power--on one side than the other, and by distinguishing the sides and watching carefully, astronomers have come to the conclusion that it presents always the same face to Saturn in the same way as our own moon does to us; in fact, there is reason to think that all the moons of large planets do this. [Illustration: THE PLANET SATURN WITH TWO OF HIS MOONS.] All the moons lie outside the rings, and some at a very great distance from Saturn, so that they can only appear small as seen from him. Yet at the worst they must be brighter than ordinary stars, and add greatly to the variations in the sky scenery of this beautiful planet. In connection with Saturn's moons there is another of those astonishing facts that are continually cropping up to remind us that, however much we know, there is such a vast deal of which we are still ignorant. So far in dealing with all the planets and moons in the solar system we have made no remark on the way they rotate or revolve, because they all go in the same direction, and that direction is called counter-clockwise, which means that if you stand facing a clock and turn your hand slowly round the opposite direction to that in which the hands go, you will be turning it in the same way that the earth rotates on its axis and revolves in its orbit. It is, perhaps, just as well to give here a word of caution. Rotating of course means a planet's turning on its own axis, revolving means its course in its orbit round the sun. Mercury, Venus, Earth, Mars, Jupiter, and all their moons, as well as Saturn himself, rotate on their axes in this one direction--counter-clockwise--and revolve in the same direction as they rotate. Even the queer little moon of Mars, which runs round him quicker than he rotates, obeys this same rule. Nine of Saturn's moons follow this example, but one independent little one, which has been named Phoebe, and is far out from the planet, actually revolves in the opposite way. We cannot see how it rotates, but if, as we said just now, it turns the same face always to Saturn, then of course it rotates the wrong way too. A theory has been suggested to account for this curious fact, but it could not be made intelligible to anyone who has not studied rather high mathematics, so there we must just leave it, and put it in the cabinet of curiosities we have already collected on our way out to Saturn.