A. MATHEMATICS AND ASTRONOMY. 41 



of flames, and which Secchi calls rays, and the j^roper hydro- 

 gen protuberances. In respect to the nature of these latter, 

 Secchi thinks that they have no relation to the spots, while 

 Sporer ascribes to them an intimate connection with spot 

 formations. By connecting his own observations with those 

 of Carrington, Sporer shows that the solar spots are more 

 frequent in the southern than in the northern hemisphere, 

 that they diminish in size and number more rapidly than 

 they increase as they pass from their successive minima and 

 maxima. Sporer also confirms a singular result previously 

 arrived at by Carrington, namely, that the spots at the time 

 of the minimum approach the solar equator, but at other 

 times are more numerous in higher latitudes. 12 A, 1873, 

 391. 



ON THE DIAMETER OF THE SUN. 



The observations of Rosa on the diameter of the sun, from 

 which Secchi has concluded that this is subject to a periodic 

 variation intimately connected with the protuberances and 

 the spots, has called forth a review of his measurements 

 by Wagner, of the Poulkova Observatory, in which he not 

 only shows the Aveakness of Secchi's reasoning, but contrib- 

 utes very valuable and important information in regard to 

 the subject, in the shape of a discussion of the observations 

 made by himself with the most refined instruments of mod- 

 ern times. Wagner states as his own conclusions that the 

 precision of the image of the sun, as it appears in the tel- 

 escope, varies much more than that of the stars, which cir- 

 cumstance evidently depends upon the influence of the hot 

 rays of the sun for the worst images coincide with the 

 most transparent atmosphere, while slight cloudiness or ha- 

 ziness in general favors the production of sharp definition. 

 Wagner therefore arranges his observations in six groups, 

 varying with the steadiness of the atmosphere. He finds 

 that in general the solar diameter, as measured by him, is 

 greater as the vision becomes poorer. Arranging his obser- 

 vations according to a period of twenty-seven and a half 

 days, which is the time of the rotation of the sun, he finds no 

 trace of a change in the solar diameter. Arranging them in 

 annual groups, however, he finds an annual period, that evi- 

 dently depends upon the fact that the condition of the at- 



