February 8, 1894] 



NA TURE 



;49 



atoms which compose a chemical molecule, is contributed to the 

 Chemiker Zeittiiig by Prof. Victor Meyer. The literature of 

 this most interesting branch of chemical study has so rapidly ac- 

 cumulated since the theory of Le Bel and Van't Iloff was pro- 

 mulgated in the year 1874, that a concise account of the im- 

 portant stages of progress which have led up to the present state 

 of our knowledge is particularly welcome. The earlier portion 

 of the memoir is devoted to the development of the idea of the 

 asymmetric carbon atom, and the growth of the conviction that 

 the occurrence of isomeric compounds represented by the same 

 constitutional formula — which differ only in their action upon 

 polarised light, and very slightly in other physical properties, 

 such, for instance, as the three lactic acids — -could only be ac- 

 counted for by the different spacial arrangement of the atoms in 

 the molecule. The fundamental assumptions of Van't Hoff are 

 very clearly expressed, and the possibilities of isomerism by 

 change in the relative positions of the various groups attached 

 at the four corners of the hypothetical carbon tetrahedron are 

 fully illustrated. A striking example is afforded in this connec- 

 tion by one of the results of the brilliant researches of Emil Fischer 

 in the sugar group, whereby we are made acquainted with no 

 Jess than thirteen distinct sugars, all of which are represented by 

 the same constitutional formulae CH20H.(CHOH)4.CH20H. 

 The second section is devoted to the stereo-isomerism of the 

 derivatives of ethylene, so ably worked out by Wislicenus. The 

 simple expIanaMon of the remarkable and long-discussed case of 

 the isomeric acids, maleic and fumaric, upon the lines of the new 

 theory, is referred to, and a similar explanation extended to 

 numerous other and more complicated of the derivatives of 

 ethylene. The third section deals with the peculiar nature of 

 the stereo-isomerism of closed-chain compounds, such as the 

 polymerised tri-aldehydes. It is then shown in a further section 

 that carbon is by no means peculiar in lending itself to stereo- 

 isomerism, but that the pentavalent nitrogen atom is likewise t 

 capable of furnishing isomers which differ structurally merely in 

 the relative positions occupied by the five attached atoms or 

 groups. The stereo-isomerism of nitrogen compounds is shown, 

 however, to be largely influenced by the weight and complexity 

 of the five attached groups. The interesting discovery of a 

 second di-oxim of benzil by Goldschmidt in Prof. Meyer's \ 

 laboratory, gave a great impulse to the study of nitrogen com- 

 pounds containing the group C = N, termed oxims, and the j 

 number of stereo-isomeric oxims which have subsequently been 

 isolated bear remarkable testimony to the use of a theory in 

 stimulating research. 



The additions to the Zoological Society's Gardens during 

 the past week include two Swainson's Lorikeets {Trichoglosstis 

 novcT-hollandia) from Australia, presented by Mr. John Biehl ; 

 a Chilian Conure {Coiiiirus smaragdinus) horn Chili, presented 

 by Mrs. Gibney ; two Eyed Liza'ds (Za^^r/a ocellata) twenty 

 European Tree Frogs {Hyia arborea) South European, pre- 

 sented by Mr. T. Keen ; a Madagascar Porphyrio {Porphyria 

 madagascariensis) from Madagascar, a Waxwing {A?)ipelis 

 garruhis), two Long-tailed Tits {Parus caudaius) European, 

 purchased ; a Hog Deer {Cervus porcintis) born in the 

 Gardens 



OUR ASTRONOMICAL COLUMN. 

 Eclipse Meteorology. — A very extensive series of meteor- 

 ological observations was made during the total eclipse of the 

 sun on January i, 1889, at Willows, California. It appears 

 that the temperature fell 6^ F. from the commencement of 

 totality to ten minutes after, while the variation of the baro- 

 meter was so nearly identical with the daily fluctuation that no 

 effect could with certainty be ascribed to the eclipse. The 

 influence on the wind, however, was very marked, its previous 

 velocity of twelve miles per hour being reduced almost to that 



NO. 1267, VOL. 49] 



of a calm. Observations with the solar radiation thermometer 

 showed that some heat was received throughout totality. An 

 attempt was also made to secure concerted observations of the 

 so-called " shadow bands " — the long dark bands separated by 

 white spaces which are seen in rapid motion on the ground and 

 sides of buildings just before and after totality. The observa- 

 tions collected seem to give decisive evidence against the view 

 that the bands are diffraction fringes in the shadow of the 

 moon, the observed velocities being far less than that of the 

 shadow ; the fact that they were prominently seen at some 

 stations, while at others they were hardly visible, indicates a 

 local origin (Ann. Harvard. Coll. Obs. vol. xxix.). 



