[ 5*7 1 
The calculations being made, here follows what I 
have found with refped to the horizontal parallax of 
Mars at the time of the oppofition. 
By the obfervation of 3 1 Aug. 
14 Sept. 
3 Od. 
4 
7 
9 
// m 
*7 
9 
27 
/ 
1 1 
30 
9 
# 
27 
20 
2 3 
40 
* 
2 7 
39 
By taking a mean or arithmetical medium between 
thefe 6 determinations, we may conclude the hori- 
zontal parallax of Mars, at the time of the oppo- 
fition, to be 27" 11"' : but as there are two determi- 
nations, which differ from each other about 3", and 
which are thofe of the 3d and 7th of Odober; we 
may rejed them, and then we fhall find the mean 
between the other four to be 27" 20"'. Hence you 
fee, Sir, that whether we reject thofe two determi- 
nations, or employ them, the horizontal parallax of 
Mars, at the time of the oppolition, comes out near 
27" 4-; a nd according to the ratio of the diftance of 
the Sun and Mars from the Earth at that time, we 
conclude the horizontal parallax of the Sun to be 
about 10" ~. 
This is what I have been able hitherto to conclude 
from your obfervations of Mars, with refped to the 
parallax of the Sun. Having made the fame calcu- 
lations from my own obfervations, and thofe of other 
aftronomers, which I could hitherto colled ; I have 
found very near the fame parallax of the Sun, by 
