299 
the Nature of the Sun. 
and jagged, according to the advancement of the clouds; 
but a coarsely circular form of the shallow in general is still, 
preserved. 
Eminent Use of the planetary Clouds. 
It has been shewn that the openings, compared to the lumi- 
nous surface of the sun, reflect less than 1 6 rays out of a thou- 
sand, and probably not more than seven. To account for this 
extraordinary darkness, it must be remembered, that accord- 
ing to the observations which have been given, hardly any but 
transmitted rays can ever come to the body of the sun. The 
shallows about large openings are generally of such a size, as 
hardly to permit any direct illumination from the superior clouds 
to pass over them into the openings ; and the great height and 
closeness of the sides of small ones, though not often guarded 
by shallows, must also have nearly the same effect. By this it 
appears, that the planetary clouds are indeed a. most effectual 
curtain, to keep the brightness of the superior regions from the 
body of the sun. 
Another advantage arising from the planetary clouds of the 
sun, is of no less importance to the whole solar system. We 
have shewn that corrugations are every where dispersed over the 
sun ; and that their indentations may be called shallows in mini- 
ature. From this we may conclude, that the immense curtain 
of the planetary solar clouds is every where closely drawn ; and,, 
as our photometrical experiments have proved that these clouds 
reflect no less than 469 rays out of a thousand, it is evident that 
they must add a most capital support to the splendour of the 
sun, by throwing back so great a share of the brightness coming 
to them from the illumination of the whole superior regions, 
S>q 2 
