378 



NATURE 



[August 14, 1890 



such bands in the red, lying on either side of the pair 7 and 8. . . . 

 It might be well to state that the line, which I judge to be the 

 auroral line, was in all cases the most noticeable, and especially 

 so in discharges of heat electricity, which seemed to occur in the 

 upper and more rarefied strata of the air." 



Solar Activity. — Prof. Tacchini gives the following results 

 of solar observations during the second quarter of this year 

 {Comptes rendus, August 4) :— 



No. of 

 days of 



obser- of spots. 



vation. 



April 19 ... 2 08 



May 20 ... 2-55 



Tune 26 ... 1-35 



Relative frequence 



Comparative area 



of days 



without 

 spots. 



0-54 

 076 



of spots, offaculse. 



1-40 

 2-58 



0-86 



1 0*40 



25-83 



810 



groups 



of 

 spots 



per day. 

 0-44 

 071 

 0-25 



A comparison of these figures with those of the first quarter 

 of rhis year shows that the spots are slowly increasing in magni- 

 tude, and that the number of days without spots is diminishing. 



The following results have been obtained for the pro- 

 minence : — 



Denning's Comet (c 1890). — Dr. A. Berberich has com- 

 puted the following orbit of the comet discovered by Mr. 

 W. F. Denning at Bristol on the 23rd ult., from observations 

 made at Nice on the 24th and 25th, and at Strasburg on the 

 27th [Astronomische Nachrichten, No. 2982) : — 



T — 1890 Sept, 247573 Berlin Mean Time, 



CO — 158 26 64 ) 



a = 96 35 42 [■ Mean Eq. 1890-0. 

 I = 99 37 67 ) 

 log q = 0-12288 



AA cos j8 = + o'-o8; A^ + o'-o6. 



Ephetneris for Berlin Midnight. 



Brightness = 1-82 on August 17, and — 1-95 on August 21, 

 that at discovery being taken as unity. 



The comet will pass perihelion about September 25, at a 

 -distance of i -33 the mean distance of the earth from the sun. 



From the ephemeris given it will be seen that the comet is 

 between /8 Bootis and Draconis on August 15. 



GEOGRAPHICAL NOTES. 



The Russian Official Messenger of August i gives the follow- 

 ing news about the work done by M. Grombchevsky during 

 la. St spring. On March 13 the expedition left Khotan for 

 N'ya. After having passed through the oasis of Keria, the 

 travellers crossed the desert, where they met with a succession 

 of barkhans (downs), reaching to the unusual height of 200 feet. 

 From Niya they visited the Sougrak gold-mines, which are 

 worked by nearly 3000 families living in caverns excavated in 

 the loess and conglomerates on the slopes of the hills. Lumps 

 of gold 2 lbs. in weight are sometimes found in these mines. 

 Leaving Niya, the expedition crossed the border-ridge, which 

 consists of several chains — the passes across them attaining 

 heights of from 10,500 to 11,000 feet — and reached Polu, 

 whence it returned to Keria. There M. Grombchevsky re- 

 ceived the good news that the expedition would be allowed to 



continue its work till January i, 1891, and that ^^203 had been 

 granted for that purpose ; so that M. Grombchevsky made 

 arrangements to start for Rudok, in Tibet, in the first half of 

 May, 



The following telegram about M. Grombchevsky's expedition, 

 dated Marghilan, July 19, has appeared in the Russian Official 

 Messenger. The expedition had reached Polu, but had been stopped 

 there by the Chinese authorities, who insisted upon the immediate 

 return of the expedition to Kashgar, and ordered the population 

 to leave their settlements and to camp in the mountains. 

 Brought to despair, M. Grombchevsky spent his last money in 

 bribing some inhabitants, and, without a guide, left Polu in the 

 night of May 17, going further south into the depth of the 

 unexplored wilderness. 



The last number of the Izvestia of the Russian Geographical 

 Society is of unusual interest, especially on account of its maps. 

 It contains three reduced photographic copies of the hypsometric 

 map of Russia, by General Tillo, and it is impossible not to ad- 

 mire the distinctness with which the two chief lines of upheaval, 

 the south-west to north-east direction, and the north-west to south- 

 east direction, appear on this map, even amidst the plateaus and 

 the depressions of middle Russia. Another interesting map 

 renders, on a scale of 7 miles to the inch, the surveys of M, 

 Grombchevsky, made during his recent attempts to reach 

 Tibet from the north. The map is accompanied by two letters 

 from the explorer, written in 'December 1889, at the sources of 

 the Khotan-daria and the Kara-kosh. The same issue contains 

 a letter from the chief of the Tibet expedition, M. Roborovski, 

 dated from Niya, December 11, 1889 ; a paper on the geodetical 

 surveys in Russia ; and a most interesting summary, by M. 

 Kuznetsoff, of his several years' study of the flora of the 

 Caucasus. 



In a communication to the Societe de Geographic of Paris, 

 M. G. Marcel, who is one of the librarians of the Bibliotheque 

 Nationale, has given some particulars of Louis Boulanger, an 

 astronomer, geometer, and geographer of the sixteenth century. 

 In 151 1 he published at Lyons a work, " Equatorii Coelestis 

 Motus," of which only one copy is knov;n. It is in the Biblio- 

 theque Mazarin, and is described by M. Marcel as hitherto 

 ignored by bibliographers. In 1514 he brought out a piracy 

 of Muller's " Cosmographias Introductio. " The globe accom- 

 panying this is regarded as the first on which the word 

 "America" is found. Another globe has been found by M, 

 Marcel at the Bibliotheque Nationale, which he regards as 

 having been made by one of the school of Schoener between 

 1513 and 1518, and on it the then new name of the New World 

 occurs four times. It is therefore either the first or the second 

 cartographic document in which America is mentioned. 



THE SCIENTIFIC PRINCIPLES INVOLVED 

 IN MAKING BIG GUNS.^ 



Part III. — Wire Gun Construction, 



A N inspection of Fig. 5 (p. 307), and of the serrated edge of the 

 ■^ curve of circumferential tension, t, shows that only the 

 inner fibre of each coil is doing its full share of resistance when 

 the gun is fired. 



Great economy of material can be effected if we can make all 

 the circumferential fibres take up a full uniform working tension 

 (say of 18 tons per square inch) when the gun is fired ; but to 

 secure this condition only approximately, the number of coils 

 would have to be largely increased, and the cost, complication, 

 and time of manufacture of a gun would be enormous. 



But, by adopting Mr. J. A. Longridge's plan of strengthening 

 the inner tube A by steel wire, wound round with appropriately 

 varying tension, we are theoretically able to make the curve of 

 circumferential firing tension, t, a straight line for a determinate 

 powder pressure ; and now all parts of the wire coil are equally 

 strained, and take an equal share in the resistance. 



The subject has been investigated theoretically by Mr. 

 Longridge, assisted by Mr. C. H. Brooks, beginninij in 1855; 

 and his theories are set forth in papers in the Proceedings 

 of the Institution of Civil Engineers in i860, 1879, 1884, em- 



' Continued from p. 334. 



NO. 



085, VOL. 42] 



