Descartes' mesolabe. Diagram and text from 'Geometria' (1639) by the French philosopher and mathematician Rene Descartes (1596-1650). A mesolabe is an instrument consisting of a set of interconnected triangles with pivoting arms that are able to slide in a rectangular framework. It is used to find two proportionals between two given line segments. Descartes' mesolabe uses a compass that pivots around point Y. As the compass opens or closes the rulers (perpendicular to YX and YZ) slide along the axis. This page is from the 1683 edition, published in Amsterdam, the Netherlands.
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