an
at six. His appearance and relative dimensions as he passes from
opposition to quadrature are shown in the last three figures of the
upper row.

Mars' polar caps may be seen with very moderate powers.

I add four sets of meridians (Plate 6), by filling in which from the
charts the observer may obtain any number of views of the planet as it
appears at different times.

Passing over the asteroids, which are not very interesting objects to
the amateur telescopist, we come to Jupiter, the giant of the solar
system, surpassing our Earth more than 1400 times in volume, and
overweighing all the planets taken together twice over.

Jupiter is one of the easiest of all objects of telescopic observation.
No one can mistake this orb when it shines on a dark sky, and only Venus
can be mistaken for it when seen as a morning or evening star. Sometimes
both are seen together on the twilight sky, and then Venus is generally
the brighter. Seen, however, at her brightest and at her greatest
elongation from the sun, her splendour scarcely exceeds that with which
Jupiter shines when high above the southern horizon at midnight.

Jupiter's satellites may be seen with very low powers; indeed the outer
ones have been seen with the naked eye, and all are visible in a good
opera-glass. Their dimensions relatively to the disc are shown in Plate
7. Their greatest elongations are compared with the disc in the
low-power view.

Jupiter's belts may also be well seen with moderate telescopic power.
The outer parts of his disc are perceptibly less bright than the centre.

More difficult of observation are the transits of the satellites and of
their shadows. Still the attentive observer can see the shadows with an
aperture of two inches, and the satellites themselves with an aperture
of three inches.

The minute at which the satellites enter on the disc, or pass off, is
given in 'Dietrichsen's Almanac.' The 'Nautical Almanac' also gives the
corresponding data for the shadows.

The eclipses of the satellites in Jupiter's shadow, and their
occultations by his disc, are also given in 'Dietrichsen's Almanac.'

In the inverting telescope the satellites move from right to left in the
nearer parts of their orbit, and therefore transit Jupiter's disc in
that direction, and from left to right in the farther parts. Also note
that _before_ opposition, (i.) the shadows travel in front of the
satellites in transiting the disc; (ii.) the satellites are e