Julyzx, 1879] 



NATURE 



331 



speculum gave a slight reddish tint to all objects) ; now the com- 

 panion is bluish white, and between these two epochs it show ed 

 more saturated colours. 



The short period of i Herculis (34 '32 years) allows us to con- 

 sider the changes of colours during two revolutions. Herschel 

 measured this system about the epoch when the companion was 

 very near to the primary ; the latter was white, the former ash- 

 coloured. At the periastrium of 1S60 Mr. Knott saw them pale 

 yellow and greenish respectively ; at other epochs the colours of 

 the two components are all the more marked the further they 

 are away from the periastrium, the companion always showing 

 warmer tints than the principal star. About the epoch of the 

 apparent periastrium M. Dembowsky desigtiated them as yellow 

 and olive coloured. Similar phenomena are shown by the other 

 doable stars given in the table, all of which are systems with 

 closed, ?>., elliptical orbits. In the double star 5i Cygni, where 

 no closed orbit has been observed, but where the small companion 

 moves in a straight line relatively to the larger one, the same 

 yellow tint has been observed from 1828 to 1873. 



In the cases of optical double-star systems, i.e., those which 

 only accidentally happen to be in the same line of sight, and 

 which show a rectilinear motion, the principal star is generally 

 yellow and the companion blue. In Mr. Brothers' catalogue, 

 which comprises 105 double-star systems, with closed orbits, 

 there are only thirty-two where the companion is blue, while all 

 the others show the same colour as the principal star. And even 

 these thirty-two systems may possibly be optical ones, in which 

 the companion is almost exclusively blue. The absence of blue 

 in the companions of double stars of short period is most 

 remarkable. 



The blue colour of the companions in the optical systems is 

 not an effect of contrast to the yellow colour of the primaries, 

 for the former are blue even if the latter are shut out of the 

 field of vision. It seems possible that, similar to the effect in 

 our atmosphere, where distant objects assume a bluish tint, 

 celestial bodies which send us their rays of light from the most 

 distant regions, may appear blue on account of the thickness of 

 the medium through which the light passes. 



M. Niesten has compiled a table of double stars with blue 

 companions, and has arranged them according to their position 

 in declination and right ascension. From this it appears that 

 these double stars are principally situated in a zone extending 

 from decl. 10° S. to 40" N., and further fthat there are two 

 maxima of occurrence, one in R.A., 4h.-6h. and the other in 

 R.A. l8h.-2oh. ; the first maximum is near the equator, the 

 other between Decl. 30° and 40° N. ; the former is therefore in 

 the constellation of Orion, the latter in Cygnus and Lyra. 

 According to Sestini, the single blue stars occur in the same parts 

 of the heavens. 



The conclusions we may draw^from M. Niesten's researches 

 are as follows : — 



I. In systems with well-established orbits, and particularly in 

 those of short period, the two components generally have the 

 same yellow or white colours. 



,' 2. In systems of which we possess sufficiently numerous re- 

 cords of the colours of the components to enable us to perceive 

 a relation between the tints and the relative positions of primary 

 and companion, the former is white or pale yellow when the 

 latter is in its periastriam, while in other positions the primary is 

 yellow, golden yellow, or orange. 



3. In these systems the companion follows the colour-fluctua- 

 tions of the principal star, and frequently surpasses the latter in 

 intensity of tint the further it moves away from the periastrium, 

 at which point in most cases its light is white, like that of the 

 primary. 



4. An equality of tints of primary and companion is found 

 in systems with rectilinear motion, as well as in those with closed 

 r>rbits and long periods. 



5. In optical groups the companion is generally blue 



These remarks are, of course, founded upon observations made 

 by different observers, and the records of colour may thus suffer 

 from personal influences ; but in many cases one and the same 

 observer recorded the colours of the components of a system as 

 yellow during a series of years, and then he saw them grow paler 

 and turn white. In other instances all astronomers agree that 

 a certain companion is blue. 



When more careful attention has been given to the question of 

 colours, both in measuring double stars as well as in; investiga- 

 I ions of the physical condition of planets, then it will be possible, 

 perhaps, to draw a great many more conclusions, and such to 



which greater probabiUty attaches, than was in the power of M. 

 Niesten, with the comparatively small number of observations at 

 his command. 



