50-1 



NA TURE 



[March 21, 1895 



diflicuU, and only one plate in twenly-Ave was, on an average, 

 sncccssfiil. It was found more easy to photograph naturally 

 mixed than artificially mixed colours. When describing his 

 methods, it was pointed out that some substance such as eosin 

 or cyanin must be added to the films to make them more 

 sensitire to red rays, and less sensitive to blue. When dealing 

 with the theory of colour photography, which was expounded 

 by Dr. Zenker as early as i86S, the speaker referred to a 

 number of difficulties which had not yet been solved. Thus, 

 io the first place, nobody has as yet demonstrated the existence 

 of the superimposed silver films in the gelatine, although they 

 should be visible under the microscopic powers now available. 

 In the next place, the presence in the gelatine film of granules 

 whose diameter is equal to several half-wave-lengths is not 

 reconcilable with the usual theory of colour photography ; so that, 

 on the whole, a comprehensive theory of the phenomena has 

 still to be established.— Mr. Archenhold gave some additional 

 details as lo the mechanical parts of the great telescope he had 

 described in the previous meeting of the Society. 



February 22. —Prof, von Hezold, President, in the chair. — 

 Prof. Lummer spoke on the necessary corrections of dioptric 

 systems, and developed theoretically the possibility of the 

 law of points holding good for certain relations between focal 

 length and aperture. Prof. Kaoul Pictet spoke on the " criiical 

 point," and explained his own views, according to which sub- 

 stances must still be in the fluid state at the criiical point. 

 This follow- from the fact that the amount of heat which must 

 be put into the substance, as reckoned from absolute zero, is 

 less than the latent heat of the liquid, and the fact that solid 

 bodies do not separate out from solution at the critical tempera- 

 ture. They must be still in solution in the fluid, since they 

 separate out in the crystalline form by a further rise of tempera- 

 ture, and go into solution again as the temperature falls to 

 the critical point. This last fact was demonstrated by the 

 speaker on a solution of iodide of potassium. 



Amsterdam. 

 Royal Academy of Sciences, January 26. — Prof, van ile 

 Sande Bakliuyzen in the chair. — Mr. Franchimont communi- 

 cated a paper on a new class of urea-derivatives, viz. the urea- 

 alcohols or ureols, one of which, ureo a.<thaDol, has been 

 prepared by the author and Mr. Van Breukeleveen. This body, 

 obtained from amino aeth.inol through Wohler's synthesis of 

 urea, forms colourless crystals, which fuse at 95°, .ind dissolve 

 readily in water, inuthyl-alcohol and ethyl-alcohol, but very 

 sparingly or not at all in most oganic solvents. It appeirs to 

 possess properties both of urea and of an alcohol. With nitric 

 acid it forms a compound, whi'"h is decomposed by so-calltd 

 real nitric acid at the ordinary temperature, with the formation 

 of carbonic acid and nitrous oxide. With benzoyl chloride it 

 yields a bcnroate, which fuses at 129", and is decomposed by 

 nitric acid in the manner described above. With acetic anhy- 

 dride and sodium .-icetate, a diacetyl derivative is obtained, 

 which fuses at 102°. — Mr. Hoogcwerff directed attention to an 

 apparatus, devised last summer by Mr. J. Boot. The object of 

 the apparatus is to easily and quickly gradu.ate retorts, pipettes, 

 and liurcttes, especially such as arc intended for techno- 

 chcmical researches. The firm of Kobb at Stiitzcrbach in 

 Thiiringen has been commissioned to make the apparatus. Mr. 

 Van dcr Waah showed that the conHition for the equilibrium 

 between coexistent phases, viz. the equality of the thcrmo 

 dynamic potential, may be deduced from ihc kinetic theory 

 byas>uming that the two phases iiitcchange an equal number of 

 particles, and may be regarded as a particular instance of the 

 more general law by which the kinirtic theory expresses the 

 density in different parts of a space, wherein the moving 

 molecules are subjected to the action of forces. — Prof. 

 Kamcrlingh Onncs communicated the resubs of investigations 

 in Ihc Leiden laboratory by : (i) Dr. L. H. .Sicrtscma on He 

 magnetic rotational dispersion of oxygen and nitrogen at a 

 ptessaie of 100 aim., giving the following relation between the 



rotation w and the wave-length K: oxygen w = C. ^ 



(, -H ?:2Z^^), nitrogen «< = C. ''^'^^ (. -f "'ll^^'^) 



and provinc »gain the superiority of Maskart's formula (see p. 

 470). (2) Dr. P. Zceman nn ihe Kerreflect in polar reflection on 

 iron and cobalt al normal iniirtcncc, lending to the conclu-inn 

 thai nfirc of the proposed lhcf>ries completely explain^ Sissingh's 

 pha«e -difference. (3) Dr. P. Zicman on ihc optic contlaote of 



NO. 1325, VOL. 51] 



magnetite, determined with regard to the relatiin betweei* ' 

 Sissingh's phase in the Kerr phenomenon and the maximum of 

 magnetisation. (4) Mr. .\. Lebret on the variation of the Hall , 

 effect in bismuth with temperature, it being found to be nearly ' 

 linear between - 38° and 239°. 



