Why Does the Leaning Tower of Pisa Lean?

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In 1172, Donna Berta di Bernardo donated 60 silver coins to the local cathedral for the purchase of stones to be used in the base of a new bell tower.

The next year, construction on the tower began and almost immediately there were problems. The tower site sat on soft ground composed mostly of clay, fine sand, and shells (the city sits between the Arno and the Serchio rivers). By the time the builders finished the second floor in 1178, the tower was beginning to lean.

Soon, construction was halted for almost 100 years, as Pisa fought wars against Genoa, Lucca, and Florence. This may have been a lucky break, as modern analysis says that the tower definitely would have toppled had construction continued without time for the soil to settle.

When work on the tower resumed again, it was leaning 0.2 degrees north of vertical, but by the time the workers started on the seventh floor, the tower was tilting one degree south. Around this time, construction stopped again for unknown reasons.

DON'T LEAN ON ME

Over the next century, construction continued intermittently.

The tower’s lean gained another 1.6 degrees. To counteract the lean, the builders made the remaining floors taller on the south side of the tower. But the weight of the additional floors only made the foundation sink further, making the lean worse. Having done what they could, the builders finished up and officially completed the tower around 1370.

Since the tower’s completion, engineers and architects from all over the world have monitored the lean and tried to correct it. These attempts have involved adding grout to the foundation masonry, wrapping plastic-coated steel pieces around the tower up to the second floor, pouring a concrete ring around the base of the tower, laying lead counterweights to the north side, installing anchored cable counterweights, and extracting soil from underneath the north side.

After the removal of more than 70 metric tons of soil in 2008, engineers announced that the Tower had been stabilized enough that it had stopped moving for the first time since construction began. Its lean is now only about four degrees (prior to the all the restoration attempts, the lean was 5.5 degrees), or about 13 feet past perfectly vertical. The Leaning Tower of Pisa should be stable for at least the next 200 years.

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Does Washing Your Fruits and Vegetables Really Do Anything?

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Washing produce is one of those habits that some people follow religiously and others shrug off altogether. If you're someone who struggles to find the motivation to cook in the first place, you might fall into the latter group. But cleaning your fruits and vegetables at home isn't just an outdated precaution: As Popular Mechanics reports, a thorough rinse could mean the difference between a meal that nourishes you and one that leaves you sick.

Produce is one common carrier of norovirus—a foodborne viral infection that triggers such symptoms as nausea, vomiting, and diarrhea. There's no way to know whether your lettuce is contaminated with harmful bacteria before it hits your plate, but cleaning it with plain tap water does make it safer to eat. According to USA Today, rinsing produce is effective enough to remove 90 percent of the pathogens left on it by the growing, harvesting, and shipping process. Rinsing is also a good way to remove any of the visible matter you don't want eat, such as grit and soil.

Cleaning your fruits and vegetables is definitely an improvement over eating them straight from your crisper drawer, but be warned that this isn't a foolproof way to avoid food poisoning. Water won't remove all the microbes living on the surface of your food, and even an extremely thorough rinse isn't enough to make produce contaminated with potentially deadly bacteria like E. coli safe to eat. But that doesn't mean the risk outweighs the benefits of including produce in your diet.

If you have a pile of veggies that need to be prepared for dinner, the best way to make them safer for consumption is to rinse them under cold water and rub them in a bowl of water, starting with the cleanest items and progressing to the produce that's more soiled. Give all the food a final rinse before moving it to the cutting board. Peeling the outside of your produce and cooking it when possible is another effective way to kill or remove stubborn bacteria.

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What's the Difference Between Pigeons and Doves?

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To the layman, the difference between pigeons and doves has something to with color, maybe. Or location. Or general appeal (doves usually get much better press than pigeons do). But what’s the actual, scientific difference between doves and pigeons?

As it turns out, there isn’t one. Paul Sweet, the collection manager for the department of ornithology at the American Museum of Natural History, says the difference is more linguistic than taxonomic.

“The word dove is a word that came into English from the more Nordic languages, whereas pigeon came into English from French,” Sweet tells Mental Floss.

Both dove and pigeon refer to the 308 species of birds from the Columbidae family, Sweet says. There’s no difference between a pigeon and a dove in scientific nomenclature, but colloquial English tends to categorize them by size. Something called a dove is generally smaller than something called a pigeon, but that’s not always the case. A common pigeon, for example, is called both a rock dove and a rock pigeon.

“People just have their own classification for what makes them different,” Sweet says. “So in the Pacific, for example, the big ones might get called pigeons and the smaller ones might be called doves, but they’re actually more closely related to each other than they are to other things in, say, South America, that are called pigeons and doves.”

The difference boils down to linguistic traditions, so feel free to tell people you’re releasing pigeons at your wedding or that you’re feeding doves in the park. Scientifically speaking, you’ll be correct either way.

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