Instrument for measuring angles

The graphometer was designed by the Frenchman Philippe Danfrie in the late 16th century. From that date, it was used for measuring horizontal and vertical angles in topography, hydrography and astronomy, among other disciplines. It usually consisted of an arc of a circle, semicircle or complete circle, marked from 0° to 180°. It had a mobile alidade or sight attached in the centre, and two pins, one at each end of the piece, that constituted the fixed alidade or fixed sights (De Lorenzo et al., 1864: 286; Mañueco Santurtun and Peláez Tremols 1987: 45 -46; Sánchez Lázaro 1990: 20-21). Many had a compass in the centre, and from the 19th century onwards, some were equipped with telescopes instead of alidades (Bennett 1987: 49-50). They were generally supported on tripods, to align their plane according to the position they should occupy during the measurements (Sánchez Lázaro 1990: 20). Those used in navigation were mounted on gimbals, a system that allowed them to remain horizontal (De Lorenzo et al., 1864:286).

Nicolas Ciarlo