♦ KNO"WLEDGE 



[Sei 



, 18, 1885. 



the real globe of the planet. Let us see -^vhether this 

 idea leads us to any results which seem to correspond Tvith 

 the phenomena actuallj presented by the great spot. 



If the origin of the disturbance were in the real globe 

 of Jupiter, then it must be presumed that the original 

 disturbance was due to the intense heat pervading the 

 whole frame of the planet and was explosive in character. 

 An outburst of compressed vapour from some gigantic 

 volcano on Jupiter, carrying upwards vast vaporous 

 masses to regions of much diminished pressure, would be 

 followed by the rapid rush outwards of the expanding 

 vapour, and by the sweeping away of the cloud masses 

 which before had covered the region of disturbance, over 

 an immense area. This area would be circular in shape 

 in the case of a non-rotating planet, or in the case of 

 comparatively shallow vaporous envelopes like those 

 which surround our earth. But in the case of masses of 

 vapour flung upwards from the real surface of a rapidly 

 rotating planet like Jupiter, with sufficient energy to 

 burst their way through cloud layers thousands of miles 

 above that surface, there would undoubtedly be a marked 

 trailing off of the vaporous masses westwards. Thej- 

 would acquire a westerly motion sufficing to give the 

 region of disturbance measurable superiority of length 

 in an east-and-west direction. For the westerly motion 

 would continue after the ui^flung vapours had reached 

 their greatest height. 



As a result of this process of westerly lagging the 

 western end of the spot might be expected to be not 

 quite so symmetrical in form as the easterly, a peculiaritj- 

 which was actually noticed. Moreover, as the whole 

 spot, or rather the whole of the cloud-region containing 

 the spot would drift steadily westwards, the planet 

 turning all the time rapidly eastwards (one rotation in 

 less than ten hours) it follows that the spot would have 

 a slightly longer rotation period than the equatorial 

 markings, — which also was actually observed. 



According to this interpretation, the great red spot on 

 Jupiter would indicate the occurrence of a tremendous 

 outburst at the planet's real surface, an outburst compared 

 with which the great earthquake at Krakatoa was as 

 child's play compared with the labours of many giants. 

 That the outburst at its commencement was sudden may 

 be well believed. Yet judging from the long continuance 

 of the great spot and of the sequent disturbance, the 

 eruptive action must have lasted a long time. Of course 

 it does not necessarily follow that the disturbance which 

 caused the great opening in the cloud envelope lasted as 

 long as the opening itself. It may well be that the 

 movements by which a distiirbed cloud-belt on Jupiter 

 returns to its normal condition, are sluggish compared 

 with the fierce action by which the disturbance is brought 

 about, at (or it may be below) the fiery surface of the 

 planet itself. Still the gigantic elliptic ring seen as early 

 as 1871, followed by a gigantic elliptic opening which 

 remained for six years, and that again by a disturbed 

 condition which has already lasted nearly three years 

 and may last much longer, — all this seems quite incon- 

 sistent with the idea that the eruptive action giving birth 

 (if my interpretation is correct) to this long-lasting 

 disturbance was itself of short duration. 



And after all, it would not be very surprising, when 

 we consider the enormous scale on which Jupiter is con- 

 structed, the tremendous heat which must in all proba- 

 bility pervade his whole frame, and the correspondinglj- 

 increased duration of all internal disturbances, if the 

 analogues on Jupiter of volcanic outbursts which on the 

 earth (so much smaller and now relatively aged) last often 

 for many weeks, should on Jupiter last, occasionally, for 



several years. Jupiter, according to all reasonable pro 

 bability, must be a very young planet. If his planetary 

 career began at the same time as the earths;, he is cer- 

 tainly much younger than our earth ; but even if he 

 began his career as a planet millions of years before the 

 earth, even then he would bo 3-ounger than the earth in 

 development. For those millions of years would be as 

 nothing compared with the vast excess of the duration of 

 Jupiter's life-stages over the duration of the corresponding 

 life-stages of the earth. Segarding Jupiter as in a much 

 more youthful stage of planetary life than the earth is 

 now passing through, and remembering that even when 

 Jupiter has reached the same stage as our earth his 

 eruptive energies will be much greater than the earth's 

 now are, we may well believe that the explosions now 

 taking place on Jupiter must be on an incomparably 

 grander scale than the mightiest volcanic disturbances 

 on the earth. Applying to Jupiter the reasoning which 

 was applied to the disturbance of Krakatoa in 1883, we 

 might readily liii.l that ivi.ua greater disturbance than 

 the Great Hid S[H)t iiidieiitod, tremendous and far- 

 reaching thiai-li tliut Jinturlanco was, could be explained, 

 as resulting fruiu a Juviuu Volcanic outburst, vaster and 

 fiercer than terrestrial outbursts because Jupiter is at 

 once a mightier and a much yotmger planet. 



SCOTLA>'D AND SCANDINAVIA.* 



Bt Peofess 



i JUDD. 



HE who enters on the study of Highland geology 

 without being prepared to encounter at every step 

 complicated foldings, vast dislocations, and stupendous 

 inversions of the strata can scarcely fail to be betrayed 

 into disastrous errors. 



The early history of Scotland is inextricably inter- 

 woven with that of Scandinavia. This proposition, true 

 as it is of the insignificant periods of which human 

 history takes cognizance, applies with even greater force 

 to the vast epochs that fall within the ken of the geolo- 

 gist. To us the separation of Scotland and Scandinavia 

 is an event of very recent date indeed ; it was not only 

 an accident, but an uncompleted accident. The Scottish 

 Islands, with the Hebrides and Donegal on the one hand, 

 with Orkney and Shetland on the other, must be regarded, 

 to use a technical phrase, as mere " outliers " of the 

 Scandinavian iieiiinsula. The great Scandinavian massif, 

 with its outlying fragment?, constitutes the " basal- 

 wreck," to employ Darwin's expressive term, of a great 

 Alpine chain. 



On other occasions I have endeavoured to show how 

 much our study of the nature and products of volcanic 

 action was facilitated by the existence of similar " basal- 

 wrecks " of volcanic mountains, like those which existed 

 in their beautiful western isles. In the same way, I 

 believe we may learn more, by the study of this 

 dissected mountain chain, ccaiceming the operations by 

 which these grand features of our globe have originated, 

 than by the most prolonged examination of the super- 

 ficial characters of the Alps or the Himalayas. Here the 

 scalpel of denudation has laid bare the innermost re- 

 cesses of the mountain masses, and what we can only 

 guess at in the Alps and the Himalayas stand in our 

 own Highlands clearly revealed to view. 



In offering a few remarks on some of the still unsolved 

 problems of Highland geology, I shall not hesitate to 



