444 P. A. Secchi on KirchhofPs Theory of Sola?- Spots. 



thing analogous to that of the formation of a cloud. Each of 

 these would make its appearance as a less luminous mass, and 

 either be sharply separated all round from the other and hotter 

 portions, like our cumuli, or be attenuated at the edges, like 

 our strati. The above radiant form, and the appearance of 

 currents precipitated into a cavity so as to form a perfectly dis- 

 tinct talus, could not at all occur, in accordance with what we 

 see in the clouds of our own atmosphere, or with what we can 

 conjecture. Any theory of the formation of spots must, in the 

 first place, explain their shape; and this the cloud theory has 

 hitherto failed to do. 



When a spot has arrived at its full development, it presents 

 to us a vast dark area ; into the latter luminous threads are pro- 

 jected, like radiant torrents, from all the circumjacent photo- 

 sphere, which penetrate, by long tortuous lines, into the interior 

 of the nucleus, thus producing the long familiar appearance of 

 rents. Now in our own atmosphere we never observe any such 

 penetrations of heated into cooler matter, accompanied by con- 

 stant and sharp separation of the two : nor, judging from ana- 

 logy, does it appear possible that such could occur in ]the sun ; 

 for the opake mass of cloud would either hide from our view 

 the torrents which strove to penetrate therein with linear motion, 

 or it would diminish the light of these torrents by cooling them. 

 Now, as we have frequently observed, and in accordance with 

 what Dawes has also recently stated (Phil. Mag. Feb. 1864, p. 156), 

 the filaments of the photosphere, which penetrate the nuclei, 

 preserve all the brilliant splendour of the photosphere itself. 

 Such a structure of the spots certainly does not agree with the 

 notion of clouds. 



When a spot arrives at its last phase, previous to dissolution, 

 the penumbra is less regularly radiated ; it appears to be formed 

 of the photosphere itself more attenuated and rarefied, so that 

 at this stage it has some resemblance to a cloud ; but, of course, 

 a true theory must account for all phases. There is one cir- 

 cumstance, moreover, of which the cloud theory gives no ac- 

 count whatever; this is the presence of faculse surrounding the 

 spots. 



These faculse, as I long ago pointed out, are simply the 

 crests of tempestuous waves, excited in the photosphere, which 

 emerge from the denser stratum of the solar atmosphere; 

 and they have every appearance of being formed of the matter 

 of the photosphere whirled round by the internal force which 

 creates the spot. If the spot were due merely to the formation 

 of a cloud, one does not see why its contour should be agitated 

 and violently ruptured. Everything indicates that the spots are 

 centres of lower temperature ; in fact I have shown this by the 



