WALKING. 123 



of the changes in <lie pressure of the foot on the ground, and 

 of the vibrations of the tuning-fork ; and this produces in a 

 single tracing the interference <>f two movements, giving at 

 the same time the notion of the sp-ice traversed, and that of 

 the time employed in passing over it. 



In order to analyse this tracing, lot us consider only, in the 

 first place, the sinuous curve which obeys at the same time 

 the tuuing-fork, and the experimental shoo on the right foot; 

 and in this curve let us only examine the elevated part that 

 which corresponds with the pressure of the foot upon the 

 ground. We see that, during the duration of this pressure, 

 the style has passed through a space on the cylinder measuring 

 about 2 centimetres ; therefore, as the displacement of the style 

 is fifty times less than that of the person walking, lie will have 

 advanced about one metre during the pressure of one foot. But 

 while he traversed this metre, he did not advance with an 

 uniform velocity; in fact, during the first half of this distance, 

 the tuning fork made about four vibrations, whilst in the 

 second, it has scarcely made two and a half. Thus the foot 

 which presses the ground with a force increasing from the 

 commencement to the end of its impact, gives the body an 

 impulse whose velocity equally increases. 



During the rise of the foot, the line traced by the tuning- 

 fork indicates also that the body of the person walking 

 progresses with an accelerated motion. That is easily under- 

 stood if we remember that, in walking, the rise of one foot 

 corresponds exactly with the tread of the other. It is, there- 

 fore, the impact of the left foot on the ground which gives the 

 body of the walking person an accelerated motion, which is 

 observed during the rise of the right foot. 



This method appears to us applicable to all cases in which 

 it is necessary to measure the relative durations of different 

 phases of movement. 



The inequality in the speed of the man who walks brings 

 with it an important consequence. When a man drags a 

 load, the effort which he makes cannot be constant ; at each 

 foot-fall a redoubled energy is produced in the traction that is 

 developed, and as this increase of effort has but a very short 

 duration, a series of shocks, as \ve may call them, occurs at 



