aw the dark hemisphere _partially_ illuminated
by secondary light, extending 30 deg. from the terminator, and thought the
effect might be produced by a very extensive twilight.[881] Others have
had recourse to the analogy of our aurorae, and J. Lamp suggested that
the grayish gleam, visible to him at Bothkamp, October 21 and 26,
1887,[882] might be an accompaniment of electrical processes connected
with the planet's meteorology. Whatever the origin of the phenomenon, it
may serve, on a night-enwrapt hemisphere, to dissipate some of the thick
darkness otherwise encroached upon only by "the pale light of stars."

Venus was once supposed to possess a satellite. But belief in its
existence has died out. No one, indeed, has caught even a deceptive
glimpse of such an object during the last 125 years. Yet it was
repeatedly and, one might have thought, well observed in the seventeenth
and eighteenth centuries. Fontana "discovered" it in 1645; Cassini--an
adept in the art of seeing--recognised it in 1672, and again in 1686;
Short watched it for a full hour in 1740 with varied instrumental means;
Tobias Mayer in 1759, Montaigne in 1761; several astronomers at
Copenhagen in March, 1764, noted what they considered its unmistakable
presence; as did Horrebow in 1768. But M. Paul Stroobant,[883] who in
1887 submitted all the available data on the subject to a searching
examination, identified Horrebow's satellite with Theta Librae, a
fifth-magnitude star; and a few other apparitions were, by his industry,
similarly explained away. Nevertheless, several withstood all efforts to
account for them, and together form a most curious case of illusion. For
it is quite certain that Venus has no such conspicuous attendant.

* * * * *

The third planet encountered in travelling outward from the sun is the
abode of man. He has in consequence opportunities for studying its
physical habitudes altogether different from the baffling glimpse
afforded to him of the other members of the solar family.
Regarding the earth, then, a mass of knowledge so varied and
comprehensive has been accumulated as to form a science--or rather
several sciences--apart. But underneath all lie astronomical relations,
the recognition and investigation of which constitute one of the most
significant intellectual events of the present century.

It is indeed far from easy to draw a line of logical distinction between
items of knowledge which ha