CHAPTER VIII. 



The Causation of Structure (continued) — Heredity — The Grand Rhythm 

 of Life— Minor Vital Rhythms. 



Rhythms. — The subject of cycles, or rhythms, is a very 

 important one, and it is necessary to take here some account 

 of it, for not only is life itself a rhythm, but the animal 

 organism is the seat of very many and diverse rhythmical 

 processes — minor rhythms within the great vital rhythm — and 

 it is because we are now treating of the great vital rhythm 

 as determined by heredity that it is proper to allude to the 

 subject of rhythm here. To treat of it in full detail would be 

 beyond the scope of this work ; for a short but comprehensive 

 article upon it the reader is referred to Herbert Spencer's " First 

 Principles," chap. x. 



All motion is characterized by rhythm. " This is an 

 inevitable corollary of the persistence of Force ; " more than 

 this it is unnecessary to say as to the causation of rhythm. 

 No matter what motion we examine we shall find it rhyth- 

 mical, be it the movement of an atom or of a world ; and 

 there is every degree of rapidity. The rhythm of the violet 

 ray of the spectrum occupies less than the 700 billionth part 

 of a second, while some of the rhythms of the heavenly bodies 

 extend over thousands, nay, even millions, of years. Turn 

 where we may, we find all movements rhythmical, — heat, light, 

 sound, electricity, vital phenomena, even social changes. 



As regards the minor rhythms occurring within the 

 great vital rhythm, some of these occur in response to 

 rhythms in the external-body-E, others independently of 

 such external rhythm. The body rhythms due to the 

 rhythmical changes of our planetary system afford the best 

 examples of the former. Thus day and night impress im- 

 portant rhythms upon plants and animals. The rhythmically 



