inclining, double-string-gnomon sundial
Date: 1738
Inventory Number: 7416
Classification: Sundial
Dimensions:closed: 2.3 × 6 × 10.6 cm (7/8 × 2 3/8 × 4 3/16 in.)
case: 2.6 × 12.4 × 7.9 cm (1 × 4 7/8 × 3 1/8 in.)
Accessories: case; plumb bob
DescriptionThis is a most unusual inclining horizontal sundial with a double-string gnomon. The hour scales are split in two on the inclining hour plate so as to be read with one or the other string-gnomon. The western side has hours VI-XII for morning hours. The eastern side has hours XII-VI for the afternoon hours. Each scale is divided into 5 minute intervals with Arabic numerals indicating every 15 minutes.
The horizontal sundial is set up for the latitude of 49°, which is noted by the inscription, "H'. prop 49. de." There are acanthus leaves engraved in the center of the rectangular dial plate. A circular aperture in the plate reveals the magnetic compass below inset into the base. There is a notch at the end of the dial plate in order to tuck in the string used for the two gnomons.
The latitude scale is on a folding arm marked 0°-55°, every 1° in steps. A delicate screw adjusts and tightens a knife-edge lever against the back of the latitude arm in order to fix it at a set position. The top of the arm reads "Lieu du / niveau." A pinhole below the inscription is used to hold a plumb line. The plumb bob is currently stored in the case. Four leveling screw feet on the base are used to make the adjustments as needed.
The slider on the latitude arm has another pinhole. This is used to find the meridian at noon by means of a spot-and-target arrangement. The purpose of this procedure would be to determine and correct for magnetic declination. There exist three silver targets at the hinge end of the dial plate. Each consists of a cross over a circle. The use of the two targets at the ends is unclear, but perhaps they were thought to be useful in cases of extreme magnetic declination.
The magnetic compass has four points on its wind rose. They are marked in Latin. The needle is blued and shaped as a double arrow. There is another adjustable needle to indicate magnetic declination on a scale running from 20°W-0°-20°E, and divided every 1°.
The underside of the base has a gazetteer of 24 French towns, plus a few European cities. Latitude is given in degrees and minutes.
The original case has a domed lid. It is made of wood covered with sharksin. It is lined in red velvet. There are two brass hooks and eyes.
Signedon underside of hour plate: fait et Inventé par Jacques / le Maire de la Societé / des Arts au genié / A · Paris 1738
FunctionAn inclining horizontal sundial can be adjusted for use at different latitudes.
Historical AttributesThis unusual double-string gnomon design was invented by the maker of this sundial, Jacques Le Maire, in 1738. It was not adopted by other makers, perhaps because of its complex construction.
ProvenanceDavid P. Wheatland, Topsfield, MA, 1952; gift to CHSI, c.1985.