Coal mining in this country gives employment to an army of 765,000 men. The word “army” has a sinister appropriateness in this connection, since out of every thousand men employed in the industry three are killed and one hundred and eighty injured annually. _The World’s Coal Resources_ In order of output, the leading coal-producing countries of the world are: United States, Great Britain, Germany, Austria-Hungary, France, Russia, Belgium, Japan, China, India, and Canada. The total production during the latest year for which data are available was about 1,346,000,000 tons. How long will the world’s coal supply last? This is a question to which various answers have been given. Geologists are able to furnish a rough estimate of the amount of coal now in the ground and near enough to the surface to be mined; but with the growth of the world’s industries the demand for coal is increasing by leaps and bounds, and nobody can safely predict how much will be needed at any future time. The world’s “coal reserves”--that is, the amount of coal remaining unmined--are estimated at 8,154,322,500,000 tons. In the United States it is estimated that we have used only four-tenths of one per cent. of our available coal supply. At the _present_ rate of consumption the coal in this country would last about 4,000 years; but if the present rate of _increase_ in consumption should be maintained, it would last only 100 years! Fortunately for posterity there are sources of heat, light and power which are not, like the fuels, exhaustible. Water-power, for example, is a permanent asset, and there are other inexhaustible sources of energy, such as solar heat and the internal heat of the earth, which Man’s ingenuity will someday turn to good account. [Illustration: Courtesy of “Coal Age” CARS FOR CARRYING EXPLOSIVES INTO MINES] _SUPPLEMENTARY READING_ COAL CATECHISM _By W. J. Nicholls_ THE STORY OF AMERICAN COALS _By W. J. Nicholls_ A YEAR IN A COAL MINE _By Joseph Husband_ YEAR BOOK OF THE U. S. BUREAU OF MINES STORY OF A PIECE OF COAL _By E. A. Martin_ THE COAL FIELDS OF THE UNITED STATES (U. S. Geological Survey, Professional Paper 100) _By M. R. Campbell_ ⁂ Information concerning these books may be had on application to the Editor of The Mentor. _THE OPEN LETTER_