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THE PLANET JUPITER.

so, the permanence of some of the features of the planet, con-trasted with the incessant, and at times exceeding’ly rapidchanges visible in others, is extremely puzzling.

When, however, we know so little, we must not let ourignorance suggest unnecessary difficulties. Rather let it teachus to wait, and watch, and learn. We can at any rate say that,in the increasing speed of the rotation of spots as we approachthe equatoreal parts, there is a close resemblance to what takesplace upon the Sun . In the comparative permanence of thepositions of the principal belts, there is a resemblance to thepermanence of the zones upon each side of the Sun ’s equatorin which Sun -spots are found. In the size of the planet thereis a nearer approach (although the interval is still immenselygreat) to the size of the Sun , than in that of any other body inthe Solar System . Nor can we tell how much more, in bygoneages, before it had cooled down to its present condition, Jupiter may have resembled the existing state of the Sun ; nor howfar, in ages to come, the Sun ’s condition may resemble thatwhich we now see in Jupiter .

We know but little of either ; but we can see many points ofresemblance between them, many suggestive analogies. Andyet we would not for a moment infer that Jupiter , althoughit may be in a state of considerable heat, and give out someintrinsic light,* is in anything like so hot or luminous a con-dition as the Sun .

Here we must draw to a close our discussion of the possiblecondition of this great planet, only detaining our readers fora few additional moments in order to mention two or threeespecially interesting observations of the transits of Satellites,or of their shadows across the Great Red Spot, which havebeen recently made. They deserve special attention becausethey are such that, if they be carefully studied, and contrastedwith future occurrences of a similar kind, they may enable usto decide how far the spot is in any degree self-luminous, orthe contrary.

* See the commencement of this lecture, p. 295. Also Lecture VI.,p. 149, with reference to the comparative light of the planets Jupiter and Mercury.