The Visby lenses are a collection of lens-shaped manufactured objects made of rock crystal (quartz) found in a viking grave in Gotland dating from approximately the 10th century. In Geometry, a lens is a Convex Shape comprising two circular arcs joined at their endpoints Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in A Viking is one of the Norse ( Scandinavian Explorers Warriors Merchants, and pirates who raided and colonized wide areas is a county, province and municipality of Sweden and the largest Island in the Baltic Sea. Some of them are mounted in silver and may have been carried as a pendant, but others appear not to have been used as jewellery. Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen A pendant (from Old French) is a hanging object generally attached to a Necklace or an Earring. The lenses have good optical properties, comparable to lenses manufactured in the 20th century. A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging The twentieth century of the Common Era began on They are unusual in being aspheric, having an ellipsoidal profile. An aspheric lens or asphere is a lens whose surfaces have a profile that is neither a portion of a Sphere nor of a circular cylinder. An ellipsoid is a type of quadric surface that is a higher dimensional analogue of an Ellipse.
The optimization was achieved by craftsmen long before mathematicians could describe the shape and properties of aberration-corrected lenses. It seems that this knowledge was lost for at least 500 years, until Descartes calculated the idea [sic] shape of a focusing lens but, lacking the necessary equipment, he could not produce it. Aspheric lenses for spectacles were not made until the 1950's. [1]
They may have been used for magnification by craftsmen for fine work, as reading stones, or to start fires. A reading stone was an approximately hemispherical transparent object placed on top of text to magnify the letters so that people with Presbyopia could read the text [2] There has been some speculation that they may possibly have been used as part of a telescope. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. [3][4]
Some of the properties of one of the lenses are as follows:[5][6]
- Diameter: 50 mm
- Focal Length: 22–35 mm
- Angular resolution: 25–30 μm
The Vikings at Visby on Gotland are known to have participated in trading networks reaching as far as Constantinople, so it is possible the lenses originated in the Middle East with only the silver mounts being of local manufacture. Geometry, a diameter of a Circle is any straight Line segment that passes through the center of the circle and whose Endpoints are on the The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light. Angular resolution describes the resolving power of any image forming device such as an optical or Radio telescope, a Microscope, a Camera A Viking is one of the Norse ( Scandinavian Explorers Warriors Merchants, and pirates who raided and colonized wide areas Visby is the only city on the Swedish Island of Gotland; it is arguably the best-preserved Medieval city in Scandinavia Constantinople (Κωνσταντινούπολις Konstantinoúpolis, or gr ἡ Πόλις hē Polis, Latin: la CONSTANTINOPOLIS However, subsequent excavations at Fröjel on Gotland have shown evidence of manufacture of beads and lenses from rock crystal as unworked items of crystal coexist with partially completed objects
. . . we have found many traces of rock crystal in the area, from raw material to finished beads and lenses. . . . [7]
The rock crystal itself would have been imported, as it is not native to Gotland.
Where they got the raw material is still a matter of discussion, but probably got if [sic] from the area around the Black Sea. [8]
Pieces of rock crystal, both in the form of raw material, half finished beads, lenses and well made faceted beads have been found at Fröjel during the excavation. This summer, we found something like 4 or 5 crystal lenses and several beads, and it all points to the conclusion that rock crystal was imported to Fröjel and used for making beads as well as lenses. [9]
The excavation reports have good accompanying pictures.
Some of the lenses can be viewed at Gotlands fornsal, a historical museum in Visby.
References
- ^ Medieval lenses exhibit modern performances. By Oliver Graydon.Featured in Opto & Laser Europe, Issue 56. November 1998.
- ^ Viking Age Fire-Steels and Strike-A-Lights
- ^ 5 April, 2000, BBC News: Did the Vikings make a telescope?
- ^ The visby lenses. Schmidt O, Wilms KH, Lingelbach B. Aalen University of Applied Science, Germany.
- ^ Webarchive backup: Visbylinserna—historiska förstoringsglas? (Swedish)
- ^ The Visby lenses—Historical Magnifying Glasses?
- ^ Carlsson, Fröjel Excavation Report 8, 23rd of August 1999
- ^ Carlsson, Fröjel Excavation Report 7, 18th of August 1999
- ^ Carlsson, Fröjel Excavation Report 9, 1st of September 1999
External links
- Jewellery as Form of Personal Expression (includes picture of a silver mounted lens)
- Die Visby-Linsen (German, includes pictures of all the lenses found at Visby)
- Institut für Augenoptik Aalen, Projekte & Aktivitäten, Visby Linsen (German)
- Der Zeit voraus: Asphärische Linsen aus dem 11. Jahrhundert; Bernd Lingