402 Dr. J. R. Mayer on Celestial Dynamics. 



also hold good in some measure for the sun. As, however, the 

 mean temperature of the solar atmosphere must considerably 

 exceed that of our atmosphere, the density of the former will not 

 vary so rapidly with the height as the latter does. If we assume 

 this increase and decrease on the sun to be ten times slower than 

 it is on our earth, it follows that at the heights of 25, 50, and 

 300 miles a rarefaction of 10, 100, and a billion times respect- 

 ively would be observed. The solar atmosphere, therefore, does 

 not attain a height of 400 geographical miles, or it cannot be as 

 much as -^— th of the sun's radius. For if we take the density 

 of the lowest strata of the sun's atmosphere to be 1000 times 

 greater than that of our own near the level of the sea, a density 

 greater than that of water, and necessarily too high, then at a 

 height of 400 miles this atmosphere would be 10 billion times 

 less dense than the earth's atmosphere ; that is to say, to human 

 comprehension it has ceased to exist. 



This discussion shows that the solar atmosphere, in compa- 

 rison with the body of the sun, has only an insignificant height ; 

 at the same time it may be remarked that on the sun's surface, 

 in spite of the great heat, such substances as water may possibly 

 exist in the liquid state under a pressure thousands of times 

 greater than that of our atmosphere. 



Since gases, when free from any solid particles, emit, even at 

 very high temperatures, a pale transparent light — the so-called 

 lumen philosophicum — it is probable that the intense white light 

 of the sun has its origin in the denser parts of his surface. If 

 such be assumed to be the ease, the sun's spots and faculse seem 

 to be the disturbances of the fiery liquid ocean, caused by most 

 powerful meteoric processes, for which all necessary materials 

 are present, and partly to be caused by the direct influence 

 of streams of asteroids. The deeper and less heated parts 

 of this fiery ocean become thus exposed, and perhaps appear to 

 us as spots, whereas the elevations form the so-called faculse. 



According to the experiments made by Henry, an American 

 physicist, the rays sent forth from the spots do not produce the 

 same heating effect as those emitted by the brighter parts. 



We have to mention one more remarkable circumstance. The 

 spots appear to be confined to a zone which extends 30° on each 

 side of the sun's equator. The thought naturally suggests 

 itself that some connexion exists between those solar processes 

 which produce the spots and facube, the velocity of rotation of 

 the sun, and the swarms of asteroids, and to deduce therefrom 

 the limitation of the spots to the zone mentioned. It still re- 

 mains enigmatical by what means nature contrives to bring 

 about the uniform radiation which pertains alike to the polar 

 and equatorial regions of the sun. 



