A. MATHEMATICS AND ASTRONOMY. 23 



ABSOEPTIOX OF THE SOLAR ATMOSPHERE. 



Dr. H. C.Vogel, the director of the private observatory of 

 Herr von Btilow, at Bothkamp, has made a first attempt to 

 accurately determine the relative chemical intensity of the 

 solar rays from different points of the sun's disk. His results, 

 though only preliminary, show that the sun's atmosphere ab- 

 sorbs the chemical rays more rapidly than the visual rays, 

 or, more accurately, that the relative action on silver chloride 

 of the rays that reach us from the sun's limb, as compared 

 with that of those that come from the centre of his disk, is- 

 less than their relative action on the optic nerve. The rays 

 from the sun's limb have a photograj^hic intensity of only 

 fourteen per cent, of those from the centre. The intensity 

 diminishes as we proceed toward the limb very nearly as the 

 sine of the distance from the centre. Yogel especially sug- 

 gests the importance of determining for the solar atmosphere 

 its transparency to special spectral lines, as by applying the 

 above method of study we may be able to arrive at a direct 

 determination of the solar atmospheric absorption j^recisely 

 as is done for the earth's atmosphere. Sachsc. Gesellschaft, 

 1872. ^__ 



MEASUREMENT OF AN ARC OF THE MERIDIAN. . 



In Ocean HigJitcays we find a notice of the great w^oi'k un- 

 dertaken in the way of measuring a segment of the meridian 

 in the centre of Europe, and of obtaining by these measure- 

 ments a European meter, with the co-operation of all the 

 states. A congress was lately held at Vienna with special 

 reference to this object, at which all the European states 

 were represented, witli the exception of England and France. 

 Adopting for the European measure of length the meter which 

 Vice- Admiral Mathieu and his commission had already fixed, 

 it was decided to beofin the measurement of a central Eu- 

 ropean segment of a meridian having its northern end at 

 Christiania and its southern end at Palermo. Six French 

 commissioners are to assist in the work of the congress, two 

 of them chosen by the War Department, two by the Paris 

 Observatojy, and two by the Academy of Sciences. 



A correspondent of the same journal strongly urges upon 

 the English government to unite with all the other European 



