FORCE OF BIRDS. 213 



present day measure mechanical force under the form of work. 

 It is necessary for this purpose to know what resistance is 

 met with by tbe wing at each instant of its movements, 

 and the direction in. which it repels from it this resisting 

 medium. 



Such an estimate requires a previous knowledge of the 

 resistance of air against surfaces of different curvature moving 

 with various degrees of velocity ; it supposes at the same time 

 that we know the movements of the wing as well as their 

 velocity and direction at every instant. 



. This problem will perhaps be the last which we may hope 

 to solve, but we may even now study from other points of 

 view the force exerted by the muscles of the bird, and esti- 

 mate some of its characteristics. 



Thus, we may obtain experimentally a measure of the maxi- 

 mum effort which these muscles can exert. This measure may 

 not really correspond with the real effort displayed in flight, 

 but it may keep us from forming exaggerated estimates. 



If the calculations of Borelli, or even those of Navier were 

 correct, we ought to find in the muscles of the bird a very 

 considerable statical force. Experiments show, however, that 

 these muscles do not seem capable of more energetic efforts 

 than those of other animals. 



Experiment. Our first experiment was made upon a buz- 

 zard. The creature being hoodwinked was stretched upon its 

 back, with its wings held on the table by bags filled with 

 small shot. The application of the hood plunges these birds 

 into a sort of hypnotism, during which we can make any num- 

 ber of experiments upon them, without their evincing any pain. 



We laid bare the great pectoral muscle and the humeral 

 region, we placed a ligature on the artery, disarticulated the 

 elbow-joint, and took away all the rest of the wing. A cord 

 was fixed to the extremity of the humerus, and at the end of 

 this cord was placed a scale-pan, into which small shot was 

 poured. The trunk of the bird being rendered perfectly im- 

 movable, we excited the muscle by means of interrupted in- 

 duced currents ; while the artificial contraction was produced, 

 an assistant poured into the pan the small shot, until the 

 force of contraction 'of the muscle was counteracted. At this 



