A. MATHEMATICS AND ASTRONOMY. 15 



the principal radiant point in right ascension 47 and declina- 

 tion 56, two other secondary radiant points existed, the posi- 

 tions of which were respectively right ascension 5*7, declina- 

 tion 51, and right ascension 64, declination 63. At least 

 three fourths of the 1200 stars observed by them belonged 

 to the first or principal radiant. 6 ^, LXXXI., 317. 



THE ABSORPTION OF THE SOLAR ATMOSPHERE. 



Professor S. P. Langley, of the Allegheny Observatory, as 

 a result of the photometric study of the solar surface, finds 

 that the brightness of the umbra of the solar spots is con- 

 siderably greater than that hitherto accepted. The blackest 

 umbra being, according to him, from five to ten thousand 

 times as briQ;ht as the-ll moon. The lioht of the sun is 

 absorbed by the solar atmosphere in a greater proportion 

 than is its heat. About one half of the radiant heat of the 

 sun is absorbed, or sufi:ers internal reflection by the atmos- 

 phere of the sun itself. This atmosphere is comparatively 

 thin; new matter is constantly being added to it or taken 

 away from it by the continual changes of the interior sur- 

 face. The alteration in its absorptive power would materi- 

 ally afiect the temperature of our globe, so that even the ex- 

 istence of life on our earth is evidently dependent upon the 

 constancy of the absorption of this solar envelope. If there 

 are, then, any cyclical changes in the depth of this solar at- 

 mosphere, they would be accompanied by corresponding cyc- 

 lical alterations in tlie earth's temperature. 12 A, XIL, 443. 



vogel's positions of clusters and nebula. 



Dr. H. C. Vogel, already distinguislied by his accurate ob- 

 servations of the positions of nebulae and clusters at Leipzig 

 in 1867, was engaged by Dr. Bruhns, the Director of the Leip- 

 zig Observatory, to co-operate in a work which that observa- 

 tory had undertaken, namely, the re-observation of the stars 

 down to the tenth magnitude, between the north declinations 

 of 9 50' and 15 10'. Dr. Bruhns so extended the plan pro- 

 posed by the German Astronomical Society, which was con- 

 cerned only with star-positions, as to include the determina- 

 tion of the position of all nebulae and clusters Avithin the 

 zone, and this Dr. Vogel has executed. Dr. Bruhns's plan also 

 includes re-observation of the double stars in his zone. TJiree 



