on the Planet Venus. 
151 
when the eye looks perpendicularly through the dense atmo- 
sphere of Venus, and by no means in the small crescent 
form of light, when the lines of vision are much longer and 
more oblique through that atmosphere: it is in the former 
position of the planet alone that it can be seen distinctly, but 
even then not always equally so. One of the finest scenes of 
this kind was afforded (for example) by the observation I have 
adduced of the 9th, when Dr. Chladni viewed the planet with 
me. A less striking inequality, though perfectly certain, was 
discovered by my learned friend Dr. Olbers, July 31, 1793, at 
n h 5' in the forenoon, which we both observed and delineated 
in the same place, and exactly similar, after we had been ob- 
serving since 3 11 15' in the morning, but till that time saw no 
inequality. Were these small indentations or darker places 
merely atmospherical, no reason can be perceived why they 
should shew themselves only in the boundary of illumination, 
and not in the other enlightened parts also. 
( b ) The same thing appears, moreover, from the irregular 
form which the arch bounding the illumination sometimes as- 
sumes, and from the phenomenon thence arising of the much 
smaller size of one horn, and particularly the southern, in the 
crescent-shaped phases of the planet ; as is shewn, on the same 
grounds, by the observations contained in my former memoir 
on the rotation. 
Were these observations, as is alleged of the rest, nothing 
but fallacy, I should wish to know the reason, why that decep- 
tion happens only sometimes, continues only some hours, and 
almost always takes place on the southern horn only, very sel- 
dom on the northern. Whoever compares together the obser- 
