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
Journal of the Royal Statistical Society in parallel to Series A-C as a Royal Statistical Society publication in 1993, having previously been published by the Institute of Statisticians. Since 2004 the Society has published "Significance", which consists of articles on topics of statistical interest presented at a level suited to a general audience. From September 2010 "Significance" is jointly published with the American Statistical Association and distributed to members of both societies. Journal of the Royal Statistical Society The Journal of the Royal Statistical Society is a peer-reviewed scientific journal of statistics. It comprises three series and is published by Blackwell Publishing for the Royal Statistical