VOL. LXXXV,] PHILOSOPHICAL TRANSACTIONS. 485 



at the top. The preceding shelving side was rendered almost invisible, by the 

 overhanging of the preceding elevations; while the following was very well ex- 

 posed: the spot being apparently such in figure as denotes a circular form, 

 viewed in an oblique direction. Near the following margin were many bright 

 elevations, close to visible depressions. The depressed parts less bright than the 

 common surface. The penumbra, as it is called, about this spot, was a con- 

 siderable plane, of less brightness than the common surface, and seemed to be 

 as much depressed below that surface as the spot was below the plane. Hence, 

 if the brightness of the sun is occasioned by the lucid atmosphere, the intensity 

 of the brightness must be less where it is depressed; for light, being transparent, 

 must be the more intense the more it is deep. 



Oct. 12, 1794, the whole surface of the sun was diversified by inequality in 

 the elevation of the shining atmosphere. The lowest parts were every where 

 darkest; and every little pit had the appearance of a more or less dark spot. A 

 dark spot, on the preceding side, was surrounded by very great inequalities in 

 the elevation of the lucid atmosphere; and its depression below the same was 

 bounded by an immediate rising of very bright light. Oct. 13, 1794, the spot 

 in the sun observed yesterday was dravyi so near the margin, that the elevated 

 side of the following part of it hid all the black ground, and still left the cavity 

 visible, so that the depression of the black spots, and the elevation of the faculae, 

 were equally evident. 



It will now be easy to bring the result of these observations into a very narrow 

 compass. That the sun has a very extensive atmosphere cannot be doubted; and 

 that this atmosphere consists of various elastic fluids, that are more or less lucid 

 and transparent, and of which the lucid one is that which furnishes us with light, 

 seems also to be fully established by all the phenomena of its spots, of the faculae, 

 and of the lucid surface itself. There is no kind of variety in these appearances 

 that may not be accounted for with the greatest facility, from the continual agi- 

 tation which we may easily conceive must take place in the regions of such ex- 

 tensive elastic fluids. It will be necessary however to be a little more particular, 

 as to the manner in which I suppose the lucid fluid of the sun to be generated in 

 its atmosphere. An analogy that may be drawn from the generation of clouds 

 in our own atmosphere, seems to be a very proper one, and full of instruction. 

 Our clouds are probably decompositions of some of the elastic fluids of the at- 

 mosphere itself, when such natural causes, as in this grand chemical laboratory 

 are generally at work, act on them; we may therefore admit that in the very ex- 

 tensive atmosphere of the sun, from causes of the same nature, similar phe- 

 nomena will take place; but with this difterence, that the continual and very 

 extensive decompositions of the elastic fluids of the sun, are of a phosphoric 

 nature, and attended with lucid appearances, by giving out light. 



