36 MOVEMENT 



all degrees of speed and all kinds of movement. A 

 horizontal line signifies a period of rest, and the 

 length of the line, or, in other words, the number of 

 divisions which it occupies, is a measure of the 

 duration of this period of rest. 



Irregular movement is expressed by a curve, the 

 inclination of which, i.e. the tangent, indicates from 

 moment to moment the rate of progression. Further, 

 each point of the curve indicates according to its 

 relation to the horizontal and vertical scales the time 

 occupied and the distance travelled since the com- 

 mencement of the movemeat. 



Chart of a Train travelling along a Line. — A 

 geometrical expression for all sorts of movement has 

 become now almost universal, since the engineer Ibry 

 made use of it to chronicle the progress of trains along 

 a railway. Nowadays every one is familiar with these 

 charts, in which are to be seen lines intersecting one 

 another in all directions. Variations both as regards 

 inclination and direction express the speed and the 

 route taken by all trains running on the track. 

 Fig. 26 is an example of such a chart placed by the 

 directorate at the service of its employes. To the 

 left of this chart, along the axis of the uprights, are 

 printed in series the names of the various stations. 

 These stopping-places are separated on the chart by 

 intervals proportional to the number of kilometres 

 which actually intervene as they occur on the line. 

 In the horizontal direction, i.e. along the axis of the 

 abscissae, time is registered by periods of an hour; 

 these are again subdivided into periods of ten minutes. 



To indicate that a train should arrive at a given 

 hour at a particular point on the line, its position 

 is marked on the chart opposite the station at which 

 it is expected, and vertically above the division which 

 corresponds to the time at which it is due. As the 



