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tribution in formulating the rules governing the output of a mill. This he did by ingenious
experimentation with rotor models; he then reduced his test data to simple mathematical
expressions.
Stevin (1548-1620), born in Bruges, was well-known indeed for a range of writings
on mathematics, mechanics, hydraulics, military devices, and so on, including music and
precepts for citizens! Along with his writings, he had many inventions patented and devised
many improved components for a variety of engineering artifacts. In his work on
windmills, he concentrated on calculating the relationships between dimensions, speeds, and
number of gear teeth in order to estimate output. Mechanics was not a very exact science
in his day. The concepts of energy, power, and eficiency were unformulated, and there
were often no names for them. However, he was the leader in applying what was available
in mechanics and mathematics to practical attempts to calculate the output of a mill in terms
of the water raised by a scoop-wheel and to use such calculations to prove his suggested
improvements. In a published collection of this notes, “Van De Molens” [see Forbes 1966,
p. 327], he gives calculations for some 20 mills, either existing, improved, or projected.
Leeghwater (1575-1650), born in North Holland, lived a generation after Stevin. In his
early life, he was a carpenter and millwright who had a natural talent as an inventor and
engineer on a large scale. He used windmills in large numbers for his drainage schemes
and made many improvements over the years. None of these resulted in patents, but his
skills were widely recognized at home and abroad. He made his reputation by draining a
large lake called the Beemster (which had an average depth of 3 m) in one year by using
26 windmills. In another scheme to reclaim a polder (swamp), he used 51 drainage mills
pumping out water at the rate of 1,000 m
3
/min. His vision was such as to encompass the
draining of the Haarlemmermeer with the aid of 160 mills. His study of this was published
in 1641 and passed through 17 reprints; the last edition was published in 1838. In 1848,
the drainage was inally accomplished after plans were revised several times, but the power
was supplied by steam engines.
Smeaton (1724-1792), who was born in the north of England, came much later than the
other two engineers, but he contributed the irst sound, basic rules of windmill performance.
He was a remarkable civil engineer in several branches of the ield, primarily in structures
such as bridges, lighthouses (the Eddystone among them), windmills, and water wheels, but
also in land drainage, canals, harbors, steam engines, and materials (such as cement and cast
iron). Smeaton was above all a very careful experimenter; he taught himself and, by
example, many others the application of systematic experiment to technological improve-
ment.
Smeaton's chief contribution to molinology was his paper entitled “On the Construc-
tion and Effects of Windmill Sails,” which was given to the Royal Society [1759; see also
Tredgold 1836], The paper makes very interesting reading, and although it was given some
230 years ago, it is still available in many technical libraries. This paper describes what
might have been the irst use of scale models for obtaining the algebraic relationships
governing full-size machines. Smeaton had no wind tunnel to use and so he invoked the
principle of
Galilean invariance
and mounted his model on a whirling arm in still air, as
shown in Figure 1-16. He still had few accepted laws of energy or standard units with which
to obtain numerical values of power, but at least he could run tests at constant speeds and
measure, by the raising of weights, the work done by the rotor.
Figure 1-16 follows the original drawing of Smeaton's apparatus. The rotation of the
rotor support arm
(FG)
was accomplished by the mysterious hand
(Z)
at the left pulling the
cord that turned the barrel on the shaft
(DE).
Speed was adjusted so that the support arm
made one turn in the time the pendulum
(VX)
made two vibrations. This whirling-arm
apparatus was not a new idea, but in his customary manner Smeaton improved on others'
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