"Derby" miner's electric safety lamp with lead plug lock

This is an example of a modern electric safety lamp. The case of the lamp is made of pressed steel, is of cylindrical construction and consists of two portions. The lower portion accommodates the secondary cell which has two concentric cylindrical plates within which is a tube for egress of the evolved gases. The cell is prevented from rotating by the engagement of a projection on the inside of the case with a corresponding hollow on the bottom of the cell. The upper portion carrying the bulb and glass is held by a bayonet joint and locked by a lead rivet. The lock is a separate unit from the case, and, when damaged, Can be easily replaced. The bulb is mounted on a rubber cushion, which acts as a shock absorber, and is protected by a thick yellow -tinted glass dome. The light is switched on and off by slightly twisting the upper portion relative to the lower. A metal reflector is provided which is of amber colour, designed to assist in the overcoming of " nystagmus."