January i6, 1896J 



NA TV RE 



249 



atmospheres, according to the chemical compounds oi their 

 spectra, are coolest. A, Brester. 



Delft (Holland), November 30, 1895. 



The above amplification of Dr. Brester's views, as to the 

 cause of variability in red stars, calls for a few remarks. 

 Althoujjh opinions may differ as to the constitution of stars of 

 Group II., it is generally agreed that those of Group VI. are in 

 an advanced state of condensation, with cool, absorbing atmo- 

 spheres, and it is in the latter group of stars that we find the 

 full development of the fluted absorption spectrum which Dr. 

 Brester ascribes to acetylene. Experimental evidence does not 

 certainly indicate that this gas is responsible for the dark flutings 

 observed, for other compounds of carbon give a similar spectrum ; 

 but, to whatever the flutings may owe their origin, they are a 

 result of KirchhoflPs law. Notwithstanding" that it is in these 

 stars of Group VI. we should most expect the bright lines on Dr. 

 Brester's theory, no bright lines have been recorded in variable 

 stars belonging to the group ; that is, there is no visible chemical 

 luminescence. 



It is in the variables of Group II. that the bright line phenomena 

 occur, but the associated dark flutings of metals, or their 

 compounds, do not lead us to suppose that the temperature is 

 lower than in the other group of stars with fluted spectra. 

 Hence, luminescence does not seem to be more probable in 

 Group II. than in Group VI., unless we accept the view put 

 forward by Mr. Lockyer, that the physical constitutions of the 

 two groups of stars are essentially different. If the stars of 

 Ciroup II. consist of uncondensed swarms of meteorites, it is 

 certainly conceivable that the luminosity of the hydrogen in the 

 interspaces may be partly due to electrical excitation ; this view 

 involves the supposition that these stars are becoming hotter. 



It may be further remarked that there is abundant experi- 

 mental evidence to show that the line spectrum of hydrogen can 

 coexist with a fluted spectrum. Acetylene, for instance, 

 exhibits such a mixture, and hence luminescence is not more 

 necessary to explain the luminous phenomena in the case of 

 hydrogen than in the case of the absorbing vapours which give 

 the flutings associated with them in stars. 



The Writer of the Note. 



Mount Wosho. 



As my' name has been mentioned in Nature for December 5, 

 1895 (p. 107), in connection with recent explorations in Africa, 

 allow me to say that snow clothing on Mount Wosho must have 

 been added by an outsider, for in page 1 10 of my work on Ethio- 

 pian geography, published five years ago, I have expressly said 

 that snow does not exist in that country. In page 387 of the 

 same volume, I have given up all Mount Wosho's claims to an 

 immense height ; but I still think it exists as a mountain, and 

 that it ought not therefore to be wiped off the map. 



Vour criticism induces me to explain how I tried to sketch 

 one in Upper Ethopia. I first employed the common method 

 by recording hours of travel and bearings by compass ; but I was 

 then forced to suppose the variation of the needle. Disturbing 

 attractions could not be eliminated, and it was seldom possible 

 to check my road by observed latitudes. However, as a warning 

 to my successors, I published this tedious work in my " Geodesic 

 d'Ethiopie " (Paris, 1873), a volume of 502 quarto pages. 



This first attempt to map the country being fruitless, I turned 

 all my attention to using a theodolite, and collected in 318 

 stations more than 4000 bearings, besides 500 of the sun, taken 

 at proper hours to get true azimuths, each of these being followed 

 by an angular zenith distance. I obtained three base-lines from 

 differences of latitudes observed on two heights situated near the 

 same meridian and connected by azimuths. The northern base 

 is nearly 51 miles long ; I got there my longitude by eight oc- 

 cultations of stars. The second base is 52 miles calculated from 

 a quadrangle, and the southern base, still more indirect, reaches 

 51 miles. I have thus carried a continuous chain of triangles 

 from the Red Sea to the frontier of Kaffa, a distance slightly 

 greater than from Calais to Bayonne. These triangles, mostly 

 with only two observed angles, have been checked here and 

 there by latitudes and independent longitudes. I got the latter 

 by a few occultations, but chiefly according to the Russian method 

 of lunar ob.servations. By this method I have calculated 857 

 positions in Ethiopia. They are given in my pages 423-440, 

 the heights being obtained by a j^w//<7j^rf coefficient for terrestrial 

 refraction. 



