ranus, as Saturn of
Jupiter. Of the circumstances of his rotation we are as good as
completely ignorant. Mr. Maxwell Hall, indeed, noticed at Jamaica, in
November and December, 1883, certain rhythmical fluctuations of
brightness, suggesting revolution on an axis in slightly less than eight
hours;[1140] but Professor Pickering reduces the supposed variability to
an amount altogether too small for certain perception, and Dr. G. Mueller
denies its existence _in toto_. It is true their observations were not
precisely contemporaneous with those of Mr. Hall[1141] who believes the
partial obscurations recorded by himself to have been of a passing kind,
and to have suddenly ceased after a fortnight of prevalence. Their less
conspicuous renewal was visible to him in November, 1884, confirming a
rotation period of 7.92 hours.

It was ascertained at first by indirect means that the orbit of
Neptune's satellite is inclined about 20 deg. to his equator. Mr.
Marth[1142] having drawn attention to the rapid shifting of its plane of
motion, M. Tisserand and Professor Newcomb[1143] independently published
the conclusion that such shifting necessarily results from Neptune's
ellipsoidal shape. The movement is of the kind exemplified--although
with inverted relations--in the precession of the equinoxes. The pole of
the satellite, owing to the pull of Neptune's equatorial protuberance,
describes a circle round the pole of his equator in a retrograde
direction, and in a period of over five hundred years. The amount of
compression indicated for the primary body is, at the outside, 1/85;
whence it can be inferred that Neptune possesses a lower rotatory
velocity than the other giant planets. Direct verification of the trend
theoretically inferred for the satellite's movement was obtained by Dr.
See in 1899. The Washington 26-inch refractor disclosed to him, under
exceptionally favourable conditions, a set of equatorial belts on the
disc of Neptune, and they took just the direction prescribed by theory.
Their objective reality cannot be doubted, although Barnard was unable,
either with the Lick or the Yerkes telescope,[1144] to detect any
definite markings on this planet. Its diameter was found by him to be
32,900 miles.

The possibility that Neptune may not be the most remote body circling
round the sun has been contemplated ever since he has been known to
exist. Within the last few years the position at a given epoch of a
planet far beyond hi