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Page:Popular Science Monthly Volume 24.djvu/196

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184
THE POPULAR SCIENCE MONTHLY.

scribed appears particularly interesting, and that relates to the supposed resemblance between the larger planets, and more especially Jupiter, and the sun. Everybody knows that Jupiter has a conspicuous dark-colored belt on each side of his equator, for those belts are one of the commonest objects of celestial sight-seeing. Saturn too has belts similarly situated, although they are less conspicuous than those of Jupiter. All the trustworthy evidence we have points to the conclusion that these huge planets are yet in a state which has more points of resemblance to the condition of a sun than to that of a cool and solid globe. There can be little doubt that Jupiter is surrounded by a cloud-laden atmosphere of great depth, and that his geological development, so to speak, is in a stage much earlier than any whose former existence is recorded in the present rock strata of the earth. In other words, Jupiter probably has not yet a continuous solid crust, even if the formation of such a crust has been begun. But, accepting the nebular hypothesis, we must conclude that Jupiter is gradually cooling and contracting, and that eventually he will have as solid a surface as the earth's. He seems, then, to be in a transition state between a luminous sun and an opaque world, and, if so, his present condition may throw light upon the future condition of the sun, just as the moon throws light upon the future condition of our own earth. For this reason it may be interesting for the reader to compare

PSM V24 D196 Appearance of jupiter during sun flare activity.jpg
Fig. 4.

with the figures representing the belt of sun-spots seen last summer a picture of Jupiter and his belts, shown in Fig. 4. It is, of course a long step from the string of separate spots in one case to the unbroken bands in the other, and yet it is easily seen that some resemblance