=Coal-gas Lighting.=--A common method of lighting tunnel workings is by piping coal-gas into the headings and drifts from some nearby permanent gas plant, or from a special gas works constructed especially for the work. Gas lighting has the great advantage over lamps and lanterns of giving a light which is more brilliant and steady. Its great objection is the danger of explosion caused by leaks in the pipes, by breaks caused by flying fragments of rock, and by the carelessness of workmen who neglect to turn off completely the burners when they extinguish the lights. In nearly every tunnel where gas has been used for lighting, the records of the work show the occurrence of accidents which have sometimes been very serious, particularly when fire has been communicated to the tunnel timbering. =Acetylene Gas Lighting.=--The comparatively recent development of acetylene gas manufactured from carbide of calcium has given little opportunity for its use in tunnel lighting, and the only instance of its use in the United States, so far as the author knows, is the water-works tunnel conduit for the city of Washington, D. C. Col. A. M. Miller, U. S. Engineer Corps, who is in charge of this work, describes the method adopted in his annual report for 1899 as follows:-- “It had been the practice to do all work underground by the light of miners’ lamps and torches. This means of illumination is very poor for mechanical work. The fumes and smoke from blasting, added to the smoke from torches and lamps, render the atmosphere underground, especially when the barometer conditions were unfavorable to ventilation, very offensive and discomforting to the workmen. An investigation of the subject of lighting the tunnel by other means, more especially at the locality where the mechanics were at work,--brick and stone masons, and the workmen on the iron lining,--resulted in the selection of acetylene gas as the most available and economical in this special emergency. Accordingly, an acetylene gas plant for 300 burners was erected at Champlain-Avenue shaft, and one for 60 lights at Foundry Branch. The engine-houses at the shafts, the head-houses, and localities in the tunnel, when required, are lighted by these plants. “Gas pipes were carried down the Champlain-Avenue shaft and along the tunnel both in an easterly and westerly direction, with cocks for burners at proper intervals every 30 feet; and this system sufficed for illumination from Hock Creek to Harvard University, a distance of over two miles. The plant erected at Foundry Branch was in like manner utilized for the illumination from that point in both directions.