29- 



NATURE 



[December 12, 1918 



equipped with almost every known type of oil-engine, 

 utilising in consequence in the case of several types 

 various means to reconcile conditions of maximum 

 propeller and engine efficiency, such a- mechanical 

 gearing and electric transmission. The powers so far 

 are relatively small, 200 h.p. per cylinder being the 

 maximum recorded. In one case the main Diesel 

 engines are of the Willans and Robinson type, with 

 six working cylinders 12 in. b) c8 in., and develop 

 320 b.h.p. at 250 revs, per minute. This ■-peed is 

 reduced by gearing to too revs, per minute at the 

 propeller. This method has a number of advantages 

 in the application of Dies,] engines to marine pro- 

 pulsion. The problem is not quite analogous to 

 mechanically geared turbines, and the question of the 

 ability of mechanical gearing to stand up to its work 

 under conditions of uneven turning moments is the 

 principal one that can be raised in connection with 

 this application of gearing. 



The latest catalogue (No. 176) of Messrs. W. HelTer 

 and Sons, Ltd., Cambridge, gives particulars of 

 upwards of 1300 works dealing with a variety of sub- 

 jects. Main of the books offered for sale are first 

 editions, and not easily obtainable. The section 

 devoted to science and mathematics is not lengthy, 

 but the catalogue is worthy of the attention of readers 

 of NATURE because of it and that headed "Books 

 for Librarians." In the former section we notice 

 long runs of Biometrika, the British Association 

 Reports, the Conchologist, the Philosophical Magazine, 

 vols. i. to xcii. of NATURE, and complete sets of the 

 Proceedings of the Physical Society of London and 

 the Proceedings of the Renal Society of Medicine. In 

 the section of " Hooks for Librarians" are to be found 

 a complete set, to 11,14, of the Journal of Physiology 

 and long series of the Journal of the British Astro- 

 nomical" Association, Memoirs of the Royal Astro- 

 nomical Society, the Journal of the Royal Geographical 

 Societv, the Geological Magazine, the Journal of the 

 Royal' Microscopical Society, and the Proceedings and 

 Transactions of the Zoological Society of London. 

 The catalogue will be sent free upon application. 



The next volume to be published in Messrs. 

 Conslable and Co.'s "Staple Trades and Industries" 

 series will be "Tea," by D. Hunter. Other 

 volumes are in preparation. Messrs. Henry Frowde 

 and Hodder and Stoughton announce "War Neuroses 

 and Shell Shock," Lt.-Col. F. W. Mott, illustrated; 

 "Orthopaedic Effects of Gunshot Wounds and their 

 Treatment," Capt. S. W. Daw; "Medical and Sur- 

 Aspects of Aviation," II. Graeme Anderson; 

 "The Anatomy of the Peripheral Nerves," Lt.-Col. 

 \. \l. Patefson; and "The Early Treatment of War 

 Wounds," Col. II. M. W. Gray. Messrs. Heinemann 

 {Medical Books), Ltd., will publish shortly "Pensions 

 and the Principles of their Evaluation," Drs. LI. J. 

 Llewellyn and A. Bassett Jones. Messrs. Longmans 

 and Co.'s new list includes "Naval Architects' Data," 

 J. Mitch. II, edited by E. I.. Attwood; vols. ii. and 

 iii. of "A System of Physical Chemistry," Prof. 

 W. C. McC. Lewis; vol. 1. of the third edition of 

 " British Birds," written and illustrated 1>\ A. Thorburn ; 

 and new edition- of "Recent Advances in Organic 

 Chemistry," Dr. A. W. Stewart, and "Dental Surgerj 

 and Pathology," J. F. Colyer. Messrs. Witherby and 

 Co. announce the publication, in serial form, of " De 

 \ ugels van Nederland," by Dr. E. D. van Oort. The 

 work will be issued in forty parts, and contain four 

 hundred coloured plates. It will be written in I lie 

 Dutch language, with the scientific names given, in 

 addition, in English, French, and German. 

 NO. 2563, VOL. I02] 



OUR ASTRONOMICAL COLUMN. 



DWARI STARS. — In the course of an article which 

 appi 1 in the November issue of Scientia, Dr. 

 A. C. D. Crommelin discusses the evidence which 

 suggests that dwarf stars are tin- innsi numerous class 

 of stars in space. Such stars, which are to be regarded 

 as small in volume rather than in mass, may comprise 

 about three-fourths of the total number of star-, but 

 onlv a few of them are known, because at a very 

 moderate distance Lhej become too faint to be included 

 in our star catalogues. As examples of dwarf stars, 

 Barnard'^ runaway star in Ophiuchus and the 

 "Proxima Centauri " of Innes are described in detail. 

 Barnard's star has a proper motion of 103" per annum 

 and a parallax of 0525", anil is unique as being the 

 only star having a proper motion which is sensibly 

 increasing as a result of diminishing distance. The 

 velocity of approach is about 100 km. per second, and 

 this would cause the annual proper motion to increase 

 bj per century, which is in satisfactory agree- 

 ment with the available observations. The spectral 

 type of the star is M<">. and its luminosity 1/2000 that 

 of the sun. From its high speed a small mass is 

 probable, and if the star be assumed to have a mass 

 one-eighth that of the sun, and a somewhat greater 

 density, the surface brightnes- would be 1/170 that 

 of the sun. 



The Sin's Rotation. — The application of the 

 spectroscopic method to the investigation of the sun's 

 rotation has led to such different results as to have 

 suggested to several observers that the rate of rotation 

 must he variable. Mr. R. E. De Lury, however, has 

 maintained for some time that the differences in the 

 results are not of solar origin, but arise from varying 

 amounts of atmospheric haze, which superposes an 

 unmodified solar spectrum on the' displaced spectra at 

 the solar limbs. He returns to the subject in a further 

 discussion of the observations made at Ottawa 

 (Astrophys. Journ., vol. xlviii., p. 195), ami concludes 

 that there is at present no sound reason for believing 

 that the rate of the sun's rotation is variable. In 

 general, high values of the rotation were obtained 

 during brighter conditions, and low values during 

 hazier conditions. Thus the low values of rota- 

 tion obtained by Evershed and Royds in 1012-13 

 may well have been due to the haziness produced by 

 the Katmai eruption in June, iqt2, which also 

 caused a great reduction in the measured values of 

 the solar radiation. 



The Canadian 72-iN. Reflecting Telescope.— The 

 Fleeting telescope which has been erected by 

 the Canadian Government on Observatory Hill, near 

 Victoria, B.C., has been finally completed by the 

 installation of the optical parts, and is now in regular 

 successful operation. Further interesting details of 

 the instrument are given by the director, Dr. J- S. 

 Plaskett, in a communication to the Journal of the 

 Royal Astronomical Society of Canada (vol. xii.. 



p. 399). The disc of glass, 73! in. in diameter, about 

 [3 in. thick, with a central hole 6 in. in diameter, 

 and weighing nearly 5000 lb., was successfully cast 

 and annealed at the works of the St. Gobain Class 

 Co., in Charleroi, Belgium. It was completed in July, 

 1914, and was ' fortunately shipped from Antwerp 

 about a week before the declaration of war. The 

 grinding and figuring of the mirror to a focal length 

 of so ft. was carried out by the Brashear Co.. at Pitts- 

 burgh. The maximum deviation of the final curve 

 from theoretical perfection amounted only to about 

 one-eighth of a wave-length, or double the accuracy 

 required bv the specifications. The secondary mirror 



