MEMORIE DELLA SOCIETÀ DEGLI SPETTROSCOPISTI ITALIANI 



On the comparison of certain theories of the solar structure 



with observation 



by S. P. Langley, Director of the Allegheny Observatory (*). 



In memoirs alrcady published (1), allnsion has been raade to the interest whicli 

 would attend stndies of the aluiost nnknown interior of the nmbrae of sun-spots, 

 and of forins there which owing to the relative darkness are hitherto nearly un- 

 described , and allusion has also been made to certain so-called « cristalline » 

 shapes seen at tiuies, and which are especially associated with large spots and 

 periods of great disturbance. 



Doubtless owing to the difficulty of seeing appearances so delicate, these « cri- 

 stalline » types bave never been minutely delineated , and it has been natnrally 

 assumed that their existence lent some confirmation to the views of those who re- 

 gard the photosphere, as the luminons covering of an incandescent fluid, and con- 

 sider spots as deposits of cooling matter, more or less analagous to the scoriaceous 

 deposits of terrestrial volcanoes. M. E, Gautier has iu a very iuteresting communica- 

 tion to M. Faye (2), referred to these forms, and to my description of them. They 

 are indeed so remarkable and at first sight so apparently confirmalory of the views 

 alluded to, that only after long study I bave been led to think them not so much 

 assimilable to the products of cooling upon a liquid snrface, as to certain cloud 

 forms of our own atmosphere. 



In fonrnishing material for a public examination of these details, whose stndy is 

 so emiuently instructive, it is necessary, as has bean already remarked, (since pho- 

 tography cannot yet seize them), to make drawings in which the single aim of the 

 designer is to set down with a minute fidelity, speciflc forms; aiming in short, much 

 more to produce a piece of accurate topography, than a picture; while it is on stn- 

 dies made of this minute exactness that discussion will be most profitable, their 

 reproduction for the press is a work of so much labor that this kind of illustration 



(") Vedi note a pag. 7. 



(i) American Journal of Science, february 1874. Royal Astronomical Society's Nofices, march 1874. 



(1) Comptes rendus, may 18, 1874. 



Giornale di Scienze Nat. ed Econ., Voi. XI. — 187S. 1 



