yan. 26, 1888] 



NATURE 



311 



of weight, by M. G. Defforges. The apparatus constructed by 

 MM. Brunner Brothers on the principles here laid down has 

 already been applied with satisfactory results to the measurement 

 of absolute gravity at Paris, Lyons, Dunkirk, Algiers, Laghwat, 

 and Nice.— On elliptical polarization by transmission through 

 metals, by M. Georges Meslin. The author heie studies the 

 modifications which polarized light undergoes in its passage 

 through metal plates thin enough to be transparent. As in 

 metallic reflection, the two polarized vibrations in the plane of 

 incidence and in the perpendicular plane undergo in relation to 

 each other a certain retardation, while the rectilinear polarization 

 becomes elliptical.— On the application of the phenomenon of 

 transversal magnetization to the study of the coefficient of 

 magnetization of iron, by M. Paul Janet. This question is here 

 studied by means of a method of mutual induction which presents 

 \ several advantages over other processes-, and which may be easily 

 \ applied to the study of the influence of the medium in the 

 phenomena of induction. — On the decreasing solubility of the 

 sulphates, by M, A. Etard. The author has already shown 

 that between 103° and 150° C. the sulphate of copper becomes 

 less soluble according as the temperature increases. He now 

 finds that most of these salts undergo a certain disturbance at 

 some point of the line of complete solubility, beyond which point 

 the solubility increases less rapidly and even remains almost 

 stationary. Details are given for the sulphates of zinc, 

 manganese, and potassium. — Symmetric disposition of the 

 centres of the four chief continents, by M. Alexis de Tillo. By 

 graphic processes the author finds that the co-ordinates of the 

 orographic centres of the continents are as under : Asia (with 

 Europe) 43° N., 85° E, of Greenwich ; Africa, 4° N., 27° E, ; 

 North America, 45° N-, 102° W. ; South America, 14° S., 56^ W. 

 The geometric centre of the Old and New World lies in the 

 region of the Azores and Canaries, and the meridian of Delisle 

 (20" W. of Paris) may in some respects be regarded as the 

 natural meridian of the globe. 



Berlin. 

 Physical Society, December 23, 1887.— Prof, du Bois 

 Reymond, President, in the chair.— Prof. Schwalbe gave a 

 detailed account of the research which Dr. Aubel and Prof, 

 Spring have carried out on the rapidity of the interaction between 

 acids and zinc which is mixed with lead. — Prof. Vogel made a 

 statement of his observations of the solar eclipse of August 19. 

 As is well known, the observations. during the whole°of the 

 lengthy period of totality were unproductive of results at all 

 stations except those in Siberia — which were not much utilized 

 by observers — owing to unfavourable weather. The speaker 

 appears to have been among the most fortunate at Jurjewetz, 

 where he was stationed in company with the Belgian astronomer 

 Niesten, and the Russian astronomers Kortazzi and Belopolski, 

 for at this place the sun was momentarily visible through the 

 clouds. As a matter of fact, several photographs were success- 

 fully obtained, on which, as shown by a specimen exhibited, 

 a corona and several protuberances were visible. These photo- 

 graphs, however, scarcely suffice as a basis for any scientific 

 research. Prof. Vogel had also received a photograph of the 

 eclipse taken in clear weather by an amateur in the Ural 

 Mountains ; it showed a complete but small corona, and near it 

 is the image of a star, probably Mercury. Unfortunately no 

 details are given about this photograph. The iJhotographer 

 Karelin has secured some very interesting results at Ju^ewetz. 

 This observer, using a very sensitive apparatus, had obtained 

 some very successful photographs of the lunar eclipse, which had 

 taken place about a fortnight before the solar eclipse. The 

 plates were only exposed for 1/60 of a second, and working upon 

 this experience he obtained photographs during the solar eclipse 

 by a similar exposure of 1/60 of a second. The results were quite 

 satisfactory, and from this the important conclusion may be arrived 

 at that exposures of the above very short duration may be used 

 during future solar eclipses, Herr Karelin has further taken a 

 photographic landscape during the eclipse, and from a com- 

 parison of the time necessary to obtain this with the time 

 required by the speaker's son to obtain a similar picture during 

 full moon, the speaker concluded that the brightness during the 

 solar eclipse was fifty-six times as great as that of the full moon. 

