June 17, 1922] 



NA TURE 



79 



indigo from the plant has been tackled, as Prof. 

 Armstrong showed, with marked success. The research 

 has a practical value far beyond the indigo question, 

 since it connotes the systematic study of the physi- 

 ology of a leguminous crop, thus helping to fill a 

 lacuna in agricultural science widely recognised as 

 one calling for early attention in view of the great 

 economic importance of leguminous plants. In the 

 discussion of the paper the chairman (Sir Thomas 

 Holland), while recognising the financial difficulties of 

 the Indian Government, deplored the decision to stop 

 this promising research, and suggested that the funds 

 required from the Government for its continuance 

 would be essentially of the nature of a loan, since 

 the special export cess levied in 191 8 for assisting 

 research on indigo could be made to support the cost 

 of the investigation. 



A SMALL brochure on " Safety First " in X-ray 

 work, issued by Messrs. Watson and Sons, Kingsway, 

 shows that the recommendations of the X-Ray and 

 Radium Protection Committee have not been in vain. 

 The two Memoranda which have been issued by this 

 Committee are reproduced in extenso, and it is evident 

 that Messrs. Watson are doing their best to induce 

 their clients to accept the protective measures pre- 



scribed. This is a welcome step in the right direc- 

 tion, for if radiological work throughout the country 

 is to be free of risk to those engaged in it, it will be 

 brought about only by those in charge of the installa- 

 tions insisting upon guarantees of safety. These 

 guarantees can be provided at a small percentage 

 cost of such installations, and we look confidently to 

 the time when the National Physical Laboratory 

 Certificate of Safety will become a sine qua non for 

 practical work of this character. 



Sir William Tilden and Prof. J. C. PhiUp are 

 editing for Messrs. George Routledge and Sons, Ltd., 

 a new series of volumes dealing with chemistry. 

 Those for which arrangements have so far been made 

 are : — " The Metastability of Matter," Prof. E. Cohen ; 

 " Oxidation and Reduction in Organic Chemistry," 

 Dr. O. L. Brady ; " Physical Aspects of Organic 

 Chemistry," Prof. T. M. Lowry ; " Atomic and Mole- 

 cular Structure in Relation to Properties," Dr. I. 

 Langmuir ; " The Energy Factor in Chemical Change," 

 Prof. J. R. Partington ; " Space Formulae in Carbon 

 Compounds," Prof. J. F. Thorpe and Dr. C. K. Ingold ; 

 " Adsorption," Prof. J. W. M'Bain ; and " The Theory 

 of Quantitative Analysis and its Practical Applica- 

 tion," Prof. H. Bassett. 



Our Astronomical Column. 



A Very IMassive Star. — A paper by Prof. Plaskett 

 on a spectroscopic binary of very high mass was 

 read by Prof. Newall at the meeting of the Royal 

 Astronomical Society on June 9. The star is of the 

 sixth magnitude, and shows two spectra with consider- 

 able difference of brightness, but both measurable. It 

 is difficult to imagine any explanation of the double 

 spectrum other than duplicity of the star, as the 

 spectral type indicates a fair amount of condensation, 

 and the distance between the stars is of the order of 

 half an astronomical unit. As there is no evidence 

 of light- variation, it is presumed that eclipses do not 

 occur ; it is therefore estimated that we see the 

 orbit open to the extent of some 15°. The minimum 

 \alues of the masses are given as about 70 times that 

 of the sun for each component, the combined mass 

 being about four times as great as that of any previ- 

 ously determined. 



The Rotation Period of Mars. — Mars is the only 

 planet of which the rotation period is exactly known. 

 The periods of Jupiter and Saturn are often con- 

 fidently stated to the fraction of a second, but it 

 must be remembered that these values represent 

 merely the rates of drifting and changeable spots in 

 the vaporous envelopes of the two planets. We 

 cannot perceive anything of the material features 

 forming the real surface scenery of either Jupiter or 

 Saturn, for they appear to be continuously veiled. 



Mars, however, displays its actual surface markings 

 to our view. We detect objects on its disc which 

 are similar in shape and position to those which were 

 discovered and delineated by Hooke, Cassini, and 

 Huygens in the last half of the seventeenth century. 

 There can be no doubt that the markings seen to- 

 day are identical with those traced by the old 

 observers about two and a half centuries ago. 



The rotation period of Mars, according to the best 

 determinations, is 24 hours 37 minutes 22-6 seconds, 

 but there is a suspicion that this is too long, to the 

 extent of about one-twentieth of a second. 



NO, 2746, VOL. 109] 



Radial Motions of Spirals and Clusters. — 

 C. Wirtz contributes an article on this subject to 

 Astronomische Nachrichten, 5153. He quotes figures 

 for 29 spirals of which only four show approach, 

 and deduces a systematic recession of 840 km. /sec, 

 finding for the sun's velocity 712 km. towards R.A. 

 54°, N. Decl. 83° ; galactic Long. 95°, N. Lat. 23°. 

 Omitting two doubtful figures the velocity, longitude, 

 and latitude become 693 km., 90° and 29°, a shift of 7° 

 from the first result. It appears that the nebulae 

 in lower galactic latitudes tend to approach, those 

 in high latitudes to recede, while the brighter ones 

 (that is, either the nearer or the more massive ones) 

 tend to approach and the fainter ones to recede. 



The radial motions of ten globular clusters indicate 

 a systematic approach of 55 km./sec, and give a solar 

 velocity of 348 km. towards R.A. 11°, N. Decl. 77°, 

 galactic Long. 90°, N. Lat. 15° ; or, omitting the 

 systematic motion of approach, the velocity, longitude, 

 and latitude become 373 km., 79° and 19°, only 12° 

 from the first point. The number of clusters is too 

 small for trustworthy analysis, but there is some 

 evidence of greater velocity in low galactic latitudes, 

 and of increasing velocity with increasing distances 

 (using Shapley's parallaxes). There is an interesting 

 resemblance between the apices derived from spirals 

 and clusters, but the great difference in velocities 

 leaves it doubtful whether it has any significance. 



The author points out that trustworthy proper 

 motions of the above spirals would enable a good 

 estimate of their distances to be derived ; a pre- 

 liminary analysis of the few proper motions available 

 {Astronomische Nachrichten, vol. 206, p. 114, 191 8) 

 gave for the solar apex R.A. 110°, N. Decl. 34°, 

 annual motion 0-027". This point is 52° distant from 

 the first point found from radial motions. This 

 discordance is not too discouraging considering the 

 meagreness of the material, and the large discordances 

 that are found for the apex relatively to the stars 

 belonging to the galactic system. 



