Page 298 - Encyclopedia Of World History

648 berkshire encyclopedia of world history

Table 1.
Energy Densities of Common Fuels
(based on Smil 1991)

Fuel Density (MJ/kg)
Dried dung 10–12
Air-dried straw 14–16 animals thus greatly improved the productivity of tradi-
Air-dried wood 15–17 tional farming: Even slow plowing was three to five
Charcoal 28–29 times faster than hoeing.
Lignites 10–20 However, these gains had to be paid for by devoting
Bituminous coals 20–26 more time to caring for these animals and devoting
Anthracites 27–30 increasing amounts of land to their feeding. For example,
Crude oil 41–42 feeding the peak number of U.S. farm horses and mules
Gasoline 44–45 in 1919 (21 million) required about 20 percent of the
Natural gas 33–37 (cubic meters) country’s farmland. Obviously, only countries endowed
with extensive farmland could afford this burden: The
option was foreclosed for Japan, China, or India. Heav-
wasting about 80 percent of the initially used wood in the ier draft animals and better implements eventually cut the
process. This waste would put a great strain on wood time that was spent in producing staple crops. For exam-
resources even if charcoal’s use was limited to space heat- ple, all field work on a hectare of wheat required 180
ing and cooking, but its expanded use in various manu- hours in medieval England, 120 hours in early
factures and in metallurgy made it an acutely limiting nineteenth-century Holland, and 60 hours on the U.S.
factor. For example, in 1810 the metallurgical charcoal Great Plains in 1900. However, in any society where
needs of the United States prorated annually to a forested food production was energized solely by human and ani-
area of roughly 50 by 50 kilometers, and a century later mal muscles most of the labor force had to be employed
they would have amounted to an area of 170,000 square in agriculture. The rates ranged from more than 90 per-
kilometers, equal to a square whose side is the distance cent in imperial China to more than 66 percent in the
between Philadelphia and Boston.The constraint is clear: post-Civil War United States, and in all traditional agri-
No global steel-dominated civilization based on charcoal cultures adults were also commonly helped by children.
could exist, and coal-derived coke took over. Limits were also obvious in warfare because even
trained muscles could impart relatively restrained destruc-
Human and tive force to the tools of war, a reality made clear by com-
Animal Muscles paring kinetic energies of common preindustrial weap-
Similarly, the limited power of human and animal mus- ons.The kinetic energy of a single stone ball shot from a
cles constrained productive capacities as well as aggres- medieval cannon equaled that of five hundred arrows dis-
sive forays of all traditional societies. Healthy adults can charged from heavy crossbows or one thousand thrusts
sustain work at 40–50 percent of their maximum aero- delivered with heavy swords. Pregunpowder battles thus
bic capacity, and for men (assuming muscle efficiencies of consisted of limited expenditures of muscular energy, a
20 percent) this translates to 70–100 W of useful work. reality that explains frequent preference for either sieges
Small bovines (cattle and water buffalo) can sustain or stealthy maneuvers.Wars became much more destruc-
about 300 W, lighter horses around 500 W, and heavier tive only with the introduction of gunpowder—in China
animals 800–900 W (one horsepower is equal to 745 during the tenth century and in Europe at the beginning
W).These rates give common equivalences of at least four of the fourteenth century.
men for an ox and eight to ten men for a horse. No less Speed of travel was another obvious constraint
importantly, heavier draft animals can develop briefly imposed by animate metabolism and by inefficient con-
maximum power well in excess of 3 kW and can thus version of wind. Speedy running and horse riding were
perform tasks unattainable by men (plowing heavy soils, used only for urgent messaging, and impressive distances
pulling out tree stumps). Larger numbers of stronger draft could be covered in a single day: The maximum on