150 
Mr. Schroeter's new Observations 
not be a decisive contradiction, if some observations made at 
the same time by another person, were in opposition (though 
that is not the case) to so many of mine, made in various ways, yet 
agreeing together; because, when fallacy of vision is in ques- 
tion, it may always be doubted which of the two observers is 
deceived ; since this depends on the goodness of sight and of 
instruments, but much more on care and caution.* 
I confess impartially, that, before reading the observations 
contained in my two memoirs, I should have formed the same 
judgment from those of the abovementioned author that he 
has done; and on that account his paper is highly valuable to 
me, as leading to a more scrupulous examination of new truths. 
3. However, that which these new observations, here com- 
municated, clear up and confirm, in correspondence with my 
older ones, on the mountains and rotation, is, that the planet 
Venus has very considerable mountains and elevated ridges; 
and indeed the most and the highest in her southern hemi- 
sphere. This appears 
( a ) From the observations of the boundary of illumination, 
which is not sharply terminated, and seems formed of light 
and greyish shadow indistinctly intermingled. This is chiefly 
to be perceived only about the time of the greatest elongation, 
* By comparing the respective times of the two observers, it appears that both of 
them viewed the planet on the 4th of April at y h 30', p. m. ; the 5th April at 6 h 38', 
the 6th April at 6 h 38', and the 7th at y h 15', exactly at the same time, and saw ex - 
actly the same appearance. The comparison of these observations is the more in- 
structive, because I did not, like my opponent, observe Venus only once, but as often 
as was possible each day, and at other times, on the same days, found evident changes', 
for this shews plainly enough, that whoever wishes to see the same, and as much, in 
Venus, must observe with equal industry, and on each day as many hours as possible, 
with the same care. 
O 
