CJEPTEMBER 



i8yi] 



NATURE 



439 



D^ 



JUPITER AND HIS MARKINGS. 



)URING the last few years, Jupiter has been situated so far 

 south of the equator that telescopic observations have 

 had to be pursued under all the disadvantages inseparable from 

 viewing an object at a low altitude. But the conditions are 

 now much improved ;^ the planet, though still in south declina- 

 tion, will be some il° north of his position in 1890, and will 

 therefore remain much longer above the horizon, and present a 

 better defined and larger disk than during the few preceding 

 oppositions, so that the study of his surface-markings may be 

 resumed under very encouraging circumstances. 



The great red spot has been visible and its appearance and 

 movements closely watched during thirteen years, for it was in 

 July 1878 that it was first announced as a striking object. But 

 it probably existed long before this, for the drawings of previous 

 observers include forms which have a very suggestive resem- 

 blance to the red spot, though they are under a less conspicuous 

 aspect. There is, in fact, little doubt that this marking is an 

 old feature, but it is liable to considerable variations of tint, 

 inducing obvious changes in its general appearance as presented 

 to telescopic observers. Layers of cloud, moving with unequal 

 velocities and at different elevations above the surface of the 

 planet, probably overlap the spot and partially obliterate it at 

 times, but its definite elliptical outline has been always pre- 

 served, and its dimensions have not varied materially. It is 

 the colouring of the spot that has exhibited inconstancy, and 

 especially that of the central region, which changed from a brick- 

 red in 1878-81 to a very light tint, differing little, if at all, from 

 the other parts of the planet's disk in the same latitude. But 

 the margin of the spot has been more durable, and it was 

 visible for several years as a pink ellipse, offering a great 

 similarity to the ellipse seen by Gledhill in 1869-70. 



After a somewhat precarious existence, the spot appears to be 

 recovering prominence, though its present aspect will not bear 

 comparison with the features it presented about twelve years 

 ago. Still it is now a fairly conspicuous marking, with a depth 

 of tint far more pronounced than in the years 1884-85, The 

 central part of the spot appears to have regained the reddish 

 hue, and the general appearance of the object is sufficiently 

 marked to recall the grand views it afforded at the period of its 

 best display. 



The variable motion of the spot has formed one of its most 

 interesting attributes, and I give below a table of the mean 

 rotation-period deduced from observations during the last eleven 

 oppositions of Jupiter: — 



Limiting 



1879 July 10— 



1880 Sep. 27— 

 i88i July 8— 



1882 July 29 — 



1883 Aug. 23— 



1884 Sep. 21— 



1885 Oct. 24— 



1886 Nov. 23 — 



1 888 Feb. 12— 



1889 May 28— 



1890 May 22 — 



On August 7, 1891, I re-observed the spot with a 10 inch 

 reflector, power 252, and found it well-defined and fairly con- 

 spicuous. It passed the central meridian of the planet at 

 iih. 32m., so that it followed Marth's zero meridian (System 

 II.) only 3 minutes. This nearly agrees with two observa- 

 tions by Mr. A. S. Williams in May last, which placed the 

 spot 4 minutes behind the zero meridian. Mr. Marth's com- 

 putations are to be found in the Monthly No'.ices for March 

 1891, and they supply a valuable guide to all students of Jovian 

 phenomena. 



Apart from the red spot, it is desirable that the white spots 

 near the planet's equator, and the similar markings which verge 

 the northern side of the north equatorial belt, should be assidu- 

 ously followed, and their individual rotation periods ascertained 

 from a number of fresh observations. These markings are 

 severally controlled by proper motions of very irregular cha- 

 racter, and some singular alternations of visibility also affect 

 ihem. Mr. Williams finds that the equatorial white spots have 

 exhibited a great slackening of speed in recent years. This 



NO. II 40, VOL. 44] 



variation apparently affects the entire equatorial zone, and it 

 will be important to determine the exact extent of it, and 

 whether it is sustained in the present year. The changes of 

 velocity alluded to are scarcely progressive in the same direc- 

 tion ; we may expect to find an acceleration sooner or later to 

 compensate for the relatively slow movement of the spots in the 

 few past years. It is not unlikely that the various markings 

 show oscillations of speed recurring at uniform intervals. 



