280 SPECIAL RESULTS IN THE URANOLOGICAL 



were indeed, and even still are, very imperfect,) may render 

 it possible to obtain frequent observations of those inountain- 

 like clouds belonging to the outermost vaporous solar atmo- 

 sphere ( 48 ). 



It is only at two periods of the year, viz. on the 8th of June 

 and 9th of December, that the solar spots describe on the 

 Sun's disk neither convex nor concave curves, but straight 

 lines parallel to each other and to the solar equator ; and if 

 we examine the zones in which the spots are most fre- 

 quent, we find as a characteristic circumstance that they are 

 rarely seen in the equatorial zone itself, from about 3 North 

 to 3 South latitude, and that they are entirely wanting in 

 the neighbourhood of the poles. They are on the whole 

 most abundant in a belt between 11 and 15 north of the 

 equator, and generally more frequent in the northern 

 than in the southern hemisphere ; or, as Sommering thinks, 

 are to be seen farther from the equator in the northern than 

 in the southern hemisphere. (Herschel, Outlines, 393 ; 

 Cape Observations, p. 433.) Galileo had already assigned 

 29 of north and south heliocentric latitude for the extreme 

 limits of the spots. Sir John Herschel has extended these 

 limits to 35; as has also Schwabe. (Schum. Astr. Nachr., 

 No. 473.) Single spots have been found by Laugier 

 (Comptes Rendus, T. xv. p. 944), as far as 41, and by 

 Schwabe even as far as 50. A spot described by La Hire 

 in 70 North latitude must be regarded as a phenomenon of 

 most rare occurrence. 



The above described distribution of the spots on the Sun's 

 disk, their rarity on the equator itself and in the polar regions, 

 and their arrangement parallel to the equator, have given 

 occasion to Sir John Herschel to conjecture that obstacles 



