;o6 



NA TURE 



[July 26, 1900 



be obtained. It is hoped that by this arrangement the 

 difficulties which have been found to impede the prompt 

 circulation of the journals of the society, which are of 

 necessity published in a somewhat different manner from 

 a regular periodical, may be finally removed. 



An important contribution to our knowledge of the 

 liquefaction of gases is contained in a paper on the lique- 

 faction of air and its application to the manufacture of 

 oxygen and nitrogen, by M. Georges Claude in part i. of 

 the Bulletin of the French Physical Society for session 

 igo6. M. Claude adopts the principle of expansion -with 

 external work instead of expansion without external work 

 as utilised in the plant devised by Linde, Hampson, and 

 others. The result, it is contended, is to effect a surprising 

 economy, while it becomes possible to employ very much 

 smaller pressures than those hitherto considered necessary 

 and to dispense with auxiliary cooling. The liquid air, 

 obtained in this way at very small cost, can be used as a 

 commercial source of oxygen and nitrogen. The two 

 elements are separated by a process of fractional dis- 

 tillation ; in the apparatus devised for this object, M. Claude 

 displays remarkable ingenuity. The principle of " recuper- 

 ative cooling " is adopted, liquid air in one vessel being 

 caused to evaporate by means of gaseous air compressed 

 at 2 to 3 atmospheres circulating in pipes surrounded by 

 the cold liquid. The nitrogen distils off more readily than 

 the oxygen from the liquid air in the one vessel, whilst in 

 the other oxygen is liquefied before nitrogen during the 

 condensation of the air. Finally, nearly pure oxygen and 

 nearly pure nitrogen are obtained. A machine has been 

 constructed capable of supplying looo cubic metres of 

 oxygen, containing 96 per cent, to 98 per cent, of the pure 

 element, per day, with the expenditure of an amount of 

 energy equal to only i/aoth or i/joth that required in the 

 processes based on the electrolysis of water. It is contended 

 that the results obtained invalidate the assumption made 

 by Dewar and confirmed by Linde that in the liquefaction 

 of air the two component gases condense simultaneously ; 

 m reality, the more volatile nitrogen is condensed after the 

 oxygen, and the process of liquefaction is strictly the inverse 

 of vaporisation. 



The fourteenth volume of the Bulletin of the Philo- 

 sophical Society of Washington has now been completed by 

 the publication of the brochure entitled " Organisation and 

 Proceedings." This volume contains abstracts of papers 

 and other communications brought before the society during 

 the sessions 1900-1904. 



A SECOND edition of the Class List and Index of the 

 periodical publications in the Patent Office library has been 

 published, price 6d., at the Patent Office, 25 Southampton 

 Buildings, Chancery Lane. 



Mr. Edwin Anthony has issued through Messrs. George 

 Routledge and Sons, Ltd., a pamphlet, price sixpence, on 

 decimal coinage, weights, and measures, in which he dis- 

 cusses the question as to whether this country should 

 adopt them, and passes in review the various arguments 

 for and against the use of decimal coinage and weights 

 and measures. 



Messrs. Charles Griffin .ind Co., Ltd., have pub- 

 lished a fifth, revised edition of Prof. G. A. J. Cole's " Aids 

 to Practical Geology." The work has been brought up to 

 date without increasing its size, so that it will maintain 

 the leading position it has gained among manuals of 

 determinative geology. 



NO. 1917, VOL. 74] 



OUR ASTRONOMICAL COLUMN. 



Reflecting Telescopes of Short Focus; — In No. 5, 

 vol. xxiii., of the Astrophysical journal. Prof. Vogel dis- 

 cusses the relative efficiency of short-focus reflectors for 

 astrographic work. 



Prompted by the discovery of the Nova Persei nebula. 

 Prof. Vogel turned his attention to the subject of reflectors, 

 and finally obtained an excellent parabolic mirror, of 40 cm. 

 effective aperture and 93 cm. focal length, from Mr. B. 

 Schmidt, of Mittweida, Saxony. 



With this instrument numerous problems of practical 

 interest in reflector work have been investigated, and the 

 results are tabulated in the present paper. Prof. Vogel 

 also compares the efficiency of an instrument of this type 

 with that obtained from other types of photographic tele- 

 scope. For instance, he found that with an exposure of 

 thirty minutes on the Pleiades nebula he obtained a photo- 

 graph showing all the detail seen on Keeler's plates with 

 four hours' exposure using the Crossley reflector. The 

 nebula? around 7 Cassiopeia appear quite as distinctly in 

 forty minutes as on the plates taken by Dr. Roberts with 

 ninety minutes' exposure on October 25, 1895. 



The Astronomical Society of Canada. — The Trans- 

 actions, for 1905, of the Royal Astronomical Society of 

 Canada contain a number of papers of astronomical interest, 

 a few of which are mentioned below. In the presidential 

 address Mr. C. A. Chant made a summary review of the 

 progress of astronomy during 1905, referring, among other 

 things, to the spectroheliograph work which is being 

 systematically prosecuted at the Yerkes, Meudon, South 

 Kensington, and Potsdam observatories, and to the 

 important results which these researches in solar physics 

 may lead us in the study of terrestrial meteorology. Other 

 papers selected for publication deal with sun-spots and 

 magnetic storms, colour photography of the corona, stellar 

 classification, and the new problem in solar physics recently 

 enunciated by Dr. C. L. Poor. 



Magnitudes and Places of 251 Pleiades Stars. — At the 

 desire of Prof. Wolf, Herr K. Schiller has continued the 

 researches of Dr. Dugan on the photographic magnitudes 

 and mean places of the fainter stars of the Pleiades group, 

 and now publishes his results for 251 stars in No. 4102 of 

 the Astronomischc Nachrichten. The places for 1900, and 

 a formula connecting the magnitude scale of the present 

 series with that employed by Dr. Dugan, are given in the 

 paper. 



Elements and Ephemeris of Jupiter's Seventh Satel- 

 lite. — In No. 4101 of the Astrononiische Nachrichten. Dr. 

 F. E. Ross publishes the following elements of the orbit of 

 Jupiter's seventh satellite, derived from observations made 

 during the two most recent oppositions, and corrected for 

 the principal perturbations : — 



January 00 G.M.T. Elements 

 Equator. 



eferred to Earth's 



i8°g ^=o-2c8 



i=ii8° «=i''3S6 



a =291° log (7=8-8946 



!'=25'28' Period = 2597 days 



This satellite is only about 2 per cent., or 170,000 

 miles, more distant from Jupiter than the sixth, but, on 

 account of their large eccentricities, they do not approach 

 within two million miles of each other. The inclination 

 of their orbits to each other is 28° i'. 



In addition to the foregoing elements, Dr. Ross also 

 publishes an ephemeris, corrected for perturbations and 

 giving the position angle and distance of the seventh 

 satellite, for every fifth day between August 15, 1906, and 

 April 27, 1907. 



Observations of Minor Planets and Comets. — ^The re- 

 sults of a large number of observations of minor planets, 

 comets, and comparison stars, made by Dr. J. Palisa with 

 a wire micrometer attached to the 27-inch refractor of the 

 Vienna Observatory, are given in Nos. 4099 and 4100 of 

 the Astronomischc Nachrichten, by Prof. E. Weiss. The 

 list of objects includes comets 1904 i and ii, and 1905 ii. 

 iii, v and c, and 296 comparison stars. 



