Linda Harman, age 13, of Cumberland, Md., for her question:

WHEN WAS THE CLAVICHORD INVENTED?

The oldest form of stringed keyboard instruments is the clavichord. It was invented in the early 1400s and continued to be popular until the early 1800s. The clavichord is a predecessor of the piano.

The clavichord has a rectangular case with the keyboard lengthwise to the left and the soundboard at the right end. The strings run from tuning pins at the right end of the case, over a bridge set on the soundboard, to hitch pins at the back and left end of the case.

Each key has a small upright brass blade, or tangent, at its rear end. When the player depresses the front of the key, the tangent rises, striking the string, both setting it in vibration and determining its sound length, which is from the bridge to the tangent.

To the left of the tangent, the vibrations of the string are silenced by felt woven through the strings near the hitchpin. When the key is released, the felt silences the string.

By varying finger pressure on the key, the player can produce a vibrato.

A typical 18th century clavichord is about five feet long with a range of five octaves.