The levels of energy consumption had remained confined to bare necessities and the possibilities of surplus retention were very limited. Most of the demands for energy by these societies were available in the form of food procurable locally.
It was with the growth of agriculture on the one hand and the domestication of animals on the other hand that the need for newer sources of energy arose and the consumption of energy multiplied.
The most important change was in the basic source of energy: manpower was gradually replaced, first by the power of draught animals. Donkey-driven mills were employed as early as the fifth century BC to crush ore from the silver mines at Laurion, and their use had extended to the grinding of corn in Greece by about 300 BC.
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The next major development was the use of the water and wind energy. One of the most important uses of water energy was in agriculture for irrigation purposes. The distribution of water to cultivated fields through channels has been an old practice.
Early evidence pertaining to irrigation of this type relates to Mesopotamia and dates back to about eighth century BC. This irrigation was helped by the proximity of the Tigris and the Euphrates, which assured a constant supply of water. As described by Seton Lloyd, “Almost the whole of the alluvial plain is capable of being prodigiously fertile agricultural land; and a great part of it has clearly at one time or another been under cultivation.
Evidence of this is the profuse network of ancient irrigation canals, now abandoned, whose spoil- banks, like parallel ranges of small hills, run far out into the plain beyond the scanty farmlands of the present day.”
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The evidence from Harappan settlement suggests that small bunds were erected across the rivers to use the flow energy of water for spreading fresh alluvial soil along the banks. This soil was then used as agricultural field. The knowledge of the
Harappans about water energy is further supported by the discovery of the famous dock-yard at Lothal. It points to the fact that knowledge relating to the tidal currents was tactfully used in creating the dock so that ships could come in with flow-tides and could go out into the sea with ebb-tides. A very early use of water energy was in driving wheels. The evidence relates to about second or first century BC in Egypt. The wheel was submerged in running water which made it turn.
This rotary movement was transferred via a fixed axle to a flat millstone. This type of mill was used for grinding cereals or oil-producing plants. In fact this was the stage when natural energy and mechanical contrivances were combined.
This gave a remarkable boost to the use of energy as it enhanced its driving power substantially. The early waterwheels, first used to drive mills for grinding grain, were subsequently adopted to drive sawmills and pumps, to provide the bellow action for furnaces and forces, to drive tilt hammers or trip hammers for forging iron, and to provide direct mechanical power for industrial mills. Until the development of steam power during the industrial revolution waterwheels were the primary means of mechanical power production, rivalled only occasionally by wind mills.
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Thus, many industrial towns sprang up at locations where water flow was perennial. In an old reference to a watermill dating back to about 85 BC, appearing in a poem by an early Greek writer, the liberation from toil of the young women who operated the querns (primitive hand-mills) for grinding corn was celebrated.
According to Greek geographer Strabo, King Mitheradates VI of Pontus in Asia used a hydraulic machine, presumably a watermill, by about 65 BC. Early vertical-shaft water mills that drove querns were known in China by first century AD, and were used throughout Europe by the end of the third century.
A horizontal-shaft water mill was first described by the Roman architect and engineer Vitruvius about 27 BC. The Roman mills were adopted throughout much of medieval Europe and waterwheels of increasing size were made almost entirely of wood.
In addition to flowing stream water, ocean tides were also used though rarely to drive waterwheels. Like watermills, windmills were among the original prime movers that replaced animal muscle as a source of energy. They were used for centuries in various parts of the world, converting the energy of the wind into mechanical energy for grinding grain, pumping water, and draining lowland areas.
The first known wind device was described by Hero of Alexandria (c. first century AD). The earliest known references to wind driven grain mills, found in Arabic writings of the ninth century AD, refer to a Persian millwright of AD 644, although windmills may actually have been used earlier.
One of the limitations of both the water wheel and the windmills was that it was usually necessary for the power they generated to be utilised on the spot. There were, nevertheless, systems for transmitting power over land, often for considerable distance, but the power-loss must have been much. As with waterwheel, it is difficult to estimate the power output of windmills.
A large Dutch windmill of the eighteenth century, with a 100 feet (approx. 30 metres) sail-span, probably generated about 10 horse power (h.p.) in 20 miles per hour wind speed. Smaller mills, with a 24 ft (approximately 7 m.) span, probably yielded about 5 h.p.
Theoretical considerations show that the windmill in its traditional form could not, at best, yield more than 30 h.p. It was not, therefore, a powerful prime mover by modern standards, and a substantial proportion of such power as it did develop must have been dissipated in the clumsy transmission system, even after iron gearing had been introduced. The foundations for the use of steam power are often traced to the experimental work of the French physicist Denis Papin.
In 1679 Papin invented a type of pressure cooker, a closed vessel with a tightly fitting lid that confined steam until high pressure was generated. It was given more efficient and workable form by a Scottish instrument maker James Watt in 1765 that developed a steam engine.
Although far more difficult to build, Watt’s hortative engine opened up an entirely new field of applications; it enabled the steam engine to be used to operate rotary machines in factories and cotton mills.
Other important development with regard to energy utilisation had been the discovery of a device by Michael Faraday who converted mechanical energy into electric energy. This led to the development of electric generators whereby thermal energy was used to power the mechanical energy and in turn generate electric energy.
The greatest advantage with the electric energy has been the possibility of transmission of energy to distant places from the source of its generation. Similarly another major energy resource has been the nuclear energy which has a great potential.
