January 15, 1920] 



NATURE 



511 



to the best conditions for the commercial heat-treatment 

 of this alloy. A theory of the mechanism of harden- 

 ing during the ageing of duralumin is proposed, based 

 on the decreasing solubility with decrease of tempera- 

 ture of CuAlj in aluminium. The precipitation of 

 this compound, suppressed during quenching, pro- 

 ceeds during ageing, and takes place in a higlily dis- 

 persed form. To the presence of this highly dispersed 

 constituent is due the hardness of the aged alloy. 

 Those interested may obtain a copy of the paper 

 on application to the Bureau. 



A SHORT list of books dealing with entomology, con- 

 taining 165 titles, has just been issued bv Mr. F. 

 Edwards, 83 High Street, Marylebone, W.i. Many of 

 the books listed are much reduced in price. 



The latest scientific catalogue (New Series, No. 89) of 

 Messrs. J. Wheldon and Co., 38 Great Queen Street, 

 W.C.2, contains upwards of 1500 items relating to 

 pure and applied chemistry, astronomy, electricity, 

 mathematics, meteorology, physics, etc. In addition, 

 particulars are given of many sets and long runs of 

 scientific serials and transactions of scientific societies 

 which Messrs. Wheldon have for disposal. The price 

 of the catalogue is 2d. 



The following are among the announcements of 

 books to be published by Messrs. Macmillan and Co., 

 Ltd., between now and Easter: — "Cytology: With 

 Special Reference to the Metazoan Nucleus," Prof. 

 W. E. ."Vgar, illustrated; "The Principles of the Phase 

 Theory : Heterogeneous Equilibria between Salts and 

 jfe their .Aqueous Solutions," D. Clibbens, illustrated; 

 »» "The Theory of Determinants in the Historical Order 

 of Development," Sir Thomas Muir (vol. iii. : The 

 Period 1861 to 1880); "A Manual of the Timbers of 

 the World : Their Characteristics and Uses," A. L. 

 Howard, to which is appended an account of the 

 Artificial Seasoning of Timber by S. Fitzgerald, illus- 

 ISA trated ; " Essays on the Surgery of the Temporal 

 ^m Bone," Sir Charles A. Ballancc, with the assistance 

 ^M' of Dr. C. D. Green, 2 vols., illustrated; "Space, 

 B Time, and Deity " (Gilford Lectures at Glasgow, 

 m 1916-18), Prof. S. Alexander, 2 vols.; "Implication 

 and Linear Inference," Dr. B. Bosanquet; " MTnd- 

 Energy," Prof. H. Bergson, translated by Prof. H. 

 Wildon Carr, in collaboration with the author; "The 

 Idea of Progress : -An Inquiry into its Origin and 

 Growth," Prof. J. B. Bury; "Essays in Critical 

 Realism : A Co-operative Study of the Problem of 

 Knowledge," Profs. D. Drake, A. O. Lovejoy, J. B. 

 Pratt, A. K. Rogers, G. Santayana, R. W. Sellars, 

 and C. A. Strong; "A Critical History of Greek 

 Philosophy," W. T. Stace; "Through Deserts and 

 Oases of Central .Asia," Miss Ella Sykes and Brig- 

 Gen. Sir Percy Sykes, illustrated; "The Handbook to 

 Cyprus," H. C. Luke and D. J. Jardine, new edition ; 

 "The Ila-speaking Peoples of Northern Rhodesia," 

 Rev. E. W. Smith and the late Capt. A. M. Dale, 

 2 vols., illustrated; " .\mong the Natives of the 

 Loyalty Group," Mrs. E. Hadfield, illustrated; "Eng- 

 land," edited by F. Muirhead (The Blue Guides); and 

 " Highways and Byways in Northumbria," P. A. 

 Graham, illustrated by Hugh Thomson. The Open 

 NO. 2620 \OI,. 104J 



Court Co. (Chicago and London) will publish 

 shortly " .\ History of the Conceptions of Limits 

 and Fluxions in Great Britain from Newton to Wood- 

 house," Prof. F. Cajori. It will form No. 5 of the 

 Open Court Classics. 



OUR ASTRONOMICAL COLUMN. 



Spectroscopic Determination of Stellar Parallax. 

 — Since this method of parallax determination was 

 devised the number of stars of which the parallax 

 has been measured trigonometrically has increased 

 considerably. With the view of testing the accuracy 

 of the curves used for deducing absolute magnitude 

 from the relative strength of certain spectral lines, 

 Messrs. W. S. Adams and G. Stromberg have made an 

 exhaustive comparison between their spectroscopic 

 parallaxes, which now number some 1500, and the 

 parallaxes deduced from direct measures and proper 

 motions ; the results are given in Proc. Nat. .'\cad. 

 Sci., July, 19 19. The stars are divided into five spec- 

 tral groups, A7 to F8, F9 to G8, G9 to K3, K4 to 

 K9, and Ma to Md. The .spectroscopic method has 

 not yet been applied to types Bo to Aj, as suitable 

 spectral lines have not been found. The graphs show 

 very satisfactory accordance, the weakest point 

 being the fainter absolute magnitudes in the first 

 group, where the spectroscopic determinations of 

 distance are smaller than those measured directly. 

 The last two groups indicate very clearly the division 

 into giant and dwarf stars ; this is also faintly indi- 

 cated in the second and third groups, but not ,at all 

 in the first. 



The authors draw the satisfactory conclusion that 

 ' in this large amount of observational material 

 hardlv a single serious contradiction has been found 

 between the spectroscopic and trigonometric results." 



Minor Planets. — Dr. F. Cohn gives his annual 

 report on the orbits of recently discovered planets in 

 Astr. Nach., 5030. There are now 914 planets to 

 which permanent numbers have been assigned, besides 

 several hundreds which have been observed insuffi- 

 ciently ; approximate orbits have been computed for 

 about eighty of the latter. Two of the freshly num- 

 bered planets are of special interest — No. 898 for its 

 high eccentricity, amounting nearly to 04, and No. 911, 

 since it is a sixth member of the Trojan group, the 

 mean motions of which are the same as that of 

 Jupiter. Two others, Nos. 89^ and 914, are notable 

 for large inclinations, more than 25° in each case. 



Lunar Photography with the ioo-in. Reflector. 

 — Popular .Astronomy and Pubs. .Astr. Soc. Pacific for 

 December contain reproductions of some beautiful 

 photographs taken with the new reflector at Mount 

 Wilson by Mr. F. G. Pease. Silver prints have also 

 been presented to the Royal Astronomical Society. 

 The equivalent focus is 134 ft. ; the scale is, therefore, 

 very large, and a wonderful amount of fine detail is 

 shown. Prof. Hale notes that the instrument is to 

 be called the Hooker telescope, in memory of the 

 donor of the optical parts. It is welcome news that 

 its performance comes up to the highest expectations, 

 and that the Mount Wilson conditions of seeing prove 

 equal to standing this most severe test upon them. 

 "The (radial) motions of faint stars in the heart of 

 globular clusters and in the star-clouds of the Milky 

 Way can be measured." Nebulium has been found in 

 the variable star RAquaiii, and luminous clouds of 

 calcium vapour are found to surround the star in 

 Hind's variable nebula in Taurus. It is also possible 

 to study the spectra of the faint companions of close 

 double stars. 



