No. 1071, Vol. 42] 



NA TURE 



37 



rendered even more dangerous by reason of its great volatility, 

 little has hitherto been done towards completing its chemical 

 history beyond a mere description of its more evident properties. 

 Determinations either of its density or its melting-point appear 

 never to have been attempted, and it was with the object of 

 supplying these deficiencies that the work in the Tubingen 

 Laboratory was undertaken. Everyone who has ever prepared 

 this exceptionally beautiful substance for lecture or other 

 purposes will remember the exquisite manner in which it sub- 

 limes, forming long, delicate, colourless, but very highly refractive 

 needles, bridging over from side to side of the wide tube or 

 flask in which the operation is performed. Often these elongated 

 prisms attain the length of half a dozen inches or more, and 

 frequently form an interlacing network among which may be 

 seen perched here and there star-shaped or flower-like aggregates 

 of the smaller crystals. Perhaps the most remarkable property 

 of these crystals is to be found in the manner in which they 

 resublime from one side of the vessel to the other according as 

 their position is varied as regards the direction of the light which 

 falls upon them. Drs. Seubert and Pollard prepared their 

 specimens by the old method first used by Sir Humphrey Davy, 

 the action of iodine upon mercuric cyanide, Hg(CN)2 -I- alg = 

 Hglj -f 2CNL About 10 grams of the finely-powdered and 

 well-dried mixture of iodine and cyanide of quicksilver, in the 

 proportion of one molecule of each so as to avoid the presence 

 of much free iodine in the sublimate, was placed in a wide test-tube 

 and interpersed with glass beads in order to render the mixture 

 as porous as possible. The test-tube was then placed at the 

 bottom of a wider glass tube closed at the lower end, and fitted 

 at the upper with a calcium chloride drying tube to prevent 

 access of moisture. The apparatus was then allowed to stand 

 for about three days in a position where it could receive direct 

 sunlight ; at the end of this time the reaction was almost com- 

 plete, the mixture being brilliant red from formation of mercuric 

 iodide. The lower end of the tube was then placed in a hot 

 water bath, when the iodide of cyanogen sublimed in the manner 

 above described into the upper cooler part of the tube. In order 

 to determine the melting point, small quantities were placed in 

 capillary tubes and hermetically sealed, for if the upper end were 

 left open, as is usually the case in taking a melting-point, the 

 cyanide would simply volatilize without fusion* The melting- 

 point was in this way found to be I46°*5 C, and the solidifying 

 point 143°. The vapour-density was determined by Victor 

 Meyer's method, and found to be 5*28, corresponding to the 

 simple formula, CNI. The lowest temperature at which the 

 substance becomes completely and rapidly converted to the 

 gaseous condition appears to be about 250°. The iodide is there- 

 fore analogous to the simple bromide and chloride of cyanogen, 

 CNBr and CNCl, and not to the triple polymers tricyanogen 

 bromide and chloride, CgNjBrg and C3N3CI3. 



The additions to the Zoological Society's Gardens during 

 the past week include the Wild Boars [Siis scrofa jv.) bred in 

 Scotland, presented by the Lord Hebrand Russell ; a Ring- 

 tailed Coati ^Nasiia rtifa i ) from the Argentine Republic, 

 presented by Mr. R. E. Moore ; a Louisianian Meadow Starling 

 {Stiirnella ludoviciana 9 ) from North America, a Black-bellied 

 Sand Grouse {Pteroclcs arenarius ? ) from India, presented by 

 Mr. W. H. St. Quintin ; four variegated Sheldrakes ( Tadorna 

 variegata i f,- i i) from New Zealand, presented by Captain 

 C. A. Findlay, R.N.R. ; a Rhomb-marked Snake {Psammo- 

 phylax rJioml'catiis) from South Africa, presented by Miss 

 Harris ; three Common Vipers ( Vipera herns) from Sussex, 

 presented by Dr. C. W. Cousens ; a Green Lizard {Lacerta 

 viridis), a Three-toed Skink (Scps tridactylus) from France, pre- 

 sented Mr. J. C. Warbury ; a Sooty Phalanger {Phalangista 

 fidiginosa 6 ) from Australia, deposited ; a Black headed Lemur 

 {Lemur hninneus), born in the Gardens. 



OUR ASTRONOMICAL COLUMN. 

 Objects for the Spectroscope. 

 Sidereal Time at Greenwich at 10 p.m. on May 

 I3h. 6m. 42s. 



(i) The spectrum of this bright nebula does not appear to 

 have been yet recorded. Smyth describes it as " a conspicuous 

 nebula, magnificent in size and brightness." In the General 

 Catalogue it is described as "a very remarkable object; very 

 bright ; very large ; very much extended in the direction 120° ; 

 brightens in the middle to a small bright nucleus, which is 

 possibly a double star." The nebula is in the constellation 

 Coma Berenices, and is now very favourably situated for 

 observations. 



(2) This is the famous spiral nebula in Canes Venatici. The 

 details of the nebula are so well-known that a full description is 

 not necessary here. In all but the largest telescopes it simply 

 appears as a double nebula with the two nebulosities running 

 into each other, one of them being surrounded by a ring which 

 is variable in brightness. Smyth likens this to a " ghost " of 

 Saturn. According to Huggins the spectrum is continuous, 

 but some parts were thought to be abnormally bright. Although 

 the o'oservations will not be easy, it is very important that the 

 positions of such bright parts should be measured, if only 

 approximately. In such cases as this it is probable that we 

 shall find spectroscopic connecting links between the bright-line 

 nebulae and stars which are well advanced in condensation. 

 Our knowledge of the relations between nebulae and comets is 

 also likely to be advanced in this way. 



(3) This is a very fine star of Group II. The bands are 

 very wide and dark, even in the ultra-blue, but especially in the 

 red (Duner). The star belongs to a late stage of the group, 

 and may be usefully re-examined for further details. 



(4) A star of the solar type (Vogel). The usual differential 

 observations as to whether the star is increasing in temperature 

 (Group III.), or decreasing (Group V.) are required. The 

 spectra of this class of stars should be very carefully examined 

 for remnants of the strong bands in the red, which characterize 

 the later stages of Group II., and which are also seen in 

 Aldebaran. If these are found, the star is obviously at an 

 early stage of Group HI. It has also become very important 

 to determine whether there are any stars intermediate between 

 stars like the sun and stars of Group VI., and in these more 

 detailed observations this should be borne in mind. The 

 carbon band near 1/ will probably be the first to appear, and 

 the presence or absence of traces of this band should be always 

 noted. It is most likely to occur in stars of an orange or reddish 

 tint. 



(5) Spica has a spectrum of Group IV. The only observa- 

 tions likely to be of service are those comparing the thicknesses 

 of such lines as h, E, and D with their thickness in other bright 

 stars of the same group {e.g. a Lyrse). This will determine its 

 relative temperature. 



(6) This variable will reach a maximum about May 9. It 

 ranges in magnitude from 8-9 at maximum, to < 13 at minimum 

 in a period of about 251 days. The spectrum is still doubtful ; 

 Gore writes it HI. ? A. Fowler. 



Structure of the Corona. — The Smithsonian Institution 

 has had two plates prepared, containing nine photographs of the 

 total eclipse of the sun of January i, 1889, and distributed them 

 amongst astronomers and others interested in solar physics. All 

 the photographs have been reduced to a uniform diameter, and 

 at Prof. Langley's request. Prof. Todd has contributed a de- 

 scriptive note to accompany them. In the remarks on the 

 structure of the corona it is noted : — 



(i) The axis of symmetry of the corona does not coincide with 

 the axis of revolution of the sun as determined from the solar 



