Practically all of the world's great cellos (Stradivaris, for example) date from the Baroque period; but only a few, kept in their original condition or restored to it, are called Baroque cellos. The one played by Anner Bylsma, last night in the Library of Congress, looked much like any other--smaller than average, perhaps, though that had nothing to do with its baroqueness. But its sound, particularly in the hands of a specialist in baroque style, was highly distinctive--lower in pitch; less brilliant and gentler of voice than modern instruments, and played with a very sparing, studied use of the vibrato that wows audiences in romantic string music.

Bylsma played sonatas by Vivaldi and Sammartini, dating from around 1740, and one composed nearly 50 years later by Bach's son, Johann Christoph Friedrich, which required a very different style of performance. In all three, his interpretation was virtually a textbook demonstration of what is known about 18th-century styles of string performance, besides being deeply musical. Devotees of romantic palpitations might feel that there was something missing, but this was one of those occasions when less is more.

Besides supplying expert partnership to Bylsma, harpsichordist Robert Kohnen showed an equally fine sense of period styles in two contrasting keyboard sonatas by Bach and Haydn.