ion control devices - the fantail mechanism
for keeping a windmill pointing into
the wind and the lift tenter for regulating
the gap between grinding stones - were
increasingly being used. James Watt
modified the lift tenter to form the flyball
govemor which, when connected to a
throttle valve (another Watt invention),
provided speed control for the steam engine
(see [4]-[6]).
During the nineteenth century, the
Watt engine govemor was widely adopted
and there were thousands of patents for
new and modified forms of engine governors,
few of which saw actual use [7].
During this century there also was an enormous
range of inventions for temperature,
pressure, and flow control devices. The
overwhelming majority of such inventions
were for “direct controllers;” that is,
for devices in which the measuring element
was directly connected to the control
actuator and hence the force available to
operate the actuator was dependent of the
force that the measuring device could develop.
By the end of the 19th century,
regulators of this type were in widespread use. 2
During the latter years of the nineteenth
century and the early part of the
twentieth, complex changes took place in
the organization of industry in the United
States [9], [IO]. These changes led to an
increased demand for devices for recording
information relevant to production
processes -from simple records of when
a machine was tumed on and off; to records
of temperatures, pressures and flows
for food processing plants, chemical
works and steel works; and to records of
steam pressure and carbon dioxide per