INDUSTRIAL T.ArfOUK 407 



ultaneously with the < 1 r )bs : 'ons Tie number of strokes 

 of the file per minute was, in s ,m cases leit to the discretion of 

 the workman, and in others kept at a definite rate in accordance 

 with a frequency set by a metronome. 



The method of measuring the respiratory exchanges is fully 

 described on para. 239. 



Fig. 279. 



The general arrangement of the apparatus is shown in fig. 279, 

 the subject of the experiment being an apprentice. The respir- 

 atory valve (vide fig. 218) is supported by a metal strap fixed to 

 the head. 



Calibration of the Apparatus. In fig. 280 a specimen of the 

 graphical records taken with a journeyman fitter as a subject 

 are given. 



The ordinates of the curves represent the pressures. In order 

 that the actual pressures in kilogrammes corresponding thereto 

 can be ascertained, various definite weights are applied either 



