Safety-Lamp. It was discovered by Davy that flame will not under ordinary circumstances pass through fine-meshed wire gauze; the contact with the metal cools down the particles of gas to such an extent that they are incapable of inflaming the gas on the other side of the partition. It is essential that a safety-lamp to be used in mines liable to contain firedamp (light carburetted hydrogen) should be incapable of igniting an explosive atmosphere, and this end was attained by Davy by enclosing the flame of the lamp in a chimney made of, and closed at the top with, wire gauze. The oil-holder of such a lamp is made of brass, and care is taken to so secure the gauze to the body that no opening larger than the meshes exists. When such a lamp is taken into an inflammable atmosphere, the gas is ignited inside the lamp, which may thus be filled with flame, but an explosion is avoided. The presence of burning gas in the lamp thus serves to warn miners that the atmosphere has become dangerous. In recent years many attempts have been made to make electric safety-lamps, as then it is easy to so arrange matters that there is no chance of igniting explosive gas, and at the same time the light is much increased. Secondary or primary batteries have been used, but the weight and cost of the arrangement are greater than that of the Davy lamp, and possibly from these causes, their use has up to the present time been limited.