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
President of the Royal Astronomical Society President of the Royal Astronomical Society The President of the Royal Astronomical Society (prior to 1831 known as President of the Astronomical Society of London) chairs the Council of the Royal Astronomical Society (RAS) and its formal meetings. They also liaise with government organisations (including the Department for Business, Innovation and Skills and the UK Research Councils), similar societies in other countries, and the International Astronomical Union on behalf of the UK astronomy and geophysics communities. Future presidents serve one year as President Elect before succeeding the previous president. There have been 89 RAS presidents . The first president was