Graduation of Agronomical Injlruments . 5 
which he applied in the obfervations taken in 1 678.- — However, 
notwithftanding this correction, in looking over the obfervations 
noted down as deduced each way, I frequently find a difference 
of half a minute ; not unfrequently 40" ; but in an obfervation 
of the moon, of the 9th June, 1687, 1 find a difference of 55"*, 
which upon a radius of 6 feet 9 inches amounts to more than 
T yh part of an inch. 
In the year 1689, Mr. Flamsteed compleated his mural arc 
at Greenwich ; and, in the Prolegomena before- mentioned, he 
makes an ample acknowledgement of the particular affiftance, 
care, and induftry of Mr. Abraham Sharp ; whom, in the 
month of Auguft, 1688, he brought into the obfervatory, as 
his amanuenfis ; and being, as Mr. Flamsteed tells us, not 
only a very Ikilful mathematician, but exceedingly expert in 
mechanical operations f , he was principally employed in the 
conftruCtion of the mural arc ; which in the compafs of fourteen 
months he finifhed, fo greatly to the fatisfaftion of Mr. Flam- 
steed, that he fpeaks of him in the higheft terms of praife J. 
This celebrated Inftrument, of which he alfo gives the figure 
at the end of the Prolegomena , was of the radius of 6 feet y\ 
inches; and, in like manner as the fextant, was furniflied both 
# Vol. I. of Hift. Coeleft. p. 343. 
t u Qui mechanices perquam expertus, pariter ac mathefeos peritus.” Prole* 
gomena, vol. III. p. 108. 
$ “ Sharpeius fervus meus fideliftimus, ac omnibus quidem dotibus & facul- 
** tatibus erat imbutus, quse ipfum tam fubtili & difficili operi obeundo idoneum 
**• redderent.” Prolegom. ibid. 
And on finifhing the inftrument, he fays, 16 Gradus defcribuntur five nume-> 
tl rantur et exfculpantur, artificiofa manuali opera difti domini Sharp, qui limburn 
46 partitus eft, diagonals duxit, totumque organum abfolvit et perfecit adeo 
“ ut praeftantiffimi quivis artifices poftquam illud confpexerunt et confiderarunt, 
J‘ fe exa&ius id peragere non potuifle, agnoYerint, ,, Prolegom. p. in. 
with. 
