154 



ANIMAL MECHANISM. 



animal, which are given by the line R A (anterior re-actions), 

 and from the croup for the hinder part, which correspond 

 with the line R P (posterior re-actions). 



Below are given the curves of pressure of the four feet ; 

 they are drawn at two different levels ; above are the curves 

 of the anterior, below those of the posterior limbs. In each 

 of these series the curves of the left foot are drawn with 

 dotted lines, those of the right with full lines. Whether 

 dotted or full, these lines have been made thicker for the 

 fore-limbs than for the hinder ones ; this difference, though 

 of little use in curves as simple as those of the trot, will 

 serve to render the more complicated tracings much more 

 intelligible. 



The moment when the curve begins its rise, represents the 

 commencement of the pressure of the foot on the ground. 

 The instant when the curve descends again gives the signal 

 of the rise of the foot.* It is seen from these tracings 

 that the feet A G and P D, left fore-foot and right hind-foot, 

 strike the ground at the same time. The simultaneous lower- 

 ing of the curves of the two feet shows that they also rise from 

 the ground simultaneously. Under these curves is the nota- 

 tion which represents the pressure of the left diagonal biped, f 



The second impact is given by the feet A D and P G (right 

 diagonal biped), and so on through all the length of the 

 tracing. 



This experiment confirms the correctness of the standard 

 theory of the trot, and at the same time affords additional 

 information on some points. Thus, all writers agree in 

 choosing, as the type of the free trot, the pace in which all the 

 four feet give but two strokes, and in which the ground is 

 struck in turn by the two diagonal bipeds. It is admitted 



* The duration of the pressure ought to he marked by a horizontal line, 

 but we have made the tube somewhat narrow in order to lessen the force 

 of the shocks given to the registering lever ; the narrowing of the tube 

 has slightly affected the curve, which, however, produces no inconvenience 

 in studying the rhythms. 



t Each diagonal biped is named after the anterior foot of which it forms 

 a part ; the left diagonal biped means, therefore, left fore foot, right hind 

 foot. 



