This bulletin describes the development of a number of types of lamps that meet the requirements, and discusses in detail the features and qualities of these lamps, which in November, 1916, were being put into use by mine operators in this country at the rate of about 2,000 a week. Those lamps that meet a certain minimum specification are approved by the Bureau of Mines. No manufacturer is required to obtain this approval, but the manufacturers have voluntarily submitted their lamps for investigation and criticism. None of the lamps submitted to the bureau was found acceptable in its original form, and the cooperation with the Bureau of Mines of the makers of lamps, bulbs, and cords has extended over the past three years, and the art of making safe miner's electric lamps has thereby been developed much more rapidly than would have been the case had the development been solely the result of commercial exploitation. Also, it is believed that by this method the mining public has been saved expensive and dangerous experiments, which might have cost many lives and for a time condemned the electric lamp as an impracticable device. The first specification of the Bureau of Mines as to conditions and requirements for testing electric mine lamps was set forth in Schedule 5,a issued in April, 1913, and the requirements were limited to the prevention of gas ignition. Three lamps were tested and approved under this schedule. Accumulated experience by the bureau indicated the desirability of a broader basis of approval, and another schedule, Schedule 6,b was issued in February, 1914, which was revised to the present form (Schedule 6A) in February, 1915. Schedule 6A, which is given in full on pages 45 to 53, includes requirements for both the safety and the practicability of the lamp. The original approvals under Schedule 5 were withdrawn and the lamps were retested in accordance with Schedule 6A, and a broader and more comprehensive approval issued to those lamps that passed the later tests. The bureau grants its approval as an indication of its confidence in the excellence of the lamp as a safe and practical device for lighting mines, especially those mines in which there may be inflammable or explosive mixtures of gas' and air. The approval is conferred only after thorough examination and tests have shown that the lamp reaches the standard established by the bureau. Seven portable electric mine lamps had been approved prior to August, 1916, as follows: Edison lamp, approval No. 10, approved February 24, 1915; Manlite lamp, approval No. 11,G approved July 16, 1915; Concordia hand lamp, approval No. 12, approved July 26, 1915; Wico lamp, approval No. 14, approved June 10, 1916; Concordia cap lamp, approval No. 15, approved June 17,1916; General Electric lamp, approvals No. 13 and No. 13A, approved July 11, 1916; Pioneer lamp, approval No. 16, approved July 21, 1916. Each of these lamps is identified by a plate that bears the seal of the Bureau of Mines, the approval statement, and the number of the approval. No lamp is considered as approved unless it bears this plate.