10 



THE HUMAN MOTOR 



spaces x a\, a.^a'., will be ordinates ; and we shall find that 

 the spaces have increased as the square of the time. The curve 

 described will be an arc of parabola MM '. In the same way if 

 we attach a style to a vibrating tuning-fork, the point will trace 

 a sinusoidal curve (fig. 15) on a plate covered with soot. 



Such is the principle of the graphic method of direct represen- 

 tation used for the first time by General Morin at the suggestion 

 of Poncelet, and carried to its highest degree of perfection by 

 Marey. 



The physiologist Marey (1830-1904) gave it a more practicable 

 form, utilizing transmission by air ; he invented for this purpose 

 the "tambour" which bears his name ; it is a metallic vessel 



Fie. 



closed by a membrane of indiarubber m. The moving body M 

 is joined to the centre of that membrane, which it either pushes 

 or pulls according to the direction of its movement ; the com- 

 pressions and expansions of air produced in the vessel A (fig. 16) 

 are transmitted by an indiarubber tube to another tambour B, 

 to which a style is attached at the middle of the diaphragm m'. 

 Thus all the movements of the point M are transmitted to the 

 point 1, and can be recorded on a cylinder or a revolving slab. 



The receiving tambour B can always be employed in con- 

 junction with a transmitting tambour A adapted to the nature of 

 the movement. Also, by modifying the length of the style, 

 slight movements can be magnified. It is easily seen that a 

 small displacement at m' would be expressed by the length 1,1' 

 (see Methods, Book v., 195). 



