VII FLIGHT 



259 



leans forward, bending at the hips, with the result that 

 the fore part of the foot bears all the weight, and the 

 heel tends to rise. This is not a comfortable position 

 to maintain long. But the stiffness of the bird's back, 

 due to the fusion of vertebrae, no doubt, makes the 

 attitude an easy one for him. 1 



Force Exerted in Flight. 



Borelli, a man of science of the seventeenth century, 

 calculated that a bird in flying employs a force that 

 exceeds ten thousand times his own weight. 2 This 

 astounding conclusion he arrived at by trying to 

 estimate the disadvantage at which most animal levers 

 work, the power being applied close to the fulcrum 

 while the weight is at the end of a long arm. By the 

 same methods he calculated that the force exerted 

 by a man in jumping exceeds three thousand times 

 his own weight. Obviously he has much overshot the 

 mark, but it is very difficult to devise any plan by 

 which correct results may be obtained. Professor 

 Marey has attempted to settle the question of a bird's 

 muscular power by experiment. 3 A Buzzard was 

 hooded, and so plunged into " a sort of hypnotism." 

 The Great Pectoral muscle was laid bare, the elbow- 

 joint was disarticulated, and all of the wing that lies 

 beyond was removed. A cord was fixed to the 



1 That the centre of gravity must of necessity be where it is, 

 was first shown me by Mr. R. C. Gilson. 



2 Borelli, De Motu Animalium, p. 191 : " Potentia musculorum 

 alas flectentium plus quam decies millies superat pondus avis 

 volantis." 



3 Animal Mechanism, p. 214. 



S 2 



