which fills our atmosphere all around the sun's place
in the sky. Mercury, the nearest known planet to the sun, is for this
reason always very difficult to see; and even when, in its course, it
gets sufficiently far from the sun to be left for a short time above the
horizon after sunset, it is by no means an easy object to observe on
account of the mists which usually hang about low down near the earth.
One opportunity, however, offers itself from time to time to solve the
riddle of an "intra-Mercurial" planet, that is to say, of a planet which
circulates within the path followed by Mercury. The opportunity in
question is furnished by a total eclipse of the sun; for when, during an
eclipse of that kind, the body of the moon for a few minutes entirely
hides the sun's face, and the dazzling glare is thus completely cut off,
astronomers are enabled to give an unimpeded, though all too hurried,
search to the region close around. A goodly number of total eclipses of
the sun have, however, come and gone since the days of Lescarbault, and
no planet, so far, has revealed itself in the intra-Mercurial space. It
seems, therefore, quite safe to affirm that no globe of sufficient size
to be seen by means of our modern telescopes circulates nearer to the
sun than the planet Mercury.

Next in importance to the planets, as permanent members of the solar
system, come the relatively small and secondary bodies known by the name
of Satellites. The name _satellite_ is derived from a Latin word
signifying _an attendant_; for the bodies so-called move along always in
close proximity to their respective "primaries," as the planets which
they accompany are technically termed.

The satellites cannot be considered as allotted with any particular
regularity among the various members of the system; several of the
planets, for instance, having a goodly number of these bodies
accompanying them, while others have but one or two, and some again have
none at all. Taking the planets in their order of distance outward from
the Sun, we find that neither Mercury nor Venus are provided with
satellites; the Earth has only one, viz. our neighbour the Moon; while
Mars has but two tiny ones, so small indeed that one might imagine them
to be merely asteroids, which had wandered out of their proper region
and attached themselves to that planet. For the rest, so far as we at
present know, Jupiter possesses seven,[2] Saturn ten, Uranus four, and
Neptune one. It i