We have said that the examination of the sun's spots established his rotation upon his axis. In fact, if we patiently observe the motion of a spot, or of a group of spots, we remark that it advances slowly from one edge of the solar disc to the other; for instance, if the point of departure be the eastern edge, the spot or group will advance with uniform speed towards the western edge, taking fourteen days to accomplish the distance. If we wait fourteen days more, we shall again perceive the same spot making its appearance on the eastern edge of the disc, the interval having been consumed in passing over the opposite and, of course, invisible side of the sun. The spot has therefore taken twenty-eight days to reappear, which twenty-eight days do not, however, represent the exact duration of the revolution of the sun himself. It must not be forgotten that the earth has not remained motionless during this long observation; she, too, has gone round in the sun, as the spots have done. This sort of advance, which causes us to see the same spot for a longer time than we should have seen it, if the earth remained motionless, is of three days' extent, the deduction of which from the twenty-eight given days, allows twenty-five days for the real duration of the sun's rotation upon his axis. In the sun seasons are unknown as well as days. Time seems to have no existence for the beings who occupy that radiant dwelling-place. The changes, and the succession of things for us which constitute time, are unknown to their sublime essence. Duration has no measure in that blessed world. The dweller in the sun must behold the revolution of the planets around him, performed according to the same laws, but with different rates of speed. The phases of the planets and their satellites, the phases of Mars and Venus, or those of the moon, which we perceive from the earth, are unknown to them; they see only the hemisphere of those globes which is illumined by their own immense country. They behold, in larger dimensions, the globes of Mercury and Venus, and in lesser dimensions the Earth and Mars. The distant planets, Jupiter, Saturn, and Uranus, must seem very small to them. Neptune they probably cannot see at all. The comets must be for a long time invisible to the inhabitants of the sun, who behold their flaming mass rushing towards them in ever-increasing size. They also see some comets sinking away into space, and others falling on the surface of the sun himself, to be lost and absorbed in his substance. Thus, the spots on the sun have revealed to us an important peculiarity of his astronomical character, his revolution upon his axis. They have also given us the only exact ideas which we possess of the physical constitution of the sun.