Dr. J. R. Mayer on Celestial Dynamics, 401 



observed to be covered with peculiarly marked lines much brighter 

 than the other parts of the surface ; these lines are. curved, or 

 deviate in branches, and are called faculse. Spots are often seen 

 between these lines, or to originate there. These are in all proba- 

 bility the crests of immense waves in the luminous regions of the 

 solar atmosphere, and bear witness to violent action in their 

 immediate neighbourhood." 



The changes on the solar surface evidently point to the action 

 of some external disturbing force ; for every moving power resi- 

 dent in the sun itself ought to exhaust itself by its own action. 

 These changes, therefore, are no unimportant confirmation of the 

 theory explained in these pages. 



At the same time it must be observed that our knowledge of 

 physical heliography is, from the nature of the subject, very 

 limited; even the meteorological processes and other pheno- 

 mena of our own planet are still in many respects enigmatical. 

 For this reason no special information could be given about the 

 manner in which the solar surface is affected by cosmical masses. 

 However, I may be allowed to mention some probable conjectures 

 which offer themslves. 



The extraordinarily high temperature which exists on the sun 

 almost precludes the possibility of its surface being solid; it 

 doubtless consists of an uninterrupted ocean of fiery fluid 

 matter. This gaseous envelope becomes more rarefied in those 

 parts most distant from the sun's centre. 



As most substances are able to assume the gaseous state of 

 aggregation at high temperatures, the height of the sun's atmo- 

 sphere cannot be inconsiderable. There are, however, sound 

 reasons for believing that the relative height of the solar atmo- 

 sphere is not very great. 



Since gravity is 28 times greater on the sun's surface than 

 it is on our earth, a column of air on the former must cause a 

 pressure 28 times greater than it would on our globe. This 

 great pressure compresses air as much as a temperature of 8000° 

 would expand it. 



In a still greater degree than this increased gravity do the 

 qualities peculiar to gases affect the height of the solar atmo- 

 sphere. In consequence of these properties, the density of our 

 atmosphere rapidly diminishes as we ascend, and increases as we 

 descend. Generally speaking, rarefaction increases in a geome- 

 trical progression when the heights are in an arithmetical pro- 

 gression. If we ascend or descend 2 J, 5, or 30 miles, we find our 

 atmosphere 10, 100, or a billion times more rarefied or more dense. 



This law, although modified by the unequal temperatures of 

 the different layers of the photosphere, and the unknown che- 

 mical nature of the substances of which it is composed, must 



