Elaine Becker, age 13, of Pocatello, Ida., for her question:

WREN WAS THE PIPE ORGAN INVENTED?

A pipe organ is a musical instrument with a keyboard that has compressed air vibrating inside tuned pipes to produce melodic sounds. Credit for the first organ goes to a Greek living in Alexandria named Ctesibius.

In the Third Century B.C., Ctesibfus inverted a vase to which was attached s single pipe in a small hole at the top. When water was forced into the vase through the neck at the bottom, the air trapped inside was blown through the pipe. It created a powerful sound.

Ctesibius' device led to the first pipe organ, which was called the hydraulus because water forced the air through the pipes. It had several pipes, a crude keyboard and a way of connecting the keys to valves that let the air reach the pipes.

Much force was necessary to depress the keys of this first organ. The keys were about three inches wide and the player would have to strike them with his fist.

During the early centuries of the Christian era, the hydraulus changed from the instrument that used a hydraulic system to supply air, into an instrument that used bellows.

In about 1500 the size of the keys became smaller. In fact, they were about the same size as the keys used on organs today.

At this same time, a pedal keyboard was invented that could be played with the organist's feet while playing the manual keys with his hands. This helped to expand the range of the organ, but it also made the organist's job more difficult.

It was very difficult to play the early organs. It is said that Johann Sebastian Bach had to stand on the pedals and throw his full weight against his hands when playing major chords. Only in this way was he able to force down the keys of both the manuals and the pedals.

The electric action organ of today is a highly refined instrument.

The arrangement of the manual and pedal keyboards of today's electric action organ and the way you play it are the same as they were hundreds of years ago. But of course there have been many mechanical improvements through the ages.

Through the years the human pumpers were replaced by water pumpers, which were in turn replaced by gasoline engines and even steam engines as a source of power to operate the bellows.

With engine driven bellows, however, there was always the problem of unsteady air. The development of the electronic blowers and valve actions solves this problem. Some modern pipe organs have as many as seven manual keyboards, although three or four manuals are preferred by most musicians. In the United States, a standard manual today has 61 keys and a standard pedal keyboard has 32.