MEASUREMENTS 303 



The work thus estimated includes that of the friction of the 

 axle of the windlass, and of the stiffness of the rope which is 

 wound round the barrel. In the same way we can calculate the 

 work done, and measure the power, in the case of a capstan, which 

 is, in fact, a windlass with a vertical axis. A man turning a 

 capstan would exert on one of the bars an effort F ; let I be the 

 length of the bar ; then the work done is 2 id X F per revolution. 

 Several bars are thus fitted to the head of the apparatus, and by 

 the efforts of several men the cable that carries a ship's anchor 

 is wound up. 



A winch is often used to raise the monkey of a pile-driver. 

 The rope is coiled round the barrel of the winch, and when the 

 monkey has attained the desired height it is released automatically 

 and falls on to the pile. 



In the lifting jack, by which heavy loads are lifted to a small 

 height, the power is exerted on a crank handle. 



Finally, in the coining press, the power is exerted on a hori- 

 zontal lever actuating a screw. None of these operations presents 

 any complications as regards the measurement of the effort and 

 the muscular work (see Book VI.). 



230. Smith's bellows are even simpler in that respect, owing 

 to the method by which they are worked. A dynamograph will 

 give the effort exerted on the operating cord, and a stop can be 

 provided to limit the travel of that cord so that the work done 

 can be measured. 



Various tools, worked by hand, such as pincers, screw-drivers, 

 augers, graving tools, centre bits, turning chisels, planes, nippers, 

 bow drills, violin bows, etc., either do not require much effort, 

 or are rarely used continuously. It would be interesting, how- 

 ever, to fit them with dynamographic apparatus to obtain an 

 idea of the effort which each of them requires. Fcr the violinist's 

 bow, in particular, the effort is small, but it is continuous and 

 rapid, and the registration by means of a dynamograph placed 

 in the closed hand, should therefore indicate also the speed of 

 the movement of the bow. 



The handling of the hammer and the mallet is sometimes 

 fatiguing. They are, in the majority of cases, made so that at 

 the moment of the percussion there is no appreciable reaction 

 on the hand ( 41). The useful work of the hammer is easily 

 calculated from the speed 



T = JM*; 2 



at each blow. The force of the blow is : Mt> = F/. If t is re- 

 gistered electrically F can be estimated. 



In the construction of earth-works, in agriculture, etc., the tools 

 used comprise picks, spades, and shovels. The measurement of 



