DEGLI SPETTR0SC0P1STI ITALIANI 5 



clearly as any frost-flgnre on a wiudow. Yet we liave no difficulty in secing that 

 in this case the eddies of our own atmosphere bave been in some way a principal 

 cause. (P). While recognizing the danger of pushing too far couclnsions drawn from 

 terrestrial analogy, I should tbeu (pending a more complete stndy of these appea- 

 rances) regard tbem as most nearly typified by certain clond-forms of our own 

 atmosphere. 



This spot, presented other interesting types not bere referred to, but I may 

 mention in support of previous observations, that in the upper portion of the pe- 

 nnmbra just below where a considerale part of the photosphere was islanded, the 

 sudden and abrnpt change of direction of the filaments , marked the apparently 

 unmistakeable passage of one cloud stratum over another. This disposition was also 

 marked elsewhere in the spot, Avhole banks of clouds moving one over the other 

 so as to forni a terraced appearance. (G). In very many other spots, this movcment 

 of one stratum over and freqneutly at right angles to another has been recogni- 

 zed, so that after long study I bave felt justificd in elsewhere formally announ- 

 cing it as an ascertained fact, observed not in an isolateci instance but as a ge- 

 neral characteristic of the solar surface whose features are thus again assimilated 

 to atmospheric ones in some degree like our own. 



From the precedili» fact of observation it appears that the follwing conclusions 

 may be drawn. 



1. Withont prejudice to the important cousiderations on which its distingnished 

 author has framed the theory of the exixteuce of a liquid or viscous solar shell it 

 seeuis to me, speaking simply as an observer, that from what has been stated of 

 the appearance of timbrai forms sudi a shell or crust must if it exist be at a di- 

 staile below the surface of the photosphere considerale even with reference to 

 the dimensious we bere deal with. 



2. It seems difficult to reconcile the brightsharply defined inner penumbral edge, 

 and the regular structure discerned in the umbra, with another view in which 

 this umbra is a sort of staguaut pool, formed by cold vapors or clouds which bave 

 settled there after depressing tbe general surface by their weight till the penum- 

 bral slope is determined. So mudi of the early hypothesis of Herschel as regards 

 the umbra as an opening (however made) tlirough which we look into a non-lumi- 

 nons interior of the Sun extending everywherc beueath the photosphere seems com- 

 mon to views, which ditfering widely elsewhere, agree on this point, with these 

 observations rather thau with the views peculiar to Falli er Secchi (1). 



(1) « ... il solo errore dell'illustre osservatore (I. E. Herschel) fu di estendere la massa oscura 

 su tutto il globo sotto la fotosfera, mentre in realtà essa non forma che pezze o chiazze assai li- 

 mitate.)) — P. Secchi, Memorie degli Speltroscopisti, agosto 1874. 



