TT': A. Norton— Physical Considution of the Sun. 407 



light, or in the case of the corona in part also by reflected solar 

 light* 



The probable origin of the sun's spots, and other questions of 

 solar physics that claim attention, must be left for future con- 

 sideration. I will only remark here, that it has long been ap- 

 parent that the diverse phenomena which occur at the sun's sur- 

 face are traceable, more or less directly, to the action of some 

 form of eruptive force. The present investigation seems to have 

 M to the discovery of the true nature and origin of this force : ami 

 at the same time to have revealed the process by which the sun\^ ra- 

 diation w maintained. The primary source of the solar heat Ijc- 

 mg, doubtless, as now generally believed, the process of con- 

 densation maintained by the force of gravitation. 



It is worthy of remark, in conclusion, that as comets directed 

 our attention, at the outset, toward the sun, so the sun, in its 

 turn, leads us back again to our starting point ; since we see 

 tnat It we transfer to cometary bodies the physical structure 

 ^e have recognized in the sun's upper photosphere, \ ' ' 



me energetic action of the force of hea. ..^.u.oxv^, .^. ........ y 



ui which some of the curious transformations they undergo, 

 f ,7/it^erto been involved, seems to be in a great^degi'ee dis- 

 pelled. No one doubts that comets are chiefly composed of 

 very light vapors ; though some of the larger ones mav have a 

 solid nucleus. If, as intimated, certain observed cometary phe- 

 nomena indicate that these vapors, like the solar vapors, are ar- 

 S ' 1°^ ^ certain depth at least, in envelopes, which are 

 ^Die to be greatly expanded, or even wholly expelled bv the 

 mcreasmg amount of heat received from the "sun, we have in 

 that^tl° ^ ^^ P%sical structure of comets, another indication 

 tn«ni, ^^ bodies were originally detached from the sun's pho- 

 ^spaere, m addition to that furnished by certain features of the 

 cometary motions.t 



* It is also 



conceivable that the subtil vapor streaming 

 K '^^^^^atioi^ lil^e the hydrogen, from s 



7 be doubted 



ons and deeomposi 





