Brian Pieper, age 11, of Stuart, Iowa, for his question:

HOW DOES A HEARING AID WORK?

There are two types of hearing aids: the air conduction aid, which amplifies sound and brings it directly to the ear; and the bone conduction aid, which brings sound waves to the body part of the head, usually directly behind the ear.

Hearing aids have been around for hundreds of years. The ear trumpet was popular before the 1600s. By the 1700s the audiphone or dentiphone was invented. Sound vibrations traveled through a celluloid fan shaped device which was held between the teeth. The sound vibrations traveled from the teeth to the jawbone, the skull and finally to the auditory nerves.

Today electronic hearing aids include small microphones and amplifiers that are powered by tiny batteries. They are essentially small telephones.