In my " (ieodesie" (page 195) I give the first mention of Mount 

 Wosho as /r<7/^<T<5/j' Wosho, and the following page says, "flat 

 mountain which I suppose (que je prends pour) Wosho." Page 

 438 points in No. 805 to a note (p. 448) which adds, " place pur 

 renseignements et par ces azimuts reit^res." This hearsay 

 evidence is taken from a list of days' journeys between Bonga 

 and Wosho (published in my " Geographic") without details. The 

 profile of the mountain measured from Ealle is given in the col- 

 lection of sketches belonging to my 325 tours (f horizon. More- 

 over, the zenith distance was 90^ 21', nearly the very worst to 

 be corrected by the ordinary rule for terrestrial refraction. In 

 spite of all these drawbacks, I published the resulting enormous 

 height in order to call attention to Wosho. Let us hope that 

 some explorer, after throwing a net of triangles over Walamo, 

 may put in its proper place and height the real Wosho. 



Antoine d'.\bbadie. 



Hendaye, December 13, 1895. — 



I AM aware that M. d'Abbadie did not still maintain the 

 exaggerated importance once attached to Mount Wosho, for 

 which, indeed, he is by no means solely responsible. My re- 

 mark was suggested by the fact that the great mountain reported 

 by Grixoni's expedition had again called attention to Mount 

 Wosho, and led to the idea that the earlier reports were possibly, 

 after all, correct. But until Dr. Donaldson Smith's maps are 

 published, it is no use attempting to reconcile the previous maps 

 of this region. The Writer ok the Note. 



Cactaceae in the Galapagos. 



Although the Editor has kindly replied to that part of Mr. 

 Agassiz's letter {^atite p. 199] relating to the Albatross Expedition, 

 I should like to say a few words on the other points raised by 

 him. In the first place, I regret that my communication on the 

 subject should have produced the impression of unfairness 

 towards any person or persons. Such was not my intention. 

 For the sake of my own reputation, as well as for the information 

 of those who, like Mr. Agassiz, might, from my way of expressing 

 myself, think otherwise, I may add that I did not intend to 

 convey the idea that Opuutia and Cereus are limited to Chili on 

 the west coast of America. The contrary is so well known, that 

 it did not appear neces.sary to me to enter into particulars. Of 

 course Mr. Agassiz will hold me guiltless of suppres.sing anything 

 respecting the branches of Opuntia and Cereus which he says he 

 collected, though he does not know what became of them. 



Perhaps I may also be permitted to add that Dr. Baur has 

 since sent me some \crj fine photographs of Opuntia and Cereus, 

 on a comparatively large scale, together with some notes, which 

 I laid before a recent meeting of the Linnean Society. 



Herbarium, Kew. W. BoTTiNO Hemsley. 



NO. 1368, VOL. 53] 



A Luminous Centipede. 



In Mr. Lloyd Bozward"s letter on the above .subject in this 

 week's Nature, he says that the light of the Scolopendra 

 electrica " is the same as that of the glow- worm." My experience 

 is that the light of the glow-worm is a clear little spark of light ; 

 whereas that of the Scolopendra electrica (which I have usually 

 found in the autumn) is more of a phosphorescent light, and 

 streaks of this light are left for a few seconds in the trail of the 

 animal as it crawls about, so that it is often difficult to say 

 exactly where the creature is. I have no doubt others have 

 observed the .same thing. T. Plowman. 



Enfield, N., January 11. 



The Critical Temperature of Hydrogen. 



What I object to is not Mr. Bryan's reference to Wro- 

 blew.ski's work, but his statement (explicitly founded upon 

 the absence of " fresh experiments") that my conclusions "are 

 not results of independent original investigation." In his letter 

 to Nature of January 9, Mr. Bryan does not even attempt to 

 justify this statement. My Bulletin paper was an abstract ; in 

 the full paper (Trans. Crac. Acad., vol. xxvii. p. 375), published 

 May 1895, Wroblewski's work was quoted and discussed. 



Cracow University, January 12. L. Natanson. 



A Fog Scale. 

 Considering the imjiortant part that fog plays in deter- 

 mining the character of a health resort, it is remarkable that no 



