Dr. Herschel on the Nature and Construction 
derable plane, of less brightness than the common surface, x 
and seems to be as much depressed below that surface as the 
spot is 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 is diversified 
by inequality in the elevation of the shining atmosphere. The 
lowest parts are every where darkest ; and every little pit has 
the appearance of a more or less dark spot. 
A dark spot, which is on the preceding' side, is surrounded 
by very great inequalities in the elevation of the lucid atmo- 
sphere ; and its depression below the same is bounded by an 
immediate rising of very bright light. 
Oct. 13, 1794. The spot in the sun I observed yesterday is 
drawn so near the margin, that the elevated side of the fol- 
lowing part of it hides all the black ground, and still leaves 
the cavity visible, so that the depression of the black spots, 
and the elevation of the faculse, are 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 exten- 
sive 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 sur- 
face itself. There is no kind of variety in these appearances 
