A unique 17th-Century French graphometer,

A unique 17th-Century French graphometer,
signed MARETZ A AIX, undated, first half 17th century, in a gold-tooled leather-covered box -- 28 x 17 x 11.5cm. (11 x 6 7/8 x 4½in.)

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The elements of the instrument are based on a rectangular brass plate, 25 x 14.3cm. The features are: semicircle of 180° numbered in tens both ways; 15 further bands that allow each one-degree interval to be subdivided into 4-minute intervals, according to the transversal method. At either end of the base line of the semicircle are slit sight vanes, attached by wing nuts, and at the centre of this line is the pivot point for an alidade with similar vanes. Within the semicircle is a magnetic compass (5.7cm. dia.), with original glass cover, which contains air bubbles and has a wavy surface. The needle has an arrow head and forked tail, supported on a pin so that the needle is just inside the lip of a shelf on which are engraved the degrees, 0° from the South point to 360°, divided to 2° and numbered in 10s. The compass well has 16 bipartite direction points and the names: SEPTENT . GREG . ORIENT . SIROCN . MIDI . LABECH . OCCIDENT . MAEST. [spelling as given]. This is a mix of Latin and Italian names for the winds.
Along the bottom are the signature, and a slit with a scale 0-130 divided in units (100 units in 84mm). A short brass fiducial edge gauge can be inserted to slide along the slit. Also engraved are: arms, helmed and mantled; a horizontal dial; trophies in each upper corner; two parrots and a mayfly. The brass triangular gnomon, with two pegs to fit in the holes in the dial, is made for latitude of 43°30'; the modern latitude for the Provencale Aix is 43°32'. On the underside of the plate is bolted a bracket for the ball-joint for attachment to a surveyor's staff. In a clip are four small brass fitments, purpose unknown.
The instrument is packed in a wooden box covered in crimson leather elaborately decorated with gold-tooled floral motifs. The inside is coated with rose-red cloth, which is taken into the three compartments and their lids. The long narrow compartment holds the alidade when dismounted. These lids each have a pair of brass hinges secured by thin iron nails. The lid of the box is hinged in a similar manner, with a brass latch controlled by a key (missing) and held by a pair of brass L-shaped catches.