y bodies; and some rough notion of its distance was
current. Mars, Jupiter, and Saturn were placed in that order
because that is the order of their apparent motions, and it was
natural to suppose that the slowest moving bodies were the furthest
off.

The order of the days of the week shows what astrologers considered
to be the order of the planets; on their system of each successive
hour of the day being ruled over by the successive planets taken in
order. The diagram (fig. 7) shows that if the Sun rule the first
hour of a certain day (thereby giving its name to the day) Venus
will rule the second hour, Mercury the third, and so on; the Sun
will thus be found to rule the eighth, fifteenth, and twenty-second
hour of that day, Venus the twenty-third, and Mercury the
twenty-fourth hour; so the Moon will rule the first hour of the
next day, which will therefore be Monday. On the same principle
(numbering round the hours successively, with the arrows) the first
hour of the next day will be found to be ruled by Mars, or by the
Saxon deity corresponding thereto; the first hour of the day after,
by Mercury (_Mercredi_), and so on (following the straight lines of
the pattern).

The order of the planets round the circle counter-clockwise, _i.e._
the direction of their proper motions, is that quoted above in the
text.

To explain the motion of the planets and reduce them to any sort of law
was a work of tremendous difficulty. The greatest astronomer of ancient
times was Hipparchus, and to him the system known as the Ptolemaic
system is no doubt largely due. But it was delivered to the world mainly
by Ptolemy, and goes by his name. This was a fine piece of work, and a
great advance on anything that had gone before; for although it is of
course saturated with error, still it is based on a large substratum of
truth. Its superiority to all the previously mentioned systems is
obvious. And it really did in its more developed form describe the
observed motions of the planets.

Each planet was, in the early stages of this system, as taught, say, by
Eudoxus, supposed to be set in a crystal sphere, which revolved so as to
carry the planet with it. The sphere had to be of crystal to account for
the visibility of other planets and the stars through it. Outside the
seven planetary spheres, arranged one inside the other, was a still