35° Mr. Schroeter’s Observations 
light of the illuminated hemisphere as to be almost evanescent. 
The best illustration of this, and of the known fact, that in 
the broader phases the twilight will, on account of the strong 
contrasting light of the luminous part, vanish even at the 
cusps, is given by the spots Manilius and Menelaus. Both are 
situated near the centre of the hemisphere turned towards our 
earth ; both have considerable diameters, the one of 24 and 
the other of between 14 and 16 seconds, and both appear very 
distinctly on the third day after the new moon, with a degree 
of light rather surpassing that of the twilight. These spots, 
however, notwithstanding their great diameters, vanish on ac- 
count of the increasing glare of light, so soon as four days after 
the new moon, although they be then still at some distance 
from the terminating border.* How could, therefore, a faint 
light, measuring only 2" in breadth, be visible on the third 
day after a new' moon, at the terminating border ? And how 
could it at the fourth day still appear distinctly at the bright 
cusps, where it is, indeed, of a more considerable extent, but 
still must, in consequence of its pyramidal form, soon dwindle 
away into a very narrow tapering stripe ? This, moreover, 
was precisely the case in the many observations I made on 
the planet Venus. 
From the above calculations it also appears, that the lower 
and more dense part of the lunar atmosphere, that part, 
namely, which has the power of reflecting this bright crepus- 
cular light, is only 135b Paris feet in height ; and hence it 
will easily be explained how, according to the different libra- 
tions of the moon, ridges of mountains even of a moderate 
height, situated at or near the terminating border, may par-=> 
* See Selenot. Fragm. 531. 
