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 Geological Society of Ireland 1862). The Dublin clergyman Maxwell Henry Close read a paper before the society in 1866, on the "General Glaciation of Ireland", a masterly description of the effects of glaciation, and of the evidence in favor of the action of land-ice. He became president of the society in 1878. The society gained royal patronage and a change in title in 1864. The Society did not admit women members. Throughout the latter decades of the century, for several reasons, membership slowly declined and the society was wound up in 1894. Royal Geological Society of Ireland The Royal Geological Society of Ireland traces