302 



THE HUMAN MOTOR 



The pile-driver consists of a very heavy mass called the 



"monkey," which is 

 first raised to a cer- 

 tain height and then 

 let fall on to the pile 

 to be driven into the 

 ground. In the 

 hand pile driver each 

 labourer pulls on a 

 rope, and if there are 

 n workmen and the 

 weight of the monkey 

 is P, each of them 

 will sustain on an 



FIG. -.Mi. 



Dutch scoop. 



average a weight, 



By inserting a strong spring balance, or, better still, a Marey's 

 dynamograph, in the rope, suitably cut, we can measure at any 

 moment the effort exerted by the labourer. The inclination of 

 the rope to the vertical modifies the value of that effort. 



Knowing the height to which the monkey is lifted, we can find 

 the work done per blow of the pile driver. It is easy to find out 

 how many blows of the pile driver a man makes in the course 

 of a day's work. 



In the Dutch scoop, by which water is raised by hand, the 

 height to which the water is lifted and the depth of the sumph 

 are known. A dvnamograph could be inserted in the rope, 

 which is attached to the bucket to measure the effort. If the 

 effort is applied through the medium of a lever, as in certain 

 methods of drawing water, the work done can be calculated from 

 the displacement of the power arm, which is known (fig. 214). 



The action of the muscles of the arms can be exerted 

 on windlasses either through the medium of a rope wound round 

 a drum, or by means of a crank handle, BA, mounted at the 

 extremity of the shaft BC of a winch (fig. 91 . The effort can be 

 measured by interposing a spring balance or a dynamograph in 

 the rope and by applying a spring with an indiarubber bulb to 

 the crank handle. 



Let F be the power exerted by the workman ; the arm of the 

 lever in relation to the axis of the windlass is BB ' ; call it r. It is 

 obvious that the work done per revolution is : 



T = 2nr x F. 



The effort F acts tangentially to the barrel, in the first case, 

 and to the circumference described by the crank handle in the 

 second case. 



