352 



NA TURE 



[February 9, 1893 



Comet Brooks (November 19, 1892).— The following is 

 the ephemeris for Comet Brooks for the ensuing week : — 

 Ephemeris for 12/1. M. T. Berlin. 



1-40 



1-16 



Spectra of Planetary Nebula and Nova Auriga.— 

 In .the December number of the Memorie della Societa degli 

 Spettroscopisti Italiani, among many interesting communica- 

 tions, is one by M. Eugen Gothard, relative to the great simi- 

 larity between the spectra of the late Nova and the planetary 

 nebulse. By the aid of a lo^-inch reflector and a lo-inch 

 objective prism, together with Schleussner's orthochromatic 

 plates, he has been able to obtain these photographs, the 

 wave-lengths of the lines of which are given in the table below. 

 In the memoir copies of the photographs on a somewhat larger 

 scale are given, that of the Dumb-bell nebula (G.C. No. 

 4447) showmg the image of the nebula itself, just as if no prism 

 had been used. The wave-lengths of the Nova given in this 

 table were obtained from photographs taken on September 27 

 with 2h. 15m. exposure, and on October 28 with 3h. exposure, 

 and, in M. Gothard's m ords, " gave the surprising result that the 

 spectrum of the new star perfectly agrees with that of the 

 planetary nebulse." 



The following is the table of the wave-lengths, lines I., II., 

 VI., and VII. representing the nebula lines, and III., IV., 

 and V. the hydrogen lines : — 



Sun-spots and Magnetic Perturbations in 1892. — In 

 an article under this heading in Astronomy and Astrophysics for 

 January M. Ricco brings together the facts relative to these two 

 phenomena, the magnetic perturbations being taken from the 

 photo-magnetographs of the United States Naval Observatory. 

 As the author describes in detail both kinds of observations, and 

 in addition, a tabulated statement of the records, we cannot do 

 better than abridge the table, by omitting the numerical state- 

 ments as to the magnitudes of the spots and perturbations, 

 leaving our readers to refer if necessary to the journal itself. 



In the column "spots" this means principal spots; E 

 denotes extraordinary; V. L, very large; L, large; M, 

 medium ; S, small : and N, none. 



From this table some very interesting facts may be gathered. 

 Out of the tleven cases which M. Ricco gives, no less than seven 

 instances occur VI heie the passage of the spots over the central 

 hieridian is followed by a terrestrial magnetic disturbance, and 



not only this, but the magnitudes of both vary directly. The 

 point which the author wishes to emphasize most is the apparent 

 constancy of the interval of time between these two phenomena, 

 and an important fact is that at both appearances of the great 

 February spot the same retardation occurred. In the above 

 table, with the exception of January 29, the mean interval is 

 45i kms., " thus indicating a velocity of propagation from the 

 sun to the earth of about 913 kms. per second," or " more than 

 300 times less than that of light." 



New Minor Planets. — Photography seems to be rapidly 

 increasing the number of our minor planets, that is to say, if 

 the announcements really refer to new ones. Wolf and Charlois 

 between them have discovered five this year, the former two 

 (1893 B and C), the latter three (1893, A, D, and E). 



The Lunar Surface.— At the present day the general idea 

 with regard to the peculiar features of the moon is that they are 

 the results of stupendous volcanic actions, the number and 

 activity of which surpassed anything that we can imagine. Owing 

 to the extraordmary circularity in the craters, ring plains, 

 walled plains, and to the well-known fact that many of the 

 craters have not the raised lava floor half-way up or near the 

 summit of the cone, which is such a typical terrestrial charac- 

 teristic, doubt as to their volcanic origin has often been raised. 

 In a small pamphlet which we have received from Mr. S. E. 

 Peal, Sibsagor Assam, the author suggests a " theory of glaciation" 

 in the light of recent discoveries with regard to the maximum 

 surface temperature, and also to the non-viscosity of ice at low 

 temperatures, together with the admitted possibility of snow 

 exi. ting on the moon. The author assumes the moon to be 

 constituted somewhat like our earth, and at one time to have 

 been at a higher temperature, having an atmosphere, water, &c., 

 and draws attention to the facts that there are no polar caps ;. 

 that colour is conspicuous by its absence, "a feature quite 

 opposed to terrestrial experience, except at the poles," and 

 therefore " may not the entire globe be swathed in snow ? " ; and 

 the absence of river valleys and drainage sculpturing, indicating 

 that a piling up of dry material has taken place in opposition 

 to a fluvial erosion. At the time when the lunar globe had so 

 far cooled down as to be practically rigid, the tidal action 

 would gradually turn all continents and land surfaces into shoals, 

 and at the temperate stage of development the growth of the 

 polar caps would be restricted to the shallows, extending fron> 

 them as the temperature became reduced. This advancing 

 sheet of ice would sometimes be deformated by submarine heat 

 vents resulting in a large or small bay, depending on the mag- 

 nitude of the vent. Extending seawards the " horns of the bay 

 would meet around and enclose this area of higher mean tem- 

 perature, converting it into a lagoon." Nocturnal radiation 

 and solar heat alternately would perhaps freeze and thaw the 

 ice formed thereon, and with a rare atmosphere and intense cold 

 aqueous vapour would arise from "the water (floe-covered) 

 floor during the day at least, and be carried over the ice edge 

 by diffusion when the fall in temperature would precipitate it 

 into snow, thus gradually forming a vast rampart." Century 

 after century would see the level floor gradually lowered, and 

 the ramparts increased in height. The author accounts for all 

 the peculiar forms of crater.s walls, &c., by different local con- 

 ditions (?./, land or water or submarine vents), but they are all 

 the result " of water floors left in a slowly extending glaciation 

 of the crust." 



GEOGRAPHICAL NOTES. 



At the French Congress of Learned Societies, which meets 

 on April 4 at the Sorbonne, the section of historical and de- 

 scriptive geography, is to be devoted specially to the early 

 geographical conditions of France, and to the work of French 

 travellers. The programme includes the consideration of the 

 earliest traces of human habitations, maps of caverns, &c., and 

 proceeds to classify existing dwellings according to their situation 

 and altitude. Local names in danger of falling out of use are 

 to be collected, and the limits of the old districts such as Brie, 

 Beauce, Sologne, &c.. to be investigated in order to place on 

 record the geographical conditions which led to their formation. 



In the Scottish Geographical Magazine for February Mr. 

 J. G. Goodchild gives a most interesting description of a large- 

 scale topographical model of the site of Edinburgh, which he 

 has recently constructed. The model, which is on exhibition 



NO, 



121 5, VOL. 47] 