In the same volume, Mr. Parkhurst gives an account of his 

 photometric observations of some of the asteroids, and confirms 

 the previous conclusion that there is a phase correction over and 

 above that for the defect of illuminated surface, and that this 

 correction is different for different asteroids ; the idea that large 

 errors may be introduced by rotation, however, is not con- 

 firmed. The same writer also gives the individual observations 

 of a large number of variable stars, which furnish valuable data 

 for the construction of light-curves. 



A Remarkable Cometary Collision. — Two striking 

 photographs are reproduced in the February number of Know- 

 ledge, in illustration of an article, by Prof. E. E. Barnard, on 

 the probable encounter of Brooks' Comet with a disturbing 

 medium on October 21, 1893. The comet was discovered by 

 Mr. Brooks, on October 16, but though it was kept under obser- 

 vation at the Lick Observatory, no phenomena of an extraordinary 

 kind were observed until the 21st of that month. A photo- 

 graph, then taken with a Willard photographic lens, presented 

 a remarkable appearance, the tail appearing, to use Prof. 

 Barnard's analogy, like a torch streaming in the wind. The 

 reproductions of the photographs give the impression that the 

 comet's tail swept into some dense medium, and was broken up 

 by the encounter. Indeed, Prof. Barnard thinks it impossible 

 to escape the conclusion that the tail did actually enter a dis- 

 turbing medium which shattered it. This theory is supported 

 by the photograph taken on October 22, where the tail is seen 

 to hang in irregular cloudy masses, and a large fragment appears 

 to be entirely separated from the main part. There is little 

 doubt that the tail met a mass of meteoritic matter, and so had 

 its symmetry destroyed ; at any rate, this supposition must be 

 accepted until a simpler and better one can supplant it. What 

 we have to do, as Mr. Cowper Ranyard remarks in an article on 

 the irregularities of comets' tails, is diligently to collect facts. 

 The multiplication of such photographs as those obtained of 

 Brooks' Comet, and of Swifi's Comet (1892), by Prof Barnard, 

 will certainly revolutionise current opinion as to the develop- 

 ment, and the types, of comets' tails, 



MiRA Ceti. — According tothe Co7npanion to the Observatory, 

 this famous variable star will reach a maximum about the 17th 

 inst. At the time of writing (February 3), the star is of a 

 reddish tinge, and faintly visible to the naked eye ; but, un- 

 fortunately, it is too near the sun to permit of long-continued 

 observations on the same evenmg. The magnitude at 

 maximum is very inconstant, and varies between i"7 and 50 

 (Gore). Spectroscopic observations of the star are of the highest 

 importance, and it is to be hoped that a satisfactory record of 

 its phases will be secured. The general spectrum is one of 

 Group II., but near a former maximum, Pickering photo- 

 graphed a number of bright lines, chiefly of hydrogen. Among 

 the points on which information is desirable are : (i; at what 

 phase of the variation the bright lines of hydrogen make their 

 appearance ; (2) the fluctuations in the bright flutings of carbon 

 observed by Mr. Lockyer at the maximum of 1888 (Nature, 

 vol. xxxviii. p. 621). 



Proper Motions of Stars. — The recently published 

 volume (xxv.) of the Annals of the Harvard College Observa- 

 tory contains values for the proper motions of a large number 

 of stars in the zone 50° — 55° north, the adopted values, how- 

 ever, being only at present regarded as provisional. The results 

 are derived by Prof. Rogers from the comparison of his own 

 positions for the stars in this zone, obtained with the meridian 

 circle, with the positions given for corresponding stars by earlier 

 catalogues. One section of the volume gives the values of a and 

 5, referred to the system of the Astronomische Gesellschaft, for 

 the stars included in the zone in question. 



The System of Algol — An elaborate discussion of the in- 

 equalities in the period of Algol recently led Mr. Chandler to 



