46. Electric Bells.—Electric bells operated by push buttons are rapidly coming into use for mine signaling on account of the ease and completeness with which such a system can be installed. Electric flash lights are also extensively used for signaling purposes. The principle of action and details of the wiring for electric signals and flash lights have been described in Transmission, Signaling, and Lighting.
47. Speaking Tubes.—The laws of certain states require speaking tubes, in addition to the ordinary means of signaling. These speaking tubes are generally made of 2-inch iron pipe and are from 300 to 1,500 feet long, and are often provided with whistles at the end of the pipe and at each level of the mine, by which the attention of persons at any level can be attracted or the whistle may be omitted and the attention of persons attracted merely by rapping on the pipe with a piece of iron.
Fig. 43
48. Pneumatic Gong Signal.—[Fig. 42] shows an attachment that can be connected to a speaking tube and that is widely used for signaling. It consists of a brass cylinder a fitted with a piston b containing valves c. The gong d is attached to the cylinder e inside of which the clapper f fits loosely. When the piston is pushed inwards, as shown by the arrow, by means of the handle, the air in the cylinder and in the pipe h is compressed and forces the clapper f upwards against the gong d. The arrangement of these gongs in the mine is shown in [Fig.43.] A cylinder and whistle are usually placed at each landing and a gong and whistle in the engine room, though, if desired, a cylinder, whistle, and gong may be placed at each landing and in the engine room.
49. Telephones.—Telephones connecting the different levels with the top and the engine room are now frequently used in connection with other signal systems, but they are not as well adapted as bells or gongs for rapid-hoisting signaling.
Transcriber’s Notes:
The illustrations have been moved so that they do not break up paragraphs and so that they are next to the text they illustrate.
Typographical and punctuation errors have been silently corrected.