They then remove a number of timbers; lift a quantity of brick or hard lump-coal into wheel-barrows; climb through artificial tunnels, up and down inclines, and over surfaces strewn with coal or stone; operate a machine with a device attached to it, which automatically records the foot-pounds of work done; and perform other vigorous exercise, during a period of 2 hours.
— from Transactions of the American Society of Civil Engineers, vol. LXX, Dec. 1910 Federal Investigations of Mine Accidents, Structural Materials and Fuels. Paper No. 1171 by Herbert M. (Herbert Michael) Wilson
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