Helen Bonilli, age 13, of Johnson City, Tenn., for her question:

WHEN WAS THE PIANO INVENTED?

In 1709, an Italian named Bartolommeo Cristofori worked out the principle of striking a hammer against strings to make a keyboard instrument that could be played loudly or softly by the touch of the fingers. This, technically, was the first piano.

But the piano as we know it today was actually the result of a.." long and very gradual evolution. Many people contributed to this fine musical instrument.

Ancient man came up with the idea of stretching a string and obtaining music from them. And from this, ancient man developed the harp and lyre, in which they plucked strings with their fingers.

Later, the dulcimer was developed in the Middle East. Here the strings were struck with mallets.

Then the Europeans developed the clavichord in which a keyboard was used to control the mallets. And from this came the harpsichord. in the harpsichord, quills were used to pluck the strings.

Christofori's instrument in 1709 was called the "gravicembalo col piano a forte," or "harpsichord with soft and loud." It came to be known simply as "piano."

But for a hundred years, the harpsichord continued to be the more popular of the two instruments. Not too many musicians appreciated the piano.

Christofori's hammers were flat pieces of wood covered with leather. Then, more than a hundred years later, felt was added to the hammers. Another important development during the 1800s was the invention of piano wire drawn from steel.

Also in the 1800s, a man named Sebastien Erard developed a way to make the hammer fall back part of the way from the string while the key was held down. This improvement was called the double escapement.

An American named Alpheus Babcock, living in Philadelphia, invented a cast metal plate for square pianos in about 1822. And another American, Jonas Chickering of Boston, made a grand piano in 1840 with a plate cast in one piece.

A man named John Isaac Hawkins produced the first upright piano in 1800 and an action developed by an Englishman named Robert Wornum in 1826 made this style of piano practical.

The New York City firm of Steinway and Sons developed the overstrung scale, with the longer bass strings stretched across the higher ones. The longer ones created more sound and better tone color.

Today's modern piano has about 230 steel wire strings, each tuned to one of the 88 notes of the equal temperment musical scale.

The vibrating length of each string is calculated according to certain laws of physics to determine the piano's scale or stringing pattern. The shortest string, in the high or trebel section, is about two inches long while the longest, in the bass or low section, can be as long as 80 inches.