342 



ANIMAL MECHANISM. 



at almost every flight of the bird, we succeeded in obtaining, 

 satisfactory results. During the whole of the bird's flight the 



registering lever described a kind 

 of ellipse. This ellipse, registered 

 on a plate having an advancing 

 movement from right to left, gave 

 figure 100. In order to under- 

 stand this figure, we must imagine 

 the bird flying from left to right 

 (as the tracing is to be read), 

 and rubbing the extremity of its 

 left wing against a wall blackened 

 with smoke ; the tracing which 

 its wing would leave under these 

 conditions would be identical with 

 that represented in fig. 100. 

 This curve is a kind of ellipse 

 spread out by the advancing mo- 

 tion of the plate which receives 

 the tracing. Except some trem- 

 blings of the line, which arose 

 from the imperfection of thei 

 apparatus, the trajectory of the 

 bird's wing may be compared to 

 the tracing given under the same 

 conditions by a Wheatstone's rod, 

 tuned in unison, and giving an 

 elliptical vibration. 



Fig. 101 represents a tracing 

 of this kind. 



Th e determination of the course 

 of the wing, with the difierent 

 phases of its velocity, is so im- 

 portant, that we resolved to verify 

 by various methods the reality 

 of this elliptical form. All our ex- 

 periments have furnished results 

 which agree with each other; they have shown that birds of dif- 

 ferent species describe with their wings an elliptical trajectory. 



