in about forty-two
hours and a half. The others, of course, move more slowly, but even the
most distant performs its revolution in several hours less than sixteen
days. The plane of their orbits is presented edgewise toward the earth,
from which it follows that they appear to move back and forth nearly in
straight lines, some apparently approaching the planet, while others are
receding from it. The changes in their relative positions, which can be
detected from hour to hour, are very striking night after night, and
lead to a great variety of arrangements always pleasing to the eye.

The most interesting phenomena that they present are their transits and
those of their round, black shadows across the face of the planet; their
eclipses by the planet's shadow, when they disappear and afterward
reappear with astonishing suddenness; and their occultations by the
globe of Jupiter. Upon the whole, the most interesting thing for the
amateur to watch is the passage of the shadows across Jupiter. The
distinctness with which they can be seen when the air is steady is
likely to surprise, as it is certain to delight, the observer. When it
falls upon a light part of the disk the shadow of a satellite is as
black and sharply outlined as a drop of ink; on a dark-colored belt it
can not so easily be seen.

It is more difficult to see the satellites themselves in transit. There
appears to be some difference among them as to visibility in such
circumstances. Owing to their luminosity they are best seen when they
have a dark belt for a background, and are least easily visible when
they appear against a bright portion of the planet. Every observer
should provide himself with a copy of the American Ephemeris for the
current year, wherein he will find all the information needed to enable
him to identify the various satellites and to predict, by turning
Washington mean time into his own local time, the various phenomena of
the transits and eclipses.

While a faithful study of the phenomena of Jupiter is likely to lead the
student to the conclusion that the greatest planet in our system is not
a suitable abode for life, yet the problem of its future, always
fascinating to the imagination, is open; and whosoever may be disposed
to record his observations in a systematic manner may at least hope to
render aid in the solution of that problem.

Saturn ranks next to Jupiter in attractiveness for the observer with a
telescope. The rings are almo