[ 577 ] 
glaftes; for if thefe are not ground truly parallel, 
which I am afraid they very often are not, by the 
common methods, they may eafily produce a refrac- 
tion of fome minutes. 
As a proof how near different obfervations made in 
compafs of an hour or two will agree in giving the 
fame longitude, February nth, by ten different ob- 
fervations of the diftance of the Moon from the Sun, 
I made the longitude, reduced to noon as ufual, 
28° 57', 29° 5 o', 29 0 16', 2 9 ° 22', 29* 53', 28° 59', 
29 0 30', 29 0 48', 29 0 30', 29°30 / : none of which 
differ above half a degree from 29 0 22 / , which is the- 
medium of them all. March 1 8th, by four different 
obfervations of the diftance of Pollux from the Moon, 
I found the longitude 23 0 52' twice, and 24 0 8 ; twice. 
I never found that a fingle obfervation would give the 
longitude above a degree different from the medium 
refulting from three or four obfervations, and feldom 
above half a degree ; which argues, that the error of 
any fingle obfervation never exceeded two minutes, 
and feldom one minute. 
From the whole, I congratulate the curious aftro- 
nomer and ingenious mariner, that the method of 
finding the longitude, propofed by Sir lfaac Newton, 
is by the improvement of the theory, of which he laid 
the foundation, and, by the great perfection to which 
our artifts have carried the conftruCtion of inftruments, 
rendered practicable in our times, at fea as well as at 
land, to a degree of exaCtnefs fufficient to make it 
of great and valuable utility to the extenfive naviga- 
tion and commerce of our native country. 
4 e '* 
XCIV. Off- 
