vil 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 vertebre, 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? 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. 
