WALKING. 



113 



phases, and its intensity. The registering apparatus enables us 

 to do this perfectly ; an experimental instrument placed under 

 the sole of the foot is connected with a lever which gives the 

 signals of the impact and of the rising of the foot, as well as 

 the expression of the force with which the foot is pressed upon 

 the ground. We call this first instrument the experimental 

 shoe, which may be thus described : — 



Under the sole of an ordinary shoe is fixed with heated 

 gutta percha a strong sole of india-rubber 1 \ centimetres in 

 thickness. Within this sole there is an air chamber, which 

 in fig. 1 9 is represented by dotted lines. 



Fig. 19.— Experimental shoe, intended to show the pressure of the foot 

 on the ground, with its duration and its phases. 



This chamber, having upon it a small piece of projecting 

 wood, is compressed at the moment that the foot exerts its 

 pressure on the ground. The air expelled from this cavity 

 escapes by a tube into a drum with a lever attached, which 

 registers the duration and the phases of the pressure of 

 the foot. 



Let us suppose that the experimenter is provided on both 

 feet with similar shoes, and that he walks at a regular pace 

 round a table which supports the registering apparatus ; we 

 shall then understand the arrangement of the experiment. 



The registering instruments employed are already known to 

 the reader; they resemble in all points those which have 



