68 PHYSICAL EXPEESSION. 



on different occasions. Thus the regular move- 

 ments of the heart give a regular tracing on paper ; 

 tracings obtained by movements of the fingers in 

 chorea are most irregular. By "the frequency of 

 movements" we mean the number of observable 

 movements in a minute or other division of time. 

 The term " duration of movements " is self-explana- 

 tory. " Rate " or " speed " implies the degree or length 

 of movement accomplished in a given time. The 

 term " quantity of movement " is used in the 

 sense of quantity as correctable with other modes 



Fig. 2. 



of force, as used in speaking of the law of conser- 

 vation of energy. These considerations regarding 

 movement show at once how important time is as 

 an attribute of a movement. 



Now, if two or more movements be considered in 

 relation to time, further points arise expressive of 

 the relation between the times of the one movement 

 and of the other. Two movements may be syn- 

 chronous throughout, as when two trains run on 

 lines side by side, and start at the same time, and 

 continue to move at the same rate. If two men run 

 in concentric circles at the same rate, the movement 