At present it is supposed that the fluctuations of colour in stars 

 are caused by changes in the composition of their incandescent 

 gaseous envelopes ; these changes must in turn be only effects of 

 another cause producing them ; M. Niesten does not think it 

 impossible that in the case of double stars this cause might lie 

 in the relative position of the components. 



SCIENTIFIC SERIALS 



American Chemical yournal, vol. i., Nos. 2 and 3, present a 

 good array of contributions from different American universities, 

 making in all, with reviews and reports, about 215 pages. 

 Under inorganic chemistry is to be found a description of very 

 slightly modified methods of nitrogen and phosphorus estimation 

 adapted to agricultural products, by Johnson and Jenkins ; and 

 a series of analyses of gummite and other uranium minerals 

 from North Carolina, by E. Genth, &c. Among the contribu- 

 tions to organic chemistry is a long paper by Remsden and lies 

 on the oxidation of substitution products of aromatic hydro- 

 carbons, continued from No. i . In the first portion the authors 

 describe solid orthokresol from their oxytoluic acid, and they 

 further conclude from their experiments that the presence of a 

 sulphamine gi'oup acts protectively towards a methyl group in a 

 substituted aromatic compound submitted to oxidation. A full 

 abstract of this and another interesting paper by Remsden and 

 Morse on oxidation of bromparaethyltoluene, and researches on 

 substituted benzyl compounds, by Jackson, cannot be given in 

 our space. Thorpe on heptane has appeared elsewhere. The 

 remaining communications are of minor interest. 



Btilletin de la Acadimie Royale des Sciences (de Belgique"), 

 No. 5. — The yellow substance obtained when tetrathionic acid 

 is poured into a solution of mercurous nitrate in water has been 

 proved by M. Spring to be a trithiohasic sulphate of mercury. 

 This substance showed some unexpected chemical properties, 

 which M, Spring describes, and he has succeeded in forming 

 some other;new bodies similar to it, so as to complete the list of 

 basic sulphates of mercury sufficiently for an attempt at classifi- 

 cation of these substances. — The recent terrible catastrophe at 

 the Agrappe coal-pit is the occasion of two communications by 

 M. Comet and M. Melsens, the former remarking especially on 

 the influence of depth on the instantaneous iiTuption of fire damp, 

 and the proportion of that gas met with. (The fire-damp of 

 the Agrappe pit, which ignited at the mouth of the pit, came 

 from 610 metres depth, where a new gallery was being made.) — 

 M. Renait's paper on the distinctive characters of dolomite and 

 calcite in rocks of the carboniferous limestone of Belgium is else- 

 where noticed. — There are also here two notes on Belgian 

 minerals. 



The Ri-ista Scicntifico-Industriale, Nos. 11-13, contain the 

 following papers of importance : — Researches on the electric 

 conducting power of carbons, by Prof. Riualdo Ferrini. — On 

 some new applications of the potential energy of liquid surfaces, 

 by G. Van der Mensbrugghe, discussed by Prof. C. Marangoni. 

 — On a telephonic microphone, by Prof. G. Cantoni. — On the 

 cndosmose of liquids and on an apparatus for filling endosmo- 

 meters,by Prof. C. Marangoni. — On the mutual dependence of 

 simple bodies, by P. Provenzali. — On some prehistoiic dis- 

 coveries made at Ostiano, by Dr. Giro Chistoni. — On a new 

 saccharometer or polarimeter, by M. Laurent. — On the kinzigite 

 of Calabria, by Domenico Lovisato. — On the determining causes 

 of the sexuality of Cannabis saliva, by Prof. P. A. Saccardo. — 

 On the constitution of fog and clouds, by Prof. Fernando Palagi. 

 — On a new burner for monochromatic light. — On the pheno- 

 mena which accompany the electrolysis of metallic compound-', 

 by Prof. Giuseppe Basso. — Crystallographical, optical, and 

 chemical researches on certain minerals, by Prof. Giuseppe 

 Grattarola. — On a new method to determine the melting-point 

 of organic substances, by Prof. Giorgio Roster. 



Tut. Rei'ue Internationale des Sciences (June and July). — 

 From these parts we note the following papers : — Analysis of 

 Prof. Ernst Haeckel's treatise, " Monogenetic and Polygenetic 

 Origin of the ttiree Organic Kingdoms and of the Organs," by 

 Jules Soury.— Description of the scientific balloon ascent of 

 October 31, 1878, and remarks on the exploration of great aerial 

 heights, by Louis Tridon, — On the Diatomaceie of the mouth of 



