16 



ON THE WALK OF QUADRUPEDS. 



I am truly surprised that the difficulty and absurdity of such a no- 

 tion was not perceived. They grant that an animal ought to be steady 

 in motion, lest it might totter or fall, and hence they aver, that the 

 two left feet, A and D, could not be moved together; for then the 

 centre of gravity of the quadruped, and the line perpendicularly drawn 

 from it to the ground, would fall either upon the same right line, B C, 

 where the two right feet are at rest, or beyond it on the line A D, and 

 in that posture the animal would totter or fall. 



But when the two feet, B D, diametrically opposite, are raised and 

 moved together, at the same time, the whole weight of the animal 

 ought to rest upon the two feet fixed upon the ground ; I mean the 

 line perpendicularly drawn will fall not upon the large space, but upon 

 the line A C. The animal would therefore equally totter; and tjience 

 it will have an insecure and unsteady posture at that time. 



Secondly. We may consider the figure, which the four feet form 

 after the first motion — namely, when the foot B is transferred to K, and 

 D to S ; then the two left feet, A and S, become contiguous, and the 

 right feet, K C, in turn are most removed from each other, so that the 

 four feet form a triangular figure, the longest side of which is K C, 

 and the least altitude A B. This posture therefore is not secure 

 enough, and from it, after the motion of the feet, C and A, to I and 

 V, the animal is restored to the steady quadrangular position, I S 

 V K, like the former A B C D. The firm and tottering postures of 

 this kind regularly following each other, would have been unwisely 

 ordered by Nature, when these disadvantages could have been easily 

 avoided. 



But why do we enquire for reasons, when experience contradicts the 

 facts inferred. Observe a horse moving at a slow pace, and you will 

 never see the two feet, A and C, diametrically opposite, to move at 

 the same time, but one foot is always raised from the ground while the 

 other three are at rest. By an attentive observation, you will after- 

 wards perceive that this process is followed in the quick motion of all 

 kinds of quadrupeds. 



[In birds, as we shall see in a future page, there are two species of 

 this sort of movement; — one group, like the nightingales and sparrows, 

 carrying both legs forwards at the same time, or hopping; another, 

 like the wagtails and the blue breast (Motacilla Sucica), putting one 

 foot before the other. — Editor.] 



