C 53s 3 
For, let S be the Sun,T the Earth, V Venus. Were 
there no aberration of light, the Sun would be always 
feen in its true place, or in the direction TS. But, in 
reality, in confequence of aberration, it will be feen 
20" lefs advanced in the ecliptic, or in the direction 
T.r, fuppofing STs to be an angle of 20". Now a 
calculation from tables giving the true places of the 
Sun, would fix the moment of a conjunction, to the 
time that Venus gets to TS ; but this, though the time 
of the true conjunction, would not be the time of the 
obferved conjunction ; for the Sun being then really 
feen in the direction Ts, Venus, after getting to TS, 
muft move 20", or from a to c } before the apparent 
conjunction can take place. 
But if the calculations 
are made from the appa- 
rent places of the Sun, the 
conjunction will be fixt to 
the time Venus gets to t S, 
or a line drawn through S 
parallel to s T, for in this 
cafe t will be the point of 
the ecliptic oppofite to the 
apparent place of the Sun, 
and the longitude of the 
fun feen from t will be 20 // 
lefs than its true longitude, 
and therefore the fame with 
its apparent longitude. But 
the Earth being then really 
at T, Venus will, at the 
calculated time of a con- 
junction, be obferved at a 
diflance from the Sun equal 
to the angle LTr. T his 
angle, fuppofing V T 277, 
and V S 723, maybe eafily 
found 
