injury to the breathing apparatus, and so that each may watch the
condition of the oxygen supply, as shown by the gauges in the other’s
outfit.

The training is given in the gas-tight room of Building No. 17, or in
similar rooms at sub-stations (Fig. 2, Plate XII). This room is made
absolutely dark, and is filled with formaldehyde gas, SO_{2}, CO_{2}, or
CO, produced by burning sulphur or charcoal on braziers. At each period
of training, the miners enter and walk a distance of about 1 mile, the
average distance usually traveled from the mine mouth to the working
face or point of explosion. 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. This routine is repeated
daily during 1 week, after which the rescue corps is considered
sufficiently trained for active service.

The apparatus used for recording the foot-pounds of work done by the
person operating the work machine within the gas-tight rescue room,
comprises a small dial with electrical connections, which records the
number of strokes made by the machine, and a pencil point which rests on
a paper diaphragm, fastened to a horizontal brass disk. This disk is
driven by clockwork, and makes one complete revolution per hour. When
the machine is in operation, the pencil point works back and forth,
making a broad line on the paper; when the operator of the machine
rests, the pencil point traces a single line. The apparatus thus records
the number of strokes given by the operator during a given time. From
the weight lifted, the height of lift, and the number of strokes in the