This months map measure is a small and simple affair. It is a bone-handled opisometer, or curvimeter, made by the Société des Lunetiers. Map measurers go by many synonyms- chartometer, meilograph, curvimeter etc. An opisometer is one of the simplest of designs of map measurers. These have a tracking wheel on a fine thread, with supporting frame and attached handle.

The wheel can be tracked along a line on a map, drawing, chart or anything else for that matter, then wound back along an appropriate scale to reveal the distance of the line. The example shown here is very similar in operation to models looked at previously by Three Points of the Compass, sold by suppliers such as map shop Stamfords in the nineteenth and twentieth centuries. Manufacture of the Société des Lunetiers Curvimeter probably straddles both centuries.

“for measuring straight and curved lines on plans and maps“

Design and construction has been careful to make this not only a practical instrument but also aesthetically pleasing. The ferrule into which the bone handle is screwed features decorative knurling, the handle itself has a gentle taper from the barrel to the tip and was no doubt turned on a lathe. There are no makers marks on the measure at all.

“a small serrated wheel turning on a screw axle, thus enabling the tracing of curves and windings”

le curvimeter

This is a small and delicate instrument. The Société des Lunetiers Curvimeter is just 86mm in length however the fine threaded spindle still permits the finely toothed 10mm diameter wheel to track a line of 920mm in length, or 35 inches in old money. It is a lightweight tool as well, weighing 6.4g. The lightness is partly due to its dual construction. All ‘working parts’ are made of steel. However the handle is made of bone, probably from a cow. At one end of the handle is a thread, probably cut by hand, to permit it to screw into the ferrule riveted to the spindle hanger. The other end of the tapering handle has a turned circular finial. The shape of these finials points toward the country of origin and this particular shape indicates French manufacture.

There are two aspects of the spindle wheel and hanger to draw attention to. One is the single pointer situated at one end of the axle, this can be pointed at the start and finish points when measuring a line and aids in greater accuracy. Almost un-noticed on the finely serrated tracking wheel is a single, small, stamped dot. This enables rotations to be tracked when measuring with the instrument and again provides a degree more accuracy when measuring.

The Société des Lunetiers was an association of French master craftsmen and instrument makers. In August 1849 three craft shops amalgamated and co-operated (l’Association fraternelle des ouvriers lunetiers) to create, produce and sell a variety of objects and instruments. Their first logo featured the letters S and L each side of a three arm candelabra, signifying the three branches of the fraternity. There can be some variety in the placement of letters each side of the candelabra depending on the type of manufactured object on which it is placed.

The co-operative first operated out of small Paris workshops until the late 1860s but steadily purchased further small and larger premises, many smaller businesses subsequently also coming under the umbrella Société des Lunetiers. Workshops were spread across several French provinces. A branch was even established in Hatton Garden, London.

The brand was simplified at some point in the first two decades of the twentieth century to better reflect the expansion and membership of the society.

One of the three businesses was La Compasserie, who produced compasses, theodolites and other fine optical equipment such as spectacle lenses, the latter product being from what the société took its name.

La Compasserie– ‘the compass maker’, operated out of Ligny-en-Barrois, a commune in the Meuse department in Grand Est, northeastern France. The company was renamed ‘Essel‘, the name coming from the pronunciation of its initials- SL, the modern iteration of the company today is Essilor, itself a merger of Essel and Silor (Société Industrielle des Lentilles Organiques Rationnelles) in 1972. From these, the world’s first progressive lens, the Varilux, was developed. Ligny is now the home town of the Essilor company, specialising in opthalmic lens production.

As usual, it is difficult to assign a date to such an object. Certainly opisometers of this type were being generally manufactured in the 1870s. Le Curvimètre was listed in the company’s 1907 catalogue. However some information on the box included with my example helps narrow down the one shown here as being manufactured somewhat later. The Unis France logo was introduced 29 January 1916 by the Union Nationale Inter-Syndicale des Marques Collectives as a guarantee that an item was produced in France. The logo fell out of use after World War II. This initially points us toward a range of between 1916 and early 1950’s for this particular opisometer (or more properly, box) however I doubt that these opisometers would have been manufactured to this degree of quality during the war years in France, so can probably be further pinned down. The SL logo is of the early candelabra type, prior to it being simplified so manufacture was both after 1916 (possibly after 1918) and likely prior to the 1930s. It is also possible that pre-World War I stock was subsequently sold after the war in a box branded with the Unis France logo. Note that this map measurer was undoubtably still conforming to a design set down decades earlier.

Three Points of the Compass has looked at a few more Map Measurers in detail. Links to these can be found here.