Environmental Engineering Reference
In-Depth Information
were coupled directly to the moving parts (beams
attached to a central axle) to mill grain, crush seeds and
fruits to extract oils and juices, or mill clay for tiles;
animals turned a centrally mounted drum to wind up
a rope and raise water, coal, ore, people, and animals
from mines; and animals rotated whims that were
attached to geared assemblies to enhance a mechanical
advantage. Apuleius in The Golden Ass (second century
C
.
E
.) described the misery of these working animals,
which went round and round day and night, their
''chests ulcerated by the constant rubbing of the harness,
flanks laid bare to the bone by incessant beatings, their
hoofs splayed out to enormous dimensions by the con-
stant turning.'' But these abused animals could rarely
sustain more than 400 W. On commonly used tread-
wheels it was impossible to fit more than two animals
and hence to secure more than 1 kW.
Throughout the arid Old World, camels were used for
some of the tasks that oxen and horses performed in Eu-
rope, and the Indian subcontinent and Southeast Asia
were the only regions where working elephants were
highly effective in doing heavy tasks like harvesting tim-
ber in tropical forests (Schmidt 1996). Unlike other
domesticated animals, new working elephants (12-18-
year-old adolescents) were taken from wild herds. A clas-
sic Indian text described how these beasts had to receive
expensive feed (boiled rice and plantains mixed with milk
and sugarcane) while in training (Choudhury 1734).
Working elephants thus had an unusually high energy
cost, but they more than made up for it by extraordinary
power and longevity.
primitive watermill, consisting of horizontal wheel with
paddles or scoops turning a vertical shaft: ''Demeter has
reassigned to the water nymphs the chores your hands
performed. They leap against the very edge of the wheel,
making the axle spin, which . . . turns the heavy pair of
porous millstones'' (Humphrey, Oleson, and Sherwood
1998). And in 947
C
.
E
., al-Masudi wrote the first extant
description of the birthplace of simple horizontal wind-
mills in a windy region of today's eastern Iran, where
the machines were used to drive mills and raise water
from streams (Harverson 1991). After their (highly un-
even) diffusion throughout much of the Old World,
both kinds of machines eventually assumed important
roles in the economic life of preindustrial Europe, which
helped to energize the beginnings of industrialization.
The origins of horizontal waterwheels (fig. 7.5), also
called Greek or Norse wheels, remain untraceable. These
wheels persisted for centuries in many regions of Europe
and everywhere east of Syria; their most obvious appeal
was that they could turn millstones directly without any
gears. Small ancient horizontal wheels were inefficient,
but some later designs—notably, the free-jet mills used
in Persia and Spain, with heads up to 8 m and water
ejected onto rotor blades through a wooden jet with a
tapered bore (Wulff 1966)—were fairly efficient (
>
50%)
as well surprisingly powerful (
>
3.5 kW). Vertical wheels
(hydraletae), first described by Vitruvius in 27
B
.
C
.
E
.,
turned millstones by right-angle gearing and were more
efficient. They eventually became a common and persis-
tent feature of many European landscapes.
In England in 1086 the Domesday survey counted at
least 6,000 vertical waterwheels, one for every 350 peo-
ple. By 1300 the total was about 12,000, and after an
intervening decline and stagnation, about 30,000 water-
wheels were in operation by 1850; Germany used 33,500
7.2 Water and Wind: Wheels and Mills
Antipater of Thessalonica, writing during the first cen-
tury
B
.
C
.
E
.,
left the first extant literary reference to a
