Environmental Engineering Reference
In-Depth Information
7.4
(a) Inclined, (b) horizontal, and (c) vertical treadwheels.
Reproduced from Agricola (1556) and Ramelli (1588).
a fairly flat surface to a new site, and until the intro-
duction of steam-powered railway cranes, they remained
a highly effective, practical way of tackling large lifting
tasks. The maximum useful power driving these de-
vices was inherently small. A single worker produced at
best 100 W during hours of sustained effort, and the
largest, eight-person treadwheels operated with brief
inputs of about 1.5 kW and steady flux of up to 700-
800 W.
The question of how much labor a man could be
expected to do in a day became prominent during the
late eighteenth century, when more labor was being
hired for new manufacturing (Ferguson 1971). Measure-
ments of work/day favored comparisons with horses, the
output of 2.5-14 workers being equated to 1 hp. Two
reliable rates include Guillaume Amontons' observations
of glass polishers in 1699, whose exertions during a
10-h workday he equated with raising continuously a
weight of 25 lb at 3 ft/s, and Charles-Augustin de Cou-
lomb's 1798 figure of a fair day's work, 205,000 kgm,
derived from climbing the 2923-m-high Tenerife Peak
in the Canaries in a bit less than 8 h. Amontons' calcula-
tion is equivalent to 3.66 MJ of work at a rate of 102 W,
and Coulomb's yields 2 MJ at about 72 W. We can do
little to improve on these classic values.
Many vertical devices were also powered by animals
walking inside a wheel or treading the outside rim, but
donkeys, oxen, mules, and horses were used much more
often to turn horizontal machines (Major 1980). This
was done in three ways: animals (usually blindfolded)
