nsits
sometimes take place.

[Page 114]
The movement of a superior planet, one whose orbit is exterior
to the earth, is clear from Fig. 47. When the earth is at A and
Mars at B, it will appear among the stars at C. When the earth is
at D, Mars having moved more slowly to E, will have retrograded
to F. It remains there while the earth passes on, in a line nearly
straight, from Mars to G; then, as the earth begins to curve around
the sun, Mars will appear to retraverse the distance from F to
C, and beyond. The farther the superior planet is from the earth
the less will be the retrograde movement.

[Illustration: Fig. 47.--Illustrating Movements of a Superior Planet.]

The reader should draw the orbits in proportion, and, remembering
the relative speed of each planet, note the movement of each in
different parts of their orbits.

To account for these most simple movements, the earlier astronomers
invented the most complex and impossible machinery. They thought the
earth the centre, and that the sun, moon, and stars were carried
about it, as stoves around a person to warm him. They thought these
strange movements of the planets were accomplished by mounting them
on subsidiary eccentric wheels in the revolving crystal sphere.
All that was [Page 115] needed to give them a right conception was a
sinking of their world and themselves to an appropriate proportion,
and an enlargement of their vision, to take in from an exalted
stand-point a view of the simplicity of the perfect plan.

EXPERIMENTS.

Fix a rod, or tube, or telescope pointing at a star in the cast
or west, and the earth's revolution will be apparent in a moment,
turning the tube away from the star. Point it at stars about the
north pole, and those on one side will be found going in an opposite
direction from those on the other, and very much slower than those
about the equator. Anyone can try the pendulum experiment who has
access to some lofty place from which to suspend the ball. It was
tried in Bunker Hill Monument a few years ago, and is to be tried
in Paris, in the summer of 1879, with a seven-hundred-pound pendulum
and a suspending wire seventy yards long. The advance and retrograde
movements of planets can be illustrated by two persons walking
around a centre and noticing the place where the person appears
projected on the wall beyond.

* * * * *

PROCESSION OF STARS AND SOULS.

"I stood upon the open casement,