6o6 



NATURE 



{Oct. 23, 1879 



ing velocity of rotation; yet there is a "missing link" 

 which cannot readily be supplied. Friction against 

 a surrounding medium, combing out, as it has been 

 expressed, the vapours in a longitudinal direction, .can 

 hardly be admitted on mechanical grounds ; and there is 

 difficulty in conceiving the airangement of the restoration 

 of equilibrium in currents which set in one direction over 

 the whole visible globe, if they originate by ascending 

 from warmer depths, and lagging behind in a higher and 

 more swiftly rotating region. We may remark, in pass- 

 ing, that only a trifling elevation of the luminous above 

 the grey region, with a corresponding slight difference in 

 velocity of rotation, is compatible with the undeviating 

 contour of the limb as far as our telescopes may show it ; 

 though, of course, given an unlimited duration of time, 

 the slightest preponderance would l»e ultimately adequate 

 to such an effect. Possibly the best explanation may lie 

 in some modification of electrical or magnetic polarity. 

 At any rate the influence, though predominant, is not 

 irresistible, since it neither precludes the formation of 

 belts of a certain amount of obliquity, nor mixes up in 

 confusion, though it seems to elongate, those very re- 

 markable insulated luminous masses which occasionally 

 encompass the gigantic equator in a comparatively equable 

 series with a string of great oval beads, sometimes so 

 curiously and uniformly shaded as to convey an almost 

 irresistible impression of high relief. This strange phe- 

 nomenon, not confined, as Dawes has found, solely to 

 the equator, seems wholly beyond our conjectures. Nor 

 can we satisfactorily explain those large spots, much 

 darker than the belts, as though the atmosphere were 

 there more perfectly transparent, which have occasionally 

 shown such remarkable persistency as to indicate some 

 relation to definite regions on the surface beneath them ; 

 at other times have disappeared with startling rapidity ; 

 and usually have been so far from absolute immobility 

 that every attempt to determine the rotation by their 

 means has ended in mere approximation. The occa- 

 sional detection, too, of many minute white specks, like 

 passing satellites, in various parts of the disk, has added 

 nothing to our knowledge beyond the fact of their pre- 

 sence. The abnormal flattenings of the limb which have 

 sometimes been noticed on the approach of a satellite, 

 or even without it, seem to be of an illusory nature. 

 And yet nothing should pass without attention. 



Few things in this wonderful planet are more striking 

 than the singular and beautiful colouring which occasion- 

 ally adorns the disk. For a considerable season nothing 

 beyond some feeble tinge may be made out, especially in 

 the equatorial zone ; then again we shall find purple, 

 brown, greenish yellow, orange, and rosy tints marking 

 out the surface with delicate but unmistakable variety. 

 The darker the grey of the belts, the more apt it is to 

 show a slaty purple hue; the polar regions sometimes, as 

 at present, differ slightly in tint, so that temperature 

 does not seem to be connected with it. The rosy spot of 

 .the present season south of the equatorial zone has natu- 

 rally attracted mu;h attention, and will of course be care- 

 fully watched. But as yet the origin of such varieties 

 of colour sets conjecture at defiance. To depict these 

 many changes both of form and hue will always be an 

 interesting occupation, though it is never likely to have 

 any more definite result than to deepen our sense of the 

 wonders of creation, and our reverence for its First Great 

 Cause. 



One caution may be permitted here. It would be very 

 desirable for those who attempt to delineate this magni- 

 ficent planet that they should make themselves famifiar 

 with the perspective of a globe. The telescopic image has 

 so precisely the aspect of a flat disk that it requires some 

 mental effort to realise the fact that we are gazing on a 

 great ball ; and unless this is carefully borne in mind our 

 drawings will and must be unsatisfactory. Especially it 

 is perhaps seldom imagined how very little we know of 



the Polar regions, from an obliqueness of presentation 

 amounting to virtual and unbroken concealment. From 

 the analogy of Saturn we may infer that the poles (rf 

 Jupiter present no remarkable feature ; but it must ever 

 remain a mere conjecture to all future generations. 



It scarcely needs to be mentioned that no circular 

 representation of the disk can ever give a resemblance 

 tolerable to an experienced eye. An elliptical outline, 

 apparent even with a power of 30 or 40, is too striking a 

 characteristic not to affect materially the faithfulness of 

 the picture. 



Something remains to be said as to the beautiful retinue 

 which attends on this leader of the planetary system and 

 whose perpetual change of configuration is ever a source 

 of fresh interest. In some respects they are subjects 

 only for the finest telescopes, in others a very slight optical 

 power can deal with them. The true dimensions of those 

 minute disks are, perhaps, as fairly known as can be 

 expected from measures of such difficulty ; but the sub- 

 ject of their numerous changes of brilliancy, though 

 frequently treated, cannot be said to be fairly exhausted. 

 That such changes exist, and to an extent easily recog- 

 nised in very moderate telescopes, is undeniable ; and 

 were they constant for the same orbital positions, they 

 would find ready explanation in the very natural supposi- 

 tion that they rotate like our own satellite, each on his 

 own axis, in the same time that they complete their 

 monthly period. But this idea, though it approved itself 

 to Herschel I. and Schroter, is found inconsistent with 

 observation, which shows the changes to be too irregular 

 in their returns ; and we can only infer, what, indeed, has 

 been actually shown by good instruments, both in front of 

 and outside of the face of the primary, the variable 

 darkening of portions of their disks, a result whicb, 

 interpret it how we may, by atmospheric change, or un- 

 symmetric rotation, or a combination of both (and no 

 other supposition seems to occur), removes those little 

 bodies still further from our analogies. There is no more 

 resemblance between these satellites and our moon than 

 there is between the primaries on which they respectively 

 attend. 



We must postpone our remarks on Saturn and Mars to 

 a future opportunity. 



T. W. Webb 



nordenskj'Old's arctic voyages^ 



IT is fifteen months, our readers will remember, since 

 Prof. Nordenskjold left Hammerfest in the Vc-^a 

 to prove that, if taken at the proper time, the North- 

 East Passage is perfectly practicable. And the result 

 has proved that he was right to within a day or 

 two. Nearly a year ago he had practically accom- 

 plished the passage, and was only overtaken by the ice 

 just as he was about to emerge into the Pacific. We 

 know already that during their year's enforced imprison- 

 ment in the ice to the east of Serdze Kamen, Prof. 

 Nordenskjold and his accomplished and well-selected 

 staff have made the best possible use of their time. We 

 have already, on several occasions, briefly referred to 

 some of the valuable results obtained in various depart- 

 ments of science, and the full narrative of the expedition 

 will be looked for with impatience. We hope that it will 

 be given to the world with the least possible delay after 

 the leader's return to his home in Stockholm. Meantime 

 we are concerned, not with this culmination of a long 

 series of expeditions in the Arctic waters to the north of 

 the Old Continent, but with the exploring work of its 

 leader during the previous twenty years. Mr. Leslie has 

 done good service in wading through the voluminous 

 literature of Nordenskjold' s various expeditions, and 

 culling from it the material wherewith to compile a 



■ " The Arctic Voyages 'of Adolf Erik Nordenskjold, 185E-1S79." Wilh. 

 Illustrations and Maps. (London: Macmilian and Co., i£79-) 



