September S, 1910] 



NATURE 



M 



of electromotive force, from which it is concluded that 

 these two crystalline forms are not really allotropic 

 modifications. 



Till-; July issue of the Journal of the Association of 

 Teachers in Technical Institutions has reached us. Its 

 leading contents include the address of the president of 

 the association, Mr. J. Wilson, in Birmingham last June, 

 and an address delivered by Dr. Robert Pohl to the west 

 Yorkshire branch of the associatio.i last April. Both 

 these discourses have already been dealt with in these 

 columns. 



The Cambridge University Press gives notice that it has 

 taken over the copyright and control of the " Encyclo- 

 paedia Britannica," and that it will publish the new and 

 complete edition (the eleventh) about the end of the present 

 year. The work entirely supersedes all previous editions, 

 and brings its survey down to the summer of 1910. The 

 whole of the twenty-eight volumes will be issued at one 

 time, in two forms, an ordinary paper impression and one 

 on India paper. To many readers the thin paper edition 

 will come as a great boon. 



The Geologists' Association announces that its jubilee 

 volume, " Geology in the Field," is now completed, and 

 that an index to it is in preparation, and will be issued 

 short Iv. 



OUR ASTRONOMICAL COLUMN. 



Rediscovery of D'Arrest's Comet (1910c). — A tele- 

 gram from the Kiel Cenlralstelle announces the rediscovery 

 of D'.Xrrest's comet, by M. Gonnessiat, on August 2b. 

 The comet is of the fourteenth magnitude, and its position 

 at oh. 32-6m. (.Algiers .M.T.) on the day of discovery was 

 R..\. = ibh. 48m. 25.3s., dec. = 9° 42' 50" south; this posi- 

 tion lies in Ophiuchus about 5° E. of f Ophiuchi. 



This comet was discovered by D '.Arrest in 1851, and has 

 a period of about 6-5 years. In 1903 it escaped observa- 

 tion, but was observed, after passing perihelion on May 21, 

 in the summer of 1897. 



An ephemeris for the comet is published in No. 4437 

 of the Astronomische Nachrichten (p. 344). The observa- 

 tions indicate that corrections of — im. 17s., -fj-i', should 

 be applied to M. Leveau's ephemeris {Bulletin astro- 

 nomique, vol. .\xvii., p. 81), and the following places 

 result : — 



Ephemeris oh. M.T. Paris. 



Septtmber 9 ... 17 2S S ... -16 5J'4 



M ... 17 354 •- -17 53< 



,, 13 ... 17 42'3 ... - 18 520 



15 ... 17 49'4 ■■. -19 49-2 



Owing to the low declination and the fact that the 



magnitude is only 14, observations in these latitudes are 

 not very promising. 



The Recent Occult.\tiox of rj (iEMixoRUM uv Venus. 

 — Observations of the occupation of tj Geminorum by 

 \'enus on July 26, made at several observatories, are re- 

 reported in No. 4435 of the .Astrononiische Nachrichten. 

 M-M. Baldet, Quinisset, and .Antoniadi found, at Juvisy, 

 that the times of immersion and emersion were 

 i^h. 2m. 9s. ±2S. and ijh. 5m. 39s.io.5s. (M.T. Paris) 

 respectively, the duration of the occultation being 

 3m. 30s. + 2-55. A notable feature of the emersion under 

 good conditions was the suddenness with which it took 

 place ; within ij or 2 seconds from the first suggestion 

 of reappearance, the star regained its normal brightness. 

 .Apparently the rays were not deviated more than 03", 

 and there was no change in the colour of the star. From 

 the fact that the augmentation of the star's light extended 

 over lA or 2 seconds, the observers deduce that the height 

 of the planet's atmospheri-, producing the absorption, is 

 about 80 to no km. 



NO. 2132, VOL. 84] 



Se.arcu-ephemerides for Comets 1889 V. (Brooks) and 

 1890 VII. (Spitaler). — A set of elements and a search- 

 ephemeris for Brooks's comet, 1889 V., are published in 

 No. 4437 of the Astronomische Nachrichten by Dr. 

