CERTAIN MOVEMENTS IN MAN 153 



curves are in proportion to the weight raised. On 

 comparing the curve of the height jumped with that 

 of the dynamograph, it is found that it is not the 

 absolute initial energy of the effort which conditions 

 the height of the jump, but the amount or quantity 

 of force expended, namely, the product of the force 

 and the duration of the effort ; in other words, the area 

 of the curve. 



Sometimes the lowest jumps correspond to curves 

 which show great initial effort, but sustained only for 

 a brief moment. In fact, areas of different curves, 

 which represent jumps of equal height, may be infinitely 

 varied ; a violent and brief effort producing the same 

 effect as one initially feeble but longer sustained. 



Combined Employment of Dynamography and Chrono- 

 photograpby. — Mechanical registration of movement is 

 not always feasible; for instance, in the case of a man 

 walking, it is difficult to register all the movements of 

 the different parts of the limb. Chronophotography 

 comes to the rescue, and this method can be combined 

 with the employment of the dynamograph. Let us 

 suppose that we want to discover with what force the 

 foot presses on the ground during the different phases 

 of flexion and extension of the leg, provided, of course, 

 that the foot never leaves the ground during the period 

 under observation. The application of the chrono- 

 photograph combined with the dynamograph, at once 

 suggests itself, the former recording the movements 

 executed by the leg during half a step (Fig. 103), and 

 the latter the degree of pressure exercised during the 

 same period (Fig. 104). 



It is now necessary to establish the connection 

 between the various chronophotographic images and 

 the corresponding elements of the dynamographic 

 curve. For this purpose we must count in Fig. 103 

 the number of images which correspond to the phase 



