the Nature of the Sun. 
s 95 
Hence we have reason to conclude, that there are two different 
regions of clouds, the lowest whereof is never affected in colour 
by the cause which acts upon the upper one, when shallows are 
generated. If so, these clouds are probably of a very different 
nature ; for, were they not different, they would not be dif- 
ferently affected by the same cause. Perhaps this lower region 
is a set of dense opaque planetary clouds, like those upon our 
globe. In that case, their light is only the uniform reflection of 
the surrounding -superior self-luminous region. If this be 
admitted, it will at once account for the sameness of the colour 
of the shallows, and of their tufts ; and for many other phe- 
nomena. 
Quantity of Light reflected from the inferior Planetary Clouds. 
Feb. 7, 1801. I made an artificial contrivance, for the use of 
my photometer, to represent a portion of the bright surface of 
the sun, and of an opening with a shallow surrounding it. The 
opening was represented by a small patch of black velvet, re- 
sembling nearly, in shape, the large opening in the sun which 
is now visible. This was fastened on the farthest vane of my 
photometer, covered with white paper, and arranged so as to 
be in the line of the centre. In the nearest vane, covered with 
the same paper, and equally prepared so as to move in the 
centre of the photometer, I cut a hole large enough to shew 
the black velvet on the farthest vane, with a small margin of 
its paper about it, which was intended to represent the shallow 
about the opening. The illumination of the nearest vane was 
to represent the brightness of the sun. The two vanes were 
arranged so as to be one behind the other, in a straight line ; 
