To Patricia Graham, age 12, of Jarrat, Va.., for her question:

How do we hear sound?

The pretty pink ears on the sides of your head do very little to help you hear sounds, They are merely the outer ears. Birds, seals and many other animals hear very well without having these outer ears. The real organs of hearing are located deep in the skull. These middle and inner ears are small and very complicated.

The outer ear is merely a funnel to trap sound and lead it into the inner hearing organ. Sound is vibrating energy, and it passes through the hole in the outer ear into a tunnel. This is the auditory canal, and it carries the sound waves about onerand at.quarter inches into the skull. There it is sealed with a cone shaped door of skin called the ear drum.

The vibrating sound beats on the ear drum, and the ear drum shivers and booms. The sound is carried through the drums skin into a chamber called the middle ear. There is a chain in this chamber of three, complicated little bones called the hammer anvil and stirrup. The middle ear is filled with air, and the little bones transmit the sound waves still deeper into the skull.

The tiny stirrup bone transmits the sound into the inner ear, which is a very complicated maze of tunnels and passageways. Some of these tunnels operate to help us keep our balance. Others carry sounds to the nerve endings, which send their information to the brain.

The inner ear is filled with fluids, and the sound waves pass through a chamber called the vestibule to a spiral system of tunnels called the cochlea. Some of the walls of the cochlea are lined with tiny fibers. There are about 24,000 of them, some longer and some shorter than others. These fibers carry impulses to the nerves which reach the brain.

Sound vibrations pass through the outer ear and middle ear and finally reach the liquid filled inner ear. Here they stir the thousands of tiny fibers, and they, in turn: send impulses to the tiny nerve endings. These small nerves connect to form larger nerves which lead to the brain. There the noisy information from outside is sifted and sorted. In a flash, the brain can tell whether the sound you hear came from a drum or a dog,, a train or a telephone conversation,

The ear drum is about a quarter. inch across, and the middle ear with its tiny bones is half the size of a thimble. The inner ear with its complicated systems of tunnels is about three quarters of an inch long. All these tiny parts work together to carry sound to the brain in no time at all. When you clap your hands! The brain has information from the sound waves at almost the same instant,