Transit af Mercury over the Sitn* ^D5 



Iieavefi, P == the horizontal parallax of Mercury from the 

 Surt, L •=i its longitude, a = obi. ecliptic, thtn will the 

 parallax in longitude = P cos A sine L x cos (U — P) 

 COS. a cos L sine (R — P) sine a x cos L sine A, and 

 the parallax in latitude = P cos a sine x — P sine a 

 COS \ sine R : whence we have in the present case the parallax 

 in longitude at the egress or tt = — 2"*972 cos R cos A -f 

 !2'''62032 sine R cos A 4- 1'1375 sine A, and the parallax 

 in latitude or /3 = 3"* 78 sine A — 1 "'64 sine R cos A ; of 

 which the first must be subtracted from, and the second 

 added to, the apparent place of Mercury. 



By computing the reductions from the above formulae, and 

 applying them to the times of the observed transit at the 

 different places of observation specified in the following 

 Table, the differences of their longitudes were as they stand 

 there determined. The Table also contains the quantity of 

 the reduction, and the eff'ect of parallax in longitude and 

 latitude. 



M. Von Zach observed the interior contact only, which 

 Jiiust be reduced by allowing 1™ 30* for the time between 

 the contacts ; and reduced to apparent time it gives 0*^ 41°' 

 J5"8 for the time at observation. 



The shortest distance of the centres, combined with the 

 distance at the moment of the egress, gives the middle of 

 the transit at 21^ 14™ 28^-6, and hence the time of apparent 

 conjunction at 21^ 16'"2'-1 : but as the aberration of i he Sun 

 is — 20"*2, and that of Mercury -j- 18"*33, the true con- 



T4 junction 



