Coördinates oF POSITION IN SPACE

The system here used is generally that of three planes intersecting at right angles, called axial planes. The discu ions follow closely those of Cartes i an planar coordinates, though other systems, especially Coördinates, POLAR. System in which the fixed data are an initial straight line and a fixed point upon it called the pole; the measurements are distance of the point from the pole, called radius vector, and the angle of this with the initial line. They are usually indicated by the Greek letters p and d.