ock 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.

For ages past men have known and watched the planets lying within the
orbit of Saturn, and they had made up their minds that this was the
limit of our system. But in 1781 a great astronomer named Herschel was
watching the heavens through a telescope when he noticed one strange
object that he was certain was no star. The vast distance of the stars
prevents their having any definite outline, or what is called a disc.
The rays dart out from them in all directions and there is no 'edge' to
them, but in the case of the planets it is possible to see a disc with a
telescope, and this object which attracted Herschel's attention had
certainly a disc. He did not imagine he had discovered a new planet,
because at that time the asteroids had not been found, and no one
thought that there could be any more planets. Yet Herschel knew that
this was not a star, so he called it a comet! He was actually the first
who discovered it, for he knew it was not a fixed star, but it was after
his announcement of this fact that some one else, observing it
carefully, found it to be a real planet with an orbit lying outside that
of Saturn, then the furthest boundary of the solar system. Herschel
sugg