Why Does the Leaning Tower of Pisa Lean?

iStock
iStock

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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How Does Alberta, Canada, Stay Rat-Free?

Francisco Martins/iStock via Getty Images
Francisco Martins/iStock via Getty Images

David Moe:

Alberta is the only province in Canada that does not have any rats and is, in fact, the largest inhabited area on the planet that is rat-free. Rats had to come from Eastern Canada, and it’s a long walk, so it was not until the 1950s that they finally reached Alberta. When they did, the Alberta government was ready for them: They instituted a very aggressive rat control program that killed every single rat that crossed the Alberta/Saskatchewan border.

The Agricultural Pests Act of Alberta, 1942 authorized the Minister of Agriculture to designate as a pest any animal that was likely to destroy crops or livestock; every person and municipality had to destroy the designated pests. Where their pest control was not adequate, the provincial government could carry it out and charge the costs to the landowner or municipality.

Rats were designated as pests in 1950. An amendment to the act in 1950 further required that every municipality appoint a pest control inspector. In 1951, conferences on rat control were held in eastern Alberta, and 2000 posters and 1500 pamphlets titled "Rat Control in Alberta" were distributed to grain elevators, railway stations, schools, post offices, and private citizens.

Between June 1952 and July 1953, [more than 140,000 pounds] of arsenic trioxide powder were used to treat 8000 buildings on 2700 farms in an area 12 to 31 miles wide and 186 miles long on the eastern border. Some residents were not informed that arsenic was being used and some, allegedly, were told that the tracking powder was only harmful to rodents. Consequently, some poisoning of livestock, poultry, and pets occurred. Fortunately, Warfarin—the first anticoagulant rodent poison—became available in 1953; Warfarin is much safer than arsenic, and in fact is prescribed to some heart patients as a blood thinner.

The number of rat infestations in the border area increased rapidly from one in 1950 to 573 in 1955. However, after 1959, the numbers of infestations dropped dramatically.

The provincial share of rat control expenses increased to 100 percent in 1975. All premises within the control zone from Montana to Cold Lake are now inspected at least annually. Rat infestations are eliminated by bait, gas, or traps. Buildings are occasionally moved or torn down, and in some cases, rats are dug out with a backhoe or bulldozer. In the early days they also used shotguns, incendiaries, and high explosives to control rats. It was something of a war zone.

Hundreds of suspected infestations are reported each year, but most sightings turn out to be muskrats, pocket gophers, ground squirrels, bushy-tailed wood rats, or mice. However, all suspected infestations are investigated.

A few white rats have been brought in by pet stores, biology teachers, and well-meaning individuals who did not know it was unlawful to have rats in Alberta, even white lab rats or pet rats. White rats can only be kept by zoos, universities, colleges, and recognized research institutions in Alberta. Private citizens may not keep white rats, hooded rats, or any of the strains of domesticated Norway rats. Possession of a pet rat can lead to a fine of up to $5000.

In 2004 someone released 38 rats in Calgary. By the time the rat control officers arrived, most of them were dead. The local residents had formed a posse and killed them with brooms, 2x4s, and shovels. If the authorities had caught the culprit, he could have faced a $190,000 fine (38 x $5000)—assuming his neighbors didn’t get to him with brooms, 2x4s, and shovels first. Albertans don’t want rats.

This post originally appeared on Quora. Click here to view.

Why Do Students Get Summers Off?

Iam Anupong/iStock via Getty Images
Iam Anupong/iStock via Getty Images

It’s commonly believed that school kids started taking summers off in the 19th century so that they’d have time to work on the farm. Nice as that story is, it isn’t true. Summer vacation has little to do with tilling fields and more to do with sweaty, rich city kids playing hooky—and their sweaty, rich parents.

Before the Civil War, farm kids never had summers off. They went to school during the hottest and coldest months and stayed home during the spring and fall, when crops needed to be planted and harvested. Meanwhile, city kids hit the books all year long—summers included. In 1842, Detroit’s academic year lasted 260 days.

But as cities got denser, they got hotter. Endless lanes of brick and concrete transformed urban blocks into kilns, thanks to what was known as the “urban heat island effect.” That’s when America’s swelling middle and upper class families started hightailing it to the cooler countryside. And that caused a problem. School attendance wasn’t mandatory back then, and classrooms were being left half-empty each summer. Something had to give.

Legislators, in one of those if-you-can’t-beat-‘em-join-‘em moments, started arguing that kids should get summers off anyway. It helped that, culturally, leisure time was becoming more important. With the dawn of labor unions and the eight-hour workday, working adults were getting more time to themselves than ever before. Advocates for vacation time also argued (incorrectly) that the brain was a muscle, and like any muscle, it could suffer injuries if overused. From there, they argued that students shouldn’t go to school year-round because it could strain their brains. To top it off, air conditioning was decades away, and city schools during summertime were miserable, half-empty ovens.

So by the turn of the century, urban districts had managed to cut about 60 schooldays from the most sweltering part of the year. Rural schools soon adopted the same pattern so they wouldn’t fall behind. Business folks obviously saw an opportunity here. The summer vacation biz soon ballooned into what is now one of the country’s largest billion-dollar industries.

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