Radiation
in physics, the transmission of heat, light, or actinic power (hence known as forms of "radiant enraising the temperature of the intervening medium. It takes place in all directions around a body. In a homogeneous medium it takes place in straight lines.
Radiation proceeds in vacuo as well as through air. Its intensity is proportioned to the temperature of the source, and it diminishes according to the obliquity of the rays with respect to the radiant surface, and the radiating or emissive power of a body, or its capability of emitting at the same temperature, and with the same extent of surface, greater or less quantities of heat. The energy received from a radiating body is inversely proportional to the square of the distance, and the radiation of a body is exactly proportional al to its absorbing power. If the radiating power of lampblack be reckoned at 100, that of platinum foil is 10.80; copper foil, 4.90; gold leaf, 4.28, and pure laminated silver 3.80. Solar radiation is the radiation from the sun; terrestrial radiation that from the earth into space.