History of Windmills

Introduction

Since ancient times, man has harnessed the power of the wind to provide motive power for transportation. Likewise, the technique of grinding grain between stones to produce flour is similarly ancient, and widespread. Quite where and when these two came together in the first windmill is unknown, but a likely scenario suggests a Persian origin, from where (tradition has it) the knowledge spread back into Northern Europe as a result of the Crusades. However, since the Persian mills were quite unlike the early European designs it seems just as likely that the adaptation of wind as a power source was independently discovered in Europe, albeit at a later date. (Of course wind was not the first non-human power source applied to the task of grinding corn - it was preceded by both animal power, and in all probability by water power).

European millwrights became highly skilled craftsmen, developing the technology tremendously, and as Europeans set off colonizing the rest of the globe, windmills spread throughout the world.

The pinnacles of windmill design include those built by the British, who developed many advanced "automatic control" mechanisms over the centuries, and the Dutch (who used windmills extensively to pump water and for industrial uses, as well as to grind grain).

As steam power developed, the uncertain power of the wind became less and less economic, and we are left today with a tiny fraction of the elegant structures that once extracted power from the wind. These remaining windmills, scattered throughout the world, are a historic, and certainly very photogenic, reminder of a past technological age. A number of mills have been restored, either visually, or in some cases back to full working order, where the trend for organic and non-manufactured foodstuffs has shifted the economics slightly back in their favour once again.

However the promise of widespread power from the wind lives on, both in the form of wind turbines producing electricity, and in the form of small scale windpumps (often largely low-tech "appropriate technology" installations) still used extensively in world agriculture.

English Windmills

Evidence of windmills in England dates from the 12th century, with earlier references to "mills" (such as in the 11th century Doomsday Book) generally held to be talking about either animal or water powered mills.

The 14th and 15th centuries provide evidence of what the early mills looked like, with illustrations occuring in diverse media such as memorial brasses, stained glass, and wood carvings, as well as the expected manuscript records.

These early illustrations all show the simple, all wooden, post mill structure.

Post Mills

Post mills are so named because of the large upright post on which the mill's main structure (the "body" or "buck") is balanced. By mounting the body this way, the mill is able to rotate to face the (variable) wind direction.

To maintain the upright post, a structure consisting of horizontal crosstrees, and angled quarterbars is used. By far the most common arrangement was 2 cross bars at right angles to each other under the base of the post, together with 4 quarterbars. Occasionally however other arrangements did occur, such as 3 crosstrees, and consequently 6 quarterbars.

Initially the crosstrees would have rested directly on the ground, (or indeed were buried in the ground for extra stability) but since this makes them very susceptible to rotting, the crosstrees were soon being placed on brick piers, to raise them off the ground.

The body of the mill housed all the milling machinery - a large brake wheel on the same shaft as the sails (the "windshaft") transferred power to a smaller gear at right angles to it, called the wallower. The wallower shared a vertical shaft with the great spur wheel, and from this smaller wheel a "stone nut" was used to drive the millstone. As larger mill bodies were constructed, additional pairs of stones could be driven, by taking further power taps, each using an extra "stone nut" off the great spur wheel. In order to apply some level of control to the mill, the brake wheel could be slowed using a large wooden friction brake around its outer edge.

As already mentioned, the whole body rotated on the central post, in order to face the wind. To allow this to happen, a tailpole or tiller beam extended from the rear of the body. By pushing on this beam (or by using some form of winch or animal power) the miller rotated his mill. The tailpole also provides a useful attachment point for a ladder to provide access to the mill.

An obvious improvement on the early post mill, is to build a roundhouse up around the crosstrees and quarterbar structure. This makes this structure a lot more protected from the weather, and provides additional storage space.

Smock Mills

Smock mills (named after the dress like agricultural costume whose shape they vaguely resemble) are a fundamental improvement over the post mill design.

Instead of rotating the whole body of the mill to face the mill, the smock mill design consists of a fixed wooden body, holding the milling machinery, together with a rotatable cap, which holds just the roof, the sails, the windshaft and the brake wheel.

By rotating just the mill cap, the body of the mill can be made much larger than in a post mill, and hence able to house more pairs of stones, and more ancillary machinery. In addition, the body can be made arbitrarily high, the extra height allowing the sails to catch more wind (and to a certain extent a taller body can allow longer sails to be employed, to the same end).

Smock mill bodies are theoretically roughly circular, though the use of straight timber means that most are actually eight sided. Other numbers of sides occur, including in England examples of six through to twelve sides. (In addition there are a number of small smock mills throughout the world which have square bodies). Many English smock mills are constructed above a more substantial brick built base, which may range from a few courses, up to several stories high.

Tower Mills

Tower mills take the smock mill design even further, by replacing the wooden body with a brick or stone built tower. Since the necessity of having straight sides (due to straight timber) is removed, true circular bodies are the common arrangement. However straight sided structures do occur, and even towers that start off with straight sides at the base, but change to a circular plan part way up (perhaps due to building the tower on what was originally a smock mill base).

By using brick or stone for the body, tower mills can be built even larger and taller than smock mills, and by being a more durable building material, the mills are more weatherproof, and more fireproof.