At noon, the sound of bells chimes over campus, marking the time with 12 strokes. Moments later the air fills with music, be it Handel or the "Star Wars" theme. Each weekday, from noon to 12:30 p.m., the public recitals fill the air with different music. It comes like a gift from the sky, without explanation, although some curious pedestrians may stop to wonder about the source. Steven Ball knows what goes through their heads: "Misconception No. 1: Where are the speakers?"

Music from the Burton Memorial Tower means that someone has sat down at an oversized keyboard of levers that strike the tower's massive bronze bells, or "carillons."

Ball is a graduate student instructor in the University's Carillon Department, the first of its kind in the country, and a carillon performer - or carillonneur - himself. About 25 University students, undergraduates and graduates, are enrolled in his credited carillon class, which is open to audition to any University student with experience on a keyboard instrument.

Although all music from the tower is performed live, the chimes marking the quarter-hours and hour are rung automatically, raising the question of why all the carillon sounds aren't programmed. Ball balked at the idea of trying to replace carollineurs with a program: "It's like playing a huge Steinway. It would be as ridiculous as using a player piano to perform Rachmaninoff," he said.

All bells are not created equal - carillons are quite distinct from church bells, for instance. Ball called the latter "signaling devices," bigger and louder bells used chiefly to announce events. Those bells produce noise by being swung, while carillons are played using a piano-like keyboard of levers that are highly sensitive to pressure. To allow a more delicate touch, the bells remain stationary and are struck from within, with the clappers, some weighing 400 lbs, attached by wires to the keyboard.

According to Ball, carillon songs evolved out of the "warning strikes" given before the hour was rung, grabbing people's attention before the time count started. To distinguish their respective carillons from those of other cities, different towns would elaborate on a simple warning strike.

"The carillon is originally a civic instrument, rather than ecclesiastical," Ball said. "Later carillon players were hired by cities." Out of these utilitarian elaborations grew both original music for carillon and adaptations of existing pieces for the instrument.

The Central Campus bells were made in England in 1936, the same year as the Tower. Last Thursday, evening performances honoring Arthur Miller took place from North Campus's Lurie Tower, near the Walgreen Drama Center where the new Arthur Miller theater opening was taking place.

Although the Tower houses classrooms for music courses and club meetings, Ball said the building is essentially in service of the bells.

"The building's purpose is to get the carillon sound to campus. Every part of the architecture is designed to get that sound out," Ball said.

The ninth floor houses the bells, the largest of which weighs 12 tons. They can be seen behind the building's clock face. That space is open to the public between noon and 12:45 p.m., when carillonneurs have their daily public recital. Visitors may walk around the instruments in the open air at the top of the tower.

"None of the technology up here post-dates the 16th century," Ball said, gesturing to the stacks of bells. He stood inside one huge carillon to demonstrate its overtones and undertones, gently pressing the 400-lb clapper against the sloping interior. The bell's lowest tones reverberated inside the bell. Tapping the surface with one of his many keys produced a high, buzzy ringing. Standing in the center of the bell makes the bell inaudible, as sound waves cancel each other out.

There are only about 200 carillons in the United States, and they're especially scarce in Europe, where they originated. Part of their scarcity because of collateral damage from World War II - Hitler melted down many bells for their valuable bronze.

The only threat to the University's bells is the air pollution that, over time, will degrade the material and alter the bells' pitch, bringing the Tower out of tune.

"I really think this is the city's instrument, the students' instrument - I'd like to see as many people take advantage of this as possible," Ball said.

The Tower is remarkably accessible for those who've heard of the opportunity. In addition, concerts take place throughout the summer and even accompany movie screenings.

In another sense, one can take advantage of "the people's instrument" simply by walking across campus with your ears open. But you could also survey the city from nine stories up, look out over campus from behind the face of a really giant clock, and see your daily trek - and your aural landscape - from a whole new perspective.