38 



NATURE 



[May 14, 1908 



Wilhelm Engelmann, and copies may be obtained in ttiis 

 country from Messrs. Williams and Norgate. The first 

 edition was reviewed at some length in Nature of February 

 8, igo6 (vol. Ixxiii., p. 338), and reference may be made 

 to that notice for a description of the characteristics of 

 the work. 



Messrs. Chapman and Hall, Ltd., have published a 

 second edition of Dr. F. H. Getman's " Laboratory 

 Exercises in Physical Chemistry." The first edition was 

 reviewed in the issue of Nature for July 28, 1904 (vol. 

 Ixx., p. 296). A chapter on thermostats has been inserted 

 in the new edition, and the chapters treating of electro- 

 motive force, solubility, and chemical dynamics have been 

 <?xtended. The measurement of radio-activity has been 

 dealt with briefly, and some other modifications made. 



The Physical Review for February contains an article 

 by Mr. F. L. Bishop on the heats of dilution of certain 

 aqueous solutions he has measured recently at the Massa- 

 chusetts Institute of Technology. He finds that if con- 

 centration be represented by the ordinate, and the heat 

 absorbed when a solution containing one gram-molecule 

 of a dissolved salt is diluted down to the concentration 

 in question be represented by the abscissa of a curve, the 

 curve is a straight line for the nitrates of potassium, sodium, 

 and barium, and approximates to two straight lines inter- 

 secting at a concentration of about 1.2 gram-molecules 

 per litre in the case of potassium chloride. The break in 

 this curve the author puts down to some chemical change 

 taking place in the solution. 



We have received from the Charles Urban Trading 

 Company, Ltd., 89-91 Wardour Street, London, W., a 

 copy of their latest catalogue, entitled " LTrbanora, the 

 World's Educator." The list, which runs to 252 pages, 

 deals with scientific and educational subjects treated in 

 such a way as to be suitable for exhibition by the bioscope 

 and microkinematograph. Films are available which 

 depict various forms of animal life, bacteriological and 

 other microscopic forms, and typical natural phenomena. 

 The catalogue provides detailed information as to the sub- 

 jects of science which can now be illustrated in such a 

 way as to bring vividly before students essential facts. 

 The actual steps in the life-histories of lowly organisms, 

 the sequence of events in the study of the habits of plants 

 and animals in their natural surroundings, and the repro- 

 duction of the details in typical operations to assist the 

 teaching of operative surgery may be mentioned as 

 examples of the way in which the kinematograph is now 

 being utilised for educational purposes. 



OUR ASTRONOMICAL COLUMN. 



The Dj (Heltum) Absorption Line in the Normal 

 Solar Spectrum. — An important statement by Mr. J. 

 Evershed, concerning the presence of the dark helium, 

 D3, line in the solar spectra photographed by Mr. 

 Nagaraja, appears in No. 396 (p. 212, May) of the 

 Observatory. Readers of these columns will remember 

 that various observers have criticised copies of Mr. 

 Nagaraja's photographs, and have arrived at the conclusion 

 that the dark line shown thereon is probably not the 

 absorption line (D,) of helium. But Mr. Evershed has care- 

 fully measured this dark line shown on a number of plates, 

 and the results of his measures lead him to the belief that 

 the line is really the helium absorption line. Micrometer 

 measures on the actual photograph from which the copies 

 were taken (May 4, 1907) give 5876-15 and 5876.17 as the 

 wave-lengths of the bright line at the limb and of the 

 dark line respectively, w-hilst from six determinations of 

 each of a series of photographs obtained during 1907 Mr. 



NO. 201 1, VOL. 78] 



Evershed obtains the mean values 5875.96 and 5875-97 re- 

 spectively. The coincidence is indeed very close, and the 

 mean value is in good accordance with the values obtained 

 by Prof. Rowland and Prof. Hale. Mr. Evershed suggests 

 that the prolongation of the darl-: line across the umbral 

 areas, a phenomenon which proved a difficulty with the 

 visual observers who criticised the results, may be due to 

 the unsteadiness of the image on the spectrograph slit 

 during a long exposure. 



