Safety lamp, Clanny, Craig and Bidder's magnetic lock, from Mr. Bidder. Maker: R. Sharp, Usworth, marking: maker's name, 1869-1872 and diagram

Safety devices were increasingly employed to prevent accidents arising from careless or improper use of safety lamps in mines, one of the most frequent temptations being for the miner to relight his own lamp in the working place. The feature of this lamp is the locking arrangement, patented in 1869 by Messrs. W. Y. Craig and S. P. Bidder, in which the locking bolt is withdrawn by a compound permanent magnet before the reservoir can be unscrewed. The bolt is unbalanced, and it is of such a weight that by careful jerking it can be released; this is obviated in a more recent lamp (inv 1886-204).