March 7, 1878] 



NATURE 



373 



immersing a plate of glass in a shallow basin containing a con- 

 centrated solution of potassic nitrate. It is encircled by a 

 platinum wire also covered by the liquid, and connected with 

 the pole of a secondary battery of fifty elements. The other 

 pole consisting likewise of platinum wire covered with an 

 insulator is held in the hand and applied to those parts of the 

 glass where it is designed to engrave. A flash of light is 

 produced by every contact with the electrode, and a mark 

 accompanies each luminous appearance. The depth and fineness 

 of the lines described depend directly on the rapidity with which 

 the electrode is moved, and the fineness of its point. 



The Deutsche Gesellschaft fiir offentliche Gesundheitspflege 

 has appointed a commission to co-operate with the government 

 meteorological stations, in endeavouring to obtain the daily 

 publication of the weather observations with probabilities for the 

 following twenty-four hours, according to the American system. 



The additions to the Zoological Society's Gardens during the 

 past week include two Brown Coatis {Nasiia nasica) from South 

 America, presented by the Hon. C. H. Wynn ; a Palm Squirrel 

 {Sciurus palmarum) from Ir.dia, presented by Miss Barclay; two 

 Rock Sparrows [Peironia stuUa), South European, presented by 

 Mr. D'Arcy Thompson ; an Ocelot {Felis pardalis), a Red and 

 Yellow Maccaw {Ara chloroptera), a Yellow Snake {Ckiloboth- 

 rus inornatus) from South America, two Black-capped Bitterns 

 {Buiorides atricapilla) from Africa, a Four-lined Snake {Cohiber 

 quadrilincattis) from Egypt, deposited ; a Yellow-cheeked Ama- 

 zon {Chrysalis autwnnalis) from Honduras, purchased ; a Red 

 Kangaroo {Macropus rufus), an Indian Muntjac {Cervtilus 

 muntjac), bom in the Gardens. 



EXTENT AND PRINCIPAL ZONE OF THE 

 AURORA BOREALIS 



TN the VVochenschrift Jiir AslronomU, Herr H. Fritz has 

 ■^ recently compared his " Catalogue ot Polar Lights," which 

 contains notes ot all aurorce which have been observed since 

 1846, with a publication of Herr A. Moberg, who gives an 

 account of all aurorse observed in Finland during the years 

 1846 to 1855 — some 1,100 in number. The comparison yields 

 some interesting results which are not without importance for the 

 theory of the phenomenon. 



It appears that out of 2,035 <^^ys of the months from August 

 to April, upon which aurorrc were seen and which are entered 

 in Herr Fritz's Catalogue, no less than i, 107 days were auroral 

 days in Finland. Of these 1,107 aurora; 794 were simultaneously 

 visible both in America and Europe, 101 only in Europe, while 

 the remaining 212 were only seen in Finland. During the same 

 period (1846 to 1855) 928 aurorse were seen in Europe or 

 America which were not visible in Finland. All these figures 

 of course refer only to the months from August to April, since 

 during the summer months no phenomena of this kind can be 

 observed in Finland on account of the brightness of the nights. 

 As HerrMoberg's observations were collected from 128 different 

 stations in Finland, we must conclude that only a very small 

 number of aurorse remained unnoticed. We thus arrive at the 

 conclusion that a great number of auroras cannot have a very 

 widely extended sphere, or that the causes of these phenomena 

 must often be of a very local character (this is confirmed by several 

 observations at high latitudes), while with another part of the 

 phenomena the extension of their sphere or district of simultaneous 

 visibility must be very considerable. The number of aurorac 

 which were seen in Finland only— at least for which up to the 

 present no data of observation elsewhere have been received — 

 is very small (212, or only 19 per cent, of the total number seen 

 in Finland). As the frequency of the phenomena incrca'^es— at 

 the time of the maximum — the number of simultaneous obser- 

 vations in Finland and America rises, while the numbers of 

 aurorse seen in Finland and Europe only, or of those exclusively 

 teen in Finland, decrease. This agrees perfectly with the well- 

 known law that with the increase of frequency of polar lights 

 their intensity and sphere of visibility increase also. If we care- 

 fully take into account the less prominent phenomena the above 

 proportions would be slightly modified, but most probably they 

 would never prove that on any day when an aurora was visible 



only in a small district in Europe, another one was simultaneously 

 seen in America. Thus the comparison made by Herr Fritz 

 contradicts Renou's view that the phenomena in America and 

 Europe change periodically. 



