and Longitude of the Royal Obfervatory at Greenwich, 
in his Memoir of an uncertainty of 15" in the latitude of 
Greenwich ; but he might have been induced to believe, 
that the latitude of this place had been well determined. 
For further confirmation of the certainty of the agronomical 
refractions, and latitude of the Obfervatory, as fettled by Dr. 
Bradley, it may be proper to add, that the Greenwich brafs 
mural quadrant underwent a trial, which all aftronomical in- 
ftruments ought to be fubmitted to, but which very few ever 
have been, on account of the difficulty and nicety of the ope- 
ration, namely, an examination of the total arc ; when it was 
found by Dr. Bradley to be an accurate quadrant, the arc 
appearing at one trial to differ only a fraction of a fecond from 
po°, and another time, after an interval of above fix years, to 
be a perfeCt quadrant. See p. 24. of Bird’s Method of con- 
ftruCting Mural Quadrants, publiffied by the Board of Longi- 
tude in 1768. In like manner he had before examined the 
total arc of the iron quadrant, firft put up by Mr. Graham, 
for the ufe of Dr. Halley, in the year 1725, by means of a 
level, and found it to be 16" lefs than a quadrant. See Bird’s 
Method of conftruCting Mural Quadrants, p. 7. and Memoires 
of the Royal Academy of Sciences at Paris, for 1752, p. 424. 
But this quadrant was, in the year 1753, re-divided by Mr. 
Bird, and, in this refpeCt, probably rendered as accurate as 
the other. See Bird’s Method of conftruCting Mural Qua- 
drants, p. 24. 
Dr. Bradley made a curious ufe of the new fet of divisions, 
foon after they were laid upon the quadrant, to re-examine the 
error of the total arc laid down originally by Mr. Graham 
(which by the plumb-line and level he had found to be 1 6 7/ lefs 
than a quadrant in 1 745) according to the following paffage 
contained in the manufcript before cited. 
“ Auguft 
