246 PHILOSOPHICAL TRANSACTIONS. [ANNO I716. 



parallax, while she passes over the sun's disk, in such elevations of the pole 

 as are near the Tropic; and still more so near the equator. For Venus will at 

 that time accurately enough describe within the sun's disk 4 minutes an 

 hour; and consequently, at least 11 minutes of time (by which the duration 

 of this eclipse of Venus will be contracted by reason of the parallax) answer 

 to 4 of a minute. And by this contraction alone we might safely determine 

 the parallax, provided the sun's diameter and Venus's latitude were very ac- 

 curately given ; which yet we cannot possibly bring to a calculation, in a 

 matter of such great subtlety. 



We must therefore have another observation, if possible, in places where 

 Venus possesses the middle of the sun at midnight, viz. under the opposite 

 meridian, that is, 6*^ or go'' more westerly than London, and where Venus 

 enters the sun's disk a little before his setting, and goes off a little after his 

 rising ; which will happen in the said meridian in about 56° of N. lat. that is, 

 at Nelson's harbour in Hudson's Bay. For, in the neighbouring places Venus's 

 parallax will protract the duration of the transit, and make it at least 6 minutes 

 longer; because while the sun seems to tend under the pole from west to east, 

 these places on the earth's surface will seem to be carried with a contrary 

 motion towards the west, that is, with a motion conspiring with the proper 

 motion of Venus ; consequently Venus will seem to move slower within the 

 sun's disk, and continue longer on it. 



If therefore in both places this transit happen to be duly observed by proper 

 persons, it is evident that the Mora will be longer by 17 entire minutes in 

 Nelson's harbour, than in the East-Indies; nor does it matter much whether 

 the observation be made at Fort St. George, commonly called Maderas, or at 

 Bencoolen on the western coast of the island of Sumatra near the equator. 

 But if the French should incline to make the observation, Pondicherry on the 

 western coast of the gulph of Ganga, at the elevation of 1 2°, will be a proper 

 place for that purpose: and for the Dutch, their famous emporium Batavia is 

 a fit place. And indeed I would have several observations made of the same 

 phenomenon in different parts, both for further confirmation, and lest a single 

 observer should happen to be disappointed by the intervention of clouds from 

 seeing what I know not if those either of the present or following age shall ever 

 see again ; and upon which, the certain and adequate solution of the noblest, 

 and otherwise most difficult problem depends. Therefore again and again, I 

 recommend it to the curious strenuously to apply themselves to this ob- 

 servation. 



By this means, the sun's parallax may be discovered, to within its five hun- 

 dredth part, which will doubtless seem surprising to some: but yet, if an accu- 



