Four-Point Compasses
From Inventions
Name currently used for the reduction compasses.
Description
Also called double compasses or "compass with double points" (Muzio Oddi, Fabbrica et uso del compasso polimetro [Construction and operation of the polymeter compass] Milan 1633, introduction), the instrument was used as a proportional compasses, for measuring simple proportional ratios, or as a reduction compasses to enlarge or reduce drawings. The compass was composed of two intersecting legs with points on all ends and a fixed or variable pivot depending on the proportional ratios desired. Ancient examples of this instrument have been found in the excavations of Pompeii.
Images
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Nicolas Bion. Traité de la construction et des principaux usages des instruments de mathematique : avec les figures necessaires pour l'intelligence de ce Traité, Paris, 1725, tav. VIII p.70, particolare. |
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George Adams. Geometrical and graphical essays, containing a general description of the mathematical instruments used in geometry, civil and military surveying, levelling and perspective : with many new practical problems. London, 1813., tav. I, particolare. |
Author of the entry: Filippo Camerota
