Among the original bells was the more than three-and-a-half-ton B-flat bell, the source of the lowest notes. Six bells - upper bells, higher notes - were cast and added in 1996 in order to extend the carillon's range to four full octaves.
The bells were hoisted to the top of the tower by a crane, says the academy's carillonneur, James W. Smith.
Very carefully, of course.
And how do Smith, guest carillonneurs and people who want to watch them in action get to the top of the tower?
Again, carefully, by climbing 70 steep, winding steps.
Getting to the carillon is a workout. Playing it is another.
To play the carillon, Smith sits at a bench with a keyboard of sorts in front of him. There are pedals at his feet and keys at his fingertips. The keys, called batons, are wooden levers each about 2 feet long.
Smith's predecessor, Bryan Barker, for whom the chapel tower is named, cut the fingers off a pair of gloves he sometimes wore to play the carillon.
Smith prefers to play barehanded. "You don't have a good feel for the keys with gloves," he says.
The thousands of pounds of bells in the tower don't move. Their clappers - weighing 10 to 20 pounds each - do, when Smith presses the keys with closed fists.
The carillonneur doesn't have to punch, beat or pound the batons. "It's a very gentle musical keyboard," Smith says.
Each baton is connected to another wire, which goes up into the tower and is attached to a wire attached to a clapper for each of the 49 bells.
"You don't tune the bells - ever," Smith says.
But adjustment is needed. The clapper is very close to the bell, but changes in weather can change the distance, Smith says. He will sound each note and move a gadget on each wire to make the needed adjustments.
The bell has to play without clinking when the baton is gently played, Smith says.
The carillon is 100-percent mechanical - although there is electronic amplification by microphone so the music can be heard in the nave of the beautiful old chapel.
Piano was Smith's first instrument. He came to Mercersburg Academy in 1965 as organist and choirmaster. Although he retired last year, he continues as Mercersburg's carillonneur, musically summoning students to weekly chapel programs. He plays a variety of music, recently beginning each 15-minute session with "The Star-Spangled Banner."
Michael A. Kidd, assistant director of communications, is a 1992 graduate of Mercersburg Academy.
He recalls hearing the carillon's call to weekly chapel programs.
"I don't think there's a student who doesn't remember," he says.
Don Hill, assistant head of school for external affairs, started as a math teacher at Mercersbug Academy 33 years ago.
He lives on the edge of town within earshot of the bells.
"I still notice them. They are noticed," he says.
Hill also says he and his wife have spent many a New Year's Eve in the tower, the carillon ringing in the new year.
The carillon holds a lot of nostalgia for the school's alumni, Hill says. But it also plays a vital role in the cultural dimensions of the students' education, he adds. They learn an appreciation for some of the beauty provided by the carillon and carillonneur.
Smith says he sort of played at the carillon, initially teaching himself. He later studied with the carillonneur and Mercersburg Academy alumnus Richard Strauss at the National Cathedral in Washington, D.C.
An associate member of The Guild of Carillonneurs in North America, Smith aspires to full membership in the organization. "It's sort of the zenith of your career," he explains.
Tapes of his playing have qualified him for a final test in June at Berea College in Kentucky.
Meanwhile, he'll continue to call students to chapel.