A. MATHEMATICS AND ASTRONOMY. 13 



points. The whole had a round form, whose apparent diam- 

 eter was 55 minutes of arc, or three times the diameter that 

 the earth would appear to have if placed at the same dis- 

 tance. 1 3 B, III., 134. 



THE SOLAR ATMOSPHERE. 



Zollner has published in detail his defense of his views as 

 to the nature of the solar spots, basing his reasoning prin- 

 cipally upon laws announced by Kirch off in his investiga- 

 tions of the solar spectrum. He first shows that if the low- 

 est strata of the solar atmosphere radiate as intensely as 

 they absorb, clouds in that atmosphere will be scarcely dis- 

 tinguishable, so far as any difference of brightness is con- 

 cerned between them and the neighboring atmosphere ; and, 

 secondlv, he states that it is not sufficient to assume the ex- 

 istence of clouds, but that some reasonable cause must be 

 assigned for their continued existence for weeks and months. 

 In his exhaustive analysis he shows that local cooling can 

 not be explained by conduction of heat, and that, therefore, 

 up-rushing or down-rushing currents of cooling gas can not 

 be produced by this cause. The influence of radiation being 

 thus the only resource left, he draws analogy between the 

 solar spots and the formation of dew in the earth, and seek- 

 ing those circumstances under which the radiation from the 

 surface of a body is localized for the longest time, he finds 

 that such radiation proceeds most freely when the body is 

 a solid ; hence he concludes the solar spots to be of a solid 

 nature. Poggendorff Annalen, CL., 298. 



THE DIMENSIONS OF THE SUN". 



Some of the results of the studies of Secchi having: been 

 severely criticised by Anwers, he has recently edited a work 

 by Father Rosa, which will, in part, serve as an answer to 

 these criticisms. The investigations of Rosa and Secchi are 

 based upon observations made during the past hundred years 

 at Greenwich, Dorpat, and Konigsberg, and Secchi believes 

 that they show that the body of the sun must be considered 

 as consisting of two quite independent masses, viz., a solid 

 nucleus, surrounded by an atmosphere of gas. Instead of the 

 solid nucleus, we may also understand the central portion 

 to be a mass of gas in such a state of condensation that it is 



