MATHEMATICAL PAPERS. 159 
XII Account of the Tranjit of Mercury, obferved at Cam- 
bridge, November 12, 1782. By James WINTHROP, 
ers, Ea s. l 
HE following obfervations were made at the houfe of 
. the Reverend Profeflor Williams. We ufed the fame 
clock, but obferved the tranfit from different parts of the houfe. 
The clock was regulated by the Profeffor, who reduced all the 
obfervations to apparent time. Mine were as follow : 
Firft external contact, 10? 6'41" A.M. 
Firft internal contact when the thread of light 
was formed, and Mercury recovered his 
roundnefs, — - de; okt - 
Mercury begun to appear PERO before the fe- 
cond internal contact, — - II 21 4I 
Doubtful whether the thread of light was | 
broken, II 22 44 
Second internal contact when the thread of 
light was compleatly broken, 1129 7£ 
Second external contact, | - 1 29 19. 
The magnifying power ror the reflecting telefcope ufed in 
thefe obfervations, was 260. The elliptical appearance of the 
planet was obferved by Mr. Williams as well as myfelf, at both 
paflages over the fun’s limb ; but I do not recolle& to have 
“feen it remarked of any former tranfit of this planet. An idea 
that the {mallnefs of Mercury's apparent diameter and the ra- 
pidity of his motion would not fuffer it to be of any long con- 
finuance, prevented my making more particular remarks at the 
time af the ingrefs, The certainty of a fufficient interval be- 
4c tween 
