INDUSTRIAL LABOUR 



405 



FIG. 276. 



If / is the effective travel of the file and n the number of strokes 

 the total work done in the working strokes is 



(H + H') x / X n. 



As far as the working stroke of the file is concerned the vertical 

 components VV could be replaced by equivalent weights. 



But the return stroke has also to be considered. An effort 

 h is needed for this. 



The total work done for both forward and return strokes is, 

 therefore : 



(H + H' + h) X I X n. 



Since the expenditure of energy by the human organism is 

 proportional to the total of the muscular contractions involved 

 in the carrying out of any operation, and not to the useful work 

 done, we must next calculate the muscular effort both static and 

 dynamic. 



311. Experimental Methods. Flat " bastard " files were used 

 in the experiments. They were, as usual, of constant width, but 

 of a thickness diminishing towards the point giving a slight 

 convexity to the working surfaces. They were cut on two faces 

 and one edge. The length was 34 cm., of which 26 was 

 actually used in working. The width was 3-2 cm. and the thick- 

 ness tapered from 1 cm. to -55 cm. The files were of best quality. 



F*. 277. 



