A rare chance to see and hear where it all began: Sullivan's first operetta, Cox and Box, was written at age twenty. Though played with only three characters, the genius that flowered in Ruddigore and Gondoliers is already evident. A contemporary (1862) critic noted in the journal Fun, "Mr. Sullivan's music is funny here and there, and grand or graceful where it is not funny." The man who offered that opinion was W. S. Gilbert before the fateful meeting. Also on the South House program to fill out the evening is Mozart's Impresario.

The only place in the western hemisphere that can boast an authentic rendition of the 1812 Overture is the Lowell House courtyard since the Tower has a set of Russian bells. String players, as usual, will be badly needed. Appreciative observers are always welcome as long as their dress is compatible with conductor Steve Hefling's tails-and-green-sunshade. The afternoon is a fitting rejoinder to the Adams-sponsored Raft Race.

CABOT LIVING ROOM. South House Opera, Gerald Moshell conducting. Mozart: The Impresario; Burnand & Sullivan: Cox and Box. Tickets: $1.50. Thurs., Fri., Sat., May 10-12, 8:30 p.m.

HOLMES LIVING ROOM. David J. Mostow, baritone; George Loring, piano. Songs of Schubert, Faure, V. Williams, and others. Fri., May 11, 8:30 p.m.

FIRST CONGREGATIONAL CHURCH (Cambridge). Lief Thybo, organist; Eva Borgstrom, soprano. Bach: Prelude and Fugure in D Major: Stravinsky:' Dum-barton Oaks Concerto (transcribed for organ). Tickets: $4 (students:$2). Sat., May 12, 8:00 p.m.

PAINE HALL. Apple Hill Chamber Players. Clarinet, cello and piano music by Brahms. Tickets: $2.50 (free to Harvard students). Sat., May 12, 8:00 p.m.

LOWELL HOUSE COURTYARD. Open reading of Tchaikovsky's 1812 Overture. Conducted by Stephen Hefling. Sun., May 13, Rehearsal at 2:00, Performance at 3:00. Spectators encouraged.

APPLETON CHAPEL. Mary Carter, soprano; Herbert Burtis, harpsichord. Sacred songs of Purcell. Tues., May 15, 10:00 p.m.