THE PLANET JUPITER.

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have been disposed to believe that the Red Spot is probablysituated at no very great depth in Jupiter ’s cloudy envelope.It is also thought that a very slight slackening of its rotation-speed has been recently noticed. If so, this may arise fromthe opening, or depression, by which it may be formed, havingbecome somewhat more shallow, so that its motion correspondsmore nearly with that of the uppermost layers of the cloudsand vapours of Jupiter ’s atmosphere, which would naturallymove the most slowly. But, even if so, we can in no wiseexplain why that Great Red Spot should be so permanent, orin what way it has been generated. We are quite unable todecide whether it has originated where it is at present found,or in some source situated at a vast distance beneath.

We are indeed not only disposed, as we have already stated,to leave the time of Jupiter ’s rotation upon its axis an un-solved problem, but we must allow that it is even possible thatit ought to be described as different in different latitudes. Ifso, the differing rate of movement of the spots in such loca-lities would be explained; but at the same time it would benecessary to suppose, that the planet is not only surrounded bya vaporous envelope many thousands of miles in depth (asvarious classes of observations indicate),* but that it maybe to a very great depth indeed, and perhaps to its actualcentre, vaporous, molten, or in a semi-fluid and viscous con-dition. In fact, there may be no solid globe in the planetat all; or, in other words, it may be, as suggested at thecommencement of this lecture, in a very similar condition tothat in which the Sun is believed to be by many of the bestauthorities.

The only other tenable supposition probably is, that, at somevery considerable depth, there is a globe as to whose period ofrotation we know nothing ; while the outer regions, which areall that we can observe, are in a fluid, gaseous, or cloudycondition ; a state of things which we also mentioned as pos-sible, although not probable, in the case of the Sun. But if

* We shall presently draw special attention to some of these in con-nection with the occupations of the planet’s Satellites.