702 



NATURE 



[NOVEMBKR lO, 192, 



and medallions of Dr. Liidwig Mond, Cannizzaro, 

 Liehig, Berrt'Iius. and others ; statuette of Sir James 

 Dewnr, and many iwrtraits and photographs. The 

 death of Prof. Jules Violle, an honorary member of 

 the Institution, was announced, and a resohition of 

 condolence with the family was passed. 



Thk Dr. Mann Juvenile Lectures of tiic- Koyal 

 Society of Arts for the new session will be delivered 

 respectively by I'rof. W. A. Bone and Mrs. J. W. 

 Henshaw. l^of. Bone's lectures will deal with 

 " Fire and Explosions," and be given on January 2 

 and 9. Mrs. Ilenshaw's lecture, entitled " Among 

 the Selkirk Mountains of Canada, with Ice-axe and 

 Camera," will l>e given on January 16. The lecture 

 hour in each case will be 3 o'clock. 



A TFXHNiCAL assistant is required by the Royal 

 Aircraft Establishment, South F'arnborough, Hants, 

 whose duties will be research in problems relating 

 to electric ignition. Candidates should possess an 

 honours degree in physics or electrical engineering, 

 or equivalent qualifications, and have had experience 

 of research work in electrical subjects, preferably in 

 connexion with high frequency work. Applications 

 should be addressed to the Superintendent of the 

 Royal Aircraft Establishment, quoting reference 

 A20. 



The Department of Agriculture in Kenya is 

 requiring an agricultural assistant to help the director 

 and deputy-director of agriculture in supervising 

 agricultural work, particularly native agricultural 

 serv'ices. Candidates should possess a degree or 

 diploma in agriculture, a good knowledge of tropical 

 agriculture, and have had experience in agricultural 

 practice. Written applications for the post should 



be sent to the Assistant Private Secretary (Appon 

 ments). Colonial Office, Downing Street. *- *' 

 upon forms obtainable from the same address 



Mr. B. M, Headicar, honorary secretary of the 

 Universities' Library for Central Europe, sends us 

 a list of (German chemical literature at HLs <! 

 for exchange for similar English literature put.,., 

 since 1914. Alternatively any literature of scient. 

 interest would be accepted and a quid pro quo • 

 change is not stipulated. Inquiries may be address' 

 to Mr. Headicar at the Ix)ndon School of Economici>, 

 Clare Market, I^ndon, W.C.2. The list includes 

 volumes of the Berliner Berichte, Zeilschrift f 

 angewandte Chemie, ChemiMer Zeitung, " Technis< 

 Chemisches Jahrbuch," Al>egg's " Handhuch >; 

 anorganischen Chemie," and Zeitschnff i"r ( h... 

 und Industrie der Kolloide. 



The October number of the Journal of the Koyal 

 Photographic Society is devoted to the Society's 

 Exhibition. It is copiously illustrated and contains 

 several articles which refer chiefly to pictorial matters. 

 But Dr. B. T. J. Glover, of Liverpool, writes as " 

 technician," and points out, with examples, how 

 often the gradation of the prints is falsified by under 

 exposure, over development, and manipulation, as in 

 the making of gum prints and bromoils. Indeed 

 with regard to bromoils he asks, " Can any one show 

 me a bromoil print in which they [tone values] are 

 right ? " As he also gives examples that show 

 " an exquisite quality " resulting from sound photo- 

 graphic technique, a study of his comments canii' i 

 fail to be of interest to those who favour pure photo- 

 graphy as well as to those who think that photograplu- 

 is not good enough and seek to improve it b\- \\h;tt 

 they call " control." 



Our Astronomical Column. 



A Bright Meteor. — Mr. W. F. Denning writes 

 from Bristol that on November 3, at 6'' 23'" G.M.T., 

 he observed a large meteor, equal to Venus in bright- 

 ness, shooting downwards in the southern skv from 

 295i°+6° to 308° -21°. The nucleus gave a flash 

 at the end of its flight and left a white streak. The 

 direction of the course of the object was from a 

 radiant point near fi Ursae Majoris, which supplies 

 many meteors at this time of the year and appears 

 to be a well-defined centre of recurrent radiation at 

 various periods of the year. The shower or showers 

 has or have been frequently observed in the last 

 quarter of the year and deserves more thorough 

 investigation. 



Spectroscopic and Trigonometrical Parallaxes. 

 — A. Pannekoek {Observatory, October 1923) gives 

 reasons for believing that the variation of intensity of 

 certain spectral lines is not directly a measure of the 

 star's absolute luminosity, but of the intensity of 

 gravity at its surface, which affects the ionisation of 

 its atmosphere. For the same spectral class the 

 quantity derivable from the spectrum is the ratio 

 of luminosity to mass. The mean spectroscopic 

 parallaxes of groups of stars will not be affected, but 

 those of mdividual stars will be, if their mass differs 

 from the mean mass of the class. For example, the 

 trigonometrical parallax of e Indi is 0-28', while 

 0-45' has been given as the spectroscopic value. If 

 there is no error in either value, the star's mass is 



NO. 2819, VOL. I 12] 



2-6 times the mean mass of spectral type K5. This 

 would thus appear to be a method of determining the 

 masses of the nearer stars if non-binaries, while the 

 binaries would serve to test the truth of the principle. 



W. J. Luyten contributes a paper to Proc. Nat. 

 Acad. Sci. (September 1923) in which he examines 

 the systematic errors of trigonometrical parallaxes. 

 Van Rhijn recently gave reasons for thinking them 

 to be too large from a study of the proper motions and 

 radial velocities. Luyten uses the same material as 

 Van Rhijn, but discusses it differently. He deduces 

 two graphs : one by grouping the stars by measured 

 parallaxes and forming a graph connecting mean 

 apparent magnitude with reduced parallax ; the 

 other by grouping according to apparent magnitude, 

 and again forming a g^raph. He considers that the 

 truth lies between his two graphs, and deduces that 

 the Allegheny parallaxes are not too large, as Van 

 Rhijn stated,' but if anything too small. He further 

 compares the absolute magnitudes deduced from the 

 measured parallaxes with those deduced from proi>er 

 motions. He thus obtains for the Ko giants the 

 mean absolute magnitude o-8 (two independent dis- 

 cussions gi\'e 0'6 and i"o), while the trigonometrical 

 parallaxes give 07, again suggesting that the latter 

 are if anything too small. 



It is useful to apply these tests, for the spectro- 

 scopic parallaxes would be affected by systematic 

 errors in the trigonometrical ones that were used for 

 cahbration of the spectral curves. 



