Andrew Pierce, age 15, of Dodge City, Kan., for his question:

HOW DOES AN EGG INCUBATOR WORK?

Most commercial chicken incubators are electrically heated to maintain a constant temperature of from 99.5 to 100 degrees Fahrenheit. A system of fans circulates warm air through the egg chamber and over the fertilized eggs.

It seems hard to believe, but today large egg incubators can hold up to 100,000 eggs at a time.

The relative humidity of the incubator is held at about 60 percent to reduce the loss of water content from the eggs. Mechanical devices turn the eggs several times a day, all at the same time.

Fresh air brought into the incubator keeps the oxygen level at 21 percent, the normal level of outside air.

Chicken eggs normally incubate for about 21 days.