News

If you think Philadelphia has an image problem now, think what would happen if we broke the Liberty Bell in half.

That's the ultimate worry for the folks planning the move of the famous bell to its new home this fall.

It's more than a passing concern, because the bell has not only the renowned crack (actually the repair of a crack), but also a hairline fracture that extends from the top of the visible crack right over the bell's crown, making it too risky to ring.

When riggers attempt to move the 2,080-pound, 250-year-old bell, jostling could put strain on the area around the crack, causing the hairline fracture to grow.

"Too much [strain] could literally cause the bell to fall apart," said Steven Arms, president of MicroStrain Inc., of Williston, Vt., which is helping monitor the bell for problems during its transport.

The George S. Young Co. of Philadelphia will do the actual moving, lifting the bell eight inches from its current supports using a powerful winch. Then the workers will place it into a special enclosure where it will hang from straps rather than rest on a surface.

A forklift will move the enclosed bell about 200 yards to its new home near the corner of Sixth and Chestnut Streets. It will be housed with a display on the concept of liberty.

Before the move, MicroStrain will attach dime-size wireless monitors around the crack to track every micron of shear or opening of the crack. A practice lift last month seemed to show the method would work.

The bell cracked almost as soon as it arrived in Philadelphia in 1752. Hung in the belfry of what was then the Pennsylvania State House (now Independence Hall), the bell commemorated religious and political freedom enjoyed in the colony under its Charter of Privileges.

The bell used to be rung on special occasions, including the first reading of the Declaration of Independence. But, according to the National Park Service, that tradition ended one frigid morning in February 1846, when Philadelphians rang the bell for Washington's birthday and the hairline crack started growing.

No one has rung it since, though a self-described religious wanderer struck the bell with a hammer in April 2001.

The manufacture of metal objects was not done with precision back in the mid-1700s, said Karie Diethorn, supervisory museum curator at Independence National Historical Park.

The procedure was to create the bell's form and press it into a sand pit to make a mold. Into this the foundry workers would pour the molten metal. That method created a bell full of bubbles and worse, she said. "It wasn't just bubbles - we're talking air pockets and debris like straw and gravel and all kinds of stuff."

The end result is a very brittle bell. It survived its last move in 1976, but this time they are not taking any chances.

The idea to use the MicroStrain sensors came from Andrew Lins, a conservator at the Philadelphia Museum of Art and a specialist in metals. After hearing about the challenge, the Vermont-based company volunteered to help.

MicroStrain's Arms, a biomedical engineer, said his company initially created the tiny sensors to monitor strain on people's knee ligaments. The company has since made strain monitors for bridges and car engine parts.

Arms said his company's sensors can detect a displacement along the crack as small as one-50th of the width of a human hair.

The company recently figured out a way to make the devices wireless, transmitting measurements via microwaves.

"When the bell gets moved, you really don't want to be chasing it with wires attached," Arms said.

The danger with a one-ton bell is that its own weight could create potentially disastrous stress if it were jostled too much.

When the Park Service staged its "lift test" last month, the bell was moved a few feet with the sensors attached. "The thinking was that any motion along the crack would be a precursor," to further damage, Arms said.

It worked extremely well, he said. "The sensor measuring the opening of the crack didn't see anything," he said. The detectors showed that one side of the crack moved 5 microns relative to the other side, which Arms said is minuscule.

So the bell is likely to survive its next move, Arms said.

"Maybe we're being too conservative by making all these measurements, but I think it's important to be careful."

By Faye Flam Inquirer Staff Writer

Back to headlines >>