210 ANIMAL MECHANISM. 



It generally happens that the transmission is not equally 

 easy in Loth directions ; we perceive a slight deformity iu the 

 transmitted figure, which is lengthened more or less both in 

 lieight and in width. This fault can al\va}-s be corrected; it 

 arises from the fact, that the membrane of one of the drums, 

 being more stretched than that of the other, obeys less easily. 

 We soon succeed, by various trials, in giving the same sensi- 

 bility to the t\vo membranes, which is ascertained, when we 

 find that the figure traced by the first lever is identical with 

 that of the second. 



l''.c]erii>ient to determine graphically the trajectory of the icing. 

 The following are the modifications which allow us to apply 

 this mode of transmission to the study of the movements of 

 the wing of a flying bird. 



As the apparatus must necessarily be of considerable weight, 

 we chose a large bird to carry it; strong full-grown buzzards 

 were employed in these experiments. By means of a kind of 

 corset which left both the wings and the legs at liberty, we fixed 

 on the back of the bird a thin piece of light wood on which 

 the apparatus was placed. 



In order that the lever mi^ht execute faithfully the same 

 movements as the wing, it was necessary to place the Cardan 

 joint of this lever in contact with the humeral articulation of 

 the buxzard. Therefore, as the presence of the drums -by the 

 side of the lever did not permit this immediate contact, we 

 had recourse to a parallelogram, which transmitted to the lever 

 of the apparatus the movements of a long rod, the centre of 

 motion in which was very near the articulation of the bird's 

 wing. Then, in order to obtain perfect correspondence be- 

 tween the movements of the rod and those of the buzzard's 

 \viug, we fixed on the outer edge of the wing that is to say, 

 on the metacnrpal bone of the thumb of the bird, a very tight 

 screw clip, furnished with a ring, through which slipped the 

 steel rod, of which we have before spoken. 



Fig. 99 represents the buzzard flying with the apparatus 

 just described ; underneath it hang the two transmitting tubes 

 \\hich are fixed to the registering instrument. 



\lter a great many fruitless attempts and changes in the 

 i nn.sliuctiun of (he. apparatus, which, being too fragile, broke 



