242 



ANIMAL MECHANISM. 



I 

 r; 



o 



at almost every ilight of the bird, \\c succeeded in 

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



registering lever descrilied a kind 

 of ellipse. This ellipse, registered 

 Hi a plate having an advancing' 

 movement from right to left, gave 

 ligure 100. In order to under- 

 stand thistigure, wemust imagine 

 the bird Hying from left to right 

 (as the tracing 1 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 

 tliat represented iu 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 the 

 apparatus, the trajectory of the 

 bird's wing 1 may be compared to 

 the tracing given under the same 

 conditions by a Wheatstone'srod, 

 tuned in unison, and giving- an 

 elliptical vibration. 



Fig. 101 represents a tracing- 

 of this kind. 



The determination of the course 

 of the wing, with the different 

 phases of its velocity, is so im- 

 portant, that\\e resolved to verify 

 liy various methods the reality 

 <>i' this elliptical form. All our ex- 

 periments have furnished results 

 \\hicliugree v ith each other; they have shown that birds of dif- 

 I. lent .-pri ies describe \\ith t heir wings an elliptical trajectory. 



