How Did Anything Get Powered Before Steam? A River and a Wheel

The designs are distinguished by where the water strikes the wheel, and the difference in performance is large. An undershot wheel sits in a flowing stream and is turned by the water pushing its lower paddles, which requires no fall at all and extracts only a modest fraction of the available energy. A breastshot wheel receives water at about the height of its axle, combining push with the weight of water held in its buckets. An overshot wheel receives water at the top from a channel, filling buckets that descend under gravity, and it extracts by far the most because it uses the weight of the water through the full height of the wheel rather than merely its motion.

The range of work driven by these wheels was far wider than grinding grain:

• •Grain milling, which was the most numerous application everywhere
• •Fulling cloth, by lifting and dropping heavy hammers onto woollen fabric
• •Forge hammers and bellows, which made larger ironworking possible
• •Sawmills, driving a reciprocating blade through logs
• •Pumping water out of mines, using long rods running from the wheel
• •Paper mills, ore crushing, wire drawing and dozens of other processes

The figures are modest by later standards and were transformative at the time. A typical medieval installation delivered a few kilowatts, roughly comparable to a small modern motor, which replaced the continuous labour of a substantial number of people or animals. The largest ever built were considerably more, with one constructed on the Isle of Man in 1854 reaching over a hundred kilowatts and standing more than twenty metres across. The Domesday survey of 1086 recorded around six thousand mills in England alone, which indicates a settlement of any size generally had one. That density is why mill ownership was a valuable monopoly and why tenants were frequently obliged by law to grind at the lord's mill and pay for it.

Operating these installations involved difficulties that shaped rural life and rural law. Water supply was seasonal, so a mill stood idle in drought and was endangered in flood, and millers built ponds and leats to store and control it, which required rights over land and water that generated constant litigation. Upstream and downstream users competed for the same flow, and the height of a weir determined how much each got, which is why mill disputes fill medieval court records. Ice stopped work in winter. The wheel and the wooden gearing needed continual maintenance from a skilled millwright. And millers had a poor reputation for honesty in every European country, being suspected of taking more than the agreed share of the flour they ground.

Steam power displaced these wheels from the late eighteenth century, and the reason was location rather than power, since a steam engine works anywhere while a wheel must sit on a suitable watercourse, and industry concentrating near coal and ports could not depend on scattered rural streams. Water turbines then displaced the wheel itself from the mid nineteenth century, being far more efficient, far more compact and able to use much greater heads of water, and those turbines are what modern hydroelectric stations use. The principle therefore did not disappear at all, and water remains among the largest sources of electricity worldwide, generated by machines that are direct descendants of the overshot wheel.

Where the water meets the wheel determines the yield, with an overshot arrangement using the weight of water through the full height and extracting far more than an undershot one using motion alone. These wheels ground grain, fulled cloth, drove forge hammers, sawed timber and pumped mines. England had around six thousand mills by 1086. Steam displaced them for location rather than power, and turbines replaced the wheel itself.