22S 



NATURE 



[January 3, 1895 



markings now existing are identical with those observed 

 some years ago. From 1S7S to 1SS2 the prominent 

 appariti<^n of the red spot incited observers to fully 

 investigate the phenomena of the different formations, 

 and they were found to be very discordant in their rates 

 of velocity. The red spot and equatorial white spots 

 were evidently subject to a marked retardation, causing 

 their rotation periods to increase with the time. 



As to the red spot, the slackening rate of motion it 

 exhibited in the earlier years of its presentation, appears 

 not to have been maintained since 1SS6, for Mr. Marth's 

 adopted period of gh. Sjm. 40 633. (equivalent to a daily 

 rate of 870^27) has correctly represented its mean 

 motion during the last eight years. There have been, it 

 is true, some marked deviations from the mean rate, for 

 in the years from 1SS6 to 1S90 the motion became 

 accelerated and corresponded to a rotation period of 

 about 9h. 5Sm. 40 2s., but in the three following years it 

 slackened again, and since 1891 the period has been 

 about 9h. 55m. 41 'Ss. 



At the present epoch the spot is extremely feeble in its 

 visible outlines, but on a really good night its elliptical 

 form can be distinctly traced, and it does not appear to 

 have materially changed either in its shape or dimensions 

 since 1S79. Its following end is decidedly the plainest, 

 and its southern borders have lately been conjoined with 

 a grey belt in about latitude 30' south. The com- 

 mingling of the spot and belt has been noticed here on 

 previous occasions, and it is certain that on its southern 

 side the spot exerts very little of the repellent influence so 

 often ascribed to it. On the contrary, the belts on the 

 equatorial side of the spot always run clear, and abruptly 

 bend north to allow of a clear while interval between the 

 spot and bell. The S. border of the spot and S. belt were 

 apparently in touch early in the past autumn, for Mr. Bar- 

 nard, observing the red spot with the 36-inch refractor of 

 the Lick Observatory, says: '"The belt south of it seems 

 to be in contact, if it iX^<t^ xv t actually overlap it slightly." 

 The same thing wa= noticed as long ago as October 31, 

 1893, by the aid of the 16-inch refractor of the Goodsell 

 Observatory, Minnesota, when the observers wrote " the 

 great red spot was seen by us, and the colour was exactly 

 the same as that of the belt just to the south of it, and 

 the two objects merged into one another without the 

 slightest change in intensity of colour." 



The spot now arrives at mid-transit two or three 

 minutes after Mr. Marth's zero meridian, as the following 

 observ.iii(.n-, ni.iile here will indicate: — 



Miii.tr.tn-iit I'ollows Marth's Long, of 

 - , of spcit. zero ineridUin. spot, 



h. m. m. , 



Novctnl)«r 25 10. 50 4-2 2-9 



December 12 9 46 f2 07 



19 «o 33 35 21 



It is well known that the perception of a delicate 

 planetary marking depends in a very great measure on 

 the quality of the definition. On an indifferent night the 

 red spot is practically invisible, but with steady air and a 

 sharp image the familiar pinkish ellipse, now represent- 

 ing that object, shows up distinctly in the remarkable 

 concavity of the great southern equatorial belt. The 

 latter configuration always offers an excellent guide to 

 the position of the spot, but its appearance is not 

 symmetrical, the following side of it being much more 

 strongly developed than the side preceding the spot. 



The impending disappearance of the latter has been 

 suggested by several observers from its loss of tone during 

 the last few years, but there seems to be no tangible 

 reason to suppose that we are on the point of losing this 

 truly singular object. It is indeed utterly impossible to 

 predicate anything definite as to its future history. The 

 facts gleaned during past observations are not of a 

 character to guide us to any reliable conclusion. Its 

 present fainlness may be but the prelude to a more 



NO. I314, VOL, 51] 



marked manifestation, for variation of tint is certainly one 

 of its leading peculiarities. It is doubtless the same 

 object as the the ellipse seen by Gledhill and Mayer in 

 1S69 and 1S70, and quite possibly the same formation was 

 figured by Dawes in 1S57 and in subsequent years. At 

 any rate the resemblance of the objects is eminently 

 suggestive, and altogether too sti iking to be disregarded. 



About fifteen years ago the equatorial zone of Jupiter 

 exhibited phenomena proving it to be in a stale of con- 

 siderable activity. There were white and dark spots, 

 wisps of dark material, veins of bright mailer, and other 

 irregularities all in condition of rapid change, and impart- 

 ing a very broken and variegated aspect to the northern 

 side of the great southern equatorial belt. To day the 

 indications are essentially different. The light tint of the 

 equator seems pretty even, and exhibits few noticeable 

 irregularities. Precisely on the equator there is a dark 

 belt like a narrow pencil line, but it is not now continuous 

 right round the disc. The chief seat of energy appears 

 to have been transferred to the northern side of the 

 great northern equatorial belt. 



Dark spots (some of them almost black, like satellite 

 shadows) and white patches, with oiher details of 

 structure, are plentifully arra\cd in the noithern equatorial 

 belt. The white spots I observed here in 1S85 and 1886, 

 and they have persistently maintained themselves ever 

 since. Their roiation period in 1SS6 was about eight 



1S94 November 35, loh. qm., 10-inch 'rctlcctor, power 25.'. 

 Rcgi^in of Red Spot. 



seconds less than that of 'the red spot, but in 1S90-91 1 

 found it only 26 seconds less. At present the period is 

 still a little less, and there are a number of black spots 

 in the same latitude, and subject to the same drift. One 

 of the most conspicuous of the black spots |)rccedes the 

 red spot about 3h. 20m , and one of the chief while spots 

 precedes the red about 2h. I have secured the following 

 observations of this pair of objects : — 



The northern temperate belt on which in 18S0 and 

 1 891 many rapidly moving black spots appeared, is now 

 in close contiguity with the gieat noithern belt, and 

 blends with it in certain places. A few years ago the two 

 belts were separated by a bright zone. 



There is a narrow spotted belt in about latitude 35 north. 

 In 1892 and on subseciuenl occasions I noticed this belt 

 beaded with numerous dark spots, but I have not made 

 a sufficient number of observations to dcteiminc the 

 rotation period. This belt forms a delicate object ; it is 

 very narrow, and the spots extremely small. In bad air 



