ASTROXOJIT AND METEOROLOGY. 339 



COMPOSITION OF THE SUN. 



Tn a paper read before the Royal Institute, March 17, 1865, by 

 Balfour Stewart, the following conclusions, based chiefly upon 

 evidence afforded by photography, are given in relation to the 

 composition of the sun. 



1. The existence of an atmosphere around the sun, outside of 

 its luminous envelo2)e or photosphere. This is proved by the fact 

 that photographs of the sun are less intense around the edges 

 than in the middle, which is only to be explained on the supposi- 

 tion that an absorptive atmosphere sui'rounds the sun, causing 

 more loss of power to the rays from the sides which must pierce 

 it obliquely, and thus jjass through a great depth, than to those 

 from the centre, which penetrate it by the direct and shortest road 

 possible. 



2. That the "flames" or brilliant protuberances seen around 

 the edges of the moon, in a total eclipse of the sun, belong to the 

 central orb and not to the satellite. This was proved conclusively 

 by a series of photographs taken during the eclipse of 1860, by De 

 La Rue and others. In these, the flames are shown in the succes- 

 sive pictures to have suffered gradual occultation, and to have 

 been gradually exposed in like manner by the moving planet, 

 thus clearly being attached to or connected with the sun, and not in 

 any wise related to the moon. These flames, supposed to be in 

 fact detached portions of the luminous envelope, or extensions of 

 the same into the solar atmosphere, above mentioned, were also 

 shown to possess remarkable actinic power, their shapes being 

 more developed and better defined on the photograph than to the 

 eye, and one invisible joortion producing a distinct image on the 

 sensitive film. 



3. That there are markinsrs of a regular character over the solar 

 disk, called, from their shape, willow-leaves, ripples, etc. These 

 are distinctly visible on some photograjjhs by Mr. Nasrayth. 



4. That the spots in the sim are openings in its photosphere, 

 through which itsrelativel}' dark mass is seen. This is fully dem- 

 onstrated by the order in which the spot and its penumbra (the 

 sloping sides of the opening) disappear as the luminary rotates. 



SUN-SPOTS. 



The different views of astronomers in regard to sun-spots are 

 well illustrated by the following opinions : — 



Mr. De La Rue and the Kew observers, after careful examina- 

 tion of the pictures of sun-spots, as obsci'ved by the heliograph 

 and from Mr. Carrington's maps, have come to the following con- 

 clusions: 1. Sun-spots are cavernous ; they lie below the general 

 level of the sun's luminous matter, and extend into the regions 

 beneatli it. 2. The faculte are portions of the sun\s luminous 

 matter elevated above the general level of the photosphere ; and 

 near the limlj of the sun they appear relativi^ly brighter than the 

 surrounding surface, because, on accoui^ of their greater eleva- 

 tion, the light which the}- emit is less subject to absorption by the 



