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Index |  History |  Highlights |  WhatWhenWhere
Greece and Rome
Middle Ages
     Medieval technology
     Flash locks and pound locks
     Tidal power
     A tower clock in China
     Clockwork in Europe
     The first cloth mills

15th - 16th century
17th - 18th century
19th century and beyond
To be completed

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Medieval technology: 7th - 14th century

Though there is bold innovation in medieval architecture, Europe in the Middle Ages is not notable for technological ingenuity in many other fields.

The windmill is a medieval achievement. So is clockwork, and tidal power. But more immediately effective, in practical terms, is the widespread application of a source of power already used in Greek and Roman times - that of the water mill. By the 14th century water mills are familiar in most parts of Europe with fast-flowing streams. And they are not limited to rotary purposes, such as turning millstones to grind corn. Mills now power great hammers which crush ore extracted from copper and silver mines, or which full cloth in the textile industry.


Windmills: 7th - 15th century

The first practical windmills are constructed in or before the 9th century in a region spanning eastern Iran and western Afghanistan. They are descibed in a manuscript by Estakhri, a Persian georgrapher of that period, as having horizontal sails, like the blades of a helicopter, directly linked by a vertical shaft to the millstones turning below. The date of the first windmill is often given as 644 or earlier, because a 9th-century document says that the man who in that year assassinated the caliph Omar in the mosque at Medina was a Persian builder of windmills. But a first mention of this two centuries after the event makes it unlikely to be true.

Windmills are first mentioned in Europe in the 12th century. There is a reference to one in France in 1180, and a few years later to another in England. Since this is the time of the crusades, it is likely that the idea has been brought from the Middle East.


The European windmills of the 12th and 13th century have upright sails, of the kind still familiar today. They require simple gearing, to transmit the power to the vertical shaft which will turn the millstones. And they have to be able to turn through 360 degrees so that the sails can face the wind.

In these first versions the entire working mill, complete with the millstones, has to be turned into the wind by pressure from ground level on a long pole. For this to be possible the mill structure has to sit on a sturdy vertical post, giving such mills their name - post mills.


By the 14th century there are windmills of a new design in France. Known as tower mills, they can be larger and more rigid than the earlier post mills. Now only the top part of the structure rotates. Holding the horizontal axle of the sails, it sits like a loose cap on top of the mill tower. It can be turned either by the traditional pole, from outside, or by a lever within the cap.

By the 15th century windmills are common in Europe, though rarely as economical as the watermill. The exception is the Netherlands, where there is plenty of wind and a great deal of surplus water to be lifted from low-lying areas - the original purpose of the Dutch windmills.


Flash locks and pound locks: 10th - 15th century

From the very first construction of canals, some method is necessary to cope with differences in water level. The simplest solution is a weir, to hold up the water on the higher side, with a gap in the middle which can be opened to let a boat through. The removal of the barrier, however achieved, is inevitably followed by a sudden rush of water - carrying the vessel easily through in one direction, but making passage very difficult in the other. A primitive lock of this kind is known, for obvious reasons, as a flash lock.

The development of the more sophisiticated pound lock is traditionally credited to an engineer, Chiao Wei-yo, working on the great Chinese canal system in the 10th century AD.


It is said that Chiao is required to construct two flash locks on the Grand Canal only about 200 yards apart. He realizes that he has created a pool which will be at the upper or lower level of the canal depending on which of the two barriers is open. Moreover the barrier separating patches of level water can be opened without the obstruction of water pressure.

The result is the pound lock, standard on all modern canals. The first in Europe is believed to have been built in the Netherlands in 1373 at Vreeswijk, where a canal from Utrecht joins the river Lek.


At this stage the barrier is a simple sluicegate which has to be raised and lowered like a guillotine. The process is laborious, and the water pressure against the flat surface requires a very strong construction to hold it.

The last missing piece in the design of the modern lock is the mitred lock gate. On this system each end of the lock is closed by a pair of wooden gates slightly too large to close in a normal flush position. They meet with mitred edges pointing in the direction of the higher water level. Water pressure holds them tightly together, until the level is the same on either side - at which point the gates can be easily pushed open.


The first lock with mitred gates is probably the one built in Milan in about 1500 to join two canals of differing levels. Known as the San Marco lock, it is likely that its design is by Leonardo da Vinci. As his notebooks reveal, Leonardo is interested in all aspects of hydraulic engineering; and he is employed at this time by the duke of Milan.

From the 12th century Europeans have been busy constructing canals, even with the primitive device of the flash lock. The mitre lock makes possible increasingly ambitious projects.


Tidal power: 11th - 12th century

Tide mills, damming a tidal stream at high tide to power a water wheel once the tide has fallen, are pioneered in England. Such a mill, built near the entrance to the port of Dover in about 1070, features in the records because it proves a danger to shipping. But tidal mills working without obstruction are mentioned at Bromley-le-Bow near London in 1135 and at Woodbridge in Suffolk in 1170.

