http://www.digitaljournal.com/article/109739

Crystals may have aided Viking sailors

Posted Feb 8, 2007 by Bob Norman

http://www.guardian.co.uk/science/story/0,,2007399,00.html

Special crystals called sunstones may have helped the Vikings find their way to their next pillage.
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Ancient Vikings may have known a trick that's become lost to modern sailors. Special crystals recovered from sunken Viking vessels have shown the ability to find the sun even in fog or rain.
The finding adds weight to the controversial suggestion that the Vikings exploited an unusual optical property of crystals known as birefringence to stay on course during bad weather.
The reason this works is because of a process called polarisation. Although polarisation is not apparent to the naked eye, it can be seen using birefringent crystals. This allows the crystals to point to the sun,even when it was invisible to the Viking sailors. As long as they knew the time of day and where the sun was they could find their way to their next target.
The researchers found that the crystals were likely to work in all but the worst weather conditions, they write in the journal Proceedings of the Royal Society today.
It just goes to show that modern man doesn't have all the answers. I grew up in a Navy family and I've never heard of this before. The past still has much to teach us.