Environmental Engineering Reference
In-Depth Information
108 m and 114 m, and the power of 44.7 kW (with effi-
ciency in excess of 80%) was large enough to run 30,000
spindles and 800 looms (N. Smith 1980). A better de-
sign (with inward water flow) was soon developed in the
United States thanks to the experiments conducted in
the 1840s by Uriah A. Boyden and James B. Francis. Al-
though it was a product of several innovators and of what
might be called prototypical industrial research (Layton
1979), this machine became known as the Francis tur-
bine. Turbines became the dominant prime movers in
regions where early steam power was more expensive.
By 1875 they accounted for 80% of installed power in
Massachusetts, where the Merrimack River provided
about 60 MW, averaging some 66 kW per manufacturing
establishment, mostly for textile mills (Hunter 1975).
The earliest history of windmills remains conjectural.
The first horizontal machines, with sails mounted on a
vertical axle (and thus able to turn the millstone without
any gears), were housed in buildings with slots to lead
the wind onto the cloth-covered sails, an arrangement
that restricted their power and efficiency (Harverson
1991). Lewis (1993) believes that these mills spread
during the eleventh century from eastern Iran to Byzan-
tine territory, where they were transformed into vertical
machines whose variety was brought to Europe during
the Crusades. In any case, for more than seven centuries,
beginning during the late twelfth century, windmills
contributed appreciably to the gradual intensification of
Western economic life.
Better vertical machines were readily adopted, above
all, in arid regions with strong seasonal winds (through-
out much of the Mediterranean) and in the lowlands of
Atlantic Europe, where negligible water heads made
them the only large inanimate prime mover. The early
history of windmills, their evolution into highly complex
and fairly powerful machines, and their economic impor-
tance are well reviewed in Freese (1957), Needham
(1965), J. Reynolds (1970), Beedell (1975), and Min-
chinton (1980). Details on British mills may be found
in Skilton (1947) and Wailes (1975), on Dutch ones in
Boonenburg (1952), Stockhuyzen (1963), and Husslage
(1965), and on American ones in Wolff (1900) and Tor-
rey (1976).
All early Western European machines, with the excep-
tion of low-power Iberian octagonal sail mills with trian-
gular cloth, which were transferred from the Eastern
Mediterranean, were post mills with vertically mounted
sails and an ability to turn the driving shaft into the
wind. Their gears and millstones were housed in a
wooden structure pivoting on a sturdy central post,
which was supported usually by four diagonal quarter-
bars ending in two foundation crosstrees (fig. 7.6). They
could be turned to put the sails in the most efficient po-
sition, at right angles to the wind, but they could not
realign themselves once the wind direction changed, and
they were unstable in high winds. Being relatively low
above the ground, they also had limited capacity because
wind speeds rise exponentially with altitude and the
power of mills goes up with the cube of speed. Post mills
worked in parts of Eastern Europe until the twentieth
century, but in the West they were gradually displaced
by tower or smock mills.
Both of these structures had a fixed body, and only the
top cap was turned into the wind, either from the ground
or, with taller towers, increasingly from galleries. With
the introduction of a fantail to power a winding gear (in
1745 in England) the sails could be kept automatically
to the wind. Other pre-1800 innovations included im-
provements in sail mounting, a spring-sail, a centrifugal
regulating governor that did away with difficult and
