January 8, 1903] 



NA TURE 



233 



among the text are some excellent reproductions illustrating the 

 behaviour of different lenses and speeds of shutters, and the 

 frontispiece is a contact print on Barnet platino mat bromide 

 paper. The low price of the volume (one shilling) and the 

 useful nature of the contents should render it indispensable to 

 every photographer. 



In the current number of the Comptes rendus is a note by 

 1'rof. Henri Moissan on a new method of preparing the silicon 

 analogue of ethane, Si 2 H H . This substance was originally 

 obtained by the author, in conjunction with Dr. Smiles, by the 

 partial condensation at - 200 C. of an impure silicon hydride 

 prepared by the action of hydrochloric acid upon a silicide of 

 magnesium of undefined composition. Attempts to prepare the 

 same compound from the lithium silicide, Li s Si 6 , by the action of 

 dry hydrogen chloride or a dilute solution of hydrochloric acid 

 were unsuccessful, hydrogen being the only gaseous product. It 

 has now been found that by the gradual addition of lithium 

 silicide to concentrated aqueoushydrochloricacid, thesilico-ethane 

 is readily formed in abundance and can be separated by means 

 of cooling to the temperature of liquid air. 



The same number contains an account, by M. F. Bodroux, of 

 another application of the organo-magnesium compounds to 

 organic synthesis. It has been found that if a magnesium alkyl 

 chloride or bromide, prepared in the usual way by the action of 

 magnesium upon an ethereal solution of the alkyl bromide or 

 chloride, is treated with iodine, the alkyl iodide is produced in 

 nearly quantitative yield, together with magnesium iodochloride 

 or bromide. Propyl bromide and isoamyl chloride treated in 

 this way have furnished about 80 per cent, of the theoretical 

 quantities of the corresponding iodides. The reaction is 

 equally applicable to aromatic derivatives, and will simplify 

 greatly the preparation of many monoiodo-derivatives of 

 benzene. 



The much-discussed question of the chemical character of 

 bleaching powder is revived in a recent number of the 

 Zeilschrift fur anorgariische Chemie, which contains a long 

 paper on the subject by Herr Winteler, of Darmstadt. The 

 investigation appears to have arisen from a difficulty which was 

 experienced in making good bleaching powder from electrolytic 

 chlorine, owing to the gas containing considerable quantities ot 

 carbon dioxide. The chief conclusions reached by Herr 

 Winteler are as follows. Dry chlorine does not act on dry 

 calcium hydroxide, but in the presence of moisture chlorine 

 water is first formed. This contains hypochlorous and hydro- 

 chloric acids, which then act upon the calcium hydroxide. The 

 action involves complicated equilibria, which depend on the 

 temperature, the amount of water present, the rate at which the 

 chorine is passed, &c. Bleaching powder possesses no definite 

 formula, but is a mixture of bodies resulting from the balanced 

 reactions just referred to. It contains basic calcium chloride 

 and basic hypochlorite as normal components, and may contain 

 chloride and hypochlorite as well as hydroxide and the free 

 acids. The decomposition of bleaching powder into chloride 

 and oxygen takes place when there is an excess of hydroxyl 

 ions ; on the other hand, an excess of hydrogen ions leads to a 

 decomposition into chlorate and chloride. Working upon this 

 theory of the character of bleaching powder, Herr Winteler 

 shows how it is possible to prepare a good product even when 

 using unpurified chlorine containing 6 per cent, of carbon 

 dioxide. 



The additions to the Zoological Society's Gardens during the 

 past week include a Fennec Fox (Cam's cerdo) from North 

 Africa, presented by Dixon Bey ; two Common Marmosets 

 (Hapale jacchus) from South-east Brazil, presented by Mr. \. B. 

 Joel ; two Egyptian Jerboas (Dipus aegyptius) from North 

 NO. 1732, VOL. 67] 



Africa, presented by Miss Chesterman ; two Eastern One- 

 wattled Cassowaries (Casuarius auranliacus) from New Guinea ; 

 a Blossom-headed Parrakeet (Palaeornis cyanocephalns) from 

 India ; a Gangetic Trionyx ( Trionyx gangelicits) from India, 

 deposited. 



