An early type of coal miners' lamp. It had a glass chimney surrounded by a wire gauze about 2 in (5.1 cm) in diameter. The glass chimney was covered by a perforated copper cap, and the air was fed to the flame from below through small holes and wire gauze in a lateral extension of the oil vessel. The lamp was unsafe; it passed flame when the velocity of the air current exceeded about 8 ft/s (2.4 m/s).