t 2 33 ] 
ments conftrudted under his own inlpedhon, and 
finifhed by his own hands, was enabled to corredt 
the fo much boafted tables of Lanfbergius, and to 
predidt, with a degree of precifion unknown to thofe 
times, a phenomenon, which he himfelf thought to 
be of great confequence. He immediately commu- 
nicated this important difcovery to his friend, and 
companion in his aftronomical ftudies, Mr. William 
Crabtree, and earneftly exhorted him to prepare for 
the obfervation. The date of the heavens, on that 
day, was not very favourable : however, both Mr. 
Horrox and his friend were lucky enough to obferve 
it ; the former, at a time when the limbs of the fun 
and Venus were in the point of contadt, viz. on the 
24th of November 1639, O. S. And thefe two were 
the firft, and only perfons, that ever faw Venus in the 
fun, before the prefent year. 
By the Rudolphine tables, conftrudted from the 
obfervations of Tycho Brahe, Kepler was enabled 
to predidt, in the year 1629, that Venus would pafs 
over the fun's difk in the year 1761 : and my worthy 
predeceffor, that eminent aflronomer and mathema- 
tician, Dr. Halley, in a memoir published in the Phi- 
lofophical Tranfadtions, N° 348. exhorted the aftro- 
nomers of all countries to attend to this rare pheno- 
menon, with all poffible diligence ; as it would fur- 
niffi them with the belt means of determining the 
parallax and diflance of the fun, and, confequently, 
the dimenlions of the whole folar fyftem. How far 
the method propofed by him, will enable us to folve 
this difficult problem, muft be left to time to difcover, 
when the obfervations, made in places properly fitu- 
ated, can be compared with thofe made here, and 
Vol. LII. Hh in 