 Prof, Vogel had intended to photograph the spectrum of the 

 corona, but was not successful in his attempt. He further 

 exhibited a photograph of the spectrum of pure oxygen contained 

 in a Geissler tube and made luminous by the sparks from a 

 battery. The photograph was then photographically enlarged. 



so that It could readily be seen by a large audience at the same 

 time, and in this form it showed the red and green line, together 

 with a long series of bands and lines extending far into 

 the ultra-violet region. Many of the lines described by Dr, 

 Schuster as single could be seen to be double in this photograph. 

 One of the chief things shown by the enlarged photograph is that 

 the oxygen-spectrum of the positive pole, and of the negative 

 pole, as well as the spark-spectrum of the oxygen itself are here 

 combined into a single spectrum. The speaker intends to apply 

 this method of magnifying the photographs to the spectra of 

 other gases, and thus make the enlarged spectra accessible for 

 teaching purposes in the form of diagrams, 



January 6, — Prof, du Bois Reymond, President, in the 

 chair.— Prof. Oettingen, of Dorpat, spoke on the explosion 

 of a mixture of hydrogen and oxygen obtained by electro- 

 lysis. As is well known, Bunsen has advanced the 

 following view, based on his experiments, on the explosion 

 of electrolytic gas : by the explosive union of the oxygen 

 and hydrogen, when the spark is passed, a temperature 

 of 3000° C. is produced, the water formed being at once dis- 

 sociated at this temperature ; the temperature of the mixture of 

 gases formed by the dissociation then falls, whereupon a new 

 union between the two takes place, and so on ; hence the ex- 

 plosion of electrolytic gas is to be regarded as made up of a 

 series of partial explosions following each other in rapid 

 succession. The speaker had intended several years ago to subject 

 Bunsen's theory to an experimental investigation, and hoped to 

 be able to analyze the phenomenon by the use of a rapidly 

 revolving mirror. As a matter of fact, when the mirror was rotated 

 at a suitable speed, the image observed was not that of a single 

 narrow strip of light, but was rather of considerable width ; it 

 was not found possible to interpret this image, notwithstanding 

 that the somewhat complicated experiments were repeated many 

 times. An endeavour was next made, with the assistance of a 

 photographer, to obtain a record of the image, which was 

 equally unsuccessful. He then underwent a cour.-e of photo- 

 graphic study ; and when he had acquired sufficient experience, 

 he last year repeated his former expeiiments, with a positive 

 result, using the new methods of sensitizing the plates for the 

 less refractive parts of the spectrum, and the most sensitive 

 possible dry plates. The speaker had further shown, by a 

 spectroscopic examination of the light emittted during the 

 explosion of electrolytic gas, that the light is due, not to the 

 combustion of the gases, but of sodium, which is doubtless 

 accounted for by the incandescence of small particles of glass 

 torn oft' by the passage of the sparks. He hence introduced, in 

 accordance with the method of Dewar and Liveing, portions of 

 finely powdered salts of various metals, such as copper, zinc, 

 lithium, and cadmium, &c., into the eudiometer in which the 

 explosion of the electrolytic gas was to be made, and now 

 obtained, not only excellent spectra of the respective metals, but 

 also quitedistinct p!:otographs of theimages inthe rotating mirror. 

 A plane mirror was used, placed at fixed distances from the 

 eudiometer and camera, which projected the images of the 

 successive events takins; place during the explosion on to the 

 flat sensitized plate. The speaker exhibited a series of the 

 photographs thus obtained : these presented the following 

 appearances, most clearly when the salt used was chloride of 

 copper. In the first place, a bright point, corresponding to the 

 place of passage of the spark, from which a short bright ray 

 passed both upwards and downwards in the tube ; then secondly, 

 at a fixed distance from this and occupying the whole length of 

 the eudiometer, a bright image intersected lengthways from end 

 to end by zigzag lines and transversely by parallel sinuous waves. 

 The speaker interpreted the above images by referring the inter- 

 secting zigzag lines to a series of waves of impulse caused by 

 successive explosions ; he considered on the other hand that the 

 sinuous waves are due to the small particles of the metal which 

 are set in motion by the impulse waves, and hopes to render this 

 explanation still more probable by a new series of experiments 

 on the explosion of carbon-disulphide. According to Prof, 

 Oettingen, the experiments of Berthelot, and Vieille, and_ of 

 Mallard and Lechatelier, have no bearing upon the explosion 

 which he has studied, occurring as it does in a few thousandths 

 of a second, but refer to the combustion which occurs subse- 

 quently to the explosion. — Dr. Kotter spoke on the problem of 

 determining the pressure exerted by the earth, discussed the 

 difficulties in the way of estimating the pressure which the earth 

 exerts upon a wall built into it, and stated the limits withir 



