WINDLASSES AND CRANES. 57 
to stand upright on the deck of boats passing under them. When on the 
contrary sailing vessels are used on a canal, drawbridges of various kinds 
are constructed, which may be opened to allow the passage of the boats. 
The common drawbridge is raised vertically on hinges by means of a 
windlass or other machinery. olling bridges are those which are 
drawn back horizontally on rollers, and turning bridges move aside by 
revolving on a vertical axis or hinge. PJ. 10, jig. 7, is a side view of an 
iron turning bridge of 40 feet span; jig. 8 is a top view of one wing with the 
roadway partially removed; jig. 9 is one of the inner ribs or semi-arches 
which support the roadway. Both wings turn about an axis at c, c, and 
when they meet they are rounded off in such a manner as to slide past each 
other when turned. This bridge is preferable to a drawbridge, being more 
readily moved and more durable. 
I. WINDLASSES AND CRANES. 
Of the great variety of machines which have been invented to facilitate 
the labor of raising weights which manual labor alone could never move, 
we propose to describe and illustrate only the most important and inter- 
esting. 
Wrnptassrs and Jacks are simple machines designed for raising heavy 
weights. The simplest forms of these are too well known to require illus- 
tration. A windlass of more elaborate construction is represented on pl. 12, 
where jig. 10 is an end view, jig. 11 a front view, and jig. 12 the bottom 
frame. The wooden drum a is mounted on an iron axle, which also carries 
the spur-wheel 6, which is driven by the pinion ¢, the axle of which is 
turned by the two winches dd’ ; the frame B rests on rollers ff, which 
may be made to run on a railway. The windlass is used in building and in 
manufactories, where heavy loads require to be moved from one place to 
another. In France they are employed, as shown in jig. 10, to lift the 
bodies of mail coaches, p, off the ordinary wheels, 5, and place them upon 
the railroad trucks, c. The ropes or chains pass down over the pulleys, g g. 
Cranes have a two-fold motion ; that by which the load is raised, and a 
rotary motion by means of which it may be deposited in another place. 
The frame of a crane consists of a post or upright beam, from the upper 
end of which projects horizontally or obliquely upwards a beam called the 
jib, at the end of which the load is raised, and which is supported by a 
brace or stay. The post turns on pivots at both ends, or sometimes on the 
lower end only. At the end of the jib is a pulley, over which, in cranes 
of asimple construction, passes a rope from the load to a drum which is 
turned by winches, or, when heavy loads are to be raised, by a spur-wheel 
and pinion, as in the machine last described. Cranes are generally erected 
on wharves for the unloading of vessels, and they are universally employed 
in foundries and machine shops, where enormous loads are lifted and moved 
by means of them. 
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