On Cycles 157 



We see something very like this actually happen in the 

 yearly revolutions of the planets round the sun. But the 

 relations between, we will say, the earth and the sun are 

 not reproduced absolutely. These relations deal only with 

 a small part of the universe, and even in this small part 

 the relation of the parts inter se has never yet been re- 

 produced with the perfection of accuracy necessary for our 

 argument. They are liable, moreover, to disturbance 

 from events which may or may not actually occur (as, 

 for example, our being struck by a comet, or the sun's 

 coming within a certain distance of another sun), but of 

 which, if they do occur, no one can foresee the effects. 

 Nevertheless the conditions have been so nearly repeated 

 that there is no appreciable difference in the relations 

 between the earth and sun on one New Year's Day and 

 on another, nor is there reason for expecting such change 

 within any reasonable time. 



If there is to be an eternal series of cycles involving the 

 whole universe, it is plain that not one single atom must 

 be excluded. Exclude a single molecule of hydrogen from 

 the ring, or vary the relative positions of two molecules 

 only, and the charm is broken ; an element of disturb- 

 ance has been introduced, of which the utmost that can 

 be said is that it may not prevent the ensuing of a long 

 series of very nearly perfect cycles before similarity in 

 recurrence is destroyed, but which must inevitably pre- 

 vent absolute identity of repetition. The movement of 

 the series becomes no longer a cycle, but spiral, and con- 

 vergent or divergent at a greater or less rate according to 

 circumstances. We cannot conceive of all the atoms in 

 the universe standing twice over in absolutely the same 

 relation each one of them to every other. There are too 

 many of them and they are too much mixed ; but, as has 

 been just said, in the planets and their satellites we do see 

 large groups of atoms whose movements recur with some 

 approach to precision. The same holds good also with 

 certain comets and with the sun himself. The result is 



