VOL. LXXVI.] PHILOSOPHICAL TRANSACTIONS. 33 



strument, or line of collimation, by observation of the zenith stars, with the 

 face of the instrument on the east and on the west side of the wall : and that 

 having made the index stronger (to prevent flexure) than that of the sextant, and 

 thereby heavier, he contrived, by means of pullies and balancing weights, to re- 

 lieve the hand that was to move it from a great part of its gravity. 



I have been the more particular relating to Mr. Sharp, in the business of 

 nstructing this mural arc ; not only because we may suppose it the first good 

 and valid instrument of the kind, but because I consider Mr. Sharp as the first 

 person who cut accurate and delicate divisions on astronomical instruments ; of 

 which, independent of Mr. Flamsteed's testimony, there still remain considerable 

 proofs : for, after leaving Mr. Flamsteed, and quitting the department above- 

 mentioned ; * he retired into Yorkshire, to the village of Little Horton, near 

 Bradford, where he ended his days about the year 1743 ; and where I have seen 

 not only a large and very fine collection of mechanical tools (the principal 

 ones being made with his own hands,) but also a great variety of scales and in- 

 struments made with them, both in wood and brass, the divisions of which were 

 so exquisite, as would not discredit the first artists of the present times : and I 

 believe there is now remaining a quadrant, of 4 or 5 feet radius, framed of 

 wood, but the limb covered with a brass plate ; the subdivisions being done by 

 diagonals, the lines of which are as finely cut as those on the quadrants at 

 Greenwich. The delicacy of Mr. Sharp's hand will indeed permanently appear 

 from the copper-plates in a quarto book, published in the year 17 18, intitled, 

 " Greometry improved by A. Sharp, Philomath," of which not only the geo- 

 metrical lines on the plates, but the whole of the engraving of letters and figures, 

 were done by himself, as I was told by a person in the mathematical line, who 

 very frequently attended Mr. Sharp in the latter part of his life. I therefore 

 consider Mr. Sharp as the first person that brought the affair of hand division to 

 any degree of perfection. 



Some time about the establishment of the mural arc at Greenwich, the cele- 

 brated Danish astronomer Olaus Roemer began his domestic Observatory, which 

 he finished in the year 1715, as we are informed by his historian Peter Horre- 

 bow, in the 3d volume of his works, in the tract, intitled, Basis Astronomige, 

 published in the year 1741. In this tract is the description of an instrument 

 which not only answered the purpose of the meridian arc ; but, its telescope 

 being mounted on a long axis, became also in reality what we now call a Tran- 

 sit Instrument ; and which furnished, so far as I have been able to learn, the first 

 idea of it. One end of the axis of this instrument being the centre of the 



* Mr. Sharp continued in strict correspondence with Mr. Flamsteed so long as he lived, as ap- 

 peared by letters of Mr. Flarasteed's found after Mr. Sharp's death ; many of which I have seen. — 

 Orig. 



VOL. X.VI. F 



