772 



NATURE 



[February lo, 192 1 



consumers abroad. The first action of the company 

 was to establish a showroom in Paris, which is now 

 well stocked with samples. Not only can visitors 

 to the showroom obtain full information regarding 

 the apparatus, but also in most cases facilities are 

 available for the demonstration of the exhibits. 

 Although the showroom has been open for a few 

 months only, the results are most encouraging, and 

 a considerable number of inquiries are being dealt 

 with daily. Paris is found to be essentially suitable 

 for a centre of this sort, as is shown by the fact that 

 the visitors' book already contains names of visitors 

 from thirteen different countries. The general cata- 

 logue is divided into nine sections under the following 

 headings; — (i) Chimie, Industries chimiques. (2) 

 Electricity, Industrie dlectrique. (3) Marine. (4) 

 Aviation, A^rodynamique. (5) M^tallurgie, M^canique 

 de precision, etc. (6) M^decine, Bacteriologie, Physio- 

 logie, Ophtalmologie, etc. (7) Topographic, G60- 

 di^sie, Astronomic, M^t^orologie, Dessin. (8) Physique 

 exp6rimentale. (9) Photographie, Cin^matographie. 

 It will be seen that the range of apparatus covered 

 is very extensive. In connection with their Paris 

 showroom the "B.S.A.M." have formed a reference 

 library of English scientific and technical books 



which are at the disposal of visitors. The showroon* 

 Is under the management of Mr. F. C. Dannatt. 



Dr. Norman R. Campbell is bringing out, through 

 Messrs. , Methuen and Co., Ltd., a work entitled 

 "What is Science?" the aim of which is to explain 

 whaf science really is and the kind of satisfaction 

 which may be derived from its study. Two other 

 books in Messrs. Methuen 's spring list make an 

 especial appeal to readers of Nature, viz. " Atomic 

 Theories," by F. H. Loring, and "Biological 

 Chemistry : The Application of Chemistry to Bio- 

 logical Problems," by Prof. H. E. Roaf. The first, 

 named volume is written to give in a concise and 

 simple form an account of all the important theoretical 

 and experimental researches on the atom, its structure, 

 and the arrangement of electrons in atoms, in mole- 

 cules, and in ions. The second may be regarded as 

 an introduction to the more specialised branches of its 

 subject. It will consist of three sections, dealing 

 respectively with a brief description of the parts of 

 organic and physical chemistry which relate to bio- 

 logical chemistry ; the accumulation of energy by 

 plants and the interconversion of carbohydrates, fats, 

 and proteins ; and the liberation of energy from the 

 food substances. 



Our Astronomical Column. 



Interesting Binary Stars. — Mr. J. S. Plaskett 

 investigates, in vol. i., No. 2, of the Publications of 

 the Dominion Astrophysics Observatory, Victoria, 

 B.C., the orbit of the spectroscopic binary U Coronae. 

 Both spectra are visible, each being of type B3. The 

 following are the elements of the two stars in terms 

 of the sun, the brighter star being placed first: — 

 Radii, 290, 474; masses, 427, 1-63; and densities, 

 0175, 0015. Taking the surface intensity of the 

 bright star to be —2-7 magnitudes, as compared with 

 the sun, of which the absolute magnitude is 486, the 

 distance is deduced as 400 parsecs. It is, however, 

 noted that the fainter star, though of the same spep- 

 tral type, has only one-eighth of the surface bright- 

 ness ; this indicates that the correlation of surface 

 brightness with type is less close than some physicists 

 have assumed. 



Two other eclipsing binaries of type B, ^u" Scorpii 

 and V Puppis, are discussed by Miss A. C. Maury in 

 Popular Astronomy for January. The masses come 

 out fairly large in these rases, (m+m,) sin' j being 16-5 

 and 33 respectively. These would not be very different 

 from the real masses, for, owing to the occurrence of 

 partial eclipses, i cannot differ very much from qo°. 

 /i' Scorpii IS stated to be of the /3 Lyrae type, show-ing 

 double eclipse and continual variation. Stellar tides 

 are suggested in explanation of part of the change of 

 light, and also of changes in the character of the 

 spectrum. 



A famous visual binary, 70 Ophiuchi, is discussed 

 by F. Pavel, of Neubabelsberg, in Ast. Nach.. No. 

 5082. It is shown that the irregularities are explicable 

 on the assumption that the principal star is describing 

 the following small orbit owing to an unsern com- 

 panion :—T= 18000, = 0033", c = oi, X=i5o°, 1 = 0°. 

 period = 65 v. The author then obtains for the orbit of 

 the visual pair :—T= 1805-065, a=4-4q5', 6 = 0-4088, ()> = 

 20016°. ,0=166-648°, ^ = 122-184°, i = 58-'743°, period = 

 87-710 V. He obtains 0-36 for the ratio of masses, and 



NO. 2676, VOL. 106] 



106 times the sun for the joint mass of the system 

 on the assumption that the parallax is 0-225". 



The Green Ray or Flash. — It has often been 

 noticed when the sun is setting behind a well-defined 

 horizon that the last appearance of the disc is a 

 bright green flash. Various explanations have been 

 put forward, some asserting that it was a case of 

 complementary colour, due to fatigue of the retina. 

 This was negatived by the flash being seen at sun- 

 rise. Another view was that the sea-water had some- 

 thing to do with it, but it was found that the effect 

 could also be seen at a distant land horizon. There 

 remained the explanation of atmospheric dispersion; 

 but here again there were diversities of view, some 

 holding that the normal colour dispersion would 

 suffice, others invoking abnormal phenomena of the 

 nature of the mirage. 



h'Astronomie for December contains an interesting 

 research by MM. A. Danjon and C. Rougier, of thi 

 Strasbourff Observatory. They installed a spectro 

 scope on the roof of Strasbourg Cathedral, and wer 

 able to demonstrate that the phenomenon arises fron 

 normal dispersion. There is an image of the sun 

 produced in light of each wave-length, and as th'- 

 sun gets low these images are more and more wide!' 

 separated. When the sun was a few degrees abo\ 

 the horizon the observers were able to obtain a spec- 

 trum showing red only when the slit was at the lower 

 limb, and a spectrum with the red absent when it was 

 at the unper limb. When the altitude is less the blue 

 and violet are altogether absorbed, and the srreen 

 image of the sun's upper limb is the last visible at 

 sunset. Their horizon was formed by distant low 

 hills, but they point out that a sea horizon may be 

 better in that the presence of the bands of water- 

 vapour helps to separate the red light from the green. 

 The spectra obtained are reproduced in the article, 

 and seem to settle the nature of the phenomenon 

 beyond a doubt. 



