widq, and 

 M. Marcy has also declared that birds with a quick, narrow wing-stroke 

 have always very long wings. By means of these long, narrow wings (fig. 478) 

 M. Tatin has reduced the time during which the wing reaches a suitable 

 position for acting on the air when it first descends. Granted the fact, so 

 long established, that a bird flies more easily if it rests its wing against 

 a great volume of air, it will be understood that the maximum speed of 



Fig. 477. Mechanical bird. 



movement will also be the most advantageous as regards the reduction of 

 expended force. The inventor, finding that he could not prevent his mechanical 

 birds from losing force in proportion as they attained considerable speed, 

 remedied this defect by placing the centre of gravity in front. Inconsequence 

 of this, the bird in full flight preserves the same equilibrium as the bird 

 hovering in the air, and its speed is, to a certain extent, passive, the mass of 

 air pressing of its own accord against the wings, all expenditure of force 

 therefore being utilized for suspension. Thus has M. Tatin been enabled 

 to increase the weight of his appliances, without increasing the motive power, 

 and yet obtains a double course. 



The movement made by the wing round a longitudinal axis, by means 

 of which it always exposes its lower surface in front on rising, is obtained 

 by the mechanism illustrated in fig. 478 a. 



