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XLV. A fecond Letter to the Right Hon. 
the Lari of Macclesfield, P ref dent of the 
Royal Society , concerning the 'Tranft of 
Venus over the Sun y on the 6 th of June 
1761; by the Rev. Nathanael Blifs, M. A. 
Savilian Profeffor of Geometry in the Uni - 
verfty of Oxford, and F. R. S. 
Read Jan 7, 
1762. 
My Lord, 
T H E interior conj'undtions of the pla- 
nets Mercuiy and Venus, that hap- 
pen near the ecliptic limits, have always engaged the 
attention of aftronomers, as they furnifh the belt 
means of determining fome of the moft important 
elements in the theory of thofe Planets. The tranfits 
of the former have been often and carefully obferved 
by the moft eminent aftronomers, ever fince the in- 
vention of the telefcope ; and, it may be prefumed, 
that the elements of Mercury’s theory are eftablilhed 
as accurately as can be expedited. The opportunities 
of obferving Venus upon the fun’s difk occur fo feldom, 
that the aftronomers of thefe days have reafon to think 
themfelves peculiarly happy, in being eye-witneffes 
of fo rare a phenomenon ; more particularly too, as the 
advantages refulting from the obfervationsof this tranfit, 
are, in all probability, of the greateft moment. The 
firft, and only obfervation of this kind, was made by 
our ingenious countryman, the Rev. Mr. Jeremiah 
Horrox, a young gentleman of very diftinguifhed 
abilities, who, by his own obfervations, with inftru- 
ments 
