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A method of determining the apparent lead: didance 
of the centers of the Sun and Venus from the ob- 
fervation of the total duration of the tranfit ob- 
lerved any one place, and alfo the geocentric lead 
didance of the centers. 
JET BC PL [Tab. XVII. Fig. i.] reprefent the 
difk of the Sun, LSP the ecliptic, OR the 
geocentric path of Venus over the Sun, AD the ap- 
parent path at any place, to the north of the plane 
of Venus’s orbit, SM the geocentric lead didance of 
the centers, A K the parallax of latitude at the in- 
ternal contact at the ingrefs, ND the parallax of la- 
titude at the internal contadt at the egrefs, Ab the 
parallax of longitude at the ingrefs, and rD the 
parallax of longitude at the egrefs. It is required 
to find S F, which is a perpendicular let fall from 
the center of the Sun on the apparent path, and from 
thence to find S M the geocentric lead didance of the 
centers of the Sun and Venus. 
If the parallax of longitude at the ingrefs retards, 
and the parallax of longitude at the egrefs accelerates, 
the total duration will be diortned by the fum of 
thefe two parallaxes of longitude, viz. by Ab and 
c D, and if we make no allowance for thefe paral- 
laxes, the apparent path will appear to have been 
B C, confequcntly a perpendicular from the center of 
the Sun on BC will be SE, longer than the perpen- 
dicular on the true apparent path by F E. But fince 
it is certain that the parallaxes of longitude do not 
deprefs or elevate the planet, and only alter the po- 
Y v 2 fition 
