III. An Account of the Appearance of Mercury, 
pajfing o'Ver the Suns Visk^ on the ipth of Octo- 
ber, iyiy determining the mean Motion , and 
fixing the Nodes of that (planet’s Orb . By Ed- 
mund Halley, LL. 2). Afiron. peg. and 
S . S'. 
T HE Tranfit of the Planet Mercury , over the Difk 
of the Sun , being one of the moft curious and 
uncommon Appearances that the Heavens afford, our 
Aftronomers, both at home and abroad, made due Pre- 
paration to obferve, with the utmoft Exadnefs, that 
which happened on the 29th of October, 17^3, which 
I had predided in the Year 1691 {Phil. Tranf. 
N 0 193 .) would be, in Part, vihble in England. 
And the Sky proving, more than ordinary, favourable at 
that Time, we were enabled to obferve the Ingrefs on 
the Sun ' s Limb, with the greateft Accuracy. 
Accordingly, the fame Day, Otfob. r^.ftyl. •vet. at 
Greenwich in the Royal Obfervatory , I tirft perceiv’d,, 
with my 24 Foot 1'ube, the Planet making a (mail 
Notch in the Sun' sLitnb at 2 h 4T 23^ T. app. And 
at 2 h 41' 2 he was wholly enter’d, making an interi- 
our Contad, the Light of the Sun's Limb juft beginning 
to appear behind his dark Body ^ which, notwithftand- 
ing the Slownefs of the Motion, was, in a Manner, in- 
ftantaneous. Then, applying the Micrometer to the 
faid 24 Foot Tube, I open’d it fo as to take in i6 / 15 /; 
equal to the Sun's Semidiameter at that time and 
cauling the northern Edge of the Sun , to move exactly 
along one of the Pointers, I waited till the Center of 
Mer - 
