What Is the Longest River in the World?

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The answer to the question “What’s the longest river in the world?” might sound simple—find the source, the mouth, and measure—but in between those steps are strange definitions, fractals, hydrology, and especially national pride. It’s an issue so complicated that several hydrologists contacted by Mental Floss explained that river length isn't even considered a useful measure anymore. So, what is the longest river in the world?

HOW LONG IS A RIVER?

According to Laurel Larsen, assistant professor at the University of California Berkeley’s geography department, “The length of a particular river is the longest possible along-thalweg continuous distance from the headwaters (1st order stream) to the mouth of a river.”

To unpack those terms, the thalweg is “the line connecting the lowest or deepest points along a stream bed or valley.” First order stream is more complicated. There are two major ways to classify stream order, but the most common is the Strahler method. In this method, streams without any tributaries entering—streams that are just starting out the river—are first order. When two first order streams join together they form a second order stream, and when two second order streams join they form a third order (but if a first order stream intersects with a second order, the main river stays a second order stream).

The source of a river then is considered to be the furthest distance to the source of a stream that has no inputs—although, in practice, this can be extremely difficult to determine. And it's not a perfect system. (For historical reasons, the source of the Mississippi is often treated separately from the Missouri, despite the conventional definition grouping them into one river system.)

As for the mouth? That’s also contentious. For some rivers, the mouth is relatively simple to determine. But for large rivers entering the ocean, like the Amazon, where the mouth is placed can make all the difference.

ARE WE GOING TO ANSWER THE QUESTION?

The longest river has generally been the Nile, with the Amazon coming in second. But in 2007 Brazilian scientists announced that a new analysis put the Amazon on top. They got this by identifying a new source, but more importantly a new mouth. Traditionally, the mouth of the Amazon has been located on the north side of Marajó Island. But this new report wrapped the river around the south side of the island to the Pará River and then out into the ocean.

What side of an island the mouth is on might not seem relevant, but Marajó Island is the size of Switzerland. The new source plus the new mouth gave a distance longer than the Nile.

This was controversial. The Pará River is usually associated with the Tocantins River, not the Amazon. And more recent studies have tended to agree that, although there is some Amazon water in it, the Pará is distinct from the Amazon. Which means that the current best guess for the longest river in the world is still the Nile.

But there’s another, more fundamental issue with measuring a river: What does length even mean?

SO WHAT’S THE PROBLEM?

The early 20th century mathematician Lewis Fry Richardson made the observation that Spain and Portugal disagreed on their border length. Spain said it was 987 km and Portugal maintained it was 1214 km. The disagreement wasn’t down to disputed territories or anything like that; Richardson explained that it was the length of the measuring stick. As the measuring stick gets smaller, it’s able to more accurately capture the curves and nuances of bends and curves in complex borders.

The same trick appears with rivers. Rivers meander and have small curves. And if you zoom in further, more little bends and twists might appear in the thalweg.

It’s called the coastline paradox—the length of something complex is basically impossible to determine because the length keeps increasing the smaller the measurement goes.

For both this reason and the inherent difficulties of determining length, several researchers have told Mental Floss that river length just isn’t something that particularly matters, and what is really important is drainage area, which is the area of land that contributes water to the river. Unlike river length, a few elevation measurements make this a much easier metric to calculate. And according to an article in Nature, using this metric, the Amazon is dramatically the largest river in the world, with a drainage area of 6.3 million square kilometers. If it were a country, the drainage basin would be the seventh largest in the world just behind Australia.

The Nile falls down to fifth, behind the Congo, the Mississippi, and the Ob. So in the measurement that matters to hydrologists today, the Amazon wins it.

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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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What Is the Wilhelm Scream?

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What do Star Wars, The Lord of the Rings, Pirates of the Caribbean, Harold and Kumar Go to White Castle, Toy Story, Reservoir Dogs, Titanic, Anchorman, 22 Jump Street, and more than 200 other films and TV shows have in common? Not much besides the one and only Wilhelm Scream.

The Wilhelm Scream is the holy grail of movie geek sound effects—a throwaway sound bite with inauspicious beginnings that was turned into the best movie in-joke ever when it was revived in the 1970s.

Just what is it? Chances are you’ve heard it before but never really noticed it. The Wilhelm Scream is a stock sound effect that has been used in both the biggest blockbusters and the lowest low-budget movies and television shows for over 60 years, and is usually heard when someone onscreen is shot or falls from a great height.

First used in the 1951 Gary Cooper western Distant Drums, the distinctive yelp began in a scene in which a group of soldiers wade through a swamp, and one of them lets out a piercing scream as an alligator drags him underwater.

As is the case with many movie sound effects, the scream was recorded later in a sound booth with the simple direction to make it sound like “a man getting bit by an alligator, and he screams.” Six screams were performed in one take, and the fifth scream on the recording became the iconic Wilhelm (the others were used for additional screams in other parts of the movie).

Following its debut in 1951, the effect became a regular part of the Warner Bros. sound library and was continually used by the studio’s filmmakers in their movies. Eventually, in the early 1970s, a group of budding sound designers at USC’s film school—including future Academy Award-winning sound designer Ben Burtt—recognized that the unique scream kept popping up in numerous films they were watching. They nicknamed it the “Wilhelm Scream” after a character in the first movie they all recognized it from, a 1963 western called The Charge at Feather River, in which a character named Private Wilhelm lets out the pained scream after being shot in the leg by an arrow.

As a joke, the students began slipping the effect into the student films they were working on at the time. After he graduated, Burtt was tapped by fellow USC alum George Lucas to do the sound design on a little film he was making called Star Wars. As a nod to his friends, Burtt put the original sound effect from the Warner Bros. library into the movie, most noticeably when a Stormtrooper is shot by Luke Skywalker and falls into a chasm on the Death Star. Burtt would go on to use the Wilhelm Scream in various scenes in every Star Wars and Indiana Jones movie, causing fans and filmmakers to take notice.

Directors like Peter Jackson and Quentin Tarantino, as well as countless other sound designers, sought out the sound and put it in their movies as a humorous nod to Burtt. They wanted to be in on the joke too, and the Wilhelm Scream began showing up everywhere, making it an unofficial badge of honor. It's become bigger than just a sound effect, and the name “Wilhelm Scream” has been used for everything from a band name, to a beer, to a song title, and more.

But whose voice does the scream itself belong to? Burtt himself did copious amounts of research, as the identity of the screamer was unknown for decades. He eventually found a Warner Bros. call sheet from Distant Drums that listed actors who were scheduled to record additional dialogue after the film was completed. One of the names, and the most likely candidate as the Wilhelm screamer, was an actor and musician named Sheb Wooley, who appeared in classics like High Noon, Giant, and the TV show Rawhide. You may also know him as the musician who sang the popular 1958 novelty song “Purple People Eater.”

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