Traditional windmills. Before the advent of steam power, heavy work was performed by harnessing the power of the wind or water. The windmills seen here were used to pump water from a lower to an upper level in order to drain land. Windmills were also used to grind corn for flour. The large sails drove the rotation of the millstones via a series of cogs. One of the skills of the miller was the adjustment of the blades so that the mill ran at a fairly constant rate. Photographed in Holland.