440 P. A. Secchi on KirchhoiFs Theory of Solar Spots. 



which is the before-mentioned quadric surface ; hence the qua- 

 dric surface and the cubic surface intersect in the two lines 



(where B l3 6 2 are the roots of the quadric equation 2 — ^ 6 } + 1 = 0); 



and they consequently intersect also in an excubo-quartic curve, 

 which is the theorem required to be proved. 

 Blaekheath, March 26, 1864. 



LXVIII. On Kirchhoff's Theory of Solar Spots. 

 By P. A. Secchi*. 



I^HE theory of solar spots proposed by Prof. Kirchhoff, in 

 place of the one hitherto received, was briefly noticed by 

 us in the Bull. Meteorologico delV Osserv. Romano (No. 2, vol. ii.). 

 The proposer having by his beautiful spectrum discoveries, 

 meritoriously acquired an immense popularity and esteem, his 

 theory has attracted considerable attention ; a few remarks on 

 the subject, therefore, based on the various researches which 

 have recently been made, will not be out of place. 



Prof. Kirchhoff rejects the theory of W. Herschel as well as that 

 of Wilson j which two theories, we may here observe, are 30 far 

 distinct that the confutation of the one does not necessarily in- 

 volve the fall of the other. Herschel imagined the solar nucleus 

 to be solid and dark-coloured, but surrounded by two strata of 

 luminous clouds, separated from one another by a non-luminous 

 stratum, and he attributed the spots to the rents in these enve- 

 lopes. According to him, the nuclei consist of the compara- 

 tively dark body of the sun itself seen through apertures in both 

 atmospheres ; and the penumbrse are occasioned by the larger 

 rents of the second luminous stratum. Prof. Kirchhoff objects 

 to these two atmospheres — which, we admit, always appeared 

 objectionable to us also, on the ground of their being unneces- 

 sary, and of their necessitating a simultaneous rent in both. 

 Numerous careful observations made with powerful instruments 

 led us some time ago to the conclusion that the penumbrse were, 

 for the most part, formed either by filaceous currents of the 

 matter which constitutes the sole photosphere enveloping the 

 sun, or by the attenuation of the latter until it became trans- 

 parent ; at the same time we drew attention to the presence, 

 within- the spots, of veli and cirri, more luminous than their 

 nuclei, but less so than their penumbrse — thus confirming the 

 discovery of Dawes, who justly complains that hitherto attention 

 has not been paid thereto by those who have occupied themselves 

 with the subject. 



* From II Nuovo Cimento, tomo xviii. p. 81. 



