THE SUN AND SOLAK PHENOMENA. 55 



times, and I can assure you that I have nowhere found anything in them similar to what you 

 mention. Go, my son, and tranquillise yourself ; be assured that what you take for spots 

 in the sun are the faults of your glasses, or of your eyes." Scheiner was not allowed to 

 publish his opinions under his own name ; and they appeared anonymously. 



Some general results of observation may now be succinctly stated. The spots are not 

 uniformly obscure. They consist of a central portion, characterised by intense blackness, 



termed the nucleus, surrounded by a very 

 distinct belt of a lighter shade, called the 

 penumbra. The two portions do not 

 gradually blend, but are separated by a 

 well-defined boundary ; and this is true of 

 the exterior part of the penumbra, which 

 is in general sharply distinguished from the 

 luminous region around it. By photometrical experiments, Herschel determined that 

 representing the wholly luminous part of the solar surface by 1000, the relative brightness 

 of the penumbra will be represented by 469, and that of the nucleus by 7. On some 

 occasions, though rarely, a large nucleus has appeared without any penumbra ; and on the 

 other hand, a penumbra without a nucleus has been seen. 



The spots are of very irregular shape, and varying magnitude. Sometimes they are 

 numerous, but small, while individual spots appear of enormous dimensions. The latter 

 are usually formed by simultaneous enlargement on all sides of the nucleus and penumbra 

 from a comparatively minute speck. On the last day of June 1830, a spot of vast extent 

 was observed. Its diameter was estimated at 23,000 miles ; and being nearly circular, its 

 area included about 443,000,000 of square miles. But Mayer, in 1754, perceived a spot 

 equal to ^th of the sun's apparent diameter, which gives it an absolute diameter of more 

 than 45,000 miles. Still greater magnitudes are reported. 



Both in form and dimensions, the spots are subject to great changes, which transpire 

 with astonishing rapidity. Two or more, situated very close together, will frequently 

 expand towards each other, and form one large spot. On the contrary, one of great extent 

 has been seen suddenly to crumble into" several smaller. Dr Wollaston observed a spot 

 which seemed to burst in pieces, like a lump of ice thrown upon a hard surface. Herschel 

 states, that on the 19th of February 1800, he fixed his attention on several spots ; but on 

 looking off, even for a moment, they could not be found again. Sir John Lubbock also 

 remarks, that he has observed spots visible to the naked eye, of which, on the following 

 day, not a trace could be distinguished, even with the aid of a good telescope. These 

 rapid and extraordinary changes indicate that the material subject to them cannot be 

 solid, or liquid, but gaseous. 



It is a remarkable circumstance connected with the solar spots, that they invariably 

 appear near the equator, but apart from it. By Galileo they were seen as far as 29 of 

 latitude, north and south. But Scheiner found them extending to 30, and called the 

 intermediate region, on this account, the "royal zone." They have, however, been 

 occasionally observed at a greater distance on both sides of the sun's equator, but never at 



