LAMP

a device for producing illumination, consisting originally of a vessel containing a wick soaked in combustible material, and subsequently such other light-producing instruments as gas and electric lamps. The lamp was invented at least as early as 70,000 BC. Originally it consisted of a hollowed-out rock filled with moss or some other absorbent material that was soaked with animal fat and ignited. In the Mediterranean area and the Middle East, the earliest lamp had a shell shape. Originally, actual shells were used, with sections cut out to provide space for the lighting area; later these were replaced by pottery, alabaster, or metal lamps shaped to resemble their natural prototypes. Another basic type of primitive lamp, found in ancient Egypt and China, was the saucer lamp. Made of pottery or bronze, it was sometimes provided with a spike in the centre of the declivity to support the wick, which was used to control the rate of burning. Another version had a wick channel, which allowed the burning surface of the wick to hang over the edge. The latter type became common in Africa and spread into East Asia as well. In ancient Greece lamps did not begin to appear until the 7th century BC, when they replaced torches and braziers. Indeed, the very word lamp is derived from the Greek lampas, meaning a torch. The pottery version of a Greek lamp was shaped like a shallow cup, with one or more spouts or nozzles in which the wick burned; it had a circular hole in the top for filling and a carrying handle. Such lamps usually were covered with a heat-resisting red or black glaze. A more expensive type was produced in bronze. The standard form had a handle with a ring for the finger and a crescent above for the thumb. Hanging lamps made of bronze also became popular. The Romans introduced a new system of manufacturing terra-cotta lamps, using two molds and then joining the parts together. In metal, shapes became more complex, sometimes assuming animal or vegetable forms; very large versions for use in circuses and other public places appeared during the 1st century AD. Very little information is available about medieval lamps, but it would appear that such as existed were of the open, saucer type, and considerably inferior in performance to the closed lamps of the Romans. The great step forward in the evolution of the lamp occurred in Europe in the 18th century with the introduction of a central burner, emerging from a closed container through a metal tube and controllable by means of a ratchet. This advance coincided with the discovery that the flame produced could be intensified by aeration and a glass chimney. Until the late 18th century, the primary fuels burned in lamps included vegetable oils such as olive oil and tallow, beeswax, fish oil, and whale oil. With the drilling of the first well for petroleum oil in 1859, the kerosene lamp (paraffin in British usage) grew popular. In the meantime, however, coal gas and then natural gas for illumination were coming into wide use. Coal gas had been used as a lamp fuel as early as 1784, and a thermolampe using gas distilled from wood was patented in 1799. Although coal gas was denounced as unsafe, it won increasing favour for street lighting, and by early in the 19th century most cities in the United States and Europe had gaslighted streets and increasing numbers of homes converted to the new fuel. The early gas lamps made use of a simple burner in which the yellow light of the flame itself was the source of the illumination. But during the 1820s a new form of burner was introduced in which a controlled amount of air was admitted to the gas current, producing a high-temperature but nonluminous flame that heated a refractive, noncombustible material to a very high temperature. This became the source of light; the higher the temperature of the material, the whiter the colour of the light and the greater the output. By the 1880s, a woven network of cotton threads impregnated with thorium and cerium salts was the standard light-emitting material used in gas lamps. The development of the electric lamp at the turn of the 19th century stemmed the trend toward gas lamps, and by 1911 the conversion of gas fixtures for use with electricity had begun. Soon electricity was rapidly replacing gas for general illuminating purposes. In England and Europe, however, gas enjoyed wide use for a number of years longer.