[ i84 ] 
not having obferved the tranfit of 1761, I had con- 
ceived a prejudice that it would not be polfible to 
oblerve the external contact with any accuracy, and 
therefore I negled'ed to make any other minute of 
what I faw of it, but that 1 was certain that the Pla- 
net was upon the Sun by 5'' after feven, by my regu- 
lator. Mr. Cyril Jackfon, a ftudent of ChriH; Church, 
who obferved in the fame room with me, told me, 
wdicn all was over, that he thought he had notice of 
the Planet’s approach, by a more vehement undulation 
in that part of the Sun’s limb where the Planet en- 
tered than in any other, which he perceived a very 
lliort time before he faw the Planet. I confefs that 
I was not fenfible of this circumftance. 1 obferved 
with an 18 inch refledor ; Mr. Jackfon iifed a re- 
frador of Mr. Dollond’s of nine feet. The wind 
w'as high, and very troublefome to both of us, by the 
motion it gave to our inlbruments. 
When the Planet had been fo long upon the Sun’^ 
limb, and fo large a part of its circle wms plainly en- 
tered, that I thought the internal contad: was near at 
hand, I was much aftonifhed to find the fhape of 
the black fpot fuddenly altered from a large fegment 
of a circle, to what 1 have attempted to exprds very 
rudely by a (ketch, fee Tab. VII. Fig. i. where 
the lower part, which (fill feemed the fegment of a 
circle, is conneded with the Sun’s limb, by a kind of 
ligament of darknefs terminated on each fide by fight 
lines. The ligament detached itfelf from the Sun’s 
limb; and the light, as I thought, was vifible, all 
round the Planet, at 21' ^ 2 ", by my regulator, 
and not earlier to my eye. And this I fet down as 
the internal contad. The moment that I perceived 
the 
