524 



NA TURE 



[SicrTiCMBER :8, iS>: 



Mr. Tohn Daniel has sent us an advance-proof of a paper 

 on " Polarization, using a thin Metal Partition in a Voltameter." 

 The investigation h.id its starting-point in an observation of 

 Dr. L. Arons', who noticed that ordinary gold leaf, used as a 

 partition in an H„S04 voltameter, allowed a current of "2 or 

 •3 ampere to pass without any visible development of gas upon 

 the metal, wliich was pasted over a hole iJs cm. in diameter, 

 bored in a glass plate. The glass plate slid in grooves in a 

 wooden frame, which was placed in the middle of the glass- 

 voltameter. When platinium-foil (o'l mm. thick) was sub- 

 stituted for the gold-leaf, there was a profuse escape of gas 

 from the metal partition. Mr. Daniel has made similar experi- 

 ments with partitions of gold, silver, aluminium and platinum 

 of various thicknesses, and with various electrolytes, and has 

 obtained for the different substances, values of the " critical 

 thickness" above which polarization at the parti: ion takes place, 

 as well as some other interesting facts as to "critical current 

 density," &c. He finds, for instance, that the "critical thick- 

 ness" in good-conducting solutions of HjSOj, CuSOj and 

 NaCl, is greater than -00009 mm., but less than '0004 mm., 

 in the case of gold ; while -00015 mm., and -002 mm. are 

 the corresponding figures for platinum, with a current density 

 of not more than O'l ampere per square cm. of the metallic 

 partition. Between these "critical limits" the polarisation for 

 a given current increasts with the thickness. In CuSOj, all 

 the plates except those below the critical thickness were de- 

 stroyed by oxidation, and a similar effect was noticed in NaCl, 

 in which gold and silver below the critical thickness were quite 

 unaffected, while above it they could not be used on accoun t 

 of the chemical action. 



Notes from the Marine Biological Station, Plymouth. — Last 

 week's captures include the Ascidian Ascidia mollis. The 

 tow-nets continue to yield the regular autumn forms, among 

 which the Liphonophore Mttggima atlantica and the larvce of 

 the Polychoeta Magelona and Terebella have generally been 

 plentiful. An interesting feature of recent tow-nettings has 

 been the presence of numerous minute free-floating colonies of 

 certain Didemnidne. Young Echini and Asterimc of this 

 season's growth are now plentiful at a depth of five fathoms 

 and in coralline tide-pools respectively. The following animals 

 are breeding :^The Hydroid Sirtularella Gayi, the Nemertine 

 Amphipsrits dissimulaiis, the Archiannelid Histriobdella 

 Ho7Hari, and the parasitic Cirrhipede Sacciilina. 



The additions to the Zoological .Society's Gardens during 

 the past week include a Leadbeater's Cockatoo (Cacaliia Icad- 

 beatcri) from Australia, presented by Miss Mercy Grogan ; a 

 Common Quail {Cottiriiix comiitunis) British, presented by Mrs. 

 Mazelin ; two Black-pointed Teguexins {Tiipiimmlii; nigra- 

 'ftmclalus) a Crowned Snake [Scy/a'e coronatiim), a Tree Boa 



(Coralliis hortttlanus), a Snake {Leptognathus nel»ilalus) 



from Trinidad, W.I., presented by Messrs. Mole and Urich ; 

 two Hamsters [Cricetus frumentariiis, white var. ) European, a 

 Black-headed Caique (Caica melanocephala) from Demerara, a 

 Corean Sea Eagle (Haliahis branickii) from Corea, a Black- 

 pointed Teguexin {Tupinambis nigro-punctatus), a Tree Boa 

 {Corallus hortulaiius), a Boddaert's Snake {Coluber boddicrti) 

 from Trinidad, W.I., deposited ; a Golden Plover (Charadrius 

 pluvialis) British, purchased. 



OUR ASTRONOMICAL COLUMN. 



Nova (T) Aurig.« Spectrum.— In the current number of 

 the Astronomischen Nachrichten (No. 3189) Mr. W. W. 