OUR ASTRONOMICAL COLUMN. 



Comet 1902 d. — From observations made at Hamburg on 

 December 3 and 11, and at Paris on December 22, Herr Ebell 

 has calculated the following elements and ephemeris for this 

 comet : — 



T = 1903 March 23-544 Berlin M.T. 



»= 5 43 32'6 

 Si = 117 29 51-2 



i = 43 54 17 4 ] 

 log ,/ = 0-443876 



19030 



Ephemeris 12/1. M.T. Berlin. 



1903 a S log A Brightness. 



h. m. s. a , 



Jan. o ... 7 3 10 ... +3 47-3 ... 0-2925 ... 1-4 



4 ... 7 o 19 ... +4 54-1 ... 0-2880 ... 14 



8 ... 6 57 23 ... + 6 46 ... 0-2847 •■■ ''5 



12 ... 6 54 27 ... +7 i8-2 ... 0-2825 ■■• r 'S 



16 ... 6 51 34 ... +8 344 ... 02816 ... J'S 



20 ... 64847 ... +9526 ... 0-2818 ... 1-5 



Unit brightness at time of discovery. 



On December 22d. toh. 44m. -3 Paris M.T., the comet was 

 observed in the following position by M. Bigourdan at Pnris : — 

 a (apparent) = 7h. 9m. 7s. -4, 8 (apparent) = + i" 32' 55". 



M. Fayet has found that this comet has the greatest peri- 

 helion distance recorded for any comet since that of 1729. 



Observations of Variable Stars.— In No. 3837 of the 

 Astronomische Nachrichten, M. M. Luizet, of the Lyons Obser- 

 vatory, publishes his observations of five variable stars and gives 

 his results for each slar in a tabular form. 



The result of 285 observations of Algol, made between 

 November 18, 1897, and March 12, 1902, indicates a possible 

 slight negative correction to the elements published by Mr. 

 Chandler in No. 509 of the Astronomical Journal. 



One hundred and filty-seven comparisons of the irregular 

 variable e Aurigce indicate great irregularities in the brightness 

 of this star, which on December 10, 1901, was actually one or 

 two degrees fainter than v Persei. 



One hundred and fourteen comparisons of W Orionis were 

 made between October 26, 1898, and March 19, 1902, and 

 these show that both the duration of the period and the magni- 

 tudes at maxima and minima vary greatly. 1'he following 

 elements show the closest agreement to the observations : — 



Maximum 1899 February 22\ , v 



Minimum 1899 March 10 /+3 2cl - 32 *■■> 



but there are several observations which are not reconcilable to 

 this period. 



Observations of T Monocerotis and <T Geminorum have also 

 been made, and tables of their maxima and minima are given by 

 M. Luizet. 



The Spectrum of e Auriga. — From the investigation and 

 measurement of spectrograms obtained during 1901 and 1902 by 

 Prof. Harlmann and Dr. Eberhard, Prof. H. C. Vogel has 

 found that e Auriga; is a spectroscopic binary which has a very 

 long period. 



The spectrograms referred to show that the hydrogen lines 

 in the violet region, beyond H and K, stand out with excep- 

 tional prominence in ihis star, and a close investigation as to 

 the cause has led to the conclusion that the spectra of two 

 stars — one of the a Cygni type, the other lying between the 

 limits of Types I. and II. (a Persei, 7 Cygni) — are present, the 

 one being exactly superimposed on the other. 



Observations with a Binocular Telescope. — In 

 Popular Astronomy, No. 100, Mr. D. W. Edgecomb de- 

 scribes the performances of the 6^-inch binocular telescope, 

 made by Messrs. Alvan Clark and Sons. 



In describing the features of the Moon, Jupiter and Saturn 

 as seen with the binocular, the writer states that the objects 



