3. Power Generation

The water wheel was used as a source of power for many years. The evolution of the water wheel was driven by population growth and the need for greater food output. The Egyptian Nora (~700 BC) was used to lift water for irrigation. The Romans milled grain during the fourth century AD and at the time of William the Conqueror, England had about 5000 grist mills. By 1790, there were about 2000 grist mills in colonel America. By the time of the Civil War, there were some 55 000 water wheels in use, many powered manufacturing facilities. Power generated by the water wheel (~10 hp) was transmitted through gear trains to achieve a required output torque and speed. Grist mills typically have a gear ratio of 25 : 1 with the millstone having the higher speed and lower torque. Wooden gear teeth were common.