 Campbell communicates his observations of the spectrum of 

 Nova Aurigfc since its reappearance in August. At this time 

 the continuous spectrum was very faint, the spectrum consisted 



NO. 1248, VOL. 48] 



of isolated bright lines, and the three brightest lines li.\d the in- 

 tensities and positions of the characteristic nebular lines, the 

 result being that the spectrum of this new star was announced 

 to be that of a planetary nebula. That this view h.as not been 

 universally adopted is shown by Vogel's paper on the same star, 

 and he inclines to the opinion that the bright lines are chromo- 

 spheric, and that the brightest line is not the nebula line. In 

 the present paper Mr. Campbell has made more visual andloiM 

 exposure photographic observations of nebular spectra, andfiiuu 

 no less than five other lines which are in the spectrum of the 

 new star. The nebula he uses here for comparison are : Orion, 

 G.C. 4390, N.G.C. 7027, G.C. 4964, G.C. 4373. and >" ll» 

 photographs of their spectrum he obtains 12, 12, 7, 10, and J 

 lines respectively that appear to him to be new. Tne tabulated 

 list of lines brings out very clearly, that with the exception of 

 the line 451, the identity of which is uncertain in these nebulae, 

 the Nova lines are matched perfectly in one or more of them, 

 allowing for the fact that they (the Nova lines) were shifted 

 about five-tenth metres (in August and November, 1S92) to- 

 wards the violet. The Nova spectrum, as Mr. Campbell say«, 

 "certainly differs no more from the nebular spectra than the 

 nebular spectra differ from each other." As for the lines, 4857, 

 4336, 4098, and 396 are the well-known hydrogen lines ; 5001, 

 4953, the first and second nebular lines, while all the otherscor 

 lespond well with the nebular lines. The presence of these four 

 hydrogen lines and the chromospheric line 4472, strengthen*, 

 as he says, his argument, and he concludes with the words that 

 "if the spectrum is not conceded to be nebular, I must aik 

 what else we should expect in that spectrum if it were 

 nebular?" 



The Firehall of January 13, 1893.— In the Anuriam 

 Jotcrnal op Science (vol. xlvi. September, 1893), Prof. H. 

 A. Newton contributes a discussion of all the observations that 

 were made of the large fireball that was observed in America in 

 January last. The great interest attached to this fall lay in the 

 fact, as previously mentioned in this column, that Mr. Lewis, of 

 Ansonia, Conn., happened to obtain a very good picture of the 

 trail as it passed in the line of sight of his instrument while he was 

 photographing the comet Holmes. Prof. Newton seems to have 

 taken great pains to have the information as accurate as possible, 

 and has even had some of the observers cross-examined, so to 

 speak, on many particular points. The plate on which the 

 photograph was taken^is 4 by 5 inches, and the meteor went nearljF 

 centrally across it, the photographed portion being about 1^ 

 long. Several stars of the tenth magnitude in the middie, and 

 some of about the eighth, near the margin of the plate, are shown 

 on the negative, so that some fairly good measurements of the 

 position of the track have been procured. The co-ordinates of 

 seven points of the trail have thus been measured, and a very 

 slight curvature of the path is indicated by the results but not 

 clearly proven, the curvature being caused, as suggested by 

 Prof. Newton, by " the atmosphere's resistance of the irregularly 

 shaped body." An enlarged print of the photograph (about 20 

 inches long) accompanies the paper. The striking feature of it is 

 the irregularities of light on the path, and also its increase in fre- 

 quency as the end of the plate is reached. This is due, as sup' 

 posed, to a rotation of the stony mass, " more rapid at the end 

 than at the beginning, and that the unequal amounts of burned 

 material were thrown oft" according as a well burned or a raw 

 surface was for the instant in front." 



NITRO-METALS, A NEIV SERIES OF 



COMPOUNDS OF METALS WITH NITROGEN 



PEROXIDE. 



A REMARKABLE new series of compounds, formed by the 

 direct union of nitrogen peroxide with certain metals, and 

 of a nature somewhat akin to that of the metallic carbonyls 

 recently discovered and investigated by Mr. .Mond and his co- 

 workers, are described by MM. Sabatier and Senderens m the 

 September number of the Bulletin de la Socikc Chiimqut. 

 It was observed that when vapour of peroxide of nitrogen 

 in a state of tolerable purity was allowed to stream at ths 

 ordinary temperature over metallic copper, cobalt, nickel, or 

 iron, these metaU being in the finely-divided and pure condition 

 obtained by the recent reduction of their oxides by hydrogen, 

 rapid absorption of the nitrogen peroxide occurred with the 

 formation of definite compounds possessing properties ot an 



