72 PHILOSOPHICAL TRANSACTIONS. [aNNO 1725. 



northern edge of the sun to move exactly along one of the pointers, he waited 

 till the centre of Mercury came to move along the other, as he found it to do 

 at 3^ 1"^ l6". But refraction contracting this difference of declination about 5 

 seconds, the sun being then but about 1 l" high, he concluded that the centres 

 of the sun and Mercury were truly in the same parallel of declination, at 3'' 3™ 

 nearly. 



At Wansted in Essex, Mr. Bradly, Savilian Professor of Astrononiy, ob- 

 served with the Hugenian telescope, of above 120 feet long, the total immer- 

 sion, or interior contact of the limbs, at 2*^ 26"" 45' aeq. time, that is 2*^ 42™ 

 SS"* app. time, or 12 seconds later than I found at Greenwich ; most of this 

 difference being due to the difference of our meridians. And applying the 

 micrometer to that vast radius, he measured the diameter of the planet 10" 45'*. 

 At 2^ 48"" 57' he found the difference of declination between the southern limbs 

 of the sun and planet by the microuieter, in a 15-foot tube, to be 15' 19". 

 Therefore, allowing the observed semidiameter of the planet, and the refrac- 

 tion, the said difference was nearest 15' 30", and consequently Mercury more 

 southerly than the sun's centre in respect of declination, O' 45". 



Mr. George Graham, in Fleet-street, London, observed the first impression 

 on the sun's limb at 2*^ 41"" 9' app. t. and at 2'' 42"' 19' Mercury was entirely 

 within the disk. At 3^ 6"" 41' he measured with a micrometer, in a 12-foot 

 tube, the distance of his centre from the nearest limb of the sun, 2' 13". And 

 again, at 3*" 25"^ 2.1% their distance was found 3' 57"- At 3*^ 34"' 43' he 

 measured the difference of delination, from the northern limb of tlie sun, 

 14' 57", which, corrected by refraction, becomes 15' 4", that is, l' 1 1" more 

 northerly than the sun's centre. 



In the Observatory at Paris, Sig. Maraldi observed the first appearance of 

 Mercury on the sun's limb at 1^ 50"' 13' app. t. and the interior contact at 

 2^ 51"' 48'. And Mr. de Lisle, observing apart, concluded the same at 2^ 51"' 

 37% but suspects it might have been some few seconds later. This gentleman 

 has communicated his observation at large, from whence we shall only borrow 

 the following observed latitudes. 



At 2'' 56"' 20' Latitude Borea Mercurii 3' 36" 



3 00 40 3 42 



3 10 20 3 46 



3 16 12 3 55 



At Bononia, in Italy, Sig. Manfredi observed Mercury indenting the sun's 

 limb at 3'' 26"' 22'; and that he was gotten entirely within, at 3'' 27"' 45'. And 

 these are the observations most to be depended on that have been received 

 from abroad. 