The Light-curve of B Cephei. — Between June, igo6, 

 and September, 1907, Mr. Joel Stebbins, of the Illinois 

 University Observatory, made a large number of observa- 

 tions of 5 Cephei with a polarising photometer attached 

 to the 12-inch refractor. Seventy-four observations, each 

 consisting of ninety-si.x settings, were made, giving a total 

 of 7104 settings, and every precaution was taken to make 

 each observation perfectly independent and free from 

 systematic errors ; a sixth magnitude companion at a 

 distance of 41" was the only comparison star employed, ■ 

 but there is no evidence to show that all the variation ' 

 exhibited is not due to the well-known variable. The 

 light-curve obtained from the observations shows secondary 

 fluctuations with maxima at 4-6 and 0-4 days. A ma.ximum 

 occurred on 1906. July 3-29 ( = J.D. 2417395-29) and a 

 minimum on Julv 1-87 ( — J.D. 2417393-S7), G.M.T. ; the 

 range of magnitude Is shown to be 0-76 {Astrophysical 

 Journal, vol. xxvii., No. 3, p. 188, April). 



The Masses of a Carin.^ and o Pavonis. — In a recent 

 note in these columns (No. 2005. p. 520, ."^pril 2) we 

 directed attention to a communication from Mr. Gore to 

 the Observatory in which tha writer, basing his conclusions 

 on spectroscopic observations made at the Lick Observa- 

 tory, showed that the binaries o Carinie and a Pavonis 

 should have very small masses. From a letter now pub- 

 lished In the same journal (No. 396, p. 215, May), from 

 Mr. H. C. Plummer, it appears that Mr. Gore's deductions 

 were based on a slight misapprehension as to the data 

 given In the Lick publication, and his results are therefore 

 erroneous. Mr. Plummer 's correction shows that it is 

 quite impossible to justify the inference that the systems 

 of these two stars are necessarily of very smalF mass. 



The New Tower Telescope of the Mount Wilson 

 Solar Observatory. — No. 3, vol. xxvii., of the .Astro- 

 physical Journal (p. 204, April) contains an interesting 

 description, by Prof. Hale, of the tower telescope recently 

 erected at the Mount Wilson Observatory. We gave a 

 brief description of the instrument proposed in our issue 

 of February 28, 1907 (p. 424, No. 1948), and for fuller 

 details must refer our readers to Prof. Hale's illustrated 

 description of the actual instrument. The advantages ex- 

 pected to be obtained by this form of telescope mounting 

 have been fully realised, and only one or two minor 

 modifications, e.g. the reduction of the thickness (12 inches') 

 of the mirrors employed, will have to be made. Among 

 the illustrations reproduced In Prof. Hale's paper there is 

 an excellent photograph of a sun-spot spectrum, on the 

 scale of Rowland's map, which shows with remarkable 

 clearness the " widened lines " in the ^ region. 



Further Observations of Jupiter's Eighth Satellite. 

 — In No. 4246 of the Astronomische Naihrichten (p. 367, 

 May i) Sir W. H. M. Christie gives the positions of the 

 newly discovered eighth satellite of Jupiter. The plates 

 from which these positions were deduced were obtained on 

 March 31 and .\prll 3 with the 30-Inch reflector, and the 

 position of the satellite referred to three or four faint com- 

 parison stars. The positions of the latter were then deter- 

 mined, with reference to some thirty A.G. Catalogue stars, 

 on a plate taken with the 13-inch astrographic refractor. 



Observations of Perseids in 1907. — The results of the 

 observations of the Perseids, made by three sets of 

 observers connected with the Kasan Observatory during 

 the nights of August 11, 12, and 13, 1907, are given by 

 Herr W. Milowanov in No. 4246 of the Astronomische 

 Nachrichlcn (p. 353, May i). The paths of 201 Perseids 

 were recorded, and the general radiant was found to be 

 a = 43°-S, 5=+54°-o (19050). The real paths of some 

 forty meteors were computed, the mean heights at the 

 beginning and end of their visible traces being 127 km. 

 and 86 Icni. respectively. , 



