P. A. Secchi on KirchhofFs Theory of Solar Spots. 441 



The attention of observers has recently been drawn to the 

 willow-leaf structure of the sun's envelope, indicated by Nasmyth. 

 To this gentleman — who used a large reflector provided with 

 oculars, not darkened, but in which the intensity of the light 

 was diminished and rendered tolerable to the eye by reflexion 

 from a glass plate — the sun appeared to be formed of innume- 

 rable bright elliptical patches, in the form of leaves, and super- 

 posed on each other; at the contours of the penumbras they 

 appeared to be more isolated, and resembled interlaced leaves, 

 which projected separately into the interior of the nucleus itself. 



Circumstances have not been sufficiently favourable as yet to 

 permit us to recognize this structure; in this respect, indeed, 

 Mr. Dawes has not been more fortunate, for he found the solar 

 structure, described by Sir J. Herschel as consisting of a kind 

 of luminous flakes, more in accordance with the phenomena ob- 

 served by himself during many years of research ; and with re- 

 spect to the penumbras, he admits that there are bright portions 

 like currents, which, commencing in the nuclei, traverse the 

 penumbrae, and retain all the brilliancy of the photosphere rather 

 than of the penumbrae. This agrees with our own observations ; 

 for we have always insisted upon the three distinct constituents 

 observable in every spot — i. e. the real nucleus, the penumbras, 

 and the semiluminous cirri. To explain this phenomenon it is 

 not necessary to have recourse to two strata of luminous clouds ; 

 the assumption of a single incandescent photosphere mixed with 

 less luminous vapours (as seen in eclipses) will suffice ; through 

 the rents made in this photosphere, by causes difficult to pre- 

 dict though easy to conjecture, the less bright central portion of 

 the sun is seen. 



This assumption of an obscure central part, however, is pre- 

 cisely what appears to be most absurd to Prof. Kirchhoff. " How 

 is it possible," says he, " to admit the absurd hypothesis accord- 

 ing to which, at its contact with a body so incandescent as is 

 the photosphere, and under so intense a radiation, the sun's 

 nucleus has not yet arrived at a state of incandescence and 

 fusion V With all due respect to so distinguished a philosopher, 

 we believe that there is here some exaggeration. In the first 

 place, no one ever said that the nucleus is cold; and if obscure, 

 its obscurity is merely relative. Galileo in his day asserted 

 this ; and photography proves that the chemical intensity of the 

 nucleus is so great that, in order to obtain an image of the same, 

 it is necessary to operate instantaneously, otherwise this image 

 equals in brilliancy that of the photosphere. The difference in 

 luminosity, therefore, is small; and if we could isolate one of 

 these nuclei, we should probably find it difficult to distinguish 

 the same from a portion of the sun itself. In order to prove 



