But, of course, such experiments are not essential to the argument by which the paradox is overthrown. This argument simply is, that the moon as she travels on her orbit round the sun--the real centre of her motion--turns every part of her equator in succession towards him once in a lunar month. At the time of new moon the sun illuminates the face of the moon turned from us; at the time of full moon he illuminates the face which has been gradually brought round to him as the moon has passed through her first two quarters. As she passes onwards to new moon again, the face we see is gradually turned from him until he shines full upon the other face. And so on during successive lunations. This could not happen unless the moon rotated. Again, if we lived on the moon we should find the heaven of the fixed stars turning round from east to west once in rather more than twenty-seven days; and unless we supposed, as we should probably do for a long time, that our small world was the centre of the universe, and that the stars turned round it, we should be compelled to admit that it was turning on its own axis from west to east once in the time just named. There would be no escape. The mere fact that all the time the stars thus seemed to be turning round the moon, the earth would not so seem to move, but would lie always in the same direction, would in no sort help to remove the difficulty. Lunarian paradoxists would probably argue that she was in some way rigidly connected with the moon; but even they would never think of arguing that their world did not turn on its axis, _unless_ they maintained that it was the centre of the universe. This, I think, they would very probably do; but as yet terrestrial paradoxists have not, I believe, maintained this hypothesis. I once asked Mr. Perigal whether that was the true theory of the universe--the moon central, the earth, sun, and heavens carried round her. He admitted that his objections to accepted views were by no means limited to the moon's rotation; and, if I remember rightly, he said that the idea I had thrown out in jest was nearer the truth than I thought, or used words to that effect. But as yet the theory has not been definitely enunciated that the moon is the boss of the universe.