no explanation can yet be given. It was of course at once
observed that between Mars and Jupiter one place is vacant, and it has
now been ascertained that this is occupied by a zone of Minor Planets,
the first of which was discovered by Piazzi on January 1, 1801, a worthy
prelude to the succession of scientific discoveries which form the glory
of our century. At present over 300 are known, but certainly these are
merely the larger among an immense number, some of them doubtless mere
dust.

JUPITER

Beyond the Minor Planets we come to the stupendous Jupiter, containing
300 times the mass, and being 1200 times the size of our Earth--larger
indeed than all the other planets put together. It is probably not
solid, and from its great size still retains a large portion of the
original heat, if we may use such an expression. Jupiter usually shows a
number of belts, supposed to be due to clouds floating over the surface,
which have a tendency to arrange themselves in belts or bands, owing to
the rotation of the planet. Jupiter has four moons or satellites.

SATURN

[Illustration: Fig. 53.--Saturn.]

Next to Jupiter in size, as in position, comes Saturn, which, though far
inferior in dimensions, is much superior in beauty. To the naked eye
Saturn appears as a brilliant star, but when Galileo first saw it
through a telescope it appeared to him to be composed of three bodies in
a line, a central globe with a small one on each side. Huyghens in 1655
first showed that in reality Saturn was surrounded by a series of rings
(see Fig. 53). Of these there are three, the inner one very faint, and
the outer one divided into two by a dark line. These rings are really
enormous shoals of minute bodies revolving round the planet, and
rendering it perhaps the most marvellous and beautiful of all the
heavenly bodies.

While we have one Moon, Mars two, and Jupiter four, Saturn has no less
than eight satellites.

URANUS

Saturn was long supposed to be the outermost body belonging to the solar
system. In 1781, however, on the 13th March, William Herschel was
examining the stars in the constellation of the Twins. One struck him
because it presented a distinct disc, while the true fixed stars,
however brilliant, are, even with the most powerful telescope, mere
points of light. At first he thought it might be a comet, but careful
observations showed that it was really a new planet. Though thus
discovered by Herschel it had often been