Do they remind you of something else that is steeped in mystery, is crystal like and also displays amazing manufacturing qualities (the Crystal skulls).
Visby lenses
The lenses are bi-aspheric and two of them have very good imaging properties. Their surface appears to be an oblate ellipse, while the surface nearest the eye approaches a parabola.[3]
The best example of the lenses measures 50 mm (2.0 in) in diameter and has a thickness of 30 mm (1.2 in) at its centre, with an angular resolution of 25–30 μm.
The Visby lenses provide evidence that sophisticated lens-making techniques were being used by craftsmen over 1,000 years ago, at a time when researchers had only just begun to explore the laws of refraction. According to Schmidt and his co-workers, it is clear that the craftsmen worked by trial and error, since the mathematics to calculate the best form for a lens were not discovered until several hundred years later.[1] It has been suggested that the knowledge required to make such lenses was restricted to only a few craftsmen, and perhaps a single person.
Excavations at Fröjel on Gotland in 1999 discovered evidence of local manufacture of beads and lenses from rock crystal, with unworked pieces of crystal coexisting with partially finished beads and lenses.[4][5] Prior to the Fröjel finds it had been suggested that the lenses were not produced by the Vikings, as there are hints that they were in fact produced in Byzantium or Eastern Europe.[1] The Vikings of Gotland were known to have participated in trade networks that reached as far as Constantinople.
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