254 



NA TURE 



[JULV 12, 1894 



burst by the violence of the explosion. The pressure produced 

 was found to be equal to that of one of the gunpowders recently 

 tested by M. Berthelot, but the combustion appears to be a 

 relatively slow one ; the temperature of deflagration is about 

 1550-1400°. Hence the ammonium salt of diazoimide is a re- 

 markable explosive on account both of the force developed 

 during explosion and of its low temperature of deflagration. 

 The products of the decomposition are ammonia, hydrogen and 

 nitrogen. The ammonia was actually liquefied in the cylinder. 

 The temperature is not sufficiently high to dissociate ammonia, 

 so that there is first a decomposition into ammonia and diazo- 

 imide and then a subsequent decomposition of the latter into its 

 elements. This probably accounts for the extreme force of the 

 explosion, the energy which would otherwise have been absorbed 

 in eflTecting the dissociation of the ammonia being available in 

 the explosion. The mercurous salt of diazoimide, X^Wg-.M *»s 

 obtained by precipitating a dilute aqueous solution of the ammo- 

 nium salt with mercurous nitrate. The precipitate requires 

 very careful washing and drying, owing to its highly explosive 

 character. Its explosive decomposition is extremely rapid, 

 analogous to that of fulminate of mercury, and the tempera- 

 ture of deflagration high, about 2700°. The mercuric sail, 

 NjHg, may be conveniently obtained from the mercurous salt 

 by Hrcomposing it with sulphuric acid, and treating the solution 

 of diazoimide thus prepared with freshly precipitated yellow 

 mercuric oxide. The greater portion of the salt separates as a 

 white precipitate, but it is somewhat soluble in cold water, and 

 very considerably soluble in hot water, from which long aciciilar 

 crystals are deposited on cooling. It is the most dangerously 

 explosive of the salts investigated, and the experiments have 

 unfortunately had to be abandoned on account of serious acci- 

 dents to M. lietthelot's assistants. It is much more sensitive 

 and therefore more dangerous than fulminate of mercury, and 

 explodes when least expected and in a most violent manner. It 

 furnishes ihe same volume of gaseous products of decomposition 

 as fulminate of mercury. 



The additions to the Zoological Society's Gardens during the 

 past week include a Rhesus Monkey {Maccuus rhesus) (rom 

 India, presented by Mr. Conrad W. Cooke ; a Macaque 

 Monkey (Macacus cyuomolgus) from India, presented by Mis. 

 Wheeler; a Cheetah (Cyn„-liirus jul'alm) from Somali-land, 

 presented by Mr. William Mure ; four Hedgehogs [Eriuaccus 

 turofitus), British, presented by Mr. F. C. Smith ; two Senegal 

 Touracous {Corylliaix fersa) from West .\fiica, presented by 



Miss E. B. Redwar ; a Falcon [F<il<o, sp. inc. ) captured at 



lea, presented by Mr. Arthur L. .Sclater ; four Anolises 



(AnoH.', sp. inc.) from North .\merica, presented by the 

 Southern Curio Company ; a Crowned Lemur {Lemur corona- 



lull from Madagascar, three Opossums (Didelphys, sp. inc.) 



from South America, deposited ; two Obsolete Tinamous 

 (Cryflurui obsolelus) from Brazil ; a Smooth Snake (Coroiiella 

 lavii) from Austria, purchased ; ihree Indian Cobras {Naia 

 Itifudiaiis) from India, received in exchange. 



OUR ASTRONOMICAL COLUMN. 



The Si'ECTRUM ok the Orion Nkiiui.a. — Two papers on 

 Ihe spectrum of the nebula in Orion ate contained in the cur- 

 rent number of Astronomy and Astro- Physics, one by I'rof. J. E. 

 Keelcr, and the other by Prof. \V. W. Campbell. The former 

 observer photographed the spectrum of the nebula many times 

 during Uiit winter. A comparison, of the pholographic and 

 viiual oluervaiions of nebular lines, with daik lines in the spcctia 

 of the Orion stars, indicates that an intimate relation exisis be- 

 tween the two. " Indeed," says I'rof. Keelcr, "taking into 

 account the relative intensities of the lines, the spectrum of 

 Rigel mayalmost be regarded asihe nebularspeclrum reversed. " 

