December 29, 1898] 



NA TURE 



209 



J 



JUPITER AND HIS MARKINGS. 

 U PITER is now coming into a favourable aspect in the 

 morning hours. His position about ten degrees south of 

 the equator will, however, be an unfortunate circumstance for 

 European observers. To those, however, who can command 

 an open southern sky, there will be plenty of opportunities for 

 successful research ;and,certainly, this magnificent planet deserves 

 all the study that can be possibly devoted to him. In 1899 it 

 is to be hoped that a great number of drawings will be made, 

 and that the latitudes of the belts and spots will be micro- 

 metrically determined. We also require a fresh and extensive 

 series of the times of transit of the principal light and dark 

 markings, so that their longitudes and rate of drift relatively to 

 the zero meridian may be ascertained. The latter element 

 requires close attention at every opposition, as the velocities of 

 the various currents are frequently changing, and it is possible 

 they are regulated in definite cycles. 



During the last opposition the planet received widespread 

 notice from many observers, including Brenner, Fauth, Gledhill, 

 Hough, MacEwen, Phillips, Comas Sola, Stanley Williams, 

 myseif and others. No very special phenomena were presented 

 to arouse so much interest, but the disc was replete with a 

 variety of interesting formations. The equatorial region ex- 

 hibited an abundant series of dark and bright spots. These 

 were moving more rapidly than similar and probably identical 

 features last year, the difference of velocity being about 10 seconds. 

 It will be important to determine whether a further acceleration 

 of speed occurs in 1S99. In 1S97 the mean rotation of the 

 equatorial current was 9h. 50m. 34-6s. according to Mr. 

 Williams, while in 1898 the writer found it 9h. 50m. 23-6s. 



In the north tropical zone there were .several dark elongated 

 spots visible during the last opposition. These completed a 

 rotation in about "15^ seconds less than the red spot. This 

 latitude, about 15° N.'of the equator, appears to be very prolific 

 in the production of dark and light spots, which in certain cases 

 remain visible over considerable intervals. During the past 

 few years these markings have presented some difficulties as to 

 their identification, for some of them appear to be subject to 

 variations in form and tint, and perhaps to temporary obscura- 

 tion. They also, during different oppositions, exhibit a variable 

 rate of velocity. Thus in 1894-5 ^ ^^^'y ^'^'^'^ ^"^ definite spot 

 was seen on the northern edge of the north temperate belt. In 

 the next opposition two other spots, which were known as the 

 "violin" and "garnet" spots, were displayed in the same 

 latitude, though the north side of the belt seemed to have 

 vanished. In 1897 no conspicuous spots were detected in this 

 zone, but several were seen in 1898, and one of these may 

 possibly have been identical with the chief spot of 1S94, and 

 with the violin spot of 1S95-6, as the following comparison of 

 longitudes and rotation periods, obtained at Bristol, will 



indicate : — 



, - , Rotation 



Longitude 



period. 



Dark spot 

 "Violin" spot 



"^■'* 9 55 ir^ 



.. , , <, , ,. r 189S March 23 



Dark spot "A | j^j^ ^ 



followed the zero meridian >f System II. by about fifty-three 

 minutes. 



The question has often been asked as to whether the great 

 red spot of modern times is identical with Cassini's spot of 1665 

 and following years ? There seems a large amount of significant 

 evidence to support the affirmative view. The observations 

 spread over the 234 years, from Cassini's first observation to 

 the present time, do not afford many connecting-links, but the 

 probabilities are all on the side of identity. 



Though the ancient object is generally called Cassini's spot, 

 it was really discovered by Robert Hooke, with a telescope of 

 twelve feet focus and two inches aperture, on 1664 May 9. 

 He detected, " at about nine o'clock at night, a spot in the 

 largest of the three obscure belts of Jupiter, and found that 

 within two hours afterwards the said spot moved east to west 

 about half the length of the diameter." To Hooke, therefore, 

 belongs the credit of discovering this object, and the indication 

 it afforded of fixing the exact time of rotation of the planet. 

