124 Mr. Schroeter's new Observations 
observations hitherto, as for instance those on the visible lu- 
minous spots in the dark part of the moon, on the apparent 
changes of the moon's surface, &c. have been confirmed by 
others. 
From these remarks, the answer will readily present itself, 
3. How the author of that paper could look upon my ob- 
servations on the rotation of Venus as unfounded, though 
there are so many of them which agree together, and he had 
not read and compared them; and could think the period of ro- 
tation as much undetermined as before. Whoever deigns to 
bestow some attention on my memoir on the rotation of Ve- 
nus, will soon find, 
( а ) That certainly I did' not go to work carelessly, but first 
arrived gradually at an approximate estimation by almost innu- 
merable observations made in very different ways. 
Although I perceived, as early as in the year 1786, some lumi- 
nous spots of Venus, which seemed to me to shew a period of 
rotation of about 24 hours, as Dom. Cassini had also thought , 
yet I suffered them to lie unpublished six years, because I was 
doubtful whether some delusion might not have intermixed 
itself; until at length a favourable opportunity accidentally 
led me to pursue the investigation of this subject hi. an entirely 
different manner. 
(б) It will also be found that the author, among his obser- 
vations, which taken altogether are but few, cannot shew a 
single one in which he observed at the same time with me. But 
every person conversant in these- subjects will agree with me, 
that in order to prove the inaccuracy of my observations, or at 
least render them doubtful, it is essentially necessary, that an 
impartial observer should have directed his attention with 
