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Bennett, J. and Johnston, S., The Geometry of War, 1500-1750 (Oxford, 1996)

55. This instrument reproduces Zubler's 'new geometrical instrument' (see catalogue no. 54), the only substantial differences from the illustrations in Zubler's book being the replacement of the central plate by a semicircular arc, and the absence of a compass. The arms carry linear scales, each graduated from 0 to 1000, as recommended by Zubler; diagonal lines are ruled across each division of ten, so that the scaled length can be read to 1 according to where one of these diagonals cuts a transverse scale, divided 1 to 10, on a bevelled edge of each sliding sight. The link to Zubler's book is very strongly reinforced by the fact that engraved letters on the instrument - 'A' at the pivot, 'B', 'C' and 'D' on the semicircle, 'E' and 'F' at the ends of the arms and 'G' and 'H' on the moving sights, coincide with the key letters on the first plate in the book, which illustrates the detailed construction of the instrument.

The reverse has a pair of sectoral scales, each marked: 'Linea recta divisio'.

Length (leg): 286 mm

Inventory no. 51,706

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