 But Cassini took the marking under his special charge, seeing, 

 as he did, the important deductions to be made from it. Ob- 

 serving it frequently in the summer of 1665, he ascertained the 

 rotation period as gh. 56m. I have gene over many of Cassini's 

 observations, and make the corrected period of rotation 

 gh. 55m. 47-55. in 1665-1672. Cassini says he was assured 

 of the preciseness of one mean revolution to one-eighth of a 

 minute. On 1672 March i, he saw the spot in transit on two 

 occasions (viz. at 7.30 and 17.26), and announced to the French 

 Academy of Sciences on the following day that the spot might 

 be again seen in transit on March 3 at 9.8 p.m. The .\cademy 

 thereupon deputed two of its more prominent members to 

 verify Cassini's prediction. With this purpose in view, they 

 repaired to the observatory, and, in company with Cassini, 

 actually observed the spot return exactly as foretold by him. 



The spot seen by Hooke and Cassini was about one-tenth of 

 the apparent diameter of Jupiter ; this would be about 9000 

 miles, and equivalent to the width of the spot in recent years. 

 The oval shape it now presents maybe due to the rapid rotatory 

 motion of the sphere, which we know has the effect of spreading 

 out objects in a longitudinal direction. Several new belts have 

 been formed under the eyes of observers. But in the case of the 

 red spot, its material may have been sufficiently solid to with- 

 stand the windingout process beyond the eUiptic form which 

 became its permanent shape. 



If the spot which Hooke saw on 1664 May 9, was the same 

 as the relic of the red spot observed at Bristol on November 29 

 last, then in the interval of 85,670! days no less than 207,084 

 rotations have been performed, if we adopt the mean rate as 

 gh. 55m. 40s. during that long interval. It is quite possible to 

 trace back the spot or its accompanying hollow in the great 

 southern belt to 1 831, and a further search amongst old drawings 

 of Jupiter may take its history safely back to the time of Sir 

 William Herschel and J. H. Schroeter. W. F. Denning. 



/ 1894 November 5 

 I, i8g5 May 9 ... 

 f 1895 September 26 

 ■\ 1896 February 9 ... 201 'I J 

 1896-7 Spot apparently invisible. 



The decreasing longitude of the spot agrees fairly well, and the 

 rapid increase of velocity is well marked along the series, but 

 the evidence that the objects were identical is certainly not 

 conclusive. If the spot was temporarily hidden in lSg6-7, its 

 rate was probably gh. 55ni. 307s. It is curious that in 1S90 

 Prof Barnard found ihe rate of a dark spot in same latitude 

 gh. 55m. 30-35. ; while in i8gi Prof. Hough derived a value of 

 gh. 55m. 27 -4s. from a mean of two spots. From a comparison 

 of a large number of rotation periods of this current at different 

 times, it appears a probable inference that the time oscillates 

 between gh. 55m. 26s. and gh. 55m. 41s. in a period of about 

 seven years. This is somewhat doubtful, but the variation of 

 rate seems well marked and to give evidence of regular 

 periodicity. It will be especially interesting to redetermine the 

 rotation period during 1899 if spots are still displayed in this 

 latitude. 



With reference to the red spot, I re-observed it on November 

 29 at igh. 55m., when it was on the central meridian, and 



NO. 1522, VOL. 59] 



THE NEW LIVERPOOL MUSEUMS 

 EXTENSION BUILDINGS. 



THE present museums buildings were erected in i860 by the 

 late Sir W. Brown for the splendid natural history 

 collections bequeathed to the City of Liverpool by the Xlllth 

 Earl of Derby in 1851. These were so extensive that the 

 accommodation they required necessitated the building of what 

 was, at that time, one of the largest museums in England 

 outside the Metropolis. Since that date the collections have 

 been constantly added to, not so much by purchases, as by gifts 

 — some of them of the highest value— from donors possessing 

 an interest in natural science, and appreciating, in advance of 

 their time, the importance of that subject as a means of educa- 

 tion, with the result that, to-day, every available foot of space 

 in the museums has long been occupied— every cellar even being 

 stored to its utmost capacity— so that any intelligible arrange- 

 ment of their contents has now become well-nigh impossible. 

 Within the past decade, also, the change in the public attitude 

 has been growing very rapidly towards an appreciation of 

 museums as institutions of high educational value and import- 

 ance. This is due. no doubt, to the rapid increase of scientific 

 and technological knowledge, and to the advocacy of no one in 

 Europe so specially as Sir William Flower, who, by his writings, 

 and, perhaps, principally by the methods, inaugurated by him, 

 of displaying and labelling the specimens in the Natural History 

 Museum in' South Kensington, has made manifest, not the 



