found to fill the void. Notwithstanding the service which the
so-called Law of Bode has indirectly rendered to astronomy, it has
strangely enough been found after all not to rest upon any scientific
foundation. It will not account for the distance from the sun of the
orbit of Neptune, and the very sequence seems on the whole to be in the
nature of a mere coincidence.

Neptune is invisible to the naked eye; Uranus is just at the limit of
visibility. Both planets are, however, so far from us that we can get
but the poorest knowledge of their condition and surroundings. Uranus,
up to the present, is known to be attended by four satellites, and
Neptune by one. The planets themselves are about equal in size; their
diameters, roughly speaking, being about one-half that of Saturn. Some
markings have, indeed, been seen upon the disc of Uranus, but they are
very indistinct and fleeting. From observation of them, it is assumed
that the planet rotates on its axis in a period of some ten to twelve
hours. No definite markings have as yet been seen upon Neptune, which
body is described by several observers as resembling a faint planetary
nebula.

With regard to their physical condition, the most that can be said about
these two planets is that they are probably in much the same vaporous
state as Jupiter and Saturn. On account of their great distance from the
sun they can receive but little solar heat and light. Seen from
Neptune, in fact, the sun would appear only about the size of Venus at
her best, though of a brightness sufficiently intense to illumine the
Neptunian landscape with about seven hundred times our full moonlight.

[22] Mr. P. Melotte, of Greenwich Observatory, while examining a
photograph taken there on February 28, 1908, discovered upon it a very
faint object which it is firmly believed will prove to be an _eighth_
satellite of Jupiter. This object was afterwards found on plates exposed
as far back as January 27. It has since been photographed several times
at Greenwich, and also at Heidelberg (by Dr. Max Wolf) and at the Lick
Observatory. Its movement is probably _retrograde_, like that of Phoebe
(p. 240).

[23] In the history of astronomy two salient points stand out.

The first of these is the number of "independent" discoveries which have
taken place; such, for instance, as in the cases of Le Verrier and Adams
with regard to Neptune, and of Lockyer and Janssen in the matter of the
spectroscopic method of