1. The production of the field of disturbance in space by the matter existing elsewhere. One portion of space is considered to influence (more strongly if it contains matter) its neighbor, the latte to pass on the condition in turn to its neighbor, and so on until the disturbance has been extended throughout the universe. This situation is analogous to the spreading of waves over the surface of a pond. There are partial differential equations to describe accurately how the neighbors act on one another.