304 THE HUMAN MOTOR 



the work done requires the knowledge of the weight displaced 

 (the tool and its load), as well as the height to which it is lifted. 

 The strictly useful effect is the work done and the weight of earth 

 displaced, etc. To drive a pickaxe or spade into the earth a 

 certain resistance has to be overcome. It is therefore necessary 

 to divide the handle into sections and adapt an appropriate 

 dynamograph to it in order to find the expenditure of energy. 



231. Exercise of the Fingers. Here speed is an important 

 factor, as in the work of instrumental musicians, writers (in the 

 manual sense of the word), engravers, sempstresses, embroiderers, 

 etc. When the fingers have to operate keys (fig. 215) the latter 

 can be fitted with small tambours, which will indicate the pressure 

 applied. In addition, by means of a wire and a light counter 

 weight, the displacement can be registered and the amount of 

 work done calculated. Marey himself proceeded as follows : 

 Above each key of the keyboard of a harmonium, small bellows 

 were arranged, each connected by a special tube to a similar 

 bellows, operating an inscribing style. ( A ) Thus 

 Q a record of the notes played was obtained, with 



their durations represented by longer or shorter 

 J marks. In reality, these measurements are not 



very useful, the real factor to be considered in 

 this kind of fatigue being the speed of the move- 

 ments. 



F.O. 215* 232. Work of the Muscles of the Leg. These 



Piano action are certam ly tne strongest or the human muscles. 

 Their normal rhythm and fatigue can be studied 

 by means of Capobianco's ergograph. The work done on a 

 bicycle or on a treadle of a grindstone, for example, is easily 

 estimated ( 221), especially ii the foot is fitted with an experi- 

 mental shoe and the pedal with a Marey tambour with an internal 

 spring (212). 



In the case of bicycles, special dynamographs are used, such as 

 Scott's cyclogmph or Marey 's dynamometrical pedal.(*) 



If F is the uniform pressure on each pedal and d is the diameter 

 of the circle of the pedal, the work done will be F X d. Per 

 stroke of the pedal (both legs working) it is approximately : 



T = 



This is the work performed by the legs, and it is also the work 

 done in advancing the loaded bicycle. It is clear that, by each 

 stroke of the pedal the bicycle advances a distance D, depending 

 on the gear. If R is the sum of the resistances overcome (resist- 

 ance to rolling, passive resistances of the bearings and of the 

 transmission, and resistance of the air) then 



(*) Marey : Le Mouvement, p. 12, 1894. 



( 8 ) Bowny (Comptes Rendns Sciences, 15 June, 1896). 



