THE SUN AND SOLAR PHENOMENA. 



57 



miles, more than six times the diameter of the earth. One of vast extent was observed 

 on the last day of June 1830. Its diameter was estimated at twenty-three thousand 

 miles, and being nearly circular, its area included about four hundred and forty -three 

 millions of square miles. The greatest magnitude of spots mentioned by Laplace is four 

 or five times that of the earth. But both in form and dimensions they undergo rapid 

 changes, sometimes breaking into two or more. Dr. Wollaston observed one to burst in 

 pieces like a lump of ice thrown upon a hard surface. Few continue longer than six 

 weeks before their final disappearance. While the sun has often been seen without spots, 

 at other times hundreds have been counted; and their presence or absence has been 

 supposed to affect the terrestrial temperature, and consequently the fertility of the seasons. 

 During the cold and wet summer of 1823, when the thermometer at Paris rose only to 

 twenty -three degrees of Reaumur, the sun exhibited no spots. But there were many in 

 the years 1836 and 1837 when the weather was unpropitious, and vegetation backward, 

 while the excessive heat of the summer of 1807 was attended with solar spots of great 

 magnitude. This was the case also with the year 1783, remarkable for its fertility, for 

 the dry fog which enveloped the greater part of Europe, followed by the terrible Calabrian 

 earthquake. This collision of circumstances renders it premature to suppose any influence 

 exerted upon the atmosphere of our globe by the exhibition or non-appearance of spots 

 on the sun. 



Conjecture has been busy respecting the nature of these appearances, their cause, and 

 probable indications concerning the physical constitution of the body to which they 

 belong. The early observers, indulging the vagaries of imagination, supposed them to 

 be the fuel of the solar furnace, or ashes floating on the surface of an abyss in a state of 

 ignition, or the smoke of volcanic explosions. But the views first broached by Dr. Wilson 

 of Glasgow, founded upon a minute observation of their peculiarities, now generally 

 obtains among astronomers. A spot consists of a dark nucleus. This is surrounded by a 

 very distinct belt of a lighter shade, called the umbra. Clear indications appear that 

 the nucleus is beneath the level of the solar surface, and that the umbra is the shelving 

 sides of the excavation. On being carried from the centre of the disk towards the sun's 

 western limb, the umbra becomes impaired on the side nearest the centre, and entirely 

 disappears. Then the nucleus is nipped on the same side, contracts to a line, and altogether 

 vanishes, while the umbra on the opposite side retains nearly its former dimensions. The 

 view exhibits this gradual change. The eye will at once perceive that these appearances 



are exactly those which depressions will present in the course of rotation. Herschel's 

 subsequent investigations have corroborated this view of Dr. Wilson, that the spots are 

 EXCAVATIONS in the luminous matter around the sun, the nucleus being his dense and 

 dark body appearing through the openings. He supposed his outermost coating, or 

 visible surface, to be a luminous atmosphere, perhaps several thousand miles in thickness, 

 beneath which is another more dense and highly reflective, throwing back the light of 

 the upper regions, and forming the shady belt of the solar spots. In his interior physical 

 constitution, therefore, that magnificent phantom, or globe of fire, which the ancients 



