[ 345 ] 
or a M given, therefore the third fide S M may be 
found, therefore S M the geocentric leaft diftance of 
the centers is found ; and if to S M, we add or fub- 
tradt the parallax of latitude for the apparent middle 
of the tranfit, the fum or difference will be the ap- 
parent leaft diftance of the centers. 
EXAMPLE. 
To find the apparent lead diftance of the centers 
at Tobolfk. 
The total duration obferved at Tobolfk was 
5 h 4 ^ 53 7/ a ^d 9' z" (— to t ^ e effedl of the paral- 
laxes of longitude and latitude both for the ingrefs 
and egrefs, on the fuppofition that the Sun’s parallax 
is — 8", 5) to this total duration, the fum 5 11 57' $6" 
is — to the central duration, confequently 2 h ^8 / ^8 // 
is — the central femi-duration : reduce this time in- 
to fpace, and it will be found — to 71 5", 956 — 
AM or ^ M, and S A or S a (— difference of the 
femi-diameters of the Sun and Venus) — 9 r6 // , there- 
fore S M will be found — : 571", 37 — the geocen- 
tric leaf: difiance of the centers of the Sun and Ve- 
nus. The parallax of latitude, computed on the 
above fuppofition of the Sun’s parallax, for the appa- 
rent middle of the tranfit at Tobolfk, will be found — 
i4 7/ > 13* w hich being added to the geocentric leafi 
difiance of the centers above found, the Sum 585 v , 50 
will be the apparent leaft diftance of the centers at 
Tobolfk. 
XLVIII; An 