Of 2,878 days on which aurorje were observed in America 

 during 1826 to 1855, there are 1,065 on which aurorse were also 

 seen in Europe, so that at least every third observation was 

 simultaneous in both parts of the world. For the years during 

 which more exact observations were made, viz., from 1846 to 

 1855, and again from 1868 to 1872, we find that during the 

 former period out of 1,691 auroras 657 were simultaneously 

 observed both in America and Europe ; and during the latter 

 period out of 715 no less than 397, or far more than half the 

 number. If the catalogues were more perfect the number of 

 simultaneous observations would, beyond doubt, be found to be 

 still greater. Some observations made in Scotland give similar 

 results to those dating from P'inland, but their publication must 

 at present be delayed, since the American data for comparison 

 are still wanting. 



The local occurrence of aurorse does not sf eik favourably for 

 the hypothesis which places the phenomenon among the cosmical 

 ones. Some ten years ago Herr Fritz published his views with 

 regard to the geographical distribution of aurorse, and constructed 

 a system of lines which he termed Isochasms — i.e., curves of 

 equal frequency of aurorse. The outlines of this system weie as 

 follow : — The zone of greatest frequency and intensity of aurorse 

 began near Barrow point (72° north latitude) on the northern 

 coast of America ; thence it passed across the great Bear Lake 

 towards Hudson's Bay, crossing the latter at 60" N. lat., passing 

 over Naln, on the coast of Labrador, keeping south of Cape 

 Farewell ; its further course was between Iceland and the Far Oer 

 to the vicinity of the North Cape in Norway, and thence into 

 the Arctic Sea. According to the observations then in posses- 

 sion of Herr Fritz, the line passed round Novaya Zemlya and 

 Cape Tsheljuskin, approached the north coast of Asia, in the 

 eastern part of Siberia, in the longitude of Nischni Kolymsk, and 

 thence returned to Barrow Point. 



Now after ten years, in spite of the vastly accumulated material 

 of careful observations, there appears no necessity to change 

 Herr Fritz's system of curves in any essential detail ; indeed 

 certain parts of the same, which were at first only based on 

 probability and supposition, the part of the principal zone 

 between the north of Norway and Nishni Kolymsk as an instance, 

 we now know with perfect certainty to be correct. Nearly 

 identical, perhaps entirely so, with the line of greatest frequency 

 is the line which marks the limit of visibility of aurorse towards 

 the pole or the equator ; since to the north of the line in ques- 

 tion the aurorse are only seen in the direction of the equator. 



PARIS ACADEMY PRIZES FOR 1878 



1. T7 XTRAORDINARY PRIZES. — Grand prizes in the Mathemati- 

 -'--' cal Science. — i. The application of the theory of elliptic 



transcendants or ahelians to the study of algebraic curves. 



2. It is known that the great axis of the orbit which a planet 

 describes round the sun is not affected by any secular inequality 

 of the order of the two first powers of the disturbing masses. 

 Examine if there exists in the value of this great axis secular 

 inequalities of the order of the cube of the masses, and, in the 

 case where these inequalities are not rigorously destroyed, give 

 the means of calculating their sum, at least approximately. The 

 prize is a medal of the value of 3,000 francs. 3. Study of the 

 elasticity of crystallised bodie?, from the double point of view of 

 experiment and theory. Prize the same as No. 2. 



Grand prizes in the Physical Sciences. — Study of the mode of 

 distribution of marine animals on the littoral of France. A 

 medal of 3,000 francs value. 



An extraordinary prize of 6,000 francs will be awarded as a 

 recompense for any progress calculated to increase the efficacy of 

 the French naval forces. 



II. Mechanics.- I. The Poncelet prize of a medal of 2,000 

 francs value, and a complete copy of Poncelet's works, arc 

 awarded to the work contributing most to the progress of the 

 mathematical sciences, pure or applied, published in the course 

 of the ten years preceding the judgment of the Academy. 2. A 

 Monty on prize, a medal of 427 francs value, will be awarded to 

 any one who, in the judgment of the Academy, is most deserv- 

 ing, by inventing or improving instruments useful to the progress 

 of agriculture, the mechanical arts, or the sciences. 3. The 

 Plumey prize, a medal of 2,500 francs value, awarded to the 



