276 THE RHYTHM OP MOTION. 



at intervals. Very many persons have their epochs of 

 vivacity and depression. There are periods of industry fol- 

 lowing periods of idleness; and times at which particular 

 subjects or tastes are cultivated with zeal, alternating with 

 times at which they are neglected. Respecting which slow 

 oscillations, the only qualification to be made is, that being 

 affected by numerous influences, they are comparatively 

 irregular. 



87. In nomadic societies the changes of place, deter- 

 mined as they usually are by exhaustion or failure of the 

 supply of food, are periodic; and in many cases show a 

 recurrence answering to the seasons. Each tribe that has 

 become in some degree fixed in its locality, goes on increas- 

 ing, till under the pressures of unsatisfied desires, there re- 

 sults migration of some part of it to a new region a process 

 repeated at intervals. From such excesses of population, 

 and such successive waves of migration, come conflicts with 

 other tribes ; which are also increasing and tending to diffuse 

 themselves. This antagonism, like all others, results not in 

 an uniform motion, but in an intermittent one. War, ex- 

 haustion, recoil peace, prosperity, and renewed aggres- 

 sion: see here the alternation more or less discernible in 

 the military activities of both savage and civilized nations. 

 And irregular as is this rhythm, it is not more so than the 

 different sizes of the societies, and the extremely involved 

 causes of variation in their strengths, would lead us to an- 

 ticipate. 



Passing from external to internal changes, we meet with 

 this backward and forward movement under many forms. 

 In the currents of commerce it is especially conspicuous. 

 Exchange during early times is almost wholly carried on at 

 fairs, held at long intervals in the chief centres of popula- 

 tion. The flux and reflux of people and commodities which 

 each of these exhibits, becomes more frequent as national 

 development leads to greater social activity. The more 



