6 Mr . Smeaton’s Obfervatlons on the 
with fcrew and diagonal divifions, all performed by the accurate 
hand of Mr. Sharp. But yet, whoever compares the different 
parts of the table for converfion of the revolutions and parts of 
the fcrew belonging to the mural arc into degrees minutes and 
feconds with each other, at the fame diftance from the zenith 
on different fides ; and with their halves, quarters, &c. will 
find as notable a difagreement of the fcrew- work from the hand-* 
divifions, as had appeared before in the work of Mr. Tompion ; 
and hence we may conclude, that the method of Dr. Hook, 
being executed by two fuch mafterly hands as Tompion and 
Sharp, and found defective, is in reality not to be depended 
upon in nice matters. 
From the account of Mr. Flamsteed it appears alfo, that 
Mr. Sharp obtained the zenith point of the inftrument, or line 
of collimation , by obfervation of the zenith ftars, with the face of 
the inftrument on the eaft and on the weft fide of the wall + : 
and that having made the index ftronger (to prevent flexure) 
than that of the fextant, and thereby heavier, he contrived, by 
means of pullies and balancing weights, to relieve the hand that 
was to move it from a great part of its gravity *f . 
I have been the more particular relating to Mr. Sharp, in the 
bufinefs of conftrudting this mural arc ; not only becaufe we may 
fuppofe it the firft good and valid inftrument of the kind, but 
becaufe I look upon Mr. Sharp to have been the firft perfon 
that cut accurate and delicate divifions upon aftronomical inftru- 
mentsj of which, independent of Mr. Flamsteed’s teftimony, 
there ftill remain confiderable proofs : for, after leaving Mr. 
Flamsteed, and quitting the department above-mentioned 
* Hill:. Cceleft. voi. II, Appendix. f Prolegom. p. 109. 
X Mr. Sharp continued in ftrid correfpondence with Mr. Flamsteed fo long 
as he lived, as appeared by letters of Mr. Flamsteed’s found after Mr. Sharp’s 
death j many of which I have feen. 
lie 
