ested calling it Georgius Sidus, in honour of George III., then
King; but luckily this ponderous name was not adopted, and as the other
planets had been called after the Olympian deities, and Uranus was the
father of Saturn, it was called Uranus. It was subsequently found that
this new planet had already been observed by other astronomers and
catalogued as a star no less than seventeen times, but until Herschel's
clear sight had detected the difference between it and the fixed stars
no one had paid any attention to it. Uranus is very far away from the
sun, and can only sometimes be seen as a small star by people who know
exactly where to look for him. In fact, his distance from the sun is
nineteen times that of the earth.

Yet to show at all he must be of great size, and that size has actually
been found out by the most delicate experiments. If we go back to our
former comparison, we shall remember that if the earth were like a
greengage plum, then Uranus would be in comparison about the size of one
of those coloured balloons children play with; therefore he is much
larger than the earth.

In this far distant orbit the huge planet takes eighty-four of our years
to complete one of his own. A man on the earth will have grown from
babyhood to boyhood, from boyhood to the prime of life, and lived longer
than most men, while Uranus has only once circled in his path.

But in dealing with Uranus we come to another of those startling
problems of which astronomy is full. So far we have dealt with planets
which are more or less upright, which rotate with a rotation like that
of a top. Now take a top and lay it on one side on the table, with one
of its poles pointing toward the great lamp we used for the sun and the
other pointing away. That is the way Uranus gets round his path, on his
side! He rotates the wrong way round compared with the planets we have
already spoken of, but he revolves the same way round the sun that all
the others do. It seems wonderful that even so much can be found out
about a body so far from us, but we know more: we have discovered that
Uranus is made of lighter material than the earth; his density is less.
How can that be known? Well, you remember every body attracts every
other body in proportion to the atoms it contains. If, therefore, there
were any bodies near to Uranus, it could be calculated by his influence
on them what was his own mass, which, as you remember, is the word we
use to express wha