IN a world of mere phenomena, where all events are bound to one another by a rigid law of cause and effect, it is possible to imagine the course of a long period bringing all things at the end of it into exactly the same relations as they occupied at the beginning. We should, then, obviously have a succession of cycles rigidly similar to one another, both in events and in the sequence of them. The universe would eternally repeat the same changes in a fixed order of recurrence, though each cycle might be many millions of years in length. Moreover, the precise similarity of these cycles would render the very existence of each one of them entirely unnecessary. We can suppose, without any logical inconsequence, any one of them struck out, and the two which had been destined to precede and follow it brought into immediate contiguity.