A steadily improving Bach Society Orchestra presented last night a program of two Mozart concertos and shorter works by Purcell and Walter Piston. During parts of the concertos, there was still a raggedness and lack of decision which should be worked on; but much of the concert showed careful rehearsing and playing, and some sections of the Piston Sinfonietto were marked by the kind of precision and balance that has made the orchestra in previous years among the finest performing groups at college.

The string section has become more solid, and the intonation continues to improve. The main faults are an over-weighty bass, and a tendency to lose intensity on the sustained notes. A less pronounced and biting attack on each note would have supplied a smoother legato, particularly in the opening Purcell Overture, which was otherwise very satisfactory in tone.

The two soloist, Neal Zaslaw and Richard Oldberg, both possess extremely fine techniques, which enabled them to handle easily the involved passage-work with which Mozart fills out his instrumental concertos. Zaslaw, playing the first Flute Concerto, in G, used a tone which, while more breathy than some tastes prefer, is even and manageable enough for delicate articulation. Oldberg's tone also veers away from the "pure" school, toward the specifically brassy sound.

John Harbison's conducting is becoming much more relaxed, without losing any of its control. The orchestra occasionally lapsed into an unpolished, open sound, particularly in the Flute Concerto where it covered the soloist; but for the most part, Harbison's handling of dynamics was attentive, and in parts of the Piston, very exciting. A more intense beat, besides lending even more excitement, would add rhythmic sureness and vivacity. Otherwise, both his and the Orchestra's work indicates much to look forward to, and one hopes they will not become assimilated into the larger Harvard-Radcliffe Orchestra next year.