[ 35 1 ] 
the fedors, made before mine, have probably been 
liable. Indeed the fault became more glaring here, 
by the workman’s having made the diametei of 
the neck of the central pin fo large as Ag-th of an 
inch ; but that the errors cannot be entirely removed 
by leffening the neck of the pin, I can affert from 
my own experience, having caufed a pin to be made 
with the neck only T V th of an inch in diameter (and 
beyond that it cannot well be reduced) by which I 
ffcill found an irregularity in the fufpenfion of the 
plumb-line, to the amount of 3", a quantity, though 
feemingly fmall, yet of great confequence in the nice 
obfervations to which this inftrument is geneially 
applied, and which it is capable of taking to a pio- 
digious exadnefs, when the fufpenfion of the plumb- 
line is accurately provided for. Mr. Biid has con- 
trived one of fix foot length, for fettling the limits 
between Pennfilvania and Maryland, in which the 
plumb-line is adjufted fo as to pafs over againft, and 
bifletf: a fmall point at the centre of the inftru- 
ment. _ . . 
I cannot, on this occafion, omit remarking that the 
late learned Abbe de la Caille s fedor, with which 
he made his principal obfervations, from fome of 
which I inferred the probability of an annual par- 
- allax of Sirius, feems to have had a like fault with 
nay fedor, as may be inferred not only from the 
differences in the obfervations themfelves, but alfo 
from the brief account of the fufpenfion of that in- 
ftrument, contained in a letter with which I have 
been favoured by M. Delalande from 1 aiis, an extrad 
of which I prefented to the Royal Society. Vide 
Phil. Tranf. Vol. LII. Part 2. Page 607. 
Let 
