154 Mr. Schroeter's new Observations 
happens, the weather was not always favourable ; and besides-, 
the observations already communicated contain sufficiently evi- 
dent marks of a libration, whence such cases may be easily 
explained. So, for example, the mountainous ridges of the 
moon's southern edge, Leib?iitz and Doerfel, do not shew them- 
selves quite clearly at each rotation, but only sometimes ar- 
rive at their full projection. 
(c) But the very circumstance, that during more than four 
years, in so great a number of observations, I have perceived 
this phenomenon only eleven times with perfect certainty, 
and only a few other times uncertainly, and that in all the 
intervals I have expected it in vain, notwithstanding my fre- 
quent wishes, seems alone to shew, evidently enough, that I 
cannot have been deceived ; especially as those appearances 
have been seen, with various magnifying powers of different 
telescopes, and in several instances with different eyes, per- 
fectly alike, and with full certainty ; and it is not reconcileable 
to our understanding, how such a fallacy should, at different 
times, always preserve one and the same period. 
The following example, which I here take an opportunity 
of adducing as remarkable, may shew how cautious we 
ought to be, in drawing conclusions from our own obser- 
vations, against the truth of those made by others. Jan. 5, 
1 reviewed with the 13 and 25-feet reflectors the Mare Cri- 
sium (Hevel. Palus Maeotis) in the moon, and made some 
observations. The following day. Dr. Olrers of Bremen, who 
now pursues his observations with an extremely good 5-feet 
Dollond of 3f inches aperture, mentioned to me, that he had 
discovered the preceding evening , in the Mare Crisium, between 
Picard and Auzout, two small craters in the grey plain. 
