C 516 ] 
This fum of the parallaxes, which I have found 
from each obfervation, is the angle at Mars formed 
by the two vifual rays taken by two obfervers of the 
fame point of Mars. I afterwards deduced, from 
every one of thefe fix obfervations, the horizontal 
parallax of Mars, by taking it in the fame ratio to the 
total fine, which that angle at Mars is to the fum of 
the fines of the apparent diftance of Mars in the ze- 
nith of each obferver ; and I found the horizontal 
parallax of Mars as you fee hereunder. 
175 1 . Aug.31. 
Sept. 14. 
Oft. 3. 
4- 
7 - 
II 
26 
III 
42' 
the hori- 
n 
" 0 
m 
2 i 
27 
10 
zontal pa- 
0 
1 
27 
35 
rallaxes ( 
2 
34 1 
24 
34 
of $ for' 
2 
46 
20 
20 
each ob- 
3 
20 
27 
35, 
fervation. 
\3 
46. 
additional correc- 
tions for reducing 
the parallaxes to 
what they ought to 
be in the opposition 
ofMarstotheSun. 
As the horizontal parallax of Mars varies accord- 
ing to the diftance of Mars from the Earth, I have 
calculated, by Dr. Halley’s tables, the real diftances of 
Mars from the Earth at the times of your fix obfer- 
vations above-mentioned, and at the time of the op- 
pofition of Mars to the Sun j after which, making 
ufe of the ratio between thefe diftances, I examined 
how much the horizontal parallax of Mars muft be 
lefs, in each of your obfervations, than at the time of 
that oppofttion. Thefe are the quantities, which 
comprife the fmall table given above, under the title 
of corre&ions. Thefe quantities, being added to the 
parallax deduced ftmply from each obfervation, have 
given the horizontal parallax, fuch as it ought to be in 
each obfervation reduced to the time of the oppo- 
sition. 
The 
