on the Planet Venus. 
129 
northern horn, though rounded like the southern, a brighter 
pointed small inequality projected out from the faint boundary 
of light, as is expressed at a, fig. 5. It was difficult to dis- 
tinguish, but his eye, more accustomed to microscbpic ob- 
jects, saw it alike with both reflectors, and in the same place ; 
I perceived it also, though it was not striking. The observa- 
tion was continued by both of us to 8 h 30', when Venus being 
sunk too low, began to be indistinct. At this time indeed I 
could no longer distinguish that fine point ; but in every part 
of the field of the instrument something brighter appeared in 
its fixed place. 
Whoever is pleased to compare these two observations im- 
partially, I doubt will not consider them as illusions. To me 
they rather appear, in'more.than one respect, convincing and 
important. In the first evening, the southern horn, as two 
observers agreed, changed its form very quickly, that is in 15 
minutes, so much that the difference between it and the northern 
was not nearly so striking as before. In the second evening, 
the air being clearer, and the image excellent, this change was 
still quicker ; for in 1 1 minutes, during the observation itself, the 
end passed very evidently to the form of a separate point of light. 
Supposing both changes to be the same, and produced by the 
rotation, the alteration to a separate point of light must have 
happened on the first evening, at most 1 1 minutes later than 6 h 
40', when I intermitted my observation ; that is, about 6 h 51'; 
because on the second evening it took place in 1 1 minutes. But 
on the second evening, when I noticed this striking alteration, 
I no longer knew the time marked the evening before, and 
I now noted down 6 h 1 i'. Consequently this change took place 
the second time very nearly in 24 hours less 40 minutes ; and 
MDCCXCV. S 
