You needed an awfully good reason to stay inside on such a lovely afternoon as Sunday's, but the Lark Quartet provided one with its free concert at the National Academy of Sciences. This polished and warmly communicative ensemble played works ranging from Beethoven to George Gershwin and didn't miss a step.

The Lark Quartet has undergone a number of personnel changes since it was founded 20 years ago and currently consists of violinists Maria Bachmann and Deborah Buch, violist Kathryn Lockwood and cellist Astrid Schween. Bachmann also maintains a solo career, yet there is no "first among equals" grandstanding when she is working with the Lark. (The late Jascha Heifetz's chamber performances often sounded like disappointed violin concertos.) To the contrary: Even though the NAS hall has rather dry and unforgiving acoustics (high notes, in particular, were uncomfortably exposed), the four women played with an organlike euphony, as though they all shared the same musical impulses and understandings and were having a great deal of fun together.

Beethoven's String Quartet in D, Op. 18, No. 3, opened the program, an early work played for once with an emphasis on melody and comfortable good spirits rather than perceived prefigurations of the "heaven-storming" romantic the composer would become. A selection of late-20th-century ragtime by William Bolcom followed, music influenced by the spirit of Scott Jopin yet suffused with Bolcom's own allusive sense of humor. The "Three Rags for String Quartet" -- "Poltergeist," "Graceful Ghost" and "Incineratorag" -- were created for piano but translate easily and well for strings.

Stanley Silverman's arrangements of "Five Songs for String Quartet" by George Gershwin followed immediately and seemingly inevitably. This sort of crossover is usually not my thing -- in general, I'd rather hear pop songs played by pop musicians, who usually do them better -- but Silverman's renditions were so deft and sympathetic and the Lark's performances so smart and urgent that the hybrid took. "Do It Again" bubbled up with Dvoraklike schmaltz while "Sweet and Lowdown" swung out with such vigor and strength that the quartet sounded like a jazz orchestra in full sway.

Ravel's wonderful Quartet in F -- a collection of four musical prisms that constantly change their hues and designs -- closed the afternoon. Simultaneously tidy and exuberant, coolly cosmopolitan and deeply sentimental, it might have been written for the Lark players, who gave it a performance of grace, proportion and burnished brilliance.

The quartet's program Sunday afternoon ranged from Beethoven to Gershwin, with some ragtime and Ravel thrown in for good measure.