on the Planet Venus. 
167 
ther : this, however, has not been done, at least as yet ; for if 
we compare with these measurements and calculations, which 
are certainly as accurate as 1 could make them, 
(y) Dr. Herschei/s observation of the 2,0th May , 1793, when 
he measured the projection of the horns beyond a semicircle, 
in the evening likewise, about half past eight, but a day earlier 
than I did ; it will be seen that he determines the magnitude 
of this projection on a mean from two measurements, with the 
extreme exactness of decimal parts of a second, to be 18 0 9' 
8", 2. But this mean is from two measurements which differ 
from each other, not barely by seconds or minutes, but by 
many degrees. In order to judge of the dependance to be 
placed on them, I will consider each of his measurements sepa- 
rately. 
1st measure, log. 500 2,6989700 
log. 1195 3 >° 773 6 79 
9,6216021 
= 24° 44' 3 " 
I Id measure, log. 620 2,7923917 
log. 2400 3,3802112 
— 
9,4121805 
= 14° l8 " 
His two measurements, therefore, give separately, the first 
24 0 44', the second only 14 0 58'. An enormous difference of al- 
most ten degrees, which, according to my humble judgment, 
leaves the mean uncertain, not to seconds and their decimal 
parts , nor even to minutes, but properly to 5 degrees. It would 
therefore be useless to compare further with mine two examples,. 
