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THE PLANET JUPITER.

at such a time be at rest in space. Indeed, he would bealtogether at rest, were it not that we believe that the Sun and all the planets are together travelling onwards with acommon motion round some very distant centre. Those whoare accustomed to the use of the spectroscope may, however,understand, that the conditions involved would facilitate somespecially interesting observations upon the approach or reces-sion of other heavenly bodies, or upon the motion of the SolarSystem itself.

We must, however, hasten on to the consideration of some ofthe many and very interesting physical features of this wonder-ful planet; amongst which we shall find that its Spots andBelts are most important.

These the astronomers of olden time of course never saw,although they so carefully watched the movements of Jupiter that one record has been handed down, dated more thantwenty-one centuries ago, in which Ptolemy tells how, upona certain day in the autumn of the year b.c. 240, the planetwas seen to occult the star S Cancri, the same star which wasdistinctly seen near to the Sun during the total Solar eclipseof July 1878.

But now that the telescope has come to our help, it is hardlypossible to look at the disc of Jupiter with an object-glass oftwo inches, or even less, in aperture, without being at oncestruck by certain dark streaks running across its surface, in adirection approximately parallel to that in which its Satellitesare also seen to lie.

It is doubtless strange that these streaks, or belts, do notseem to have been noticed by Galileo, * and that the first obser-vation of them was not made until about twenty years afterhe detected the Satellites of the planet. But from that timeonwards, they have been constantly watched. Nor was it longbefore they were found to exhibit frequent changes ; so that

* In England we are accustomed to call Galileo Galilei by his Christianname Galileo, instead of using his family name Galilei , as is customaryamong other nations. We hope it may soon be practicable, possibly byusing both names for a while, to correct this peculiarity. (See R. A. S.Monthly Notices, vol. xxxviii., p. 258.)