Yu ^ ASTRONOMICAL Anba M 
"glafs micremeter made by Sort, with a magnifying power of 
60 ; and an aftronomical clock made by E//icoz. ^ 'T'o tegulate 
the clock with the greateft accuracy I took a large number of 
correfponding altitudes of the fun every day the weather would 
permit from the: beginning of October, and found by- the moft 
careful attention «that it kept equal time very exactly: The. 
greateft error at any time not - more than two feconds in 
twenty-four hours. 
-cOn the 12th of November the weather was fair, but the air 
was not in the moft favourable. ftate for obfervation, _ Viewing 
the fun with an excellent achromatic telefcope, I found the 
Spots on the difc well defined ; but the limb appeared to have 
_ an irregular, tremulous motion. - This tremor, or undulation 
of the fun’s limb, was of different degrees at different times ; 
but it did not a ceafe any part of the day. 
| -my eye fteadily fixed on that part 
nb e eM $: ich the planet was to enter ; and at ni 
apparent time, I faw the firft appearance “of Merc ry. 
The i se prelfioh feemed to be fudden and inftantaneous, ind wid? 
out any uncertainty as to the time. But the appearance was 
not like the conta& .of .two.circles, ¿or like that .of a well-de- 
fined black {pot entering. upon the fun ; "but rather like a dark 
oval fhadow inftantly entering and. vibiirrem? the fun's limb. 
Plate I. Fig. VIII. While Mercury was thus entering upon 
the fun, no pert of it was vifible but that which was within 
the fun’s dif. It's figure appeared tobe elliptical : The greater 
"ati emet to pa through the point of contact, and to be 
it one-third longer than the other. This elliptical appear- 
; planet made it = cg to determine when the 
= limbs 
