MOVEMENT 



represent years, days, or fractions of seconds. A 

 diagram will elucidate this method of time-measure- 



B 



C — 



1 i 2 I 3 | 4 j 5 I 6 1 7 J 8 1 



Fig. 1 Scale of hours. Time measurement. 



ment. Suppose we require to express the order and 

 sequence of three events, A, B, C, which occur 

 during a period of 11 hours. Their respective time 

 relations are expressed most clearly by the three lines 

 A, B, C, and by the scale of hours which accompanies 

 them. It may be seen by a glance at the diagram 

 that the event A commences at 2 o'clock and finishes 

 at 10 o'clock (its total duration is, therefore, 8 

 hours) ; that B, commencing at 6 and ending at 

 11 o'clock, has lasted 5 hours; and that C, com- 

 mencing at 5 o'clock and ending at a £ past 8, has 

 only extended over a period of 3^ hours. The 

 sequence of these events is accurately expressed by 

 the divisions on the scale, which correspond to the 

 beginnings of the different lines. 



Language is as slow and obscure a method of ex- 

 pressing the duration and sequence of events as the 

 graphic method is lucid and easy to understand. As a 

 matter of fact, it is the only natural mode of expressing 

 such events ; and, further, the information which this 

 kind of record conveys is that which appeals to the 

 eyes, usually the most reliable form in which it can be 

 expressed. A celebrated English political economist, 

 W. Playfair, has drawn up a table of the chronological 

 order of the reigns of the various English sovereigns. 

 From it one can see at a glance the age at which each 

 succeeded to the throne, as well as the duration of the 



