weight.

The hoisting gear consists of a double system of chains 13/16 in. in
diameter placed side by side; each chain is anchored by an adjustable
screw to the end of the jib, and, passing round the traveling carriage
and down to the falling block, is taken along the jib over a sliding
pulley which leads it on to the grooved barrel, 3 ft. 9 in. in
diameter. In front of the barrel is placed an automatic winder which
insures a proper coiling of the chain in the grooves. The motive power
is derived from two cylinders 10 in. in diameter and 16 in. stroke,
one being bolted to each side frame; these cylinders, which are
provided with link motion and reversing gear, drive a steel crank
shaft 23/4 in. in diameter; on this shaft is a steel sliding pinion
which drives the barrel by a double purchase.

In the center of the crank-shaft is a large reversing friction clutch,
which drives, through miter gear, a vertical shaft placed just in
front of the post; from the latter the slewing, racking, and traveling
motions are obtained.

The crane can be turned through a complete circle by a pinion gearing
into a machine-moulded toothed ring bolted to the top of the truck;
this ring is 11 ft. 4-7/8 in. in diameter, and contains 172 teeth 21/2
in pitch. The slewing pinion is driven by intermediate gearing from
the bottom of the vertical shaft mentioned above. For the turning
motion two distinct sets of rollers are provided; these are carried by
cross-girders placed between the side frames; one set runs against a
cast-iron roller path bolted round the bottom of the post, and the
other on the large horizontal roller path seen in the engraving. The
latter is 14 ft. in diameter; it is built up of two deep curved
channel irons with top and bottom plates forming a circular box
girder, on the top of which a heavy flat rail is riveted, and the
whole turned up in the lathe. The racking and traveling motions are
driven from the top end of the vertical shaft; the racking gear
consists of wire ropes attached to each side of the traveling carriage
and coiled round a large barrel, the outer rope being brought over a
pulley at the end of the jib. The rails for the carriage rest on
rolled joints bolted to the underside of jib. This arrangement
involves the use of an overhung traveling carriage, but enables the
jib to be of a stiff box section, the side stiffness being further
secured by wind ties.

The traveling motion is worked by a second vertical