C 4” ] 
peared to be very difficult to judge precifely of the times that 
the internal conta£ls of the body of Venus happened, by reafon 
of the darknefs of the penumbra at the Sun’s limb, it being 
there nearly, if not quite, as dark as the planet. At this time a 
faint light, much weaker than the reft of the penumbra, appeared 
to converge towards the point of contadi, hut did not quite 
reach it, fee fig. 2. This was feen by myfelf and the two other 
obfervers, and was of great affiftance to us in judging of the 
time of the internal contadls of the dark body of Venus, with 
the Sun’s limb. Fig. the 5th, is a reprefentation of the appearance 
of Venus at the middle of the egrefs and ingrefs, for the very fame 
phaenomenon was obferved at both : at the total ingrefs, the 
thread of light made its appearance with an uncertainty of feve- 
ral feconds ; I judged that the penumbra was in contact with 
the Sun’s limb 10" fooner than the time fet down above ; in 
like manner at the egrefs the thread of light was not broke off 
or diminifhed at once, but gradually, with the fame uncertainty: 
the time noted was when the thread of light was wholly broke 
by the penumbra. At the total egrefs I found it difficult to 
diftinguifli Venus’s limb from the penumbra; which of courfe 
made the fecond external contadl a little doubtful, and the pre- 
cife time that the penumbra left the Sun could not be obferved 
to any great degree of certainty, at leaft by me. Some of the 
other gentlemen, who were fent to obferve at different places, 
faw at the ingrefs and egrefs the fame phaenomenon as we did j 
though much lefs diftindt, which no doubt was owing to their 
telefcopes being of a lefs magnifying power ; for the penumbra 
was vifible through my telefcope during the whole Tranfit ; and 
Dr. Solander, whofe telefcope magnified more than ours, faw it, 
I have reafon to think, diftindter than either Mr. Green or my- 
felf; though we both of us faw enough to convince our fenfes, 
that fuch a phaenomenon did indifputably exift, and we had 
a good opportunity to obferve it, for every wifhedTor favour- 
able circumftance attended the whole of that day, without one 
fingle impediment, excepting the heat, which was intolerable : 
the thermometer which hung by the clock and was expofed to the 
fun as we were, was one time as high as 119®. The breadth 
of the penumbra appeared to me, to be nearly equal to f th of 
Venus’s femidiameter. 
G g g 2 
Tranfit 
