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What's a diving bell?

Marine Life Image Gallery Early images of diving bells depicted hard-to-believe scenarios. See more pictures of marine life.
Hulton Archive/Getty Images

Since man has walked the Earth, it seems like we've been fascinated with two things we weren't built to do -- fly like birds and swim like fish. We've all seen grainy black and white footage of some of the early flying machines, most of which involved mimicking the flight of birds by attaching wings to a human in some fashion. What doesn't exist so readily are images of our early attempts to become fishlike. This is mostly due to the lack of availability of underwater filming techniques at the time. But we do have some record of our quest for going underwater and staying there for prolonged periods.

The Greek philosopher Aristotle wrote about man's desire to spend time under the sea way back in the 4th century B.C.:

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"They enable the divers to respire equally well by letting down a cauldron, for this does not fill with water, but retains the air, for it is forced straight down into the water."

What Aristotle was referring to was the earliest version of the diving bell. This was the first attempt man made at submersing himself underwater for an extended length of time, and laid the foundation for what would centuries later become scuba diving.  Since Aristotle was a teacher of Alexander the Great, it should come as no surprise that the young conqueror allegedly used a diving bell several times -- at the age of 11 and then later at the Siege of Tyre in 332 B.C. These stories are not likely to be true, but there are paintings of Alexander sitting inside a glass barrel at the bottom of the ocean, so we know that the idea was in place. Inventor and artist Leonardo da Vinci also sketched early versions of the diving bell, though it's believed that like many of his inventions, he never followed through on its construction.

Read on to find out exactly what a diving bell is, how it works and when it was actually invented.

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Many designs of diving bells aren't bell-shaped at all.
Many designs of diving bells aren't bell-shaped at all.
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The simplicity of the diving bell actually makes it believable that Alexander the Great may have used an early version, as legend suggests. Next time you're in the kitchen get a cup, fill up your sink and push the open end of the cup straight down into the water. You'll feel some resistance, but as long as you keep the cup straight up and down there will be a pocket of air inside the cup. This is the concept behind the diving bell.

The bells were cast in all kinds of shapes made from all kinds of materials. There were wooden bells that weren't shaped like a bell at all, but barrel-shaped. Cast iron bells were square or round, bell-shaped or conical. Some looked like whisky bottles while others resembled inverted wine glasses. The thing that each had in common was that they were all very heavy. This is why iron was commonly used. Lighter materials were weighted down and balanced with ballasts and weights. The reason it needed to be so heavy was because of the resistance you feel when you push the cup into the water.

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The force of the water pushes the air up, compressing it as water enters the bottom of the open bell. While there is some water in the bottom of the bell, the bulk of it remains packed with breathable air. But there was one key limitation to this -- the bell could only go so deep and still have a usable pocket of air. A 10-foot tall (3-meter) diving bell that dove to 325 feet (100 meters) would only leave about 11 inches (30 centimeters) of air. For a while, divers simply tried shallow waters and ascended when the air was used up.

There was also the matter of decompression sickness, or the bends. This is when you ascend to the surface too rapidly after a deep dive. As you dive, pressure on your body increases, causing more nitrogen and oxygen to dissolve in your blood. Most of the oxygen is consumed by tissue, the nitrogen remains. This dissolved nitrogen is what causes the bends. If you ascend too quickly, the nitrogen leaves your blood too fast and forms bubbles. These bubbles block tiny blood vessels and can lead to strokes, heart attacks, ruptured blood vessels in the lungs and joint pain.

Divers endured these limitations while continuing to use versions of the diving bell during the Renaissance and into the 16th century. It would take some key innovators in the late 1600s and into the 1700s to improve the limitations of the diving bell.

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Diving bells were sometimes attached to frigates and schooners.
Diving bells were sometimes attached to frigates and schooners.

The first real innovation to the diving bell came when Frenchman Denis Papin figured out how to get fresh air into them in 1689. Flexible hoses attached to bellows ran into the water and up inside the bell, providing fresh, breathable air. While this helped divers stay submerged longer, it did nothing to combat the pressure and to allow for deeper dives. The next obstacle was to figure out how to get pressurized air into the bell, something Englishman Edmund Halley did just a year later.

Halley attached weighted wooden barrels to the diving bell. At the bottom of each was a hole in the side that allowed water to come in, forcing the air up. At the top, a hose ran from the barrel and led to the bottom side of the bell, where it was attached with a faucet head. The divers inside could simply turn the faucet to allow the fresh air to flow in. The barrels were alternately pulled to the surface for "refilling," and dropped back in again. By being able to control the amount of air in the bell, the divers were able to match the pressure of the displaced water. Halley's innovation made the pressure of the interior of the bell equal to that of the surrounding water.

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Things went on like this for a while, until English scientist John Smeaton invented the diving air pump in 1788. The surface pump was attached to the roof of the bell and operated by four men. In the end, it was, in concept, much like Denis Papin's original plan 100 years earlier. Using this new technology, workers were able to descend in a diving bell and repair the foundation of the Hexham Bridge in England. Smeaton also was one of the first to make the bells square, calling them "diving chests."

Other improvements over the years included adding electric lighting inside, thick convex lenses as windows, and increasing the interior space so that as many as 12 men could descend at a time. The earliest applications of the bells were to transport workers under water so that they could repair or build docks, lighthouse foundations and bridges. Early enthusiasts also tried their hand at deep shipwreck salvage, something the bells are still used for today.

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Related HowStuffWorks Articles

More Great Links

Sources

  • "Diving Bell Chronology." Thinkquest.org. 2009.http://library.thinkquest.org/28170/221.html
  • "Diving Bell." Kenyon.edu. 2009.http://physics.kenyon.edu/EarlyApparatus/Pneumatics/Diving_Bell/Diving_Bell.html
  • "Diving bells and Observation chambers." Divingheritage.com. 2009.http://www.divingheritage.com/chambers.htm
  • "Modern Diving Bells and chambers." Divingheritage.com. 2009.http://www.divingheritage.com/bells.htm
  • "The Incredible Aqualung of the Diving Bell Spider." Environmentalgraffiti.com. July 28, 2009.http://www.environmentalgraffiti.com/featured/incredible-aqualung-diving-bell-spider/13855
  • Bachrach, Arthur J. "The History of the Diving Bell." Thehds.com. 1998.http://www.thehds.com/publications/bell.html
  • Pike, Paul Scott. "Bermuda Bell Diving." Experiencebermuda.com. 2009.http://www.experiencebermuda.com/activities/bell-diving.html

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