Electric light be made with a screw-thread base, two metal pins, two metal caps or a bayonet cap. The three main categories of electric lights are incandescent lamps, which produce light by a filament heated white-hot by electric current, gas-discharge lamps, which produce light by means of an electric arc through a gas, and LED lamps, which produce light by a flow of electrons across a band gap in a semiconductor. Before electric lighting became common in the early 20th century, people used candles, gas lights, oil lamps, and fires. Cornish chemist Humphry Davy developed the first incandescent light in 1802, followed
Royal Society of Antiquaries of Ireland collections of the National Museum of Ireland. The Society achieved its aim of illustration of antiquities, not only through the published "Journal", which from its creation contained both lithographs and engravings (and later photographs), but also by a comprehensive effort to photograph the antiquities of the 32 counties of Ireland. The RSAI publishes an annual peer-reviewed Journal, generally abbreviated as JRSAI. The affairs of the Society are conducted by the elected President, Officers and Council (all of whose services are voluntary). The following have served as Presidents of the Society: Royal Society of Antiquaries of Ireland The Royal Society of