48 MOVEMENT 



a section of the original chart taken on one of these 

 journeys between Dax and Moncenx. To measure 

 from moment to moment the rate of travelling, a small 

 divided scale can be applied to the corresponding part 

 of the diagram. By means of this scale we can 

 measure the length of any portion of the curve, which 

 corresponds to the distance traversed in ten minutes. 

 In this case it can be seen that the speed was 55 

 kilometres per hour. These charts are exactly like 

 those employed by railway companies ; the method of 

 expressing periods of progression and rest is the 

 same throughout, the only difference is, that Ibry's 

 charts were theoretical, i.e. the speed of the trains 

 is supposed to be uniform, and is represented by 

 straight lines, and in ours the actual speed is experi- 

 mentally found, and expressed by variations more or 

 less pronounced. It can be seen that from Dax to 

 Eion, and from Rion to Moncenx, the line is not 

 straight but slightly curved, which means that there 

 is a slight variation in the speed. It is generally 

 immediately before, or immediately after, a stoppage 

 that these variations are noticeable. At the moment 

 that the train comes to a stop, the curve suddenly 

 changes its direction, which indicates that under the 

 influence of the brake there is a rapid transition from 

 a high rate of speed to a condition of rest. On the 

 contrary, at the moment of departure, the curve 

 describes a parabola, which indicates how gradual is 

 the acceleration, and how slowly the train gets up 

 speed. The movement of the paper must be con- 

 siderably slowed down, if we want to inscribe all the 

 phases of a long journey within the limits of a single 

 sheet of paper. Column B was obtained in this way, 

 and on it is registered a journey from Dax to Bordeaux, 

 representing a distance of GO kilometres. 



In odography the movement of the paper should be 



