on the Planet Venus. 
i6l 
two measurements, which differ from one another so very much 
as ± of the whole magnitude. I can also assure him, that the 
7-feet speculum, which I obtained in the year 1786 by his 
friendly kindness, has continued always so precious to me, that 
I have kept it in perfectly good condition to the present time. 
As to 
(c) the objection, that my calculation abounds with inaccu- 
racies, it is indeed true, that the observation of March 12th, 
1790, was not rigorously computed, yet its exactness was car- 
ried much further than is necessary in observations of this kind; 
for no one will comprehend the use of a scholastic computation 
to seconds and decimal parts of seconds, when the observations 
themselves leave an uncertainty of many minutes. However, 
to remove all doubt in this respect, and to save the author the 
trouble of a further careful comparison with his two measure- 
ments, I will here not only repeat the calculation in all its 
rigour, but also add the new one for my second measurement 
of the 21st May, 1793, and compare both together, as well as 
with that of my opponent. 
(a) Calculation of my observation of the 12 th March 1790, 
6 h o', p. m. 
The time of this observation may be taken, without scruple, 
as 6 h o' mean Paris time; for it was made after 6 o'clock at 
Lilienthal. The equation of time amounts to 10', and the dif- 
ference of meridians to 2 6 ' ; therefore, if the observation had 
been made exactly at six, this would be 5 11 44' mean time at 
Paris. 
Now, according to the latest tables by M. de la Lande, we 
have, for that moment, 
MDCCXCV. 
Y 
