1. The magnitude of a potential field U surrounding a unit element varies inversely as the square of the distance from the element m:
Applies to a gravitational field where the element m is mass and k is the gravitational constant (q.v.); to a magnetic field where the element m is a magnetic pole of strength m in ampere meters and k is 10–7 webers/amperemeter; and to an electrostatic field where the element m is an electrical charge of m coulombs and k is 9×109 newtons/coulomb. For the gravity case, the relation is called Newton’s law of universal gravitation and for the electrostatic case it is called Coulomb’s law. 2. The energy density of a seismic body wave from a point source in a homogeneous isotropic medium varies inversely as the square of the distance from the point source. Also called spherical divergence. 3. The intensity of electromagnetic energy (light or radio) varies inversely as the square of the distance from a source.