345 
on the Atmosphere of the Moon. 
an exact spherical form, without the least sensible inequality ; 
and as in both the bordering regions of the northern and 
southern hemispheres, especially in the latter, no such grey, 
prominent planes are any where discernible. It may then be 
asked, why did this faint glimmering light appear at both 
cusps, along equal arcs of the limb, of equal length and breadth, 
and of the same pyramidal form? and why did its farther ex- 
tremity blend itself with the terrestrial light of the dark hemi- 
sphere, which, according to a great number of my selenoto- 
pographic observations, is by no means the case, even with 
those grey prominent areas which, being at some distance on 
the dark side of the terminating border, are nevertheless illu- 
min ted immediately by the sun ? 
These, therefore, could certainly not derive their light im- 
mediately from the sun; whence this appearance, like the 
similar ones on the planet Venus, can only be ascribed to the 
solar rays reflected by the atmosphere of the moon upon those 
planes, producing on them a very faint, gradually diminishing, 
glimmering light, which at last loses itself in the reflected 
terrestrial light, in the same manner as our twilight blends 
itself with the light of the moon. Every circumstance of the 
above observation seems to me to confirm this supposition ; and 
hence the observation itself, which, though single, was how- 
ever a most fortunate and complete one, must appear of no 
small degree of importance, since it not only confirms the 
observations and inferences on the long contested lunar atmo- 
sphere contained in my Selenotop. Fragm. but" also furnishes 
us with many more lights concerning the atmosphere of 
planets in general, than had been afforded us by all those ob- 
servations collectively. 
