402 THE HUMAN MOTOR 



order to lift a weight Q attached to the other end of the rope, 

 P has to overcome, not only the resistance of Q, but also the func- 

 tion of rope and pulley. P is, therefore, always greater than Q. 

 This applies to the pile driver ( 228). 



In Coulomb's experiments with a pile-driver, the " monkey " 

 (the head which drives the pile) weighed 350 to 450 kg., and was 

 raised to a height of 1-1 metres. The dynamometer showed an 

 average effort of 19 kg. per man. 



Eighty blows were made in succession at a rate of 20 per 

 minute. For an actual working time of three hours, the work 

 done was therefore : 



19 X MO X 20 X 60 X 3 = 75,200 kilogramme t res. 



A pile-driver, used at the construction of the Jena Bridge in 

 the year 1808, had a " monkey " weighing 587 kg., which was 

 lifted to a height of 1-45 m. by 38 men. The load per man was 



therefore ^ == 15-45 kg. The working day was 10 hours, and 

 38 



360 blows were given, on the average, per hour. The work done 

 per man, per diem, was therefore : 



360 X 15-45 X 1-45 x 10 = 80,648 kgm. 



The work done per man per diem, therefore, seems to be about 

 80,000 kilogrammetres. 



Coulomb also made some measurements with a " drop stamp " 

 used at the Paris Mint. The punch weighed 38 kg., and was 

 raised to a height of 4 metres by two men, 5,200 blows were struck 

 per diem. The work done was therefore : 



38 X -4 x 5,200 = 79,000 kgm. 

 Coulomb considered that one man could have done the work. 



In the above experiments the effort per man was considerably 

 higher than the economical effort. The latter was shown (vide 

 para. 124) to be approximately 13 kg. at a speed of -75 metres 

 per second. It is therefore not surprising that the pile-driver is 

 not at all an economical apparatus for the utilisation of muscular 

 strength. 



308. Some experiments on the drawing of water from a well 

 confirm this conclusion. A man lifted 18 kg. at -2 metres per 

 second by a rope and pulley. (*) For six working hours the work 

 done was : 



18 X -2 X 3,600 X 6 = 77,760 kilogrammetres. 

 Coulomb measured the energy expended in drawing water from 

 a well 37 metres in depth. The tractive effort, as measured by 



(*) Navier's observations (loc. cit.). 