 Bauschinger. The probable time of perihelion passage is 

 191 1 January 8, and the ephemeris covers the period 

 .\ugust 4, 1910, to February 20, 191 1. This comet is of 

 special interest owing to its having thrown off four frag- 

 ments, one of which became brighter than the parent 

 body, in 18S9. Seen in 1903,' it was single and of the 

 fourteenth magnitude, so that its detection at the coming 

 approach is doubtful. .According to the ephemeris, the 

 comet was at its nearest to the earth at the beginning of 

 .August, and its present position (September 9) is in 

 Sagittarius at o=i9h. 37.4m., 5=— 29° 55-2' south. 



The rediscovery of Spitaler 's comet is still more 

 doubtful. Discovered in 1890, its period was found to be 

 about 65 years, but it was not seen in 1897 or 1903. How- 

 ever, Herr F. Hopfner has calculated elements for the 

 present approach, and publishes them, with nine four-day 

 search ephemerides, in No. 4437 of the Astronomisclte 

 Nachrichten. The different ephemerides are calculated for 

 different dates of perihelion passage covering the period 

 September 12 to November 15 in eight-day intervals. 



The Sl-n-spots of 1909. — A statistical summary of sun- 

 spots, as observed at the Royal Observatory of Capodi- 

 monte during 1909, is published by Dr. E. Guerrieri in 

 No. 6, vol. iv., of the Kivista di Astnmomia (Turin). In 

 it are given numerous tables showing analyses, in different 

 forms, of the frequencies, areas and numbers of spots, 

 faculae, Src, which should prove useful to anyone discuss- 

 ing solar phenomena. The mean diurnal frequency of 

 spot groups for the year was 3-6, 17 less than that for 

 1908 ; the mean diurnal number of spots was the same, 

 30-5 in each year. 



Water Vapour on Mars. — The conditions obtaining on 

 Mount Whitney during the Lick Observatory expedition 

 researches in .September, 1909, are discussed by Prof. 

 Campbell in No. 3, vol. iv., of the Journal of the Royal 

 .Astronomical Society of Canada (p. 212). Prof. Campbell 

 combats the idea that they were unfavourable, and says 

 that on September i and 2, when the photographs were 

 taken, the nights were as perfect for the purpose as could 

 be wished. He also points out that with a nearly 

 evanescent a band, the more water vapour one attributes 

 to the terrestrial atmosphere, the less remains attributable 

 to that of Mars, 



Measures of Double Stars. — Dr. Lau's tenth list of 

 double-star measures appears in No. 4436 of the .45(ro- 

 nomische Nachrichten. It contains the places, recent 

 measures, and the colours of 1222 and 6 02 stars, and 

 in some cases the formula giving the nature of the varia- 

 tion in distance and position-angle. It is not without 

 significance, perhaps, in the discussion of the colours of 

 double stars, that, in the majority of cases, where both 

 stars have the same colour the colour is given as 

 " white " ; where they differ, the colours are most often 

 complementary. 



The Permanent International Committee for the 

 "Carte du Ciel." — We have now received the volume 

 giving an account of the meeting of the permanent com- 

 mittee for the execution of the Carte photographiqite du 

 Ciel, which took place in Paris in .April, 1909. The 

 volume gives a list of those who attended, and a detailed 

 account of the discussions and resolutions ; but as the 

 meeting was reported at length in our issue of June 10, 

 1909, there is no need to refer further to its proceedings. 



Meteors and Bolides. — No. i, vol. iv., of Palaestra, a 

 monthly journal issued at .Asti, Italy, contains an interest- 

 ing paper by Prof. Guido Cora on meteors and bolides. 

 The paper was suggested by the appearance of a remark- 

 ablv fine "bolide at Casalbordino (.Abruzzi) on December 3, 

 1909, and contains a discussion of the appearance, the 

 frequencv, and the general phenomena attending the 

 appearance of meteors. 



HisTORV of Navigation. — .An interesting article on the 

 determination of position at sea, written by Prof. Marguet, 



