March 7»'90J3i 



NA rURB 



443 



In the orderly condensation of swarms, according to 

 the meteoritic hypothesis, the earlier stages are — 



3, 



Cygniaa 



rM 



Dark lines, corresponding chiefly 

 with the enhanced lines of 

 various metals. 



Aldebarifui . 



— -...!,- -' 3 .::( Dark Iines,comprising both arc and 



'"y"':'.'/" 'r \ enhanced linesof various metals. 



,1 / Dark lines, chiefly corresponding 



.....-< to those which appear in the 



1^ arc spectra of various metals. 



. .,, >.3 r Mixed bright and dark flutings and 



.<\.ntarian .. .'.;.. ..',1....-! darklines. Bright hydrogen lines 



..'"";!*""', (^ in those stars which are variable. 



Nebula ,...:.\'!?..'3 Bright lines. 



i v , . ) n»>/ V. ': .i- - . ' 



'Injhe case erf ^f^wf stars, after the maximum of luminosity 

 has been reached^; however high they ascend, short of the 

 apex; of the temperature curve, this order must be re- 

 versed, and hence- we should expect to find the spectrum 

 varying, in accordance with the foregoing sequence, but 

 in the reverse order. 



In Nova, Cpropse (i866), according to the observations 

 of Sir William Huggins and Dr. Miller, the absorption 

 spectrum was very similar to that of a Orionis, which is 

 a star of the Antarian group, so that the temperature 

 attained was relatively low ; this, indeed, is demonstrated 

 by the fact that at present it shines faintly as an Antarian 

 star, and doubtless did so before the collision. The 

 collisibri, therefore, probably did not take Nova Coronae 

 very much above its initial stage of temperature, and 

 when the disturbance was over it simply reverted to its 

 old conditions. 



The spectrum of Nova Cygni (1876) was not photo- 

 graphed, and as special attention was given by most 

 observers to the bright lines, there is no satisfactory 

 record of the absorption spectrum. 



This now appears as a nebula, and doubtless it was 

 a nebula to begin with, as Nova Coronae was a star to 

 begin with. 



In Nova Aurigte (1892), as we have seen, the com- 

 parison with a Cygni indicates that the Cygnian (that is, 

 a higher) stage was reached, and in the final stages its 

 spectrum corresponded with that of the planetary nebulaj, 

 that is, a stage lower than that reached by Nova Coronse. 

 The intermediate stages, however, were not observed, 

 possibly because the star was never very brilliant, and 

 partly because of the difficulty of observing closely 

 grouped lines, such as occur in the Polarian and Alde- 

 barian stages when they are rendered broad by such 

 •disturbances as those which were obviously present in 

 the Nova. 



The observed maximum magnitude in the case of a 

 new star will evidently depend upon the distance and 

 size qf the i-colliding masses, aft \yell as- upon the temper- 

 ature . produced by the collision. It is not remarkable, 

 thei-e^ore, that there is no apparent relation betwfeen the 

 greatest brightness and the temperature indicated: by the 

 spectra. Nova Corona, with its relatively lovv,; temper- 

 ature, shone for a time as a second ^lagnitude star, while 

 Nova Aurigae, with a much ^igher,t^niperatur;e, scarcely 

 surpassedj a ^J&r of the. fifth magnitiide. .- .,/ 



I now i^etum to Nova Pe^sei. • ',?5 't < 



If the idea that i.r\. the- present Nova the swarm which 

 gives the dark line sJDectrum. resembles a Cygni be jcon- 

 firmed, as its tfyjnperature is, reduced we may expect it to 

 pass successively thrqijgh some or all of the^ stages of 

 temperature represented by stars of the Polarian, 

 Aldebarian and Antarian groups, enhanced lines being 

 first replaced by arc lines and then by flutings. Whether 

 it remains at one of these stages or undergoes a further 

 backwardation into a nebula will be a- point of the 

 highest interest. 



If, like Nova Aurigae, the present Nova should end as 

 a nebula, it will furnish a most convincing proof ©( t,h« 

 fundamental metallic nature of nebulas. _ ,,, ,. .--i>..a. 

 NO. 1636, VOL. 63] 



'I rij conclusion, I wish to express my thanks to Dj-. 

