[ 3’8 ] 
XXXIII. Account of an Obfervation of the Right Afcen/ion and 
Declination of Mercury out of the Meridian , near his greattjl 
Elongation , Sept. 1786, made by Mr, John Smeaton, F. R. S. 
with an Equatorial Micrometer, of his own Invention and 
IVorkmanJhip ; accompanied with an Invefigation oj a Method 
of allowing for Refradtion in fuch Kind of Obfervations ; com- 
municated to the Rev . Nevil Mafkelyne, D. D. F. R . S. and 
ylfronomer Royal , and by him to the Royal Society . 
Read June 7, 1787. 
M de la Lande having announced to fome of my aftro- 
• nomical friends the utility of accurate obfervations of 
Mercury, at his two elongations the laft year, in Auguft and 
September ; I tried to get obfervations of that planet in crof- 
ling the meridian, for fome days before and after the greateft 
elongation in Auguft ; and though the ftate of the atmofphere 
about that time was not very favourable to the purpofe, yet 
there was one day that I thought unexceptionable, but could 
not perceive the leaft appearance of Mercury j at which I was 
the rather furprifed, as I had formerly feen that planet in the 
like fituation, with the fame inftrument, with perfedt perfpi- 
cuity * : and as I did not hear of any one elfe having fucceeded 
in 
* The inftrument mentioned is a tranfit, made by myfelf in the year 1768; 
at which time achromatic objeft-glafles not having been, fo far as I knew, applied 
to agronomical inftruments by others, but having found the good effedts thereof 
for 
