THE GENERATION OF POWER PAGE 1 WIND, WATER, STEAM & SPARK PAGE 2 WIND, WATER STEAM & SPARK a history of the generation of power from muscle and sinew to the internal-combustion engine JOHN WALTER THE GENERATION OF POWER CHAPTER ONE from muscle and sinew to the watermill and the wind-engine In the first century AD, Hero of Alexandria, writing in his Mechanica, summarised the technological aids available at that time to supplement the muscles of men and beasts of burden: the wedge, the wheel and axle, the screw and the compound pulley, all of which were merely variations of the lever. The origins of them had been lost in antiquity, though each embodied mechanical advantage to ensure that a small force applied through a great distance was transformed into a larger force acting through a much smaller range. The result was that the operator used substantially less effort to move a load, but did so much more slowly than he would otherwise have done. MUSCLE Gradually, the basics of mechanics emerged and attempts were made to exploit them. Levers were used in beam presses in Greece as early as 1500 BC—to extract juice from grapes or olives—and in the oars of the Greek galleys, some of the most modern being pivoted in rowlocks mounted outboard of the hull for greater efficiency. The wheel and axle allowed the development of the tread-wheel and its near relative, the animal gin (or ‘engine’), by concentrating comparatively small effort applied at the circumference of the circle to become a much greater force at the axle. Donkey mills were used to crush ore by the fifth century BC, and then to grind corn by the third century BC. The rotary motion of the tread-wheel was particularly useful, and attempts had been made to convey it through primitive trains of peg-and-lantern gearing by the time of Christ. Unfortunately, the manufacturing technology of the time was unable to make gears that were accurate enough to avoid excessive transmission losses. PAGE 5 WIND, WATER, STEAM & SPARK Tread-wheels have been used into recent time. Medieval engineers still built tread-wheel cranes which would have been familiar to a Roman of the first century AD. The Harwich Crane, the last of its type to survive in Britain, was built about 1670 for use in a dockyard; two 16ft diameter tread-wheels on a single axle provided the source of power. A surviving donkey mill in Carisbrooke Castle in the Isle of Wight dates from 1687, and, at a less public level, donkeys, horses and even dogs toiled to supply water or drive small machinery into recent times. A donkey mill worked until 1899 at Saddlescombe Farm, near Brighton; and animal gins were still being made in backward areas—e.g., the Far East or southern Africa— into the twentieth century. Efficiency was helped by development of the universal joint by Robert Hooke, in the seventeenth century. This allowed portable horse gear to be used on uneven ground. Radial shafts connected with a spur wheel, which rotated the universal-jointed drive shaft through a crown wheel. Typical of recent animal-powered machinery was a South African horse mill dating from the middle of the nineteenth century. The roundhouse contained a vertical wooden shaft supported in the floor by a stone bearing. The horse was hitched to a boom held to this main shaft by iron strapping. As the horse plodded round, guided by a cane linking its bridle with the main shaft, the large spur-peg wheel at the top of the shaft rotated a lantern gear attached to the bottom of the millstone spindle at much greater speed. The spindle ran up through the stationary bed-stone to drive the runner, the gap being adjusted when necessary by a wedged tentering beam. (Some horse mills were driven by rope and pulley instead of gearing, but the principles were otherwise much the same.) The wheel-and-axle principle, often allied with gearing, was also used on capstans, hoists and cranes. A particularly useful embodiment was in the jack, often credited to Leonardo da Vinci on the basis of Codex Atlanticus illustrations, but probably developed early in the fifteenth century. The popularity of the jack has endured largely owing to its simplicity. The earliest examples relied on a crank handle attached to a pinion wheel with very few teeth—often only three or four—which drove a larger pinion meshing with a rack on the jack-bar. A pawl-and-ratchet safety mechanism prevented the jack slipping backward when the winding effort was removed. The bar-type jack was supplemented in the nineteenth century by a screw jack, which substituted a threaded rod for the bar and PAGE 6 THE GENERATION OF POWER PAGE 7 WIND, WATER, STEAM & SPARK a worm gear for the jack pinion. However, though mechanically operated jacks have been made