[ 35 ° ] 
the fame time, offered a propofal tor the di/covery 
of the fame, by obfervations of the zenith didance 
of that dar, to be made at the ifland of St. Helena. 
But, unfortunately, when I came to let up the fedor 
there (which, through the tardinefs of the workman 
in finifhing it, I had not had an opportunity of 
proving, as I had wifhed, before my departure from 
England) I loon found a ftrange irregularity in the 
obferved zenith didances of the dars, amounting to 
io, 20, and fometimes even 30 feconds. After 
having fatisfied myfelf, by various trials, that theie 
great differences in the obfervations did not arile from 
any bending of the tube of the telelcope, which 
conditutes the radius of the indrument, or from any 
lcofenefs in the objed-glafs, or indability of the 
wooden three-legged Hand, which fupports the fedor , 
I, at lad, found the caufe of error to lie, where I 
had lead fufpeded it, in the imperfedion of the 
fufpenfion of the plumb-line (which is a fine diver 
wire) from the neck of the central pin; for, upon 
taking the loop of the plumb-line off the pin, and 
putting on again, after turning it half round, or 
putting on a new one, 1 found the plumb-line 
would apply itfelf to a different part of the limb of 
the fedor, commonly by 10, and frequently by 20 
feconds. This experiment, with the fame event, I 
had the honour of exhibiting before a committee of 
the Royal Society, for their fatisfadion, as to the 
caufe of the failure of my intended obfervations, 
September n, 1762, at the Britifh Mufeum. 
The irregularities in quedion evidently arofe from 
the fridion of the loop of the plumb-line againd the 
neck of the central pin ; a fault, to which mod of 
the 