 W- J. S. Lockyer and Mr. F. E. Baxandall, of the Solaf 

 Physics Observatory, arid to Mr. A. Fowler, of the Royal 

 College of Science, who have greatly assisted me iii 

 preparing the present note, and who, with the addition 

 of Mr. Butler, of the Solar Physics Observatory, secured, 

 the excellent set of photographs and eye observations on 

 the night of the 25th, from which the new knowledge ba^jj. 

 been derived. j 



The preparation of the slides I owe to, Mr. T, P: , 

 Wilkie. ,^ J •, ij. •,.-: 



Solar Physics Observatory, February 28. ; /. \: 



RECENT SWISS GEOLOGY. 



'T*HE glaciers of the Alps have lost considerably in 

 -*• bulk during the last forty years. This began at 

 rather different dates, for some were still advancing in 

 i860, while by 1870 the diminution . was very marked. 

 Since then there have been slight oscillations, but until 

 lately loss, ..on the whole, has exceeded gain; now, 

 perhaps, the tide has turned. The report on the Unter 

 Grindelwald glacier, by Prof. A. Baltzer,^ describes the 

 changes this glacier has undergone during the above- 

 named period,' and the results of some special obser- 

 vations made between 1892 and 1897. It was unusually 

 wen suited for the purpose, for its changes had been very 

 conspicuous, and they had been already more closely 

 observed than in many other glaciers. 



In 1858, as is shown in a photograph, the glacier 

 descended to the level of the valley beneath Grindel- 

 wald, where the Weisse Liitschine, in the summer of 

 that year, issued from an ice cave. By 1870 the glacier 

 had retreated up the glen between the Eiger and the 

 Mettenberg, exposing three great rocky steps, the exist- 

 ence of which, it may be remarked, is anything but a 

 favourable testimony to the excavatory power of ice ; 

 and its thickness higher up had so much diminished 

 that the writer looked down a cliff, fully sixty feet 

 high, on to the surface very nearly at the place where 

 he remembered stepping easily from the ice to the 

 rock on his way from the Strahleck Pass. A photo- 

 graph representing the state of the glacier in 1895. 

 on which Prof. Baltzer has indicated its former extent, 

 shows how great the change has been ; the modern ice 

 stream looking, by comparison, like a caterpillar crawling 

 to hide its diminished head in a rocky gorge (Fig. i). 

 One remarkable effect of this shrinkage (as described by 

 Mr. F. F. Tuckett in the Alpine Journal, vol.' vi. p. 30), 

 was to lay bare, in 1871, a quarry in a bed of mottled pale 

 red. and green marble, which had oncei been extensively 

 worked, but for about a century had been completely 

 hidden, beneath, the iq^. . Byihe retreat ;of the glacier 

 large areas of ice-worn rock .have b^en exposed, several of 

 which are represented by photographs in Prof. Baltzer's 

 memoir. From study of these he concludes that there 

 are two forms of ice-erosion ; Qqe— the ordinja^y-r-smpqth- 

 ing or abrading of. the rock .^^rfapes ^ the jbjt,h^r, > a- tear^ , 

 in'g and, a splitting off of frag)nent,^^ ii>Ipa?,5!s where the 

 rock is much traversed bydiyisjon^I jjla^sri As he deems 

 this tohave been less generally recogni^^d, he jllustptes it 

 by photographs. It is di^pult without actiia^iexajrnination 

 of the localities to form an opinion on this, ppintt, 'fhat 

 th^^ck, chiefly from mechanical causje^, is readily broken 

 is.^jbgyond question ;^bijt, taqugh, the fragirjents tbu^ , 

 formed would be more easily removed thai) jrom a ^oj)4 

 mass, it is doubtful whether the ice plays ''more than a 

 secondary part,- so that the remark would, , be equally 

 true^pf ^ny other kind of, erosion. Given an irregular 

 SLy:face,j the friction of ^ jt^pdy.tpoving over it w,o^lU tell 

 upon tlj^ prominences ; J>ut prabia,^ly mpE|e"piece^,.faU 

 away th^n are broken away. . ■ -;-;| of ;,|.j„_: 



1 Vol. xxxiii., part 2, of the Neiie Denkschriften der AUgemeineM 

 Schweizerhchen Gesellschaft. ,ii. ,. '/ ji) ."J , .r. 



