3 12 
Mr. Schroeter's Observations 
Considering the immense height of the mountains, and the 
great inequalities on the surface of Venus,* it is natural to sup- 
pose that, as at the times of its greatest elongations, one cusp 
frequently appears pointed and the other blunt, owing to the 
shadow of some mountain darkening the extremity of the 
latter, the same appearance may often take place in the fal- 
cated phase of the planet. But the cusp whose extremity is 
covered by a shadow, will, in this case, so far from appearing 
blunt, always exhibit a pointed appearance; it being in that 
aspect too sharp for us to distinguish accurately its true form. 
Should, for instance, the point of the cusp a. (3 7, fig. 2 , be 
immersed in a shadow from a to (3, this point, in such a case, 
though it may be somewhat blunted from « to 7, will never- 
theless appear sharp, because' its whole breadth does often not 
exceed ~ of a .second, whence its true form must needs escape 
our observation. We do not, in this instance, see the very 
faintly illuminated point a (3, nor yet the real luminous edge 
7 (3, but only its prominent and brighter part « 7 ; a deception 
this, which cannot take place in the other parts of the termi- 
nator, where indeed the same causes, viz. the shadows of 
mountains, will, no doubt, at times occasion an uneven, ragged 
appearance, but cannot materially affect the very faint light 
of the whole. 
It is, moreover, evident, that even when the extremities of 
the cusps are, as in fig. 1 , not darkened by shadows, the faint 
luminous points/^, hi, are not always visible, but can only 
* The perpendicular height of these mountains, as I have already shewn in a former 
work, is in proportion to the diameter of the planet, at least as great as the height of 
the mountains in the moon, in proportion to its much shorter diameter ; this fact I 
have had frequent opportunities to Ascertain. See Selenotop. Fragm. §. 522, 
