Of the many methods that have been devised for testing the air of mines for noxious gases none is more interesting than the use of caged canaries. These birds are much more susceptible than human beings to the effects of carbon monoxide, and show signs of distress before a man begins to feel any discomfort from the gas. In many mines they are carried in routine inspections. After an explosion the number of rescuers equipped with oxygen apparatus is always limited. These form the advance guard, and are followed by men without apparatus, who carry canaries, by observing the behavior of which they can tell how far they may safely penetrate into the mine. The Bureau of Mines has devised a special form of cage in which the canary may be revived with oxygen after being overcome with gas. Experiments show that the bird may be asphyxiated and revived again and again without suffering any ill-effects; neither does he acquire an immunity to poisoning which would make him a less reliable indicator. PREPARED BY THE EDITORIAL STAFF OF THE MENTOR ASSOCIATION ILLUSTRATION FOR THE MENTOR. VOL. 6, No. 6, SERIAL No. 154 COPYRIGHT, 1918. BY THE MENTOR ASSOCIATION, INC. THE MENTOR · DEPARTMENT OF SCIENCE MAY 1, 1918 [Illustration: Courtesy of Brown Hoisting Machinery Co. COAL-HANDLING MACHINERY ON PITTSBURGH COAL CO. DOCKS, DULUTH, MINN. An electric trolley, with 5½-ton bucket, travels on each bridge, carrying coal from the boat to storage, or to railroad car, or to screening apparatus in the rear] THE STORY OF COAL By CHARLES FITZHUGH TALMAN _Editorial Writer for the Scientific American_ _MENTOR GRAVURES_ FOSSIL FERN FROM COAL MINE · TIPPLE AT BITUMINOUS COAL MINE · COAL CAR DUMPER IN OPERATION · CHARGING COAL IN A MODERN GAS PLANT · SMOKE PROBLEM, SCENE IN PITTSBURGH BEFORE AND AFTER SMOKE CURE · RESCUE PARTY ENTERING MINE AFTER EXPLOSION Entered as second-class matter March 10, 1913, at the postoffice at New York, N. Y., under the act of March 3, 1879. Copyright, 1913, by The Mentor Association, Inc. Were it possible for the lump of coal that we burn in our stove, grate or furnace to tell its story, it would take us back millions of years to a time when vast areas of the earth’s surface were covered with swamps, supporting a luxuriant vegetation. No human being, mammal or bird yet existed. Animal life included fish, shellfish and other aquatic species, besides reptiles and insects. The vegetal forms resembled our modern ferns, horsetails, club-mosses and evergreens. The atmosphere was heavily charged with moisture, and a mild climate prevailed even in the polar regions. Such were the conditions under which, during the great Carboniferous Age, most of the existing coal-beds were deposited in the earth. [Illustration: FOREST SWAMP OF THE CARBONIFEROUS PERIOD (Coal Age). From a drawing by Potonié and Gothan]