d 
160 ASTRONOMICAL “ANd 
tween the laft contacts, enabled me to attend more particularly 
to this obfervation at the end, than at the beginning of the tran- 
fit. Ati1'21' 41^ apparant time, Mercury began to appear 
diftorted ; and from this time the thread of light grew gradu- 
ally fainter till 11^ 22' 44", when I was doubtful whether it ex- 
ifted any longer. I fet down the fecond internal conta&t at 11* 
.23' 5", when I was firft certain that the thread of light was 
broken. From the time that the center of the planet appeared 
to me to have paffed the fun’s limb, the appearance of it’s fol- 
lowing half became very irregular, being difturbed by a brifk 
undulatory motion, which continued till the end of the tranfit. 
This diftortion appears to be common to both the inferior 
planets, when in the fame fituation with refpe@ to the obferver. 
At the tranfit of Venus in 1761, it was obferved in India, Eng~ 
land and Sweden ; and at that of 1769, by almoft all who ob- 
ferved the tranfit. They indeed v vary in their ideas of its dura- 
tion ; which cannot be wondered at when we confider the dif- 
. ferent magnifying power of their inftruments, and the different 
ftrength of their eyes. Particular defcriptions of the appear- 
ance of Venus, in her two tranfits, are publifhed in Vols. LIX. 
LX. and LXI. of the Philofophical Tranfactions, with fuitable 
projections ; and'from the great refemblance they bear ito the 
‘appearance of Mercury in his laft tranfit, the conclufion is na- 
tural that they arofe from the {ame caufe. 
The object is fo fmall and remote, that-we can hindi: ex- 
pect to determine it's caufe with abfolute certainty. It will 
»mot, however, be deemed amis to remark, asa probable - cauíe 
only, that the rays proceeding from fo fmalloan | abject as that 
pert of the fun's limb which is neareft to the planet, during 
| — of the latter, are too feeble to make a full im- 
preflion. 
* 
