planet can be entirely, or even largely, due to
the feeble influence of solar heat. We are, therefore, led to seek for
some other source of such disturbances. What that source is to be will
appear obvious when we admit that Jupiter still retains a large
proportion of primitive internal heat. Just as the sun itself is
distracted by violent tempests as an accompaniment of its intense
internal fervour, so, in a lesser degree, do we observe the same
phenomena in Jupiter. It may also be noticed that the spots on the sun
usually lie in more or less regular zones, parallel to its equator, the
arrangement being in this respect not dissimilar to that of the belts on
Jupiter.

It being admitted that the mighty planet still retains some of its
internal heat, the question remains as to how much. It is, of course,
obvious that the heat of the planet is inconsiderable when compared
with the heat of the sun. The brilliance of Jupiter, which makes it an
object of such splendour in our midnight sky, is derived from the same
great source which illuminates the earth, the moon, or the other
planets. Jupiter, in fact, shines by reflected sunlight, and not in
virtue of any intrinsic light in his globe. A beautiful proof of this
truth is familiar to every user of a telescope. The little satellites of
the planet sometimes intrude between him and the sun, and cast a shadow
on Jupiter. The shadow is black, or, at all events, it seems black,
relatively to the brilliant surrounding surface of the planet. It must,
therefore, be obvious that Jupiter is indebted to the sun for its
brilliancy. The satellites supply another interesting proof of this
truth. One of these bodies sometimes enters the shadow of Jupiter and
lo! the little body vanishes. It does so because Jupiter has cut off the
supply of sunlight which previously rendered the satellite visible. But
the planet is not himself able to offer the satellite any light in
compensation for the sunlight which he has intercepted.[22]

Enough, however, has been demonstrated to enable us to pronounce on the
question as to whether the globe of Jupiter can be inhabited by living
creatures resembling those on this earth. Obviously this cannot be so.
The internal heat and the fearful tempests seem to preclude the
possibility of organic life on the great planet, even were there not
other arguments tending to the same conclusion. It may, however, be
contended, with perhaps some plausibility, that Jupiter has