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30 ASTRONOMICAL AND 



The londtude of the nonao-esimal de^-ree, at the time of 



each contact, being less than the longitude of Mercury, the 

 parallax in longitude is to be added to Mercury's longitude, 

 at the time of each, to give the visible ; and as Mercury's 

 motion in transits is retrograde, and the parallax, at the time 

 of the second external contact, was greater than at the time 

 of the first, the length of the visible transit line was greater 

 than the true, by the difference of the parallaxes. 



The true latitude, at the time of each contact, Avas in- 

 creased by the parallax in latitude j and as the geocenti'ick 

 latitude was decreasing, and the parallax, at the time of the 

 second external contact, was greater than at the time of the 

 first, the visible motion in latitude was less than the true, 

 by the difference of the parallaxes. Hence, we may easily 

 find MU and ^ U as follows: 



^ 's parallax in Ion. from ^ iit 1st exi cont. S". 333 



Do. 



at 2d. 0. 29 



Difference. 



3. 043 



^'s motion on the G's disc, with respect 

 to the ecliptick, in 4*^ 53' 32''. | • ^^' ^^''' ^^ 



1711". 06 

 Add the difference of parallaxes in lono;itude. 3. 043 



The Sun is = M U. 



1714. 103 



parallax in lat. from O at 1st 



D 



2// 309 



at 2d. 3.- 41G 



Difierence. 



1. 004 



^ 's true 



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