in many forms, the operating principles remain the same. Mediaeval man had few sources of power available to him other than muscle, wind and water. However, the idea of a spring had been appreciated for thousands of years. In a most basic form, bent saplings had undoubtedly been used to provide power—perhaps to lift small items, or provide some kind of recovery from a repetitive action. This was very different from merely using a counterweighted arm to perform useful work (e.g., the shaduf water lifter of Egypt and the Near East) and eventually led to the pole lathe. In this, a foot treadle connected to a springy pole by a cord, twisted around the work piece, provided the downward power or cutting stroke. The whip in the pole then pulled the treadle upward, rotating the work piece back to the starting position ready for the next cut. Similar principles were applied to a wide range of low power machines, including the spinning wheel and the sewing machine. They are particularly interesting in the application of cranks to transfer reciprocating action of the treadle to rotate a shaft. The appearance of a crank on an atmospheric engine in 1780–1 caused James Watt great distress, as it had been patented by a business rival—even though the prior existence of treadle lathes and similar machinery should really have invalidated the claim. Another embodiment of the spring lay in the bow, a combination of whippy wood and a drawstring which had been known since Palaeolithic times. Arguably the most important military weapon from pre-dynastic Egypt to the Middle Ages, the bow was originally made from a single piece of wood. However, more robust composite patterns were subsequently perfected by the Persians from laminates of wood and animal sinew, providing greater power within modest dimensions, and the quest led to the crossbow. Medieval crossbows were derived from Greek and Roman siege equipment powered by twisted cord, hair or sinews. The earliest of these dated back to the era of Alexander the Great and perhaps beyond him to the Phoenicians. Roman legions customarily had rock throwers and spear hurlers working on the same principle. The greatest improvement in the crossbow was the introduction of wrought iron or steel to make the bow, which apparently originated in the most advanced Italian city states at the end of the tenth century. The PAGE 8 THE GENERATION OF POWER use of bronze springs instead of twisted sinews had been suggested by Ctesibius of Alexandria in the third century BC, though the poverty of contemporary metallurgy meant that nothing of lasting significance had been achieved. By the fifteenth century, however, the crossbow had become powerful enough to pierce chain mail armour and often required a separate windlass or crannequin to retract the bowstring. Eventually, metal springs were perfected sufficiently to allow the introduction of successful spring-driven clocks. The earliest is credited to Peter Henlein, said to have been working in Nürnberg (Nuremberg) at the end of the fifteenth century. ‘Clockwork’—the spring trains that allowed clocks to work—was rapidly extended to other uses, not least being the so-called wheel locks fitted to firearms and tinder lighters. However applications were restricted by the need to periodically wind or ‘span’ clockwork mechanisms and their inability to provide much power. The same strictures applied to ‘weight drive’. Use of counterweights to ease arduous or repetitive jobs was well established, and it was soon realised that the potential energy in a suspended weight (even if only a boulder) could be converted to rotary motion. Among the uses were to drive the ‘turret clocks’ in the days before springs became universal, and to turn roasting spits. WATER The tread-wheel and the animal gin were very useful, but still required muscle power and could not be guaranteed to sustain work continuously. A better source of energy was clearly to be provided by the elements, though the state of technology once again hindered exploitation for a long time. Earth had almost nothing to offer medieval man, and no constructive use of fire could yet be seen. Only wind and water held promise. Exploitation of water is an ancient art. King Sennecharib of Assyria built an aqueduct as long ago as the seventh century BC, to be followed by Greeks and Phoenicians until systems were being built by the third century BC which could handle pressures twenty times that of the atmosphere (20 bar). This was largely due to the use of hollowed stone pipes. The Romans built some of the most spectacular aqueducts, from Aqua Appia of the third century BC, largely underground, to the triple storey PAGE 9 WIND, WATER, STEAM & SPARK arcading of the Aqua Claudia.