The new air compressors which furnish power to drive the drills, about 500 feet below the surface of the earth.

The new air compressors which furnish power to drive the drills, about 500 feet below the surface of the earth.

View of the central shaft after a naptha explosion (1867) where thirteen were killed, showing people at the top of the shaft awaiting the recovery of bodies.

Prof. Mowbray's nitro-glycerine works at the west shaft, North Adams, Mass.