A John Ismay Gunter Quadrant, English, early 18th century
Lot 3
A John Ismay clockmaker's brass quadrant, English, early 18th century,
Sold for £4,750 (US$ 7,983) inc. premium
Lot Details
A John Ismay clockmaker's brass quadrant, English, early 18th century,
The obverse is engraved along the limb with a degree scale reading by a double sub-division to 20 arc minutes and numbered by groups of ten degrees. Concentric with this is a calendar scale with five day divisions and the inscription 'Lat: 54° 48' for the Gunter quadrant diagram drawn above. In the apex is a decimal shadow square, reading to 50 parts by ten groups numbered 1-9 (ten is not engraved through lack of space), of five divisions each. On either side of this is the maker's name, and within the square a sphere carrying a universal projection is depicted mounted on a column.

The reverse of the instrument is engraved on the limb with a degree scale reading to one degree; on the left hand edge is a non-linear 0-90scale. One third of the way up the face is a second 90° scale concentric with that on the limb, and the space within this is occupied by a squared octogesimal diagram. Inclined lines arising from points on the degree scale on the limbs presumably enable the laying off of small angles. A small hole at the apex of the instrument originally carried a plumb-line. The two larger holes were fixing points for the sights that are now missing.
8in (20cm) radius

Footnotes

  • John Ismay is presumably the clock-maker who was apprenticed to John Ogden, Bowbrigg Hall, on 26 June 1711. He worked in the village of Oulton, two miles north west of Wigton, Cumberland where he may have been born and later in Wigton itself. The latitude engraved on the quadrant would have been suitable for either place. Several clocks by him are known.
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