The evolution of a mathematical instrument – II

Before the proportional compass, there were the proportional dividers, better known as the reduction compass. This was a much simpler instrument but it also worked on the same Euclidian theory of proportion applied to isosceles triangles. A normal pair of dividers has two legs joined together at one end by a hinge. The illustrations are mostly taken from Ina Prince & Patrick Rocca the authors of both Sectors: and precious mathematical and drawing instrument from the 17th and 18th century (Arithmeum Press, 2024) and Circinus: Proportional compasses from the 15th to the 18th centuries (Museo Galileo, Arithmeaum Press, Sillabe, 2024) Prince & Rocca: Sectors On the reduction compass the hinge in in the middle of the legs with two point sticking out on each side of it. The lengths of the legs on each side of the hinge are in linear proportion to each other. In the normal case, this can be 2:1, 3:1 or even 4:1. Prince & Rocca: Sectors Reduction compasses are used to scale up or down…