A
utomatic feedback control systems have been known and
used for more than 2000 years; some of the earliest examples
are water clocks described by Vitruvius and attributed to Ktesibios
(circa 270 B.C.). Some three hundred years later, Heron of
Alexandria described a range of automata which employed a
variety of feedback mechanisms. The word "feedback" is a 20th
century neologism introduced in the 1920s by radio engineers to
describe parasitic, positive feeding back of the signal from the
output of an amplifier to the input circuit. It has entered into
common usage in the English-speaking world during the latter
half of the century.
Automatic feedback is found in a wide range of systems;
Rufus Oldenburger, in 1978, when recalling the foundation of
IFAC, commented on both the name and the breadth of the
subject: "I felt that the expression 'automatic control' covered
all systems, because all systems involve variables, and one is
concerned with keeping these variables at constant or given
varying values. This amounts to conccrn about control of these
variables even though no actual automatic control devices may
be intentionally or otherwise incorporated in these systems. I was
thinking of biological, economic, political as we1 as engineering
systems so that I pictured the scope ofIFAC as a very broad one."
This divcrsity poses difficultics for historians of the subject
(and for editors of control journals), and this article does not
attempt to cover all application areas.
Thc history of automatic control divides conveniently into
four main periods as follows:
• Early Control: To 1900
• The Pre-Classical Period: 1900-1940
• The Classical Period: 1935-1960
• Modern Control: Post-1955
This article is concerned with the first three of the above; other
articles in this issue deal with the more recent pcriod.
Early Control: To 1900
Knowledge of the control systems of the Hellenic period was
preserved within the Islamic culture that was rediscovered in the
West toward the end of the Renaissance. New inventions and
applications of old principles began to appear during the 18th
century-for example, Rene-Antoine Ferchault de Reamur (1683-
1757) proposed several automatic devices for controlling the temperature
of incubators. These were based on an invention of
Cornelius Drebbel (1572-1663). The temperature was measured by
the expansion of a liquid held in a vessel connected to aU-tube
containing mercury. A float in the mercury operated an ann which,
through a mechanical linkage, controlled the draft to a fumace and