s enough about such subjects to take the
necessary trouble, can easily make a little model of Saturn and his ring
system, which will very prettily illustrate the effect of the rings both
in reflecting light to the planet's darkened hemisphere and in cutting
off light from the planet's illuminated hemisphere. Take a ball, say an
ordinary hand-ball, and pierce it through the centre with a fine
knitting-needle. Cut out a flat ring of card, proportioned to the ball
as the ring system of Saturn to his ball. (If the ball is two inches in
diameter, strike out on a sheet of cardboard two concentric circles, one
of them with a radius of a little more than an inch and a half, the
other with a radius of about two inches and three-eights, and cut out
the ring between these two circles.) Thrust the knitting-needle through
this ring in such a way that the ball shall lie in the middle of the
ring, as the globe of Saturn hangs (without knitting-needle connections)
in the middle of his ring system. Thrust another knitting-needle
centrally through the ball square to the plane of the ring, and use this
second needle, which we may call the polar one, as a handle. Now take
the ball and ring into sunlight, or the light of a lamp or candle,
holding them so that the shadow of the ring is as thin as possible. This
represents the position of the shadow at the time of Saturnian spring or
autumn. Cause the shadow slowly to shift until it surrounds the part of
the ball through which the polar needle passes on one side. This will
represent the position of the shadow at the time of midwinter for the
hemisphere corresponding to that side of the ball. Notice that while the
shadow is traversing this half of the ball, the side of the ring which
lies towards that half is in shadow, so that a fly or other small insect
on that half of the ball would see the darkened side of the ring. A
Saturnian correspondingly placed would get no reflected sunlight from
the ring system. Move the ball and ring so that the shadow slowly
returns to its first position. You will then have illustrated the
changes taking place during one half of a Saturnian year. Continue the
motion so that the shadow passes to the other half of the ball, and
finally surrounds the other point through which the polar needle passes.
The polar point which the shadow before surrounded will now be seen to
be in the light, and this half of the ball will illustrate the
hemisphere of Saturn where it is mid