EARLY BRASS AND STEEL DIVIDERS, Continental, c. second half 17th century, 9-1/4" (23 cm) overall, rather primitively shaped but with a five-leaf brass hinge. In fine condition complete with an early sheet brass cover for the tips. (8210) $875.

A NEAR-MINIATURE LODESTONE, probably Continental, c. early 18th century. Measuring 1-5/8" (4 cm) wide and only 1/2" (12 mm) thick, it is constructed with a somewhat irregular slab of naturally magnetic magnetite stone sandwiched between two iron pole pieces at the ends (to concentrate the magnetic attraction), the whole bound in brass and with a brass suspension. Condition is fine noting some rust to the iron, and one mounting nut lacking. The stone retains slight attractive power.

A lodestone was essential equipment for navigation at sea, being required from time to time to remagnetize the compass needle(s). Its power was considered magical, and its value great. The diminutive size of the present rather attractive example implies use for pocket compasses, small surveying compasses, and sundial compass needles. An uncommon size. (9192) $2600.

A DIMINUTIVE HAND-HELD SPLIT-LENS RANGEFINDING TELESCOPE, French, c. third quarter 19th century, finely signed "Micrometre a vis et a cadran, No. 1, E. Lorieux pere a Paris" and "Lorieux, Passage Dauphine 13, Paris." With an overall length of 7-3/4" (20 cm), extending to 9-1/4" by single drawtube, the telescope has erecting optics with a 1-3/4" diameter objective. The main tube is leather bound and the brass is generally blackened to minimize reflections. The objective lens itself is split into two semicircular segments mounted independently and driven in opposite directions by long screw micrometer gearing, with geared readout wheel graduated 0(0.5)60 twice and labeled "1 Degre" and with a note that each division represents one-half arcminute (of angular separation between the images). A simple graduated scale to the front indicates the coarse lens separation in degrees (0±2). The front is technically impressive, the blackened brass contrasting with dozens of bright lacquered brass mounting screws in a variety of sizes. Condition is good and functional, noting scuffing to the leather and a few scratches to the lens.

In use each half of the objective forms its own image, so one sees any object double. By adjusting the physical separation of the lenses, one can align the two images with the two ends of an object of known height or length, and thus know the range, the distance away. Thus one rather easily and accurately keeps station at sea, or determines the speed of gaining or losing on an enemy vessel, or time to landfall.

Edmond Lorieux was apparently trained by Gambey, and c. 1845 established what became a very important manufactory of navigation instruments. He was succeeded by Hurlimann, then by Ponthus and Therode, then Ponthus, and finally Lepetit (see Marcelin). We have catalogued one other micrometric telescope by Lorieux (pere), that one much larger (22" long extended), and labeled a bit differently "Micrometre Lugeol, a cadran de Lorieux," i.e., the Lugeol system, with dial plate readout (Tesseract Catalogue 53 Item 28). (9171) $2950.

Additionally, the greater arc has a set of solar scales on the reverse. Beginning on 10 March (the vernal equinox, and thus good evidence that this instrument predates the 1752 adoption of the Gregorian calendar in England) there are linear date scales (divided for every day of the year) separately for the sun North and South of the celestial equator, and a corresponding nonlinear scale of solar declination (0 to 23-1/2). Thus a sight vane could be positioned to the date, with readout of the solar declination, and simple determination of one's latitude from a measurement of the sun's altitude at noon. In our experience these scales are found on a very small number of surviving instruments. There are decorative stampings of five-lobed roses, fleur-de-lys, and geometric patterns. Condition is fine noting light wear; there are no sight vanes.

The backstaff was a vast improvement on the cross-staff, which required the navigator to sight in two directions simultaneously (not to mention looking directly at the sun). Most observations were in fact to determine the solar meridian altitude, and thus the ship's latitude. Observing with the backstaff, the sum of the readouts on the greater and lesser arcs was the solar altitude. This required correction for the solar declination on the date, provided directly on the scales here, without resort to tables.

The maker was Edmund Blow, son of a "hemp dresser," free in the Joiners guild in 1704, instrument maker in Wapping from then until 1739. He is known to have made Napier's bones as well as backstaves, and may have worked exclusively in wood. Another backstaff by him is recorded, a fine example dated 1736 and now in the Whipple Museum.

A handsome example, signed, dated, and serial numbered. (8187) $13,500.

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. (8194) $7200.

RARE NAVIGATIONAL SLIDING GUNTER, English, c.1800. This uncommon slide rule is made of boxwood, brassbound, with a 25" (63 cm) long central slider. Rule and slider are divided on both sides with logarithmic and trigonometric scales, including Chords, Rhumbs, Numbers, Sine Rhumbs, Sines, Versed Sines, Tangents, Tangent Rhumbs, Longitudes, Meridional Parts, and Equal Parts, the latter two designed specifically for sailing by Mercator's chart projections. Condition is fine throughout. A description of the "sliding Gunter" is found in Norie's A New and Complete Epitome of Practical Navigation (8th ed., 1825); it bears considerable similarity to the sliding navigational rule invented by John Robertson (1712-1776) and published by William Mountaine in 1778. In 1807 Mackay wrote, in The Complete Navigator, "But the most convenient form of this instrument [the "common Gunter's scale"] both for accuracy and dispatch is that known by the name of the SLIDING GUNTER, in which the use of a compass is superseded." We find one quite similar rule in the Science Museum collection (Inventory #1921-676). A rare and significant navigational instrument. (7263) $1950.

TOWNSHEND'S DOUBLE REFLECTING CIRCLE -- AN EXCEPTIONAL AMERICAN NAVIGATIONAL INSTRUMENT, c.1890, signed "Townshend, Patd. Jan 31, 1888," and "Stackpole & Brother, New York, 2204." The instrument is made of brass, with 8" (20 cm) diameter six-spoked main circle inset with silver scale divided every ten seconds of arc and labeled with double degrees 0 - 180 (on two sides), and 0 - 720 full circle. Two mirrors are mounted independently at the center of rotation, each with vernier (divided every ten arcseconds thus reading to 20 seconds in double degrees) arm and magnifier. Each mirror arm can be adjusted manually by long control rod, or driven in fine motion by clamp and tangent screw. One views through the adjustable telescope to the fixed mirror (with one clear and two silvered areas itself mounted tied to the telescope on long arm with clamp, tangent screw, vernier, and magnifier), then to the adjustable mirrors and to the targets. Thus one can sight three objects and measure two angular separations simultaneously (as two bright stars from the moon, for the lunar longitude method, or three coastal landmarks, for triangulation in coastal navigation). It is equipped with mahogany handle, two interchangeable achromatic telescopes, one sighting tube, screw-on solar filter, three insertable rectangular filters, and the original fitted mahogany case. Condition is very fine noting a little spotting to the original lacquer finish. Captain Townshend (1833 - 1904) was a resident of New Haven, Ct, and recommended his device for sighting sun, moon, and fixed stars, etc. Very few examples of his double reflecting circle have survived -- we can locate only those at Mystic Seaport and in the New Haven Colony Historical Society, one in a private collection, and the one offered in Tesseract Catalogue 50, Item 26. An important find. (8152) $14,500.

Surveying

Drafting