Students of this interesting planet will find abundance of 

 materials to collate and discuss. There is ample evidence of 

 the reappearance of certain features after periods of non- visi- 

 bility. Some of the more durable markings apparently suffer 

 temporary obscuration by vaporous masses suspended above 

 them in the Jovian atmosphere. The disposition of the belts is 

 also liable to changes, though not so rapidly as is generally 

 supposed, for many of the alleged variations have been due to 

 differences in telescopic definition or to the rapid rotation of the 

 planet ; circumstances which have not always teen adequately 

 allowed for. W. F. Denning. 



SCIENTIFIC SERIALS. 



American Journal of Science, August.— Some of the 

 features of non- volcanic igneous ejections, as illustrated in the 

 four " Rocks " of the New Haven region, West Rock, Pine 

 Rock, Mile Rock, and East Rock, by James D. Dana. A few 

 of the conclusions arrived at from the observations recorded in 

 this paper are that igneous eruptions occurred in the New 

 Haven region after the sandstone had been upturned. The liquid 

 rock forced its way between layers of the sandstone, and lifted 

 it up where the pressure of the rock was not too great to prevent 

 the upheaval. This intrusive action was favoured by the fact 

 that the fissure supplying the lava was inclined in the same 

 direction as the layers of the uplifted sandstone. And the folia- 

 tion of the underlying schists did not determine the course 

 and dip of the supply fissures. The paper is illustrated by 

 several excellent photographs of the formations investigated. — 

 Note on a reconnaissance of the Ouachita mountain system in 

 Indian territory, by Robert T. Hill. — The continuity of solid 

 and liquid, by Carl Barus. By means of the simple arrangement 

 described in this paper, the author is able to obtain at once the 

 isothermals and isopiestics, and therefore the isometrics, both 

 for the solid and liquid states of the substances experimented 

 upon. The relation of solidification and fusion to pressure and 

 the pressure changes of the isothermal specific volumes of solid 

 and liquid at the solidifying and melting points can alfo be 

 determined. And from such results the character of fusion and 

 the probable position of critical and transitional points can be 

 found. The author has as yet only investigated the behaviour 

 of naphthalene by his method, but the whole work throws con- 

 siderable light upon the relation of pressure to phenomena of 

 fusion and solution. — Note on the asphaltum of Utah and 

 Colorado, by George H. Stone. The author has visited all the 

 known asphalie fields of Western Colorado and North-Eastern 

 Utah. The observations he has made bear upon the origin of 

 petroleum, asphalte, natural gas, and other subterranean hydro- 

 carbons, but the facts are hardly sufficient to lead to definite 

 conclusions. — Photographic investigation of prominences and 

 their spectra, by George E. Hale. Account is given of the 

 methods employed by the author for the photography of invisible 

 solar prominences. Special attention has been directed to the 

 photography of the bright prominence lines running through H 

 and K, with a slit tangential to the sun's limb. Four reproduc- 

 tions of negatives showing prominences illustrate the paper. — A 

 gold-bearing hot spring deposit, by Walter Harvey Weed. A 

 microscopical and chemical examination of some specimens of 

 ore from the Mount Morgan Gold Mine, Queensland, demon- 

 strates that the mine is a deposit of a hot spring, the ore being 

 a siliceous sinter impregnated with auriferous hzematite. This 

 is the only hot spring deposit that has been found to contain 

 gold in commercially valuable quantities, and although the 

 sinter deposits from the hot springs of Yellowstone Park 

 resemble those from Mount Moigan, no trace of the precious 

 metals has been found in them. — Res; oration of Stegosaurus, 

 by O. C. Marsh. The species restored is Slegosaitrus ungtilatus, 

 from the Upper Jurassic of Wyoming. A plate, representing 

 the reptile one- thirtieth its natural size, accompanies the paper. 



