NEW RESULTS IN ANIMAL MOVEMENTS. 



449 



But we must not exclusively attribute to the action of the muscles 

 of the leg this uniformity in the translation of the foot. In fact, we 

 know that, during this translation, two distinct causes are working: 



1. The angular movement which the leg has around the pelvis. 



2. The horizontal translation of the pelvis itself; that is to say, of 

 the point of suspension of the leg while the latter oscillates. 



We may conceive that, by the combination of these two movements, 

 the motion of the leg may tend to become uniform ; this will happen 

 if the minima of the velocities due to the first-named species of motion 

 correspond with the maxima of the second kind of motion. It there- 

 fore becomes very interesting to determine what is really the motion 

 of the trunk of the body during different gaits. 



The apparatus already described has also served for the solution 

 of this problem. 



A cord attached to the waist transmitted to the registering appa- 

 ratus the motion of translation of the trunk. By experimenting suc- 

 cessively on various gaits, we obtained the following figure, whose 

 analysis gives some interesting results : 



//wwvvwvw'vvwvvvvvvvvvvvvvwvvv^^ 



Fig. 2. 



The undulations are far greater when the walking is very slow 

 than when it is more rapid. Thus, the motion of the body becomes 

 more uniform by reason of a higher velocity. This is the reverse of 

 what happens with the vertical oscillations of the body, which increase 

 with the velocity of progression and with an increase in the length 

 of the steps. 



The number of alternations of motion is double that produced by 

 the movement of a single foot, as shown in Fig. 1. This is readily 

 understood when it is remembered that the two feet, repeating the 

 same acts, give alternately to the body a new impulsion. 



To make clear this action we have traced, parallel to the line 2 of 

 Fig. 2, the curves P, produced by the motions of the right and of the 

 left foot. These curves, of which one is dotted, and the other full, 

 are at once recognized as similar to those of the line 2 B, of Fig. 1. 

 In fact, on observing the superposition of the different parts of these 

 curves with the curve of translation, we see that the body receives an 



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vol. vr. 