 SpectroKopists will remember that Dr. Huggins obtained an 

 anomalout spectrum of the Orion nebula in 1S89, his photo- 



NO. 1289, VOL. 50] 



graph showing a large number of fine lines apparently connected 

 with the spectra of the trapezium stars, while the hydrogen lines 

 Ha and Ht were absent. Prof. Keeler has tried lo obtain the 

 same result by photographing the spectrum in the same way as 

 Dr. Huggins, but without success. He shows that "contrary 

 to the belief which has been held up to the present time, the 

 trapezium slars have spectra marked by strong absorption 

 bands ; they have not the direct connection with ihe nebula that 

 would he indicated by a bright-line spectrum, but are in fact on 

 precisely the same footing (spectroscopically) as other stars ii> 

 the constellation of Orion. While their relation to the nebula 

 is more certain than ever, they can no longer be regarded as 

 necessarily situated in the nebula, but within indefinite limits 

 they may be placed anywhere in the line of sight." Finally, 

 with regard to the appearances that have led to the belief that 

 the nebular lines are bright in these stars. Prof. Keeler believes 

 that they aie of physiological and photographic origin, and do 

 not actually exist. It is pointed out that these conclusions 

 have an important bearing on theories of stellar development. 



Prof. Campbell's paper, which is continued from the May 

 number, deals with the spectrum of the Orion nebula and other 

 well-known nebuUx;. In it Prof. Campbell brings together all 

 his spectroscopic observations of nebula:. Like Prof. Keeler, 

 he was unable to confirm Dr. Huggins' observation of Ihe ab- 

 sence of certain hydrogen lines in the spectrum of the Orion 

 nebul.1. His photographs also show that the spectra of the 

 trapezium slars all conform to the Orion type, and contain 

 numerous dark lines, but no bright lines. l!y tabulating the 

 observaiions published up to the date of the paper, it is sliown 

 that of the twenly-five bright lines known to exist in itu- ^;hc- 

 trum of the Orion nebula, at least nineteen are dciii ily 

 matched by dark lines in ihe Orion stars, and at least lilieeii 

 by daik lines in the six faint stars situated in Ihe dense 

 parts of the nebula. Including his own observations. Prof 

 Campbell finds that ihirly-six bright lines have been observe 

 in the spectra of the seven nebula; examined by him. He h ■. 

 tabulated all the lines that have had iheir positions determined 

 either from photographs or by direct observation. 



The Nebulous Character or Nova Aurig.v;. — The 

 question of the telescopic appearance of Nova Auriga; is again 

 brought up in Astronomische Nachridilen, No. 3238. Prof. I'. 

 E. Barnard, at the end of a communication on micromeirical 

 observationsof the object, made with the 36-inch telescopeof the 

 LickObservatory, says that when he examined the star on August 

 ig, 1S92, it appeared lo be densely nebulous, and that since 

 then it h.as not appreciably changed. He has made a very 

 careful examination of the slar in order lo test whether the nebu- 

 losity was due to instrumental defects or not, and the result of 

 his investigation is the conclusion that — " When the Nova is in 

 the best possible focus it is hazy and surrounded for s''>r6' 

 with a decided nebulosity. . . . How much of this nebiili iiy is 

 due to the peculiarity of the spectrum of the Nova, I am mu able 

 to tell. Hut from my experience with nebula: I would un- 

 hesitatingly say that the Nova is distinctly and unquestionably 

 nebulous." This testimony, coming from such an experienced 

 observer as Prof. Barnard, is very important. An inspection of 

 the micrometrical observations made at the Lick Observatory, 

 (ailed to show any marked periodic variation of the star's 

 position, such as might be due to parallax. The object must 

 therefore be at an enormous distance from us. 



.\ series of observations of the relative position of Nova 

 Aurig;v and a comparison slar of magnitude 102, is also com- 

 municated to the same number of the Astronomische Nachrichltn 

 by V . kenz, of the Pulkowa Observatory. The observaiions 

 extend (rom September 1892 to March 1S94. The series shows 

 no perceptible variation in ihe relative positions of ihe two 

 stars. As regards the suspected ncliulosily, Dr. Kenz found 

 that it disappeared on pulling out Iheeyepiccc by about 3-6mm.. 

 thus indicating that the nebular appearance was due to a want 

 of definition produced by the different refrangibiliiy of the 

 light emitted by the Nova. He thinks that Ihe object has 

 never appeared so nebulous as it was in September 1S92, 

 and he suggests that this may be accounted for by the (act ihat 

 the hydiogen line at A 486 ^m (F) an^l 'liat *' ^ 495 MM '"»»= 

 diminished in intensity. 



The Ai'Is Period of the An'cient Egyptians.— The 

 Apis Period of the ancient ivgyptians formed the subject of • 

 recent paper read before the Vienna Academy by Dr. E. 

 Mahler. The author showed that this 25-ycar period could no 



