Franklin invented it, Mozart wrote for it: the 'armonica' returns

The hydrodaktulopsychicharmonicam has returned - thanks to Gerhard Finkenbeiner. Mr. Finkenbeiner, a rosy-cheeked glassmaker from Konstanz, Germany, has taken the mysterious musical ''Armonica'' (not to be confused with the mouth organ) invented by Benjamin Franklin in the late 18th century, and, by adding a motor and pure quartz glass, brought back the haunting, humming, flute-violinlike melodies of the glass harmonica.

People have been making music by running a moistened finger around the edge of a goblet since the 1600s. Musicians would ''tune'' a series of glasses by putting more or less water in them. Franklin, after hearing a performance in 1757 by an Irishman named Richard Puckeridge, decided to mechanize the musical glasses.

In 1762 Franklin arranged a series of glass bowls of graduated sizes along a horizontal spindle running the length of a trough of water. A foot pedal kept the contraption spinning, and the friction of fingertips against the wet rims of the glass bowls produced the eerie tones.

''By the 1780s,'' Finkenbeiner says in his German accent, ''the glass harmonica invented by Franklin was the talk of every social event. It was the big thing of the century. The sound was so great.''

One blind woman, Finkenbeiner says, was said to be able to play anything on the glass harmonica that could be played on the harpsichord. Mozart even composed a quintet for her, in which the glass harmonica was combined with a flute, oboe, viola, and cello. Beethoven and several other composers wrote music for the strange instrument as well.

By the beginning of the 19th century, rumors about detrimental effects on the nervous system from the glass harmonica's vibrations, Finkenbeiner says, hurt the instrument's popularity. ''People were afraid - and it just disappeared. I personally don't believe it,'' Finkenbeiner asserts. He has been producing the modern glass harmonicas since 1982.

Several musicians have kept alive musical glasses, but Finkenbeiner says the glasses have limitations: Most of the armonica music composed by Mozart, for example, can be played properly only on an armonica. ''The glasses can't play legato - smooth connected chords,'' Finkenbeiner explains, ''and the glasses have to be arranged according to each piece of music.''

He also says the musical glasses - ranging from crystal to inexpensive drinking glasses - don't produce as loud or as clear a tone as the quartz glass in the glass harmonica which is ''much louder. It's the best glass you can get, '' Finkenbeiner says, touching the rims of several glass bowls in quick succession and producing the bizarre sounds.

(The pure quartz glass comes from Finkenbeiner's main business, which is making specialized glass instruments and glass gas chambers for producing silicon chips. One foot of quartz-glass tubing costs $200, Finkenbeiner says, compared with $20 for the same amount of normal glass.)

''The glass harmonica also has a real keyboard,'' he says, pointing to the baked gold rims of certain glass bowls representing the black keys of a keyboard.

Finkenbeiner tunes each glass cup for the glass harmonica in the woods of New Hampshire, where they are either dipped in acid or ground down until they reach an international standard and are compatible with other instruments.

The price is also compatible with certain instruments - such as a harpsichord. The Finkenbeiner Concert Model, with a 3 1/2-octave range (43 notes), sells for $30,000. The least expensive Practice Model - a table-top version without cabinet - sells for $5,875. The price includes a free introductory lesson.

Finkenbeiner hopes someday an orchestra will use a glass harmonica again so that people can hear the ''very special blending of sounds.''

''It floats in the air and people think it comes from different directions. It's actually amplified in the air,'' he says.

''And it just doesn't sound the same when it's recorded. It loses something. I don't get the goosebumps I get when playing it,'' artiste Finkenbeiner says with a big smile.