5§4 



NA TURE 



[October 28, 1922 



mentation as have undergone no chemical change 

 since their deposition, as well as clastic deposits. 

 Unfortunately, he has dealt with the former type 

 of syngenetic deposits (magmatic segregations) first, 

 has then passed to the study of epigenetic deposits, 

 and then, after some 280 pages out of a total of 400 

 devoted to epigenetic deposits, he reverts to the last 

 two classes of syngenetic deposits, and this method 

 of dealing with the subject caused the reviewer to 

 overlook the fact that Dr. Berg had commenced 

 by stating that these two last classes (ore beds and 

 clastic deposits) were also syngenetic. This explana- 

 tion will, we trust, suffice to remove the wrong im- 

 pression created by the comment to which Dr. Berg 

 refers. 



Messrs. W. Heffer and Sons, Ltd., are bringing 

 out " Fundamentals of Bio-Chemistry in Relation to 

 Human Physiology," by T. R. Parsons, which is 

 intended to form an introduction to the study of the 

 chemical processes at work in the body. It is ad- 

 dressed more particularly to medical students reading 

 for examinations in physiology. Another forth- 

 coming book in the same publishers' list is " The 

 Ethnology of the American Indians," by Dr. P. 

 Radin, in which particular stress is laid upon a clear 

 delineation of the civilisations of Mexico and Peru 

 and their influence on the culture of the other 

 parts of America. A useful feature of the volume 

 should be the detailed and critical bibliography it is 

 to contain. 



Our Astronomical Column. 



A New Comet. — A new comet, 1922 c, was dis- 

 covered by Dr. Baade at Bergedorf Observatory, 

 Hamburg, on October 19, and observed by Prof. 

 Stromgren at Copenhagen on October 22, S h 15-7'" 

 G.M.T:, in R.A. ig h 52™ S7'T, N. Decl. 36 57' 38". 

 He gave the magnitude as 9-0, so the comet should 

 be visible in small telescopes. Assuming uniform 

 motion, the following are the positions for the dafl:es 

 named at 8 h p.m. : 



The comet is in Cygnus, and is due south, 15 from 

 the zenith, at 5 11 30"' p.m. 



Spectroscopic Parallaxes for Type A. — The 

 spectroscopic method has hitherto been limited to 

 spectral types F G K M. A paper by Messrs. Adams 

 and Joy (Proc. Nat. Acad. Sci., July 1922) gives the 

 details of an investigation as to its extension to type 

 A. It had already been noticed that there was a 

 difference in the general sharpness of the spectral lines 

 in stars of this type, and on examining the stars the 

 distance of which is known either by trigonometrical, 

 hypothetical, or moving-cluster parallaxes, there is 

 found to be a distinct correlation between absolute 

 magnitude and sharpness of lines. Using the letters 

 s, n to denote sharp and nebulous spectra, they give 

 the following values for the absolute magnitudes of 

 different types : Ai s o-o n 1-2, A2 s o-6 n 1-5, A3 s 

 1-2 n 1-7, A4 s 1-5 n 1-9, A5 s i-8 n 2-1, A6 s 2-1 n 2-2. 

 After this point the two coalesce. They apply the 

 formulae to the Taurus group and the Praesepe, finding 

 parallaxes of o"-024 and o"-on respectively. Certain 

 stars had already been classified at Harvard as C-stars. 

 They have very sharp and narrow lines, and the en- 

 hanced lines, especially those of strontium at 4077 and 

 4215, are very intense. There is reason to think that 

 these stars, of which a Cygni is the most prominent 

 example, are super-giants, to which the preceding 

 formulae do not apply. They are very luminous and 

 very remote, but material for assigning parallaxes is 

 at present wanting. The authors note that in all 

 spectral types sharpness of lines is associated with high 

 luminosity. They explain this by the very low 

 density of the giant stars. 



A paper by Mr. Evershed in the Mon. Not. HAS. 

 for last May noted that there were many broad hazy 

 lines in the spectrum of Sirius ; he pointed out that 

 in Sir Norman Lockyer's classification, Sirius is on the 



NO. 2765, VOL. I ioj 



descending side of the temperature curve, and quotes 

 his words that in stars of this class the hydrogen lines 

 are relatively broad. Mr. Evershed is inclined to 

 explain the widening as a Doppler effect due either 

 to rapid rotation or strong convection currents. But, 

 whatever the cause, the facts are in accord with the 

 results of Adams and Joy. 



Globular Clusters in the Large Magellanic 

 Cloud. — In Harv. Coll. Observ. Bulletin, No. 775, is 

 announced the discovery that five objects formerly 

 catalogued as nebulae are definitely globular clusters. 

 Their N.G.C. numbers are 1783, 1806, 1831, 1846, 

 1978. The status of two others, Nos. 1651, 1866, is 

 doubtful. The detection of new globular clusters 

 is interesting, since it was announced a few years ago 

 that probably all objects of this class within our 

 reach had been detected. It also enables a new 

 estimate to be made of the distance of the cloud, 

 using Prof. Shapley's formulae. At present only the 

 simple formula based on apparent diameter has been 

 applied. The diameters of the above five objects 

 are i'-g, i'-6, i'-9, i'-8, i'-S. The corresponding 

 distance is 35 kiloparsecs, or 110,000 light-years. 

 This is of the same order as Hertzsprung's estimate. 

 It makes the linear diameter of the large cloud 4J 

 kiloparsecs, so that it is comparable in size with our 

 own star system, leaving the outlying galactic ex- 

 tensions out of account. 



Variability in the Light of Iris. — Prof. Wendell 

 noted in 1904 that this minor planet was variable 

 in light to the extent of 0-35 mags, in 0-259 days. 

 Mr. Campbell found the same period but a smaller 

 range in 191 7. But Miss Harwood at the Maria 

 Mitchell Observatory finds no variation in the present 

 year. The case is like that of Eros, and may arise 

 from irregular shape of the object, the amount of 

 variation depending on the direction of the line of 

 sight ; it has been suggested that a further complica- 

 tion might arise from a shift in the axis of rotation 

 in the body of the planet, if it were rotating about 

 an axis other than a principal one. The shape of 

 the asteroids might give a clue in questions of cosmo- 

 gony, hence such researches are useful. In the case 

 of Eros, when observed for parallax there is the 

 possibility of error if the centres of light and of 

 gravity are non-coincident. Mr. Hinks, indeed, found 

 some evidence of a small oscillation of this kind, but 

 the effect would probably disappear in the mean of 

 many observations. 



