Page:Popular Science Monthly Volume 91.djvu/582

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566

��POPULATION OF THE UNITED STATES

��TOTAL COAL MINED IN THE UNITED STATES PRIOR TO IQlj

��913 PRODUCTION

���come on. Eacn li^nt remains on only a fraction of a second. The whole effect is that of a giant swinging a large red lantern. So effective is the lighting system that in the year since the barrier gate was installed not a single acci- dent has occurred. On other bridges not thus equipped the gates are out of com- mission much of the time owing to the fact that auto- mobiles run into the gate arms.

Recently a trial test was deliberately made with a street car running ten miles an hour. At that speed the car had a striking weight of fifty - three thousand - foot pounds. The street car was brought to a complete stop in fifteen feet. The car was not damaged in the least, and the motorman, who re- mained at his post, was not even severely shaken up. The barrier gate was also undamaged.

The yield- ing chain bar- rier for rail- road crossings and for bridge approaches frequented by light traf- fic, consists of two uprights or structural steel posts, one at each side of the roadway, connected at the top with a steel truss. The weight of the barrier is counterbal- anced by means of a counterweight contained within the two side posts. When struck by a vehicle the barrier gives, the chains paying cut, and gradually absorbing the energy of the shock until it brings the vehicle to a stop.

��Popular Science Monthly

We Burn Coal Lavishly, But We Have Plenty of It to Burn

��WE

��COAL RESERVE

IN THE UNITED STATES

��The coal mined in this country up to 1913 and what we still have on hand

��POPULATION OF THE WORLD OUTSIDE OF THE UNITED STATES

��TOTAL COAL MINED IN THE WORLD

OUTSIDE OF THE UNITED STATES

PRIOR TO 1913 \

��1913 PRODUCTION

���COAL RESERVE

•IN THE WORLD OUTSIDE

OF THE UNITED STATES

��Comparison between the world's population and coal reserve. We have used less than one-half of one per cent, of the total quantity

��HILE it is true that the nited States is the largest consumer of coal in the world , using nearly forty per cent of the world's total production, it is something of a comfort to know that we have not yet consumed more than one-half of one per cent of the total quan- tity which geologists esti- mate is at present contained within our borders.

The annual production of coal in the United States has increased more than eight hundred per cent in thirty-five years — from sixty-eight million tons in 1879 to more than a half billion tons in 1913. Not- withstanding the enormous amount of coal available, our exports in 1913 amounted to very little, only about four per cent of the entire output. In this year Great Britain ranked second as a coal producer. Coal was first worked in the United States in Rich- mond, Virginia, in the mid- dle of the eighteenth cen- tury, and indeed that State in proportion to its size, long surpassed all the others in varieties of coal pro- duced, and area of coal measures, though there it had the disadvantage that the coal was generally deeply buried. In 1820 the total output of coal in the country was three thousand four hundred and fifty tons; by 1850 the annual output was over seven million tons. According to the United States Geologi- cal Survey the total area of coal-beds is close to five hundred thousand square miles, of which about one-half contain anthracite and bituminous coal.

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