278 



THE HUMAN MOTOR 



portion to the deformations. Thus ordinates are found pro- 

 portional to the efforts, provided that the paper unrolls in front 

 of the point parallel to the line of the abscissa xx'. The average 

 value of the effort is the arithmetical mean of the ordinates ; 



v = 



FIG. IfiS. 



And its intensity, at any moment, is given by the correspondin 

 ordinate (fig. 168). On this principle the dynamographs o 

 Marey ( l ) (fig. 202), Hesehous ( 2 ), Grehant,( 3 ) Charles Henry,( 4 ) 

 Hulss,( 5 ) Verdin,( 6 ) and Waller ( 7 ) have been constructed. The 

 latter is in use in clinics in England, and gives the effort of the 

 pressure of the hand (fig. 169). 



In spite of their number and variety, 

 the existing types of dynamometers 

 in no way suffice to register all the 

 forces and components of forces, found 

 in the exercise of trades. Special 

 devices have had to be got out to obtain 

 records of efforts in all the possible 

 circumstances, the nature of which 

 is described later. 



209. Registration of Muscular 

 Efforts in different Occupa- 

 tions. Marey 's method is the 

 foundation of all apparatus 

 for these measurements. A 

 spring suitably disposed and 

 of appropriate strength, acts 

 directly on an indiarubber 

 bulb or on a Marey 's tympan, 

 the deformations being trans- 

 mitted by the movement of 

 the air and the elastic mem- 

 brane, to a receiving tympan 

 with a style acting on a 

 registering cylinder. The re- 

 cord can thus be amplified and 

 the ordinates will be propor- 

 tional to the efforts (see 215). 

 Professor A. Imbert was the 



F.G. 169. - 

 Waller's dynamograph. 



(*) Marey (Trav. de Laboratoire i., 11, 1875). 



( a ) Hesehous (Journ. de Physique 1889). 



( 8 ) Grehant (Comptes Rendus Biologie, 1891, 1892, 1897). 



( 4 ) Ch. Henry (ibid. 1895). 



() Quoted and described by Krummacher (Zeitsch. /. Biol. vol. xxxiii. 



( 6 ) Ch. Verdin (Comptes Rendus Biologie, 1896) 

 O A. Waller, Physiol. Humaine. 



