Billie Jo Hobson, age 10, of Darlington, South Carolina, for his question:

Where were windmills invented?

A windmill, of course, uses the force of the wind to do useful work. Nobody is certain where and when people first thought of this breezy idea. Most experts suspect that it happened in ancient Persia which later became the modern country of Iran. In any case, there are records that windmills were used there in the 7th century A.D., which was about 1,300 years ago. It was another 500 years before Dutch type windmills became popular in Western Europe.

The early windmill was a sturdy tower, topped with a circle of large oblong vanes that acted as sails to catch the wind. Sometimes the vanes were made of tough canvas type fabric. Sometimes they were made of wooden shutters. When the wind blew, it turned the circle of sails around    and they turned a large post. The turning post could be fixed to huge flat millstones to grind grain. Or it could be made to pump water or other useful work