The violin sonatas of Mozart are not virtuoso music in the manner of Paganini or Wieniawski or even of Tartini and Locatelli, who were available for Mozart to imitate if he had chosen. All they are is exquisitely formed duets, usually offering civilized dialogue, funny little tricks and some modest displays of technique in the allegros and rondos; heavenly melody in the slow movements.

A chance encounter with this music (which is all we are likely to get outside of records) generates a sense of spontaneous joy. Extended acquaintance can solidify that joy into deep satisfaction. But such acquaintance is seldom available in our concert life. It is a rare violinist who finds this modest music congenial, though some put one or two token items into their repertoire.

Last night at the Library of Congress, rare violinist Sergiu Luca and equally rare pianist Malcolm Bilson began a series of concerts presenting 16 Mozart sonatas played on original instruments: a 1750 violin without more modern improvements and a fortepiano that is a replica of the one in Mozart's home in Salzburg.

It was a beautiful experience, significantly different from virtuoso recitals that usually feature a violinist and accompanist. It was an evening of poised dialogue, mellow tone, superb coordination and self-effacing musicianship -- an evening in which even the little pause before the final plunge into a rondo theme was a special delight. There will be three more such evenings this month, and any one of them will be worth a considerable effort to hear.