The lenses examined in Visby. Top row: unmounted lenses. Bottom row: mounted lenses, except the “ball” (Photo: kleinesdorfinschleswigholstein.de/ Olaf Schmidt)
The Vikings were known to be great seafarers and probably navigated by using Sunstone crystals. They could also have been using telescopes about 500 years before the earliest recorded working telescope was invented in the Netherlands in 1608.
The late Dr Karl-Heinz Wilms from Germany first heard of the so-called “Visby” lens in 1990 when he was searching for exhibits for a Munich museum. It was named after the major town on the Swedish island of Gotland. He found a picture of the lens in a book and planned to examine the original.
But it was not until 1997 that a team of three German scientists and specialists in the field went to the island to examine what turned out to be 13 lens-shaped rock crystals.
“It seems that the elliptical lens design was invented much earlier that we thought and then the knowledge was lost,” Dr Olaf Schmidt told BBC News back in year 2000.
Three-dimensional display of one surface consisting of all sections (Photo: kleinesdorfinschleswigholstein.de)
When the lenses were tested, the team was amazed. They passed a series of tests almost as well as modern optics.
Made from rock-crystal, they have an accurate shape that betrays the work of a master craftsman. The best example measures 50 mm (2.0 inches) in diameter and 30 mm (1.2 inch) thick at its center.
“The surface of some of the lenses has an almost perfect elliptical shape,” Dr Schmidt said. “They were obviously made on a turning lathe.”
They have a flattened central area that makes them excellent magnifiers.
“They could have been used as magnifiers, allowing fine carving to be carried out, or they could have been used to start fires or to burn wounds and cuts so that they did not get infected.”
What intrigued the researchers was that the lenses were of such high quality that they could have been used to make a telescope, centuries before the first known crude telescopes were constructed.
Manufactured in Byzantium
The Gotland crystals provide the first evidence that sophisticated lens-making techniques were used by craftsmen over a 1,000 years ago- at a time when researchers had only just begun to explore the laws of refraction.
According to the researchers, it is clear that the craftsmen who figured the lenses knew more about applied optics than the scientists of the time. They must have worked by trial and error because the mathematics to calculate the best shape – as far as we know – did not become available for several hundred years.
The researchers speculate that the knowledge to make such an accurate lens was known to only a few craftsmen, perhaps only one person.
But it seems clear that the Vikings did not make the lenses themselves. There are hints that they may have been manufactured in the ancient empire of Byzantium (Editor’s note: modern Istanbul) or in the region of Eastern Europe where Scandinavian Vikings are known to have participated in trade networks.
Some of the lenses can be seen at the Fornsal Historical Museum in Visby, some are in the Swedish National Museum in Stockholm while others have been lost.
Text by: Thor Lanesskog, ThorNews