In subsequent centuries many tidal mills are built on the coasts of Britain and on the Atlantic coasts of Europe and colonial America. They remain commercially effective for just as long as their more conventional inland cousins, powered by tumbling streams.


A tower clock in China: 1094

After six years' work, a Buddhist monk by the name of Su Song completes a great tower, some thirty feet high, which is designed to reveal the movement of the stars and the hours of the day. Figures pop out of doors and strike bells to signify the hours.

The power comes from a water wheel occupying the lower part of the tower. Su Song has designed a device which stops the water wheel except for a brief spell, once every quarter of an hour, when the weight of the water (accumulated in vessels on the rim) is sufficient to trip a mechanism. The wheel, lurching forward, drives the machinery of the tower to the next stationary point in a continuing cycle.


This device (which in Su Sung's tower must feel like a minor earthquake every time it slams the machinery into action) is an early example of an escapement - a concept essential to mechanical clockwork. In any form of clock based on machinery, power must be delivered to the mechanism in intermittent bursts which can be precisely regulated. The rationing of power is the function of the escapement. The real birth of mechanical clockwork awaits a reliable version, developed in Europe in the 13th century.

Meanwhile Su Sung's tower clock, ready for inspection by the emperor in 1094, is destroyed shortly afterwards by marauding barbarians from the north.


Clockwork in Europe: 13th - 14th century

Europe at the end of the Middle Ages is busy trying to capture time. The underlying aim is as much astronomical (to reflect the movement of the heavenly bodies) as it is to do with the more mundane task of measuring everybody's day. But the attraction of that achievement is recognized too. A textbook on astronomy, written by 'Robert the Englishman' in 1271, says that 'clockmakers are trying to make a wheel which will make one complete revolution' in each day, but that 'they cannot quite perfect their work'.

What prevents them even beginning to perfect their work is the lack of an escapement. But a practical version of this dates from only a few years later.


A working escapement is invented in about 1275. The process allows a toothed wheel to turn, one tooth at a time, by successive teeth catching against knobs projecting from an upright rod which oscillates back and forth. The speed of its oscillation is regulated by a horizontal bar (known as a foliot) attached to the top of the rod. The time taken in the foliot's swing can be regulated by moving weights in or out on each arm.

The function of the foliot is the same as that of the pendulum in modern clocks, but it is less efficient in that gravity is not helping it to oscillate. A very heavy weight is needed to power the clock, involving massive machinery and much friction.


Nevertheless the foliot works to a degree acceptable at the time (a clock in the Middle Ages is counted a good timekeeper if it loses or gains only a quarter of an hour a day), and in the 14th century there are increasingly frequent references to clocks in European cities. A particularly elaborate one is built between 1348 and 1364 in Padua by Giovanni de' Dondi, a professor of astronomy at the university who writes a detailed description of his clock. A 14th-century manuscript of his text has the earliest illustration of a clock mechanism with its escapement.

The world's three oldest surviving examples of clockwork date from the last years of the 14th century.


The famous clock in Salisbury cathedral, installed by 1386 and still working today with its original mechanism, is a very plain piece of machinery. It has no face, being designed only to strike the hours. Striking is the main function of all early clocks (the word has links with the French cloche, meaning 'bell').

In 1389 a great clock is installed above a bridge spanning a street in Rouen. It remains one of the famous sights of the city, though its glorious gilded dial is a later addition and its foliot has been replaced by a pendulum (in 1713). The historical distinction of the Rouen clock is that it is the first machine designed to strike the quarter-hours.


In 1392 the bishop of Wells instals a clock in his cathedral. The bishop has previously been in Salisbury, and the same engineer seems to have made the new clock. It not only strikes the quarters. It steals a march on Rouen by having a dial, showing the movement of astronomical bodies.

With escapements, chiming mechanisms and dials, clocks are now set to evolve into their more familiar selves. And the telling of time soon alters people's perceptions of time itself. Hours, minutes and seconds are units which only come into existence as the ability to measure them develops.


The first cloth mills: 13th century

The process of fulling cloth, in medieval Europe's important textile industry, is entirely manual until the 13th century. Woven cloth is fulled to give it extra strength by compressing and binding the fibres. Traditionally this has been done by prolonged pounding, by foot or hand, of cloth which is soaked in water and fuller's earth (to remove grease from the wool).

This heavy work is replaced in England, from the 13th century, by pounding with great wooden hammers. They are raised by tappets fixed to the shaft of a water wheel and are then released to fall by their own weight. It is the first step in the mechanization of textile production, which will eventually play such an important part in the Industrial Revolution.


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