252 Observations on Locomotive Actio)}. 



cipal cause of fatigue in walking is the exertion of the neces- 

 sary propelling force ? I presume, not. 



In order to explain the machinery of walking, 

 let us imagine a body moving on a wheel of 

 spokes (by which I mean one whose spokes are 

 unconnected with each other, except at the 



centre of the wheel) ; and let us in the first in-^ 



•stance suppose this body standing at rest on 

 two of its spokes, and then to be propelled forward by some 

 external force. It is evident that while the forward spoke is 

 becoming more and more erect, the (centre of gravity of the) 

 body must rise ; and that it must afterwards fall through the 

 same degrees, till the succeeding or third spoke comes into 

 contact with the ground : also, that if the ends or feet, as they 

 may be called, of the spokes be properly shaped, the friction 

 will be but a part of that in the case of a common wheel : also, 

 that the force required to propel this body depends, cateris 

 paribus, on the infrequency of the spokes ; because that de- 

 termines the height to which the body will have to rise and 

 fall, as well as the angle which the direction of its rising and 

 falling will make with a horizontal line. This force is similar 

 to that part of the force used in walking that is necessary 

 simply to propell the body. Let us now further assimilate the 

 action of our machine to that of walking, by supposing it pro- 

 pelled, not by an extraneous force, but by the elongation of 

 the spokes, occasioned by the uncoiling of a spring or other- 

 wise, and subsequent contraction to their original length. — • 

 Here we have a very near approximation to walking. Let us 

 introduce one change more : — Let there be but two spokes ; 

 and let an internal machinery bring round the backward spoke 

 after its elongation and subsequent contraction, and }>lace it for- 

 ward, so as to be ready to meet the ground as the next spoke. 

 This third machine of ours will perfectly represent the action 

 of walking, so far as concerns our present purpose. Now it 

 is evident, as was observed before, that the first machine pro- 

 ceeds with less friction than a common wheel; i. c. if the ground 

 be smooth, with very little, and that there is no sudden check 

 or stop in the progressive movement. But whatever is true of 

 the first, with respect to friction, &c. between the gi-ound and 

 foot of the spoke, is true of the second and third forms of the 

 machine; therefore, &c. Transferring this to walking, we 

 may see that neither is it true there, that the exertion required 

 depends much on friction, or stoppage occasioned by setting 

 down the foot. In fact, this exertion is composed of two parts ; 

 one of which is that necessary simply to propell the body, and 



which 



