498 



NA TURE 



[October 21, 1909 



H = 



to one-Half the diameter of the ball. The hardness number 

 then becomes the mean pressure per unit area when the 

 diameter of the impression is one-half the diameter of 

 the ball. In practice it is convenient to employ a known 

 load, and measure the diameter of the impression obtained. 

 The hardness number is then calculated from the formula 



ir(2rf)" ' 



where P is the load in kilograms, D is the diameter of the 

 ball, d is the diameter of the impression, and n is a 

 coefficient determined by making two impressions with the 

 same ball and different loads, and applying the formula 

 _loeP, -Ing P 

 logrfi-iogrf' 



A REVISED impression of Sir Robert S. Ball's little 

 work " Time and Tide " has just been issued by the 

 Society for Promoting Christian Knowledge. 



A CHEAP edition of " Extinct Animals," by Sir E. Ray 

 Lankester, K.C.B., F.R.S., has been published by Messrs. 

 Constable and Co., Ltd. The original edition of the work 

 was reviewed in N.ature of November 2, 1905 (vol. Ixxiii., 

 No. 1879). 



We are in receipt of a new catalogue of books and 

 papers (more than 1400 in number) dealing with ornith- 

 ology which Messrs. John VVheldon and Co., of Great 

 Queen Street, W.C., have for disposal. 



The October classified list of second-hand scientific 

 instruments offered for sale or hire by Mr. Charles Baker, 

 of High Holborn, has reached us. The catalogue, which 

 contains upwards of 1300 items, will be sent free of charge 

 upon request. 



MM. \. Hermann et Fils, of Paris, have published a 

 translation into French, by Dr. Paul Lemoine, of Prof. 

 James Geikie's " Structural and Field Geology," which 

 was reviewed in these columns on July 6, 1905 (vol. Ixxii., 

 1). 223). M. Michel-L^vy has contributed a preface. The 

 price of tjie French work is 15 francs. 



A new edition (the eighth) of " Quantitative Chemical 

 Analysis," by Clowes and Coleman, has been published 

 by Messrs. J. and A. Churchill at \as. 6d. net. The work 

 has been revised and enlarged, but the size of the page 

 havfing been increased the thickness of the volume re- 

 mains as before. 



Messrs. Constable and Co., Ltd., have sent us a 

 cheap edition of " Time and Clocks," by H. H. Cunyng- 

 hame, C.B. A review of the first edition appeared in 

 the issue of Nature for January 17, 1907 (vol. Ixxv., 

 No. 1942). 



■ OUR ASTRONOMICAL COLUMN. 



Mars.-;— The advisability of watching Mars closely, at 

 this period of favourable opposition, and seasonal changes 

 on the planet itself, is illusttated by a brief message com- 

 municated to the Asironomischc Nachrichten (No. 4362, 

 p. 303, October 9) by ■ M. Jarry Desloges. Whilst the 

 planet was being observed at gh. 15m. on October 6, a 

 projection was -seen on the terminator in the neighbour- 

 hood of Electris. This projection lasted for ten minutes 

 only, whilst a similar one observed by Messrs. Lowell and 

 Slipher, on May 25, 1903, endured for only thirty-one 

 minutes ; the latter was ascribed to a cloud of dust some 

 300 miles in length. 



In No. 4361 of the same journal M. Jonckheere 

 announces the discovery, on September 28, of a canal 

 which is probably a new one, and extends from Cyclopum 

 Lucus to Hephasstus ; the same observer records a further 

 observation of the new land " Stella " on October 7. 



A large number of observations of different features are 



NO. 2086, VOL. 81] 



recorded and illustrated by M.M. Qu6nisset and Antoniadi 

 in the October number of the Bulletin de la Societe 

 astronoinique de France. Numerous canals were observed, 

 the Soils Lacus was seen to be divided, and important 

 changes in the colour and visibility of various regions were 

 c.'osely followed. M. Antoniadi is confirmed in his opinion 

 that these changes are caused by the passage of Martian 

 clouds across the various features, and, from the yellowish 

 tinge which colours the indistinct areas, he confirms the 

 opinion expressed by Prof. W. H. Pickering in 1905, that 

 these Martian clouds are probabl)' yellow. 



