-KINDS OF MOVEMENT. 67 



not consider ; movement as a property of the subject 

 considered is what we are here concerned with. In 

 this chapter we commence with the admission that 

 movements may be expressive, an admission which 

 leads us to study movements apart from their 

 cause, for the sake of simplification of the subject. 

 Movements of various kinds are the principal 

 modes of expression, as is illustrated in the fore- 

 going chapter. Indeed, it is probable that it may 

 be shown hereafter that expression by coincident 

 development * is only a mode of expression by the 

 results of molecular motion. Movements may be 

 classified according to their mode of production, 

 or our ideas thereupon ; thus, in a man, certain 

 movements are said to be spontaneous, others reflex, 

 others voluntary. 



Again, the classification may be made according 

 to the attributes of the movements kind, quantity, 

 and time ; which latter attribute includes frequency, 

 speed, duration. Other movements may be con- 

 tinuous or interrupted, and they may be considered 

 in one or in more subjects. 



As to the movements of a single subject. In all 

 physiological work any calculation concerning move- 

 ment is best made by recording such movement on 

 paper by some graphic method. Now, in looking at 

 a tracing thus produced, we see certain indications in 

 the form of the outline of the curves ; if the record- 

 ing paper always travels at one uniform rate, the 

 form of the outline will be plainly characteristic of 

 the kind of movement observed in the same subject 

 * See chap. xvi. 



