HUMAN LOCOMOTION. 51 



the transverse dilatation of muscular fibre in the process of contraction. 

 If we substitute in this figure an experimental shoe for each of the 

 myographical clips, 1 and 2, we shall have the arrangement of the 

 apparatus necessary for the study of footsteps or impacts of the foot 

 on the ground. 



The entire apparatus, as adjusted to the person of the operator, is 

 seen in Fig. 3. The piece of machinery on the head will be described 

 when we come to speak of the movements communicated to the trunk 

 by the actions of the legs. 



To understand the indications which the working of the apparatus 

 gives, the reader is referred to Fig. 4, which has been furnished by an 

 experiment in walking. Two tracings are given by the intermittent 

 pressure of the feet on the ground. The full line D corresponds with 

 the right foot ; the dotted line G with the left. The lines are read 

 from left to right. 



Knowing the arrangement of the apparatus, we can understand 

 that each impact of the foot on the ground will be represented by the 

 elevated part of the corresponding curve. The pressure of the foot on 

 the ground compresses the India-rubber sole and diminishes the ca- 

 pacity of the included air-chamber ; a part of the contained air escapes 

 by the connecting tube, and passes into the registering drum. The 

 elastic side of the latter is thus elevated, carrying up the point of the 

 lever, which in turn leaves the mark of its movement on the paper 

 carried by the revolving cylinder. Were the lever to remain undis- 

 turbed, it would simply make an horizontal line running round the cyl- 

 inder ; but, with the apparatus in use, each impact of the foot lifts the 

 pen-point of the lever, thus giving the curves traced in the figure. It 

 will be seen that the pressure of the right foot commences at the mo- 

 ment when that of the left begins to decrease ; and that in all the 



Fig. 4. Tracings op the Impact and the Risk op the Two Feet in our Ordinary Walk. 



tracings there is an alternation between the impacts of the two feet. 

 The period of support of each foot is shown by an horizontal line which 

 joins the minima of two successive curves. The impacts of the right 

 and left feet are seen to have the same duration, showing that the 

 weight of the body passes alternately from one foot to the other. It 

 would not be the same in respect to a lame person ; lameness cor- 

 responds essentially with the inequality of the impacts of the two feet. 

 The curves traced by walking may also furnish the measure of the 

 effort exerted by the foot upon the ground. The experimental shoes 



