231} CHAP. VI.

On the cause of the definite time, of an entire
_rotation of the Earth._

Diurnal motion is due to causes which have now to be sought, arising from
magnetick vigour and from the confederated bodies; that is to say, why the
diurnal rotation of the Earth is completed in the space of twenty-four
hours. For no curious art, whether of Clepsydras or of sand-clocks, or
those contrivances of little toothed wheels which are set in motion by
weights, or by the force of a bent steel band, can discover any degree of
difference in the time. But as soon as the diurnal rotation has been gone
through, it at once begins over again. But we would take as the day the
absolute turning of a meridian of the Earth, from sun to sun. This is
somewhat greater than one whole revolution of it; in this way the yearly
course is completed in 365 and nearly 1/4 turnings with respect to the sun.
From this sure and regular motion of the Earth, the number and time of 365
days, 5 hours, 55 minutes, in solar tropical years is always certain and
definite, except that there are some slight differences due to other
causes. The Earth therefore revolves not fortuitously, or by chance, or
precipitately; but with a rather high intelligence, equably, and with a
wondrous regularity, in no other way than all the rest of the movable
stars, which have definite periods belonging to their motions. For the Sun
himself being the agent and incitor of the universe in motion, other
wandering globes set within the range of his forces, when acted on and
stirred, also regulate each its own proper courses by its own forces; and
they are turned about in periods corresponding to the extent of their
greater rotation, and the differences of their effused forces, and their
intelligence for higher good. And for that cause Saturn, having a wider
orbit, is borne round it in a longer time, Jupiter a shorter, and Mars
still less; while Venus takes nine months, Mercury 80 days, on the
hypotheses of Copernicus; the Moon going round the Earth with respect to
the Sun in 29 days, 12 hours, 44 minutes. We have asserted that the Earth
moves circularly about its centre, completing a day by an entire revolution
with respect to the Sun. The Moon revolves in a monthly course around the
Earth, and, repeating a conjunction with the Sun after a former synodic
conjunction, constitutes the month or Lunar day. The Moon's mean
concentrick orbit, according to numerous observations of Copernic