130 MOVEMENT 



fifty metres. Each post was provided with a little 

 contrivance for breaking the circuit the moment the 

 performer came abreast of the post. Within the 

 laboratory a recording apparatus — "the fixed Olograph" 

 — was in communication with the telegraph wires. 



In this apparatus a needle traced a horizontal line 

 upon the paper which covered a revolving cylinder, 

 and every time the performer broke the circuit, as 

 he passed a post, the needle was displaced for a 

 moment from its course and executed on the tracing 

 a rectangular inflection.* As these inflections were 

 repeated every time the performer passed a post and 

 completed a distance of fifty metres, it followed that, 

 at the end of a given time, the odograph had described 

 a zigzag curve which showed the rate of progression. 



Time is measured on the odographic curve by 

 referring to the horizontal divisions, which are marked 

 along the axis of the abscissae, and are numbered 0-16, 

 each division representing one minute. The distance 

 travelled is measured in metres along the axes of 

 the ordinates. So that for every point of the curve the 

 time occupied and the space traversed may be estimated 

 by referring to the intersections of the vertical and 

 horizontal lines. The relationship of these two values 

 gives the actual speed. t 



Instead of the staircase line (a) traced by the 

 odograph, it is better to draw a line connecting all the 

 angular projections on the curve ; in this way were 



obtained the lines o, b, d, ?', which express by 



their variation in inclination the speed of different 

 paces. They represent a uniform rate when they are 

 rectilinear, a variable speed when they are curved. So 

 far we only know the rate of progression with its two 

 factors — time occupied and space traversed — at each 



* See, for details of the experiment, La Nature, 1887 

 t See C. B. de V Academic, November 3, 1884. 



