74 ATMOSPHERE OF THE SUN [SKCT.XXVI. 



greater degree of rarity than can be produced by our best 

 air-pumps ; consequently no terrestrial animal could exist 

 in it. This was confirmed by M. Arago's observations during 

 the last great solar eclipse, when no trace of a lunar atmo- 

 sphere was to be seen. 



The sun has a very dense atmosphere, which is probably 

 the cause of the peculiar phenomena in his photographic 

 image already mentioned. What his body may be, it is 

 impossible to conjecture ; but he seems to be surrounded 

 by a mottled ocean of flame, through which his dark nucleus 

 appears like black spots often of enormous size. These 

 spots are almost always comprised within a zone of the sun's 

 surface, whose breadth, measured on a solar meridian, does 

 not extend beyond 30^ on each side of his equator, though 

 they have been seen at the distance of 39^. From their 

 extensive and rapid changes, there is every reason to suppose 

 that the exterior and incandescent part of the sun is gaseous. 

 The solar rays, probably arising from chemical processes 

 that continually take place at his surface, or from electricity, 

 are transmitted through space in all directions ; but, not- 

 withstanding the sun's magnitude, and the inconceivable 

 heat that must exist at his surface, as the intensity both of 

 his light and heat diminishes as the square of the distance 

 increases, his kindly influence can hardly be felt at the 

 boundaries of our system, or, at all events, it must be but 

 feeble. 



The direct light of the sun has been estimated to be equal 

 to that of 5563 wax candles of moderate size, supposed to be 

 placed at the distance of one foot from the object. That of 

 the moon is probably only equal to the light of one candle 

 at the distance of twelve feet. Consequently, the light of 

 the sun is more than three hundred thousand times greater 

 than that of the moon. Hence the light of the moon imparts 

 no heat. Professor Forbes is convinced, by recent experi- 

 ments, that the direct light of the moon is incapable of raising 

 a thermometer one three-hundred-thousandth part of a centi- 



