THE SUN. 



appear of vast extent ; sometimes they will be manifested in groups, 

 the penumbra or fringes being in contact. 



The duration of each spot is also subject to great and irregular 

 variation. A spot has appeared and vanished in less than twenty- 

 four hours, while some have maintained their appearance and 

 position for nine or ten weeks, or during nearly three complete 

 revolutions of the sun upon its axis. 



A large spot has sometimes been observed suddenly to crumble 

 into a great number of small ones. 



The only circumstance of regularity which can be said to attend 

 these remarkable phenomena is their position upon the sun. They 

 are invariably confined to two moderately broad zones parallel 

 to the solar equator, separated from it by a space several degrees 

 in breadth. The equator itself, and this space which thus separates 

 the macular zones, are absolutely divested of such phenomena. 



18. Observations upon the appearances from which these infer- 

 ences have been made, have been at various times made by astro- 

 nomers, the most important being those of Sir William Herschel, 

 Dr. Pastorff, Professor Capocci, and Sir J. Herschel, who have seve- 

 rally supplied drawings of their appearance, the general similarity 

 of which, made at different places of observation, at very different 

 times, and by different observers, offers a strong evidence of their 

 authenticity. 



In the figure at the head of this chapter, we have given copies 

 of several of the most remarkable of these drawings. 



19. The superficial dimensions of the several groups of spots 

 observed on the sun on the 24th May, 1828, including the shelving 

 sides, were calculated to be as follows : 



Square Geog. miles. 



Group A, principal spot 928,000000 



Ditto, smaller spots 736,000000 



Group B 296,000000 



Group C 232,000000 



Group D 304,000000 



Total area . . . 2496,000000 



20. Independently of the dark spots just described, the luminous 

 part of the solar disk is not uniformly bright. It presents a 

 mottled appearance, which may be compared to that which would 

 be presented by the undulated and agitated surface of an ocean oi 

 liquid fire, or to a stratum of luminous clouds of varying depth, 

 and having an unequal surface, or the appearance produced by 

 the slow subsidence of some flocculent chemical precipitates in a 

 transparent fluid, when looked at perpendicularly from above. In 

 the space immediately around the edges of the spots extensive 



108 



