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minillied in the ratio of radius to the line of the polar 
diftance of Venus, will give El U, the difference of 
right afcenlion. 
As the clouds began to difperfe, and the Iky to 
become favourable, at Shirburn cattle, above two 
hours before we had any opportunity of obferving at 
Greenwich, I fhall firtt give the obfervations there 
made by Mr. Hornlby, and afterwards my own at 
Greenwich. But here I would beg leave to premife, 
that, though the numbers are given to parts of a fe- 
cond, the obfervers do not pretend to an imaginary 
exaftnefs, (for they did not eftimate the times of 
paffage nearer than a quarter of a fecond of time) but 
the numbers are fuch as refult from the turning mi- 
nutes and feconds of time into motion, and the re- 
volutions and parts of the fcrew of the micrometer 
into minutes and feconds. 
The fun’s horizontal diameter, as meafured by the 
micrometer, was 3 1' 33", and that of Venus, by fe- 
veral obfervers, 58" ; the following obfervations were 
therefore deduced, by afluming the femidiameter of 
the fun 15' 46". 5, and that of Venus — 29'. 
1. At 17 11 33' 5 o' 7 , apparent time, at Shirburn, 
the center of V enus preceded the part of the fun’s 
limb, cut by the fixed wire, 12' 3 2/ 7 in motion ; and 
the north, or upper limb of Venus, was north of the 
fouthern, or lower limb of the fun, 6' 29" .6 : there- 
fore, the center- of the fun preceded the center of 
Venus in right alcenfion 1' 3 6 r/ -9 s and the center of 
Venus was fcuth of that of the fun in declination 
9 ' 45 / / 8 - The fame, to avoid repetition, in all the 
following obfervations. 
2, At 
