The earliest type of mechanical mill is the rotary quern, a tool consisting of two small circular stones, approximately 0.4m in diameter, which would be rubbed together, the grain being ground between them. Operating a quern required lots of muscle power; it was also a very slow means of grinding flour.
People soon tried to apply other forms of power in order to save human effort. An example of this inventiveness is the animal-powered mill. Here, a horse or other beast was harnessed to the mechanism and walked around it in a circle (see illustration of a mill for raising water, above).
Natural power sources such as wind and flowing water posed more of a problem to people of an inventive nature. Four main forms of mill driven by water or wind evolved, as illustrated by the drawing to the right. The direction of the power source is shown by a red arrow. An enlarged quern features in every type. The upper millstone of the pair is attached to a shaft turned by the waterwheel or windmill sails. The upper stone rotates above the lower stone and as grain is gradually fed between them it is ground into flour. The main difference between the horizontal watermill (see illustrations left and right) and the vertical watermill is the orientation of the waterwheel: “horizontal” like a compact disc or “vertical” like the wheel of a car. The same is true of the sails of a windmill.
The main disadvantage with natural sources of power is their unreliability. Rivers can dry up in warm weather while calm periods with no wind are frequent. Since the 19th century, other forms of power have been used to drive our mills and produce daily bread, such as steam power and, more recently, electricity. The production of these forms of power is harmful to the environment, involving the combustion of fossil fuels such as coal and oil. In our search for reliability we have forgotten our wind, water and muscle-powered mills with power sources that are simple, renewable and environmentally friendly.
Photograph of camel mill for raising water in Egypt © Mildred Cookson; drawing of four mill types © Luke Bonwick, The Archaeology of the English windmill, BA dissertation, University of Reading, 2003; drawing and photograph of horizontal mill in Shetland © Martin Watts.