This is a beautiful early 19th century theodolite by Dollond, a famous family of London opticians and instrument makers in the 18th and 19th centuries. The unusual form is called a Lean's Miner's Dial, and was introduced as a mining surveying instrument in the 1790's by Joel Lean, a Cornish mine manager. It features an 8" diameter semicircular rack, about which the 9-10" telescope can be maneuvered with a knurled knob controlling a pinion gear. The semicircle is engraved with degree markings on the right side, where there is a vernier scale, capable of reading to the nearest minute. On the left side of the semicircle, is a scale of "Diff. Hypo & Base", which gives the difference between the hypotenuse and the base, i.e. the number of links to be subtracted from each chain length measured along the ground to calculate the horizontal distance (see "The Divided Circle" by J.A. Bennett, page 86). The telescope gives sharp, erect images, and the rack and pinion focus works well. The ocular lens assembly unscrews to reveal an easily accessible area for cross-hairs, and a mechanism to adjust them, but no cross-hairs are currently in place. There is a bubble level adjacent to the telescope, which works smoothly. Beneath the telescope is a fine 5.4" brass and glass-enclosed compass, with a 4.4" needle. The compass has a silvered face and a beautifully-engraved, four-pointed star, and is signed "Dollond, London". A raised outer scale is engraved to single degrees. The compass functions smoothly and accurately, and there is a functional needle-lock assembly on one side of the brass casing. The Miner's Dial is mounted on a finely turned wooden base, in much the same manner as are similar instruments in the Whipple Museum and the London Science Museum. This Miner's Dial is in excellent overall condition, noting slight streaking to some of the original lacquer, and to some of the silvering on the compass face. This is an early, decidedly-rare and aesthetically-pleasing form of surveying instrument, by an outstanding maker, and in very fine display condition.

Please E-Mail with any questions. Shipping and Insurance, for a total of $20.00, to be paid by the US buyer (shipping outside US at cost). Will be shipped immediately upon receipt of money order or cashier's check. Personal checks may be held until cleared (10 business days), unless feedback is completely reassuring. May be returned for a full refund, less shipping and eBay costs, within 7 days, if not completely satisfied.

Please follow this link to check out my other items.