THE HYDROGRAPHIC DOUBLE-MIRROR CIRCLE OF ROLLET DE L’ISLE

THE HYDROGRAPHIC DOUBLE-MIRROR CIRCLE OF ROLLET DE L’ISLE

Stock Number: 8194

$7200.

For sale, antique innovative twin-mirror full-circle outfit. The circle functions much like a sextant but with two complete sets of mirrors for smaller angles (down to 0 degrees), and for very large ones up to 180. It is complete, in excellent condition, and cased.

Dimensions

10-1/2 inches (27 cm)

Circa

c. late 19th century

Country of manufacture

France

Categories: Maritime, Navigational instruments

Description

THE HYDROGRAPHIC CIRCLE OF ROLLET DE L’ISLE, French, late 19th century, finely signed “Lorieux, A. Hurlimann, Succ’r a Paris.” The 10-1/2″ (27 cm) diameter brass circle is fitted with four mirrors, two of them mounted on the rotating index arm and set back-to-back at a fixed angle, a large-light-gathering-power telescope, and a hinged turned wood handle. An inset circular scale is divided every 0.5 from -10 to +200 half-degrees. The index arm has clamp, fine motion tangent screw, vernier to one-fiftieth of a degree, and magnifier. The instrument is equipped with its full complement of accessories, all original: two solar filters, two right angle sights, seven interchangeable filters, two adjusting tools, three spare mirrors, fitted mahogany case 13″ (33 cm) square, and key. Only the screwdriver and loupe are lacking. Condition is absolutely superb throughout. The circle functions basically as a sextant, except there are two “horizon” mirrors, and two “index” mirrors, disposed so that one pair is useful at smaller angles, the other pair at larger ones. Readings are possible from 0 degrees straight ahead all the way to 180 degrees directly behind the observer — as one mirror view becomes foreshortened, the other takes over automatically.

This is the remarkable invention of M. Rollet de l’Isle, French hydrographic engineer to the Marine (and world-famous proponent of the Esperanto language). It was still advertised in 1911 (by Ponthus & Therrode, successors to Hurlimann, who in turn was successor to the well-known firm of Lorieux established in 1845), as the model adopted by the French hydrographic marine services. A very rare example of this innovative design, in splendid condition.

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US TESSERACT

David and Yola Coffeen both have enjoyed academic careers, as planetary astronomer and as linguist/educator. But since 1982 (yes, 1982!) they have been full-time dealers in early scientific and medical instruments, under the name Tesseract. Selling primarily by catalogue (over 100 issued so far) they also have a web presence at www.etesseract.com, and can be contacted at mail@etesseract.com.

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