LIGHT, that imponderable ethereal agent or limiter which makes objects per ceptible to the sense of seeing, but the particles of which are separately in visible. It has been believed that light is a fluid or real matter, existing inde pendent of other substances, with prop erties peculiar to itself. Its velocity is astonishing, as it passes through a snare of nearly twelve millions of miles in a minute. Light, when decomposed, is found to consist of rays differently color ed; as, red, orange, yellow, green, blue, indigo, and violet. The sun is the prin cipal source of light in the solar system ; but light is also emitted from bodies ig nited, or in combustion, and is reflected from enlightened bodies, as the moon. Light is also emitted from certain putre fying substances. It is usually united with heat, but it exists also independent of it. The intensity of light, at different distances from a luminous body, is in versely as the squares of those distances, so that in this respect it follows the same law as heat, sound, and the force of grav ity. Light acts a very important part in the vegetable economy. The green color of plants and the hues of flowers entirely depend upon it. It is also found to assist in developing the forms of some of the lower classes of animals. There
are two theories respecting the nature of light. Sortie maintain that it is com posed of material particles, which aro constantly thrown off from the luminous body; while others suppose that it is a fluid, diffused through all nature, and that the luminous body occasions waves or undulations in this fluid, by which the light is propagated in the same manner as sound is conveyed through the our. The first is called the corpuscular, the second the undulatory theory ; the lat ter is now more generally entertained, several facts being wholly inexplicable on the former theory. The language, however, which is employed in treating of light is, for the most part, accommo dated to the former.—Light, in painting, the medium by which objects are dis cernel. In a picture it means the part the most illuminate I. This may happen from natural light, as the sun or moon ; or from artificial light, as a fire, candle, &e. The principal light is generally made to fall on the spot where the prin cipal figures are placed, and generally near the centre of the picture. A re flected light is that which a body in shad ow receives from a'eontiguous light ob ject.