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Who Cracked the Liberty Bell?

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Chalk the Philly landmark’s famous blemish up to faulty building materials from across the pond. In 1751, the Pennsylvania Provincial Assembly shelled out 100 pounds to London’s Whitechapel Bell Foundry for a bell to hang in the State House (known post-Revolution as Independence Hall). The Whitechapel Bell Foundry—famous for casting Big Ben a century later and listed in the Guinness Book of World Records as Great Britain’s oldest manufacturing company—dropped the ball on the bell, casting it with too-brittle metals.

When the bell arrived in Philadelphia in 1752, it cracked on its first test strike. Two local craftsmen, John Pass and John Stow, twice cast a new bell using metal from the cracked English bell. They also added more copper, to make the bell less brittle, and silver, to sweeten its tone. The recast behemoth weighed in at 2,000 pounds: 70 percent copper, 25 percent tin, and a scattering of lead, zinc, gold, silver, and arsenic. 

Once Americans gained independence in 1776, the landmark fell by the wayside until the 1830s, when abolitionists adopted the bell (dubbing it “The Liberty Bell” in William Lloyd Garrison’s anti-slavery publication, The Liberator) as a symbol for their movement.

There’s no one widely accepted story for how the recast bell got its now-famous crack. One account asserts that the bell fractured during Revolutionary War hero Marquis de Lafayette’s visit to the City of Brotherly Love in 1824. Another insists that it cracked while tolling a fire warning later that year. Craftsmen tried to prevent further damage by boring out hairline cracks on the bell, keeping them from expanding dangerously.

Two legends about the Liberty Bell’s infamous fracture remain the most popular: one contends that the bell cracked during the 1835 funeral of Chief Justice John Marshall, though it may not be historically true—Philly newspaper stories about the funeral don’t mention the bell ringing.

The cause that stuck (at least according to official city reports) was that the Liberty Bell was irreparably damaged in 1846, when Philadelphia mayor John Swift ordered the bell rung to commemorate George Washington’s birthday. The bell had been repaired earlier that year when a thin crack started throwing off the sound of the bell, but after it cracked again, it hasn’t been rung since.

The Philadelphia Public Ledger chronicled the bell’s final peal in a February 26, 1846 story:

"The old Independence Bell rang its last clear note on Monday last in honor of the birthday of Washington and now hangs in the great city steeple irreparably cracked and dumb. It had been cracked before but was set in order of that day by having the edges of the fracture filed so as not to vibrate against each other ... It gave out clear notes and loud, and appeared to be in excellent condition until noon, when it received a sort of compound fracture in a zig-zag direction through one of its sides which put it completely out of tune and left it a mere wreck of what it was."

 

 

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Big Questions
What Causes Sinkholes?
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Mark Ralston/AFP/Getty Images

This week, a sinkhole opened up on the White House lawn—likely the result of excess rainfall on the "legitimate swamp" surrounding the storied building, a geologist told The New York Times. While the event had some suggesting we call for Buffy's help, sinkholes are pretty common. In the past few days alone, cavernous maws in the earth have appeared in Maryland, North Carolina, Tennessee, and of course Florida, home to more sinkholes than any other state.

Sinkholes have gulped down suburban homes, cars, and entire fields in the past. How does the ground just open up like that?

Sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can't take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is so prone to sinkholes because it has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren't left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

About 10 percent of the world's landscape is composed of karst regions. Despite being common, sinkholes' unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

A version of this story originally ran in 2014.

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Big Questions
How Are Speed Limits Set?
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When driving down a road where speed limits are oppressively low, or high enough to let drivers get away with reckless behavior, it's easy to blame the government for getting it wrong. But you and your fellow drivers play a bigger a role in determining speed limits than you might think.

Before cities can come up with speed limit figures, they first need to look at how fast motorists drive down certain roads when there are no limitations. According to The Sacramento Bee, officials conduct speed surveys on two types of roads: arterial roads (typically four-lane highways) and collector streets (two-lane roads connecting residential areas to arterials). Once the data has been collected, they toss out the fastest 15 percent of drivers. The thinking is that this group is probably going faster than what's safe and isn't representative of the average driver. The sweet spot, according to the state, is the 85th percentile: Drivers in this group are thought to occupy the Goldilocks zone of safety and efficiency.

Officials use whatever speed falls in the 85th percentile to set limits for that street, but they do have some wiggle room. If the average speed is 33 mph, for example, they’d normally round up to 35 or down to 30 to reach the nearest 5-mph increment. Whether they decide to make the number higher or lower depends on other information they know about that area. If there’s a risky turn, they might decide to round down and keep drivers on the slow side.

A road’s crash rate also comes into play: If the number of collisions per million miles traveled for that stretch of road is higher than average, officials might lower the speed limit regardless of the 85th percentile rule. Roads that have a history of accidents might also warrant a special signal or sign to reinforce the new speed limit.

For other types of roads, setting speed limits is more of a cut-and-dry process. Streets that run through school zones, business districts, and residential areas are all assigned standard speed limits that are much lower than what drivers might hit if given free rein.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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