r at
the time of its peak development and use (1876). (From _The First One
Hundred Years_, Otis Elevator Company, 1953.)]

Since the only practical way in which the power of a steam engine could be
applied to the haulage of elevator cables was through a rotational system,
the cables invariably were wound on a drum. The travel or rise of the car
was therefore limited by the cable capacity of the winding drum. As
building heights increased, drums became necessarily longer and larger
until they grew so cumbersome as to impose a serious limitation upon
further upward growth. A drum machine rarely could be used for a lift of
more than 150 feet.[5]

Another organic difficulty existing in drum machines was the dangerous
possibility of the car--or the counterweight, whose cables often wound on
the drum--being drawn past the normal top limit and into the upper
supporting works. Only safety stops could prevent such an occurrence if
the operator failed to stop the car at the top or bottom of the shaft, and
even these were not always effective. Hydraulic machines were not
susceptible to this danger, the piston or plunger being arrested by the
ends of the cylinder at the extremes of travel.

THE HYDRAULIC ELEVATOR

The rope-geared hydraulic elevator, which was eventually to become known
as the "standard of the industry," is generally thought to have evolved
directly from an invention of the English engineer Sir William Armstrong
(1810-1900) of ordnance fame. In 1846 he developed a water-powered crane,
utilizing the hydraulic head available from a reservoir on a hill 200 feet
above.

The system was not basically different from the simple hydraulic press so
well known at the time. Water, admitted to a horizontal cylinder,
displaced a piston and rod to which a sheave was attached. Around the
sheave passed a loop of chain, one end of which was fixed, the other
running over guide sheaves and terminating at the crane arm with a lifting
hook. As the piston was pressed into the cylinder, the free end of the
chain was drawn up at triple the piston speed, raising the load. The
effect was simply that of a 3-to-1 tackle, with the effort and load
elements reversed. Simple valves controlled admission and exhaust of the
water. (See fig. 11.)

[Illustration: Figure 11.--Armstrong's hydraulic crane. The main cylinder
was inclined, permitting gravity to assist in overhauling the hook. The
small cylinder rotated the crane. (From John H. J