376 



NA TURE 



[February 19, 1903 



of such a simple apparatus possesses many advantages over the 

 ordinary gas apparatus employed in practice. 



The epidiascope, a new optical lantern, which we have 

 examined at the London branch of Mr. Carl Zeiss, of Jena, 

 is primarily intended for the projection on the screen of 

 opaque bodies, such as insects, coins, fossils, diagrams, &c, 

 in their natural colours. It is equally serviceable for pro- 

 jection of transparent objects, e.g. lantern slides, and micro- 

 scopic preparations can likewise be shown with considerable 

 magnification. The source of light is an arc-lamp of 30 

 or 50 amperes, at the focus of a parabolic reflector; the 

 light is either thrown upon, or transmitted through, the 

 object by a system of condensers and mirrors. The images 

 are brilliant and well-defined. In its primary capacity the 

 lantern gives remarkably interesting results, the images, 

 for instance, of butterflies or coins being most realistic in 

 appearance, owing, no doubt, to the fact that the shadows 

 of the objects viewed are reproduced just as in nature. 

 Dark heat rays are trapped by a water tank, so that 

 delicate biological specimens, and even living organisms, 

 may be depicted on the screen. A notable feature of the 

 instrument is its convenience in manipulation, the change 

 from opaque to transparent bodies taking but a few 

 seconds. The object chamber is large, and objects are laidi' 

 on a horizontal table without clamping. Manuscripts and 

 pictures so large as S£ inches square can be shown, hence 

 the instrument should be useful, not only to men of science, 

 but for class lectures and educational purposes. 



We have received the Proceedings of the University of 

 Durham Philosophical Society, vol. ii. part ii. Amongst other 

 papers is an interesting communication by Prof. P. P. Bedson 

 on the gases enclosed in coal. The gases enclosed in the 

 various samples of coal or coal dust were obtained by heating 

 weighed quantities of these in tubes connected to a Sprengel 

 pump and heated usually to 100° C. by means of boiling water. 

 In addition to marsh gas, carbon dioxide, oxygen and nitrogen, 

 evidence has been obtained of the occurrence of the higher 

 hydrocarbons ethane and propane. These latter are not evolved 

 so readily at ioo° C. in vacuo as marsh gas, and a partial separ- 

 ation of the hydrocarbons can be effected on the basis of this 

 property. Another point of interest in the paper is the experi- 

 mentally established fact that coal, after removal from the mine, 

 not only gives off some of its " enclosed gases," but takes up 

 the gases of the atmosphere and the oxygen more readily than 

 the nitrogen. 



The annual report for 1901 of the Smithsonian Institu- 

 tion at Washington h.as reached us. Although many details 

 of interest are described in Prof. Langley's report, most 

 readers will turn with the greatest pleasure to the valuable 

 appendix of nearly 600 pages. This appendix is a summary 

 of the most interesting scientific work of the preceding 

 year, presented in a form which will appeal, not to men of 

 science alone, but to the intelligent general reader. It con- 

 tains fifty articles by men of science of many nationalities, 

 most of them profusely and excellently illustrated. The first 

 article gives a short sketch of the history and work of the 

 Smithsonian Institution, and this is followed by one by Mr. 

 Abbof on some recent astronomical events. Prof. Riicker's 

 presidential address to the British Association at Glasgow 

 is reprinted, as well as a number of Royal Institution lec- 

 tures. Among these are that of Prof. Poynting on recent 

 studies in gravitation, Prof. Dewar's on solid hydrogen, 

 Mr. Marconi's on wireless telegraphy and Dr. Glazebrook's 

 .hi the aims of the National Physical Laboratory. Numerous 

 other interesting contributions include that by Lord Kelvin 

 on ether and gravitational matter through infinite space, 



NO. 1738, VOL. 67] 



one by Prof. J. J. Thomson on bodies smaller than atoms, 

 and several by Prof. S. P. Langley — that which appeared 

 first in Nature, on " The Fire Walk Ceremony in Tahiti," 

 is one of them ; while another shows the comparative effici- 

 ency as flying machines of various large birds and artificial 

 aerodromes. There are also papers on the utilisation of the 

 sun's energy, the Bogoslof volcanoes of Alaska, forest 

 destruction, irrigation, pictures by prehistoric cave-dwellers 

 in France, and' one on the National Zoological Park at 

 Washington by Mr. Seton Thompson. Several beautiful 

 coloured plates add to the attractiveness of the volume. 



