[ ^ ] 
and alfo to place the leaver exa&ly in the center. By 
-which means there has been no alteration required 
fince they were firfi: fixed j and the engine continues 
to work as even, and true as it is pofiible. 
I have applied wheels for reducing fridtion to fome 
other engines with great advantage, which I fhall 
take the liberty of laying before the Royal Society 
fome other time ; and fear I have trefpafied too much 
on their patience already by this long detail. 
XXIX. The Difference of Longitude between 
the Royal Obfervatories of Greenwich and 
Paris, determined by the Obfervatio?is of 
the Tr unfits of Mercury over the Sun in the 
Tears 1723, 1736, 1743, and 1753 : By 
James Short, M. A. F. R. S. 
Read June 2, y T will, no doubt, appear furprizing, 
1763- y that [ fhould attempt to determine the 
difference cf longitude between two of the moil ce- 
lebrated obfervatories in Europe ; and in which fome 
of the greateft aftronomers, that ever lived, have, 
for above eighty years, been conftantly obferving 
the motions of the heavenly bodies : yet it is moil: 
certain, that, to this day, we are ignorant of the Paid 
difference of longitude : the Englifh aftronomers 
reckoning it to be = t) r 2o // , and the French let- 
ting it down at y' io // , which, they tell us, w r as 
found 