BOOKS, PAMPHLETS, and SERIALS RECEIVED 



Books— The Pygmies : A. dc guatref.igM. t^an^hlIe<l by K. Suirr (Mac- 

 millan).— The German Iniversities. iheir Character and Historical De- 

 %eUpmcnt: Prof. F. Paulsen, translated by Prof. E. D. Perry (Macraillan). 

 — .\ Treatise on Bessel Functions and their Applications to Physics: Profs. 

 fJray and Mathews(Macmillan).— Meteorologv, Wcilher, and Methods of 

 ForecasUne, &c. : T. Russell (Macmillan)— Diary of a Journey through 

 Mongolia .-ind Tibet in 1891 and 1S91 : W. W. Kockhill (Washingion).— 

 Bourne's Handy Assurance Directory, 1S95 (SchoolioE).— An F.lcmentary 

 Texl-Book of Hydrostatics; W. Briggs and G. H. Bryan (Clivc).— The 

 Telegraphist's Guide (o the New Examinations in Technical Telegraphy: 

 J. Bell {Electricity OIBce).— The .Source and Mode of Solar Energy 

 throuKhout the Universe : Dr. 1. W. Heysingcr (Lippincott). — Handbook 

 of Jamaica, 18115 (St.anford).— Im Reiche des Llchtes: H. Gruson 

 (Braunschweig, Westermann).— Honest Money: A. T. Fonda (Macmillan). 

 — Collected Papers on some Controverted (Questions of Geology : Dr. J. 

 Prestwich (Macmillan). 



Pamphlets NSW. Government Railways and Tramways— Annual 



Report of ihe Railway Commissioners for the Year ending June 30. 189^; 

 Do., Supplement to the Railway ConTnissioners' .Annual Report.— Die 

 Reisen dcs /<ii<>« und der //t-r.'/r.r in das Antarktische Meer 1893-94 : Dr. 

 J. Petersen (Hamburg. Friederichsen). 



Serials.— Science Progress, March (Scientific Press, Ltd.) —Medical 

 Magaiine. March (Strand).- Proceedings of the Physical Society of 

 London. Vol. xiii. Part 4 (Taylor and Francis).— Eoaineering Maga.^ine, 

 March (Tucker)— Memoirs and Proceedings of the Manchester Literary 

 and Philosophic.il Siciety. 4th series. Vol. 9, No. a (M.->nchesler)— Essex 

 Institute, Historical Collections. Vol. 30 (Salem, Mass.).— Journal of the 

 Franklin Institute, March (Philadelphia). — Intern.ationales Arehiv far 

 Ethnographic. Band vii. Heft 4 (Leiden, Brill).— Himmel und Erde, March 

 (Berlin).— Rendiconto delle Sessioni della R. .^ccad:mia delle Scicnze dell' 

 Istitutodi Bologna, 1892-93, 1S93-94 (Bologna). 



CONTENTS 



Modern Bacteriology. By Mrs. Percy Frankland . 481 



Chemical Analysis. By J. W. Rodger 482 



Analytical Geometry. By R. L 483 



Our Book Shelf:— 



Angot : " Les Aurores Polaires " 484 



Kennedy : " A Few Chapters in Astronomy "... 484 

 Glazebrook : " Mechanics for Colleges and Schools : I 



Statics " 484'i 



Bell : " The Telegraphist's Guide " 484'j 



Letters to the Editor: — 



Corrections of Maximum and Ex-Meridian Altitudes. 



(IVith Diagram.)— }. '^hiX.t 48S 



Argon and the Periodic .System. ( Ifi/h Diagram.) 



—Prof. J. Emerson Reynolds, F.R.S 4S6 



Variation in Caliha /a/mins.—Piof. T. D. A. 



Cockerell 487 



Dr. M. Foster on the Teaching of Physiology in 



Schools 487 



Notes 488 



Out Astronomical Column : — 



Parti.il Kclipseof the Sun, March 26 49J 



Distribution of Minor Planets 493 



Solar Phenomena in 1893 493 



The Royal Observatory, Edinburgh 493| 



Physical Work of Hermann von Helmholtr. II. | 



By Prof. A. W. Riicker, F.R.S 493( 



Electrification of Air and other Gases. {///«.!■ 

 IraUJ.) By Lord Kelvin, P.R.S., Magnus Mac- 

 lean, and Alexander Gait . . • 49! 



University and Educational Intelligence 49' 



Scientific Serials S" 



Societies and Academies . . 5°* 



Books, Pamphlets, and Serials Received . . . ■ y>' 