The additions to the Zoological Society's Gardens during 

 the past week include two Coquerel's Mouse Lemurs (Chiro- 

 galens coquereli) from Madagascar, a Mohr Gazelle 

 (Gazella mohr) from North Africa, two Gould's Monitors 

 (Varanus gouldi), six Bearded Lizards (Ampliibolurus bar- 

 batus) from Australia, a Tamandua Anteater (Tamandua 

 tctradactyla) from South America, deposited ; a Common 

 Stoat (Mustela erminea), European, purchased. 



Correction. — In line nine from the end of Mr. G. \V. 

 Butler's letter in Nature of February 12 (p. 344), omit the 

 word of. 



OUR ASTRONOMICAL COLUMN. 



Odservations OF Comet 1903 a. — M. P. Chofardet, of the 

 Besancon Observatory, records in the Comptes rendns for 

 January 26 that on January 21 the apparent diameter of this 

 comet was l'"5 and its magnitude was about 10-11 ; a small 

 eccentric condensation towards the south was also observed. 

 On January 24 the condensation was central, and a small 

 stellar nucleus was seen. 



Determinations of Stellar Radial Velocities. — 

 As a supplement to a previous note on the determinations of 

 the radial velocities of the planets made at Meudon, M. Des- 

 landres contributes to No. 4 (1903) of the Comptes rendns the 

 results of ihe determinations of the radial velocities of 

 8 Aquila?, </> Persei and i|/ Peisei, and he also describes the spec! ro- 

 graph wilh which they were determined, together with the 

 sources of error to which the determinations are subject. 



In the case of B Aquila; (a white star of Pickering's class 

 viia. ), where the hydrogen lines are broad and the metallic 

 lines fine, the magnesium line \ 44S1 was used. The results 

 show a considerable variation in the velocity, and a mean 

 period of about seventeen days with a shorter period of three 

 days superimposed ; the star is a spectroscopic binary. 



The star <p Persei has bright hydrogen lines which show- 

 central reversals, and the fine dark reversals have been used in 

 determining the velocity, which is variable. 



In i|/ Persei, the hydrogen lines are bright and superimposed 

 on very broad dark lines, and each shows several daik reversals 

 some distance apart, exactly similar in appearance to those 

 seen in Nova Persei and other temporary stais. 



For the comparison spectrum in each case, a spark from poles 

 containing iron and titanium was used. 



The Colour of the Eclipsed Moon. — In a description 

 of the phenomena observed during the lunar eclipse of October 

 16, 1902 (Aslronomische Nachrichten, No. 3S45), Prof. E. E. 

 Barnard comments on the various colours assumed by the 

 eclipsed moon at different eclipses. He says that the appear- 

 ance of the lunar surface during the last eclipse was by far the 

 darkest he has yet obseived, being of a dull coppery n d colour, 

 whilst that of June II, 1SS1, was a beautiful blight cherry red, 

 and suggests that this variation is probably due to the differences 

 existing in the terrestrial atmospheric conditions during the 

 various eclipses. 



Prof. Barnard further remarks that the dark coloration is 

 not evenly distributed during an eclipse, for in the present case 

 he observed a dark smear running Irom east to west across the 

 eclipsed moon, and he suggests that this phenomenon was 

 probably due to st me local disturbance in our atmosphere at 

 the time of the eclipse. 



