On the Origin of the Light of the Sun and Stars. 451 



centre than the penumbra. From this he argued that a spot 

 represents a cavity of considerable depth in the sun's atmos- 

 phere ; the dark body of our luminary forming the nucleus or 

 bottom, while the penumbra represents the atmospheric walls 

 or sides of the cavern ; a consequence of which will be, that 

 when a spot is placed obliquely towards us, the wall nearest 

 us will be hidden from our view, and we shall only see that 

 which is farthest away. It will be noticed that one of the 

 spots we have sketched confirms the truth of this explanation, 

 the penumbra being to the left of the nucleus when the spot 

 was near the sun's left limb. 



Let us now consider the light-clouds, or faculee. Messrs. 

 Dawes, Howlett, and others, have observed that a spot, when 

 near the edge of the sun, does not cause an apparent in- 

 dentation in the limb, as might be expected, but that there 

 is always a thin line of light beyond. This is also seen in 

 our sketch, and the original negative at Kew from which 

 it is taken, is exceedingly instructive and well worthy of 

 minute inspection. It represents the line of light at its 

 central portion as more luminous than the general body of 

 the sun, so that the eye is impressed with the idea of an ex- 

 cessively curved or bulging out line. This may be due to the 

 elevation of the luminous ridge above the body of the solar 

 atmosphere, and is in accordance with the well known fact that 

 when faculse are observed near the limb of the sun they appear 

 much brighter than the surrounding photosphere, as if by being 

 high up they escaped a great portion of the atmospheric medium 

 which absorbs very much of the light proceeding from the 

 border. 



On the other hand, faculae have little or no excess of bright- 

 ness when near the centre of the disc, because there the light 

 travels only through a small extent of atmosphere and there is 

 not much gained by escaping it. To all this we may add, that 

 Mr. Warren De la Eue has succeeded in producing a stereo- 

 scopic image of a spot in which the faculas appear raised above 

 the surface. Now if these faculae are really elevated, this seems 

 at once to inform us that the sun's light breaks out in his 

 atmosphere and does not come from his solid body, since we 

 cannot easily suppose large masses of heavy matter remaining 

 upheld at a great height for a long period of time. "We there- 

 fore conclude that the greater proportion of the light which 

 reaches us is not derived from the solid body of the sun, but 

 from some matter which either floats in the solar atmosphere 

 or forms part of this atmosphere itself, and also that as far as 

 our observation of spots extends, there is ground for supposing 

 the sun's surface to be deficient in luminosity; and, for a 

 body of indefinite thickness, this is equivalent to a reduc- 



VOL. Y. — NO. VI. H H 



