In addition to providing you with a rewarding visual experience, waterfalls may also be beneficial to your health. An old handbook on yoga recommended that a person desiring to enhance his body and mind through breathing exercises should do so by a waterfall. In Switzerland a woman who suffered from migraine headaches would often go to a small waterfall on the River Rhone. She would spend between thirty minuets to an hour by the waterfall. "I go there just to breathe. It makes me feel better for hours." Nearly everyone would agree that visiting a waterfall is a stimulating, refreshing and energizing experience.

The answer to what causes these effects seems to be electrically charged atoms known as negative air ions. At a waterfall negative air ions are produced by the energy of the falling water. As the falling water breaks up into small droplets, electrons (negatively charged parts of an atom) are knocked loose from the water atoms. These electrons combine with oxygen atoms in the air to create negative air ions. The negative air ions are inhaled into the lungs and absorbed into the bloodstream.

Negative air ions are not known to permanently cure anything. It is believed that they help our bodies by accelerating the delivery of oxygen to our cells. Some researchers believe that negative air ions may stimulate cells that regulate our bodies resistance to disease.

On average there are 1,500 ions are found in a cubic centimeter (roughly the size of a sugar cube) of fresh air. Of these about 45%, or 675, are negative ions the remainder being positive ions. At Yosemite Falls in California a reading of 100,000 negative air ions per cubic centimeter was recorded.

References

• "The Ion Effect" by Fred Soyka with Alan Edmonds, 1977, E. P. Dutton & Co.
• Pentex, What are negative ions, a web page located at: http://www.pentax.com/ion_explain.htm
• Conor Environmental Services, Inc., Information on ions, a web page located at: http://www.consultces.com/ions.htm
• Odatus, Negative Ions, a web page located at: http://www.odatus.com/ions.html
• Aranizer, Negative Ions, a web page located at: http://www.aranizer.com/ions.htm

In 1834 a British philosophical magazine published an article by Mr. Robert Addams on an interesting optical phenomenon he had seen at the Falls of Foyers in Scotland. After gazing for a time at the falling water, he suddenly looked to the rock face to the left of the waterfall. For a fleeting moment the rocky surface seemed to move upwards, with a velocity equal to that of the falling water. The phenomenon was also observed and written about by the ancient Greek philosopher Aristotle, and has been studied by psychologists and neuroscientists.

The waterfall illusion, also known as the motion aftereffect (MAE), is an interesting and unusual experience. I have experienced the illusion many times. For me the best way of inducing it is to gaze steadily at rapidly falling water for a minute or so, and then quickly shift my view to a stationary object. For a brief instant (usually around 2 seconds) the object appears to move upwards at a speed equal to that of the falling water.

Below are a few tips to help you in viewing the waterfall illusion:

• Pick a section of the waterfall where the water is free falling vertically.
• The section of the waterfall should be 100% water. Rocks projecting through the veil of falling water will diminish the illusion.
• The flow of water should be heavy. If you can see the rock face behind the falling water the illusion will be diminished.
• Do not try to follow the falling water with your eyes. But rather just stare or gaze at the falling water.
• Try to fill your field of vision completely with the falling water. Stationary objects on the edge of your field of vision will diminish the illusion.
• Gaze at the falling water for a minute or so. The longer the better. Then quickly shift your view to a stationary object, such as a rock or tree. Also try looking at a friend's face.

The explanation of what causes the illusion is a involved one. The short explanation is that you are overloading the part of your brain that detects downward movement. This suppresses the activity in the part of your brain that detects upward movement. Then when you quickly shift your view, the suppressed part of your brain erupts with a brief flurry of activity, causing the waterfall illusion.

Binary Arts (web page http://www.puzzles.com) markets a metal disk it calls the "Tri-zonal Space Warper". It demonstrates MAE very well.

References

• The Motion Aftereffect Home Page, a web page located at: http://www.hip.atr.co.jp/departments/Dept5/MAEWWW/home.html.
• The Waterfall Illusion - An odd optical puzzle yields clues to consciousness, Scientific American, July 1995, page 18.

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