ra.iL] RHYTHM. 309 



variations we have a series of endlessly complex rhythms; 

 as is obvious from the fact that the number of individuals 

 in any species is never constant, but is continually fluctua- 

 ting about an average mean. The cumulative result of such 

 rhythms, going on through countless ages, is witnessed in 

 the rhythmical changes of organic species revealed by 

 palaeontology. In all ages specips have been encroaching 

 on each other, and while some have been growing more 

 abundant, others have gradually disappeared, Thus we find 

 successive floras and faunas, characteristic of successive 

 geological epochs, showing that "life on the earth has not pro- 

 gressed uniformly, but in immense undulations." 



For the further illustration and more abundant proof of 

 the law that all motion is rhythmical, I must refer to Mr. 

 Spencer's "First Principles," where the subject is discussed 

 much more fully than is here practicable. But our last 

 illustration, from the succession of forms of life upon the 

 earth, suggests still another supremely important aspect 

 in which the general principle must be viewed, before we 

 leave it. 



As we saw in our initial illustration, from the movements 

 of heavenly bodies, where a rhythmical motion is depen- 

 dent on only two compounded forces, the result is a closed 

 curve. Though each planet is, strictly speaking, subjected 

 to a great number of variously compounded forces exerted 

 on it by all its companion planets, yet these forces are so 

 insignificant in quantity, compared to the two chief forces of 

 solar gravity and the planet's own momentum, that they do 

 not essentially alter the result. They prevent the curve in 

 which any given plant moves from being perfectly regular, 

 but they do not prevent its being a closed curve so far as the 

 solar system alone is concerned ; so that, at the end of each 

 rhythm, the distribution of forces is very nearly the same as 

 at its beginning. If there were only two bodies concerned, 

 it would be exactly the same : every rhythm would end in 



