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
Society of Engravers Society of Engravers The Society of Engravers was founded in London in 1802 to promote British printmaking, largely because engravers were not allowed (unless they were also painters or sculptors) to join the Royal Academy, and also to enable "each individual to act with more firmness in opposing the pretensions ... of booksellers and publishers". The first President was Francesco Bartolozzi, himself in fact an R.A.. The Royal Watercolour Society (as it later became) was founded in 1804 for similar reasons. The society is described as "short-lived". Later Presidents included William Bond, and James Parker, James Pastorini and Thomas Milton