eed.
In many instances the velocity changes from year to year. And it is a
singular circumstance that in the same current a uniform motion is not
maintained in all parts of the circumference. Certain spots move faster
than others, so that if we would obtain a fair value for the rotation
period of any current it is not sufficient to derive it from one marking
alone; we must follow a number of objects distributed in different
longitudes along the current and deduce a mean from the whole."[10]

[Footnote 10: The Observatory, No. 286, December, 1899.]

Nor is this all. Observation indicates that if we could look at a
vertical section of Jupiter's atmosphere we should behold an equally
remarkable contrast and conflict of motions. There is evidence that some
of the visible spots, or clouds, lie at a greater elevation than others,
and it has been observed that the deeper ones move more rapidly. This
fact has led some observers to conclude that the deep-lying spots may be
a part of the actual surface of the planet. But if we could think that
there is any solid nucleus, or core, in the body of Jupiter, it would
seem, on account of the slight mean density of the planet, that it can
not lie so near the visible surface, but must be at a depth of
thousands, perhaps tens of thousands, of miles. Since the telescope is
unable to penetrate the cloudy envelope we can only guess at the actual
constitution of the interior of Jupiter's globe. In a spirit of mere
speculative curiosity it has been suggested that deep under the clouds
of the great planet there may be a comparatively small solid globe, even
a habitable world, closed round by a firmament all its own, whose vault,
raised 30,000 or 40,000 miles above the surface of the imprisoned
planet, appears only an unbroken dome, too distant to reveal its real
nature to watchers below, except, perhaps, under telescopic scrutiny;
enclosing, as in a shell, a transparent atmosphere, and deriving its
illumination partly from the sunlight that may filter through, but
mainly from some luminous source within.

But is not Jupiter almost equally fascinating to the imagination, if we
dismiss all attempts to picture a humanly impossible world shut up
within it, and turn rather to consider what its future may be, guided by
the not unreasonable hypothesis that, because of its immense size and
mass, it is still in a chaotic condition? Mention has been made of the
resemblance of Jupiter to the sun by virt