MEASUREMENTS 301 



It is important 'to remember that this work varies according to 

 the position of the vine-shoot in relation to the pivot of the 

 pruning shears and according to the thickness to be severed. 



227. Consider again the case of the work done in filing. The 

 workman leans on the file to make it bite, but the work done is 

 the product of the distance travelled by the file and the sum of 

 the horizontal efforts of the right and left hand, which overcome 

 the resistance of the metal. If the value of these efforts is F, 

 and if the distance traversed by the file is /, the work done per 

 stroke of the file will be 



It is not necessary to add that the same principle can be 

 applied to the measurement of the work done by the plane, saw, 

 etc. However great the static efforts of the muscles, they cannot, 

 properly speaking, figure in the useful work. 



228. Classification of the Work done by Man. Considering 

 mechanical work only, a classification could be based on the group 

 of active muscles employed according to whether they are the 

 muscles of the arms, of the legs, of the fingers, or several groups 

 at once, or, finally, whether the whole weight of the body is utilised. 



The work of the arms is the most varied, being used to push 

 or pull, either directly or through the medium of levers, crank 

 handles, ropes, and pulleys, and to actuate numerous tools and 

 apparatus. 



The file, saw, plane, pruning shears, clippers and scissors are 

 levers of the first order, having consequently the fulcrum at the 

 pivot. The example of the pruning shears gives the procedure 

 for measuring the effort of the hand and its work. 



Pump handles, sculls of boats, large vegetable or bread cutters 

 and nut crackers are levers of the second order. The effort can 

 be measured by applying to the arm of the lever, at the point 

 where the power will act, a steel blade covering a small rubber 

 bulb, the variations of pressure of the air being transmitted to a 

 receiving tambour, this being the system adopted to measure 

 the vertical effort of the left hand acting .on a file (fig. 185). 

 In the case of an oar the fulcrum is the water, the effort of the 

 rower is the power, and the boat that he propels constitutes the 

 resistance. In this case the effort could also be easily measured 

 if the relative positions of the surface of the water, the oar, the 

 boat, and the rower remained constant throughout the experiment. 

 The registering cylinder could be placed in the boat by holding it 

 suitably, as Marey's register is held in walking (fig. 180). 



