Observations on Locomotive Action. 2.5 1 



besides : each impetus thus causing a deal more ground to be 

 passed over tlian in walking, where the jirogressive motion is 

 at each step checked, and determined to the spot where the 

 foot is set down. But such a solution is not consistent with a 

 just idea of the nature of the action of walking. The velocity 

 of progression of a man walking uniformly is not materially 

 checked by any friction between his foot and the ground ; nor 

 is it momentarily stopped, as it were, and renewed at each step. 

 It continues uniform, like the velocity of a boat uniformly 

 rowed ; i. c. is never much under or over a certain mean point. 

 About the time of setting down the foot it is perhaps a trifle 

 less than the mean rate ; and just after the exertion of the mus- 

 cles of the hinder leg it is a trifle more: so that, for example, 

 if a man walk at the rate of four miles an hour, his velocity is 

 sometimes a little more and sometimes a little less than that ; 

 and so keeps passing at every step from the somewhat more to 

 the somewhat less, without ever being suddenly checked or 

 stopped, or ever differing much from that mean velocity of 

 four miles an hour, even for the smallest instant of time. 



The fatigue in walking does not arise from the quantity of 

 force neccssaj-y to propel the body (in quantity I include fre- 

 quency of application), but from other causes connected with 

 the machinery of animal bodies, which I will endeavour to 

 explain ; first observing that the truth of this assertion will 

 be perceived indirectly, by considering that in walking down- 

 hill it is so far from being necessary to use force to propell the 

 body, that, if the declivity be considerable, it is on the contrary 

 necessary to check the tendency to accelerated velocity : so 

 that if the necessary propelling force was the principal cause 

 of fatigue on level ground, we ought, comparatively speaking, 

 mile for mile, to be little exhausted in descending gentle plea- 

 sant declivities, where the ground is good and the footing 

 firm ; as, for example, on the mossy, short, elastic, yielding 

 grass on the sides of some mountains. The additional shock 

 in walking down-hill occasioned by the descent of the foot is, 

 according to my experience, very trifling on such ground as 

 I have mentioned. But if anyone should maintain that, owing 

 to this or other cause, walking down declivities cannot, be 

 compared with walking on level ground, let him imagine a 

 man standing on level ground, and constantly (or by inter- 

 vals, as he pleases) pressed forward by a jiroper force, pro- 

 perly applied against his back, — such an one as gently to force 

 liim to gather up his legs and walk, without using any pro- 

 pelling force of'iiis own : \Vouhl this enable him logo so much 

 finfhcr in a day, as to authorise us to conclude timt the prin- 



I i 'i cip:d 



