polar circles

pl. The Arctic and Antarctic Circles (q. v.). polar-clock, s . An optical instrument invented by Wheat stone for ascertaining the time of day by means of polarized light. polar-coördinates, s . pl . Elements of reference, by means of which points are referred to a system of polar coordinates. In a plane system, these elements consist of a variable angle and a variable distance called the radius vector. In space, they consist of two variable angles and a variable right line, still called the radius vector.