The mill before electricity
Long before anyone thought of making electricity from wind, windmills were working machines that turned grain into flour. They were among the most complex machines in many medieval and early modern communities, with sails, shafts, gears and stones fitted together by skilled carpenters known as millwrights. This article looks at those mills, how they worked and where they came from.
Persian vertical-axis mills
The earliest windmills that can be reasonably documented come from the Persian world. Written sources from around the tenth century describe mills in the Sistan region, in what is now eastern Iran and southwestern Afghanistan, an area known for strong and steady summer winds. Their layout was unusual by later European standards. The sails turned around a vertical shaft, and the millstones sat directly on top of it, so no gears were needed. A wall with openings funneled the wind onto only one side of the rotor so that it would push instead of cancel itself out.
Some of these mills are described as working for a long time, and similar vertical-axis mills survived in the region into modern times. The exact origin of the design, and any earlier forerunners, is not well documented, so historians speak cautiously about who invented the first windmill.
Horizontal-axis mills in Europe
Windmills of a very different type appear in European records from the late twelfth century, with early references in England, Normandy and Flanders. These mills had sails on a horizontal axle, and they spread widely across northern Europe within a century or two. Whether the idea came from the Middle East or arose independently is debated, since the European mill is a different machine and no clear line of transmission is documented.
The earliest European type is the post mill. The whole wooden body, containing the machinery, sits on a single massive vertical post and can be turned by hand, using a long tail pole, to face the wind. Post mills are cheap to build but limited in size. Later came the tower mill, where only the cap at the top rotates while a stone or brick tower stays fixed, and the smock mill, a wooden tower with a rotating cap. These larger buildings could hold more machinery and a bigger set of sails.
Inside a traditional mill
The sails turn a heavy horizontal shaft called the windshaft. A large gear on it, the brake wheel, meshes with a smaller gear known as the wallower, which converts the turning motion by a right angle to a vertical shaft. Another gear, the great spur wheel, then drives smaller gears that turn the millstones. The principle is the same as in water mills, and the mechanics rely on the wheel and axle, with gear ratios chosen so that a slow-turning set of sails produces a faster-turning stone. The craft of cutting wooden gear teeth shared some skills with the makers of mechanical clocks, since both depended on well-fitting wheels.
Two millstones do the grinding: a fixed lower one, and an upper one that turns over it. Grain falls from a hopper through the center of the upper stone and is ground as it moves outward between the grooved faces. Millers adjusted the gap between the stones to change how coarse the flour was, and the stones were redressed, or re-cut, from time to time. A brake on the wheel held the sails still, and a sack hoist was often powered by the same machinery.
Taming the wind
Wind is hard to depend on, and millers worked hard at controlling it. In bad weather the cloth on the sails could be reefed, rolled up or removed, much like the sail on a ship. Two eighteenth-century inventions made a mill easier to run. The fantail, a small set of blades mounted at the back of the cap and often credited to the English millwright Edmund Lee in 1745, turned the cap automatically to face the wind. Andrew Meikle’s spring sails of 1772 replaced cloth with shutters, like those of a Venetian blind, that opened under spring tension in a gust and spared the miller from stopping the mill to adjust them. William Cubitt patented sails in 1807 that could be adjusted while turning.
Beyond grain
Although grinding grain was the best-known job, windmills were adapted to many tasks. Mills crushed seeds for oil, sawed timber, ground pigments and other materials, and processed materials for paper making. They also drained land and lifted water. In flat countries with weak rivers, such as parts of the Netherlands and eastern England, windmills were part of daily life, and the mill became a center of a village or town.
Decline and survival
The windmill’s decline came in stages. In the nineteenth century, steam engines made it possible to mill where the wind was unreliable, and large roller mills in port cities produced flour at a scale that small local mills could not match. Electricity and diesel engines completed the change. Many windmills were abandoned or demolished. A good number have been preserved by museums and volunteer groups, and some still grind grain today for specialty flour, which keeps the knowledge of the millwright’s craft alive.