Mary Beth Hart, age 10, of Philadelphia, Pennsylvania, for her question:

What is the purpose of windmills?

Nowadays, the place to look for a windmill is on a farm, way out in the breezy countryside. Its whirling wheel is high above the ground and set at an angle to catch the wind. The harder the wind blows, the faster it spins around. The wheel is connected to shafts, gears and other moving parts inside the tall tower. This machinery is moved by the moving wheel and it uses this energy to do useful work. The machinery in one type of windmill is designed to move up and down and pump water from a well. In another type of windmill, the gears and shafts are designed to spin an electric generator.

Windmills use the free energy of the breezes and they can be made for all sorts of useful purposes. In olden days, they were far more common and more handsome than our modern metal windmills. Those lovely old Dutch windmills were used to regulate water in the canals. Others were used to grind corn. Andy has a miniature windmill in his garden. When the breezes blow, its machinery thump thumps in the ground. Its purpose, he hopes, is to scare away underground moles and greedy gophers.