These machines are used for raising heavy bodies in a perpendicular
direction. They are of various forms suitable for almost every
purpose, and to most of them are adapted two or more wheels with
teeth, one small and one large, for the purpose of obtaining power
at the expense of time (fig. 1); the small wheel is turned by a
windlass, and turns the larger one very slowly but with great power.
The common warehouse or cellar crane is generally an iron frame with
two pulleys, and the arrangement shown at fig. 1. which is usually
inside the warehouse, while the crane is outside to raise goods from
carts, &c., into the floors above (fig. 2). Cranes at the sides of
canals or rivers for landing goods are sometimes made as figs. 3 and
4; in the last there is a heavy stone placed to balance the weight
at the end of the crane. What is called the “jib crane” is often
“rigged” up on shipboard for shipping and unshipping goods (fig.
5). Cranes for very heavy purposes have been made upon the tubular
principle and consist of iron plates rivetted together so as to form
a hollow curved crane, similar to the hollow girders used in bridges.
Where goods have to be brought from one particular spot to another,
as in fig. 6, the swing crane is used. Amongst cranes may be named
the hydraulic lift; this is exactly similar to the hydraulic press,
only applied in a different manner, and is used to lift very heavy
weights but short distances, as for raising heavy goods on to railway
trucks, &c.