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Why Did Pirates Wear Eye Patches?

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The fact that some pirates wore eye patches most likely had nothing to do with a missing eye, and everything to do with being able to see—specifically, above decks and below them.

Jim Sheedy, a doctor of vision science and director of the Vision Performance Institute at Oregon's Pacific University, told the Wall Street Journal that while the eyes adapt quickly when going from darkness to light, studies have shown that it can take up to 25 minutes for them to adapt when going from bright light to darkness, which "requires the regeneration of photo pigments."

Pirates frequently had to move above and below decks, from daylight to near darkness, and Sheedy says the smart ones "wore a patch over one eye to keep it dark-adapted outside." When the pirate went below decks, he could switch the patch to the outdoor eye and see in the darkness easily (potentially to fight while boarding and plundering another vessel).

Arrrr We Sure?

Though there are no first-person sources from history that state this as fact, there's no question that keeping one eye dark-adapted works. MythBusters tested this hypothesis in their pirate special in 2007 and determined that it was plausible (only the lack of historical sources kept it from being confirmed). At least one military manual for pilots pointed out that "Even though a bright light may shine in one eye, the other will retain its dark adaptation, if it is protected from the light. This is a useful bit of information, because a flyer can preserve dark adaptation in one eye by simply closing it." Even the FAA recommends that "a pilot should close one eye when using a light to preserve some degree of night vision." 

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Big Questions
Why Is Soda Measured in Liters?
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Never a nation to fall in line, America is one of the few countries to resist the metric system. We stubbornly measure distance in miles and weight in pounds. So what’s with those two-liter bottles of soda?

First, a clarification: Soda is far from the only substance we measure in metric units. Heck, it’s not even the only beverage. Wine, liquor, and bottled water are sold by the milliliter. The healthcare field is all about metric units, too, from cholesterol levels to prescription, over-the-counter, and supplement dosages. We run 5-kilometer races, ride on 215-millimeter tires, and use 8-millimeter cameras, or at least we used to.

In most other things, we determinedly cling to our imperial measurements. Attempts to convince Americans to join the rest of the metric-measuring world have been met with great resistance.

Ken Butcher of the National Institute of Science and Technology has been working with the government’s tiny Metric Program for years. Speaking to Mental Floss back in 2013, Butcher explained that we’re so entrenched in our way of doing things that switching measurement systems now would be both chaotic and expensive.

"If we were going to start a new country all with the metric system, it would be easy," he said. "But when you have to go in and change almost everything that touches people’s everyday life and their physical and mental experience, their education, and then you take that away from them—it can be scary."

Here and there, though, when it’s convenient, we have been willing to budge. The soda bottle is a good example. Until 1970, all soft drinks in the U.S. were sold in fluid ounces and gallons, mostly in glass bottles. Then the plastic polyethylene terephthalate (PET) bottle came along, and soft drink makers decided it was time for a product redesign.

The redesign process coincided with two key factors: a short-lived wave of government interest in going metric, and the burgeoning environmental movement.

The folks at PepsiCo decided to meld all three into its exciting new vessel: a lightweight, cheap, recyclable, metric bottle, with built-in fins so it could stand up on supermarket shelves. Two liters: the soda size of the future.

The two-liter bottle took off. The rest of the soft drink world had no choice but to get on board. And voila: liters of cola for all.

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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Big Questions
Where Is the Hottest Place on Earth?
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The summer of 2017 will go down as an endurance test of sorts for the people of Phoenix, Arizona. The National Weather Service issued an extreme heat warning, and planes were grounded as a result of temperatures exceeding 120 degrees. (Heat affects air density, which in turn affects a plane’s lift.)

Despite those dire measures, Phoenix is not the hottest place on Earth. And it’s not even close.

That dubious honor was bestowed on the Lut Desert in Iran in 2005, when land temperatures were recorded at a staggering 159.3 degrees Fahrenheit. The remote area was off the grid—literally—for many years until satellites began to measure temperatures in areas that were either not well trafficked on foot or not measured with the proper instruments. Lut also measured record temperatures in 2004, 2006, 2007, and 2009.

Before satellites registered Lut as a contender, one of the hottest areas on Earth was thought to be El Azizia, Libya, where a 1922 measurement of 136 degrees stood as a record for decades. (Winds blowing from the nearby Sahara Desert contributed to the oppressive heat.)

While the World Meteorological Organization (WMO) acknowledged this reading as the hottest on record for years, they later declared that instrumentation problems and other concerns led to new doubts about the accuracy.

Naturally, declaring the hottest place on Earth might be about more than just a single isolated reading. If it’s consistency we’re after, then the appropriately-named Death Valley in California, where temperatures are consistently 90 degrees or above for roughly half the year and at least 100 degrees for 140 days annually, has to be a contender. A blistering temperature of 134 degrees was recorded there in 1913.

Both Death Valley and Libya were measured using air temperature readings, while Lut was taken from a land reading, making all three pretty valid contenders. These are not urban areas, and paving the hottest place on Earth with sidewalks would be a very, very bad idea. Temperatures as low as 95 degrees can cause blacktop and pavement to reach skin-scorching temperatures of 141 degrees.

There are always additional factors to consider beyond a temperature number, however. In 2015, Bandar Mahshahr in Iran recorded temperatures of 115 degrees but a heat index—what it feels like outside when accounting for significant humidity—of an astounding 163 degrees. That thought might be one of the few things able to cool Phoenix residents off.

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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