TIME AND PERIODICITY 13 



Periodicity generally at a longer interval of 

 pulsation equally affects the vegetal forms of life. 

 The plant is sown, grows, flowers, and fades. 



Periodicity is to us less obvious in the inanimate 

 world of molecular changes ; yet it is in operation 

 even there. But it is more especially in the natural 

 motions of those so-called material masses which 

 constitute our physical environment that Periodi- 

 city most eminently prevails. Indeed it was by 

 astronomers that the operation of this Law was first 

 definitely recognised and recorded. Periodicity is 

 the scientific name for the Harmony of the Spheres. 



The two periodic motions which most essentially 

 affect and concern us human beings are necessarily 

 the two periodic motions of the globe which we 

 inhabit its rotation upon its axis which gives 

 us the alternation of Day and Night, and its revolu- 

 tion round the Sun which gives us the year with its 

 Seasons. To the former of these, animal life seems 

 most directly related ; to the latter, the life of the 

 vegetal orders. It is evident that the forms of 

 animal life on the globe are necessarily determined 

 by the periodic law of the Earth's diurnal rotation. 

 This accounts for the alternations of waking and 

 sleeping, working and resting, and so forth. In like 

 manner the more inert vitality of the vegetable 

 kingdom is determined by the periodic law of the 



