A winch, shown at A to the right of the engraving, sets in motion a system
of gear wheels keyed at an angle, at B and C, upon intermediate shafts
that transmit motion to the four vertical threaded rods of the frame, D.
All these shaftings are 11/2 inch in diameter, and the cog-wheels, twenty in
number, are about 5 inches in diameter.
The well is formed of an octagonal wall of fire-brick, and is 20 inches
thick and 6 feet high. In the center of this masonry is embedded very
thick iron plate. The bottom of the well is isolated from the flooring of
the Exhibition hall by a thickness of boiler plate, by a filling of tire
bricks, and finally by a second thickness of boiler plate. The well is
closed by means of a large plate of iron 6 inches thick, 10 feet in
length, and 88 feet in width. The winch which maneuvers this mass is
placed at E. It actuates a system of bevel wheels, keyed at F, which
transmit motion to two horizontal screws (hidden under the stage) that
actuate the plate, H. This latter is provided with two parallel series of
five rollers each that revolve over long and strong pieces of wood covered
with rails. Electric alarms are located near the winches.
A fire-engine station is located at within twelve or fifteen feet of the
exhibition building.
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