Solar Observations : a Novel Spectroscope. — In order 

 to continue his solar observations, Mr. W. M. Mitchell 

 found it necessary, at the Haverford College Observatory, 

 to devise a large spectroscope which might be used in 

 conjunction with a small equatorial. The telescope at 

 Haverford is of 10 inches aperture and 12 feet 6 inches 

 focal length, and cannot, therefore, carry a , large, and 

 consequently heavy, spectroscope of the ordinary type. 

 .\cting upon a suggestion from Prof. Hale, he has erected 

 a spectroscope which is mounted upon, and is parallel to,; 

 the telescope tube, and finds that the device answers, 

 very satisfactorily. The beam from the lo-inch objective 

 is reflected on to the slit of the spectroscope by a 90° 

 prism, and, passing through the slit, is again reflected 

 by a similar prism on to a 3-inch coUimating lens of 

 39 inches focal length. Thence it passes to a grating and 

 back through the 3-inch lens to the eye-piece, the grating 

 and lens being slightly tilted. A negative lens placed 

 between the lo-inch objective and the first reflecting prism 

 gives a larger image, which in Mr. Milchell's observations 

 was of 32 inches diameter. The spectroscope tube is 

 constructed of wood, saturated with hot paraffin before 

 assembling to obviate subsequent warping. 



With this instrument Mr. Mitchell gets a resolving 

 power of 70,000 in the third-order spectrum, and was ablel 

 to observe visually the Zeeman effect in sun-spot lines. 

 An interesting observation on May 11 showed that at one 

 end of a spot " bridge " certain lines were doubled, whilst 

 at the other end, the farthest from the centre of the spot 

 group, the same lines were triple ; other lines were double 

 in both regions. .\ list of lines, recorded as bright in a 

 chromospheric outburst on January 21 7h. to gh. G.M.T., 

 is also given, and Mr. Mitchell urges the necessity for 

 more laboratory work in connection with chromospheric 

 radiations. 



We regret to learn that astronomical observations are 

 to be suspended at the Haverford Observatory, and, con- 

 sequently, Mr. Mitchell's observations cannot be continued. 



The .Aurora of September 23. — In No. 4361 of the 

 Astronoinischc Nachrichten (p. 287, October 7) Herr 

 Torvald Kbhl records that a fine display of the aurora 

 was observed at Odder, Denmark, on September 21, and 

 adds that a similar display was observed in Stockholm on 

 September 25. 



September Meteors. — The appearance of a magnificent 

 fireball on September 27d. 7h. 20m. is recorded by Herr 

 Kohl, who observed it at the Carina Observatory, Odder, 

 in No. 4361 of the .istronomische Nachrichten. Herr 

 Kohl finds from his meteor-catalogue that he observed 

 similar apparitions on September 27-28 in ten different 

 years between 1870 and 1909. He also has records ofj 

 meteors on December 12-13 f""" eleven years between' 

 1S75 and 190S. 



Hydrogen Layers in the S0L.4R ATMosriiERE. — In the 

 Comptes rendus for September 20 (No. 12, p. 521) MM., 

 Deslandres and d'.Azambuja review the work which hag» 

 been done in separating the various layers of calcium' 

 vapour in the sun's atmosphere, and describe the results 

 of similar researches on the hydrogen and iron vapours 

 recently carried out at Meudon. 



The image, obtained by using the centre of the Ha line, 

 differs from the Mount Wilson photographs, and shows 

 the details, exactly, of the K^ calcium images, the same 

 dark filaments and "the same bright areas. The authors 

 suggest that the Mount Wilson images were produced by 

 mixtures of the different parts of the Ha line, and that 

 the sinuosities in the edges of the various sections might 

 produce this effect. In the dispersion used at Meudon 

 I mm. = 6 A. 



