252 



ANIMAL MECHANISM. 



The movements of the two wings being perfectly symme- 

 trical in regular flight, we cause two wires, which pass sym- 

 metrically from the wings, to converge to each of the experi- 

 mental drums. Thus, drum No. 1, intended to give signals 

 of the elevation and depression of the wing, receives two 

 wires, each of which proceeds from one of the humerus bones 

 of the pigeon, at about 3 centimetres outside the articulation 

 of the shoulder. These wires rise and converge, and are 

 attached to the point «of the lever No. 1 ; while from the 

 same point proceeds an india-rubber thread,* which serves as 

 a counter-spring, and rises vertically to a hook above, which 

 holds it. 



We have before seen (fig. 102) how the lever of the 

 experimental drum receives, under these conditions, all the 

 movements of elevation and depression executed by the 

 humerus of the bird. 



Two other wires, each attached to the humerus of the 

 pigeon on each wing, and starting from the same point of the 

 bone to which were fastened the wires of drum No. 1, con- 

 verge also, turning backwards, and proceed to the lever of 

 drum No. 2. This is the drum which receives the movements 

 executed by the wing in the antero-posterior direction. The 

 two drums send their signals by air tubes to the register 

 situated in the centre of the apparatus. 



Experiment. — After having ascertained that the two levers 

 intended to trace have their points situated on the same 

 vertical, the pigeon is allowed to fly. The bird goes through 

 the movements of flight, and soon carries round with con- 

 siderable rapidity the instrument to which it is attached. 

 The operator, placed in the centre of the apparatus, has only 

 to follow for a few paces the rotation of the instrument. 

 During this time he holds in his hand the india-rubber ball, 

 and has only to compress it, in order that the two levers may 

 rest with their points against the blackened paper, and that 

 the tracing may commence. As soon as the flight is well 

 established, and seems to be carried on under satisfactory 



* In fig. 104 a spir spring has been substituted for this india-rubber 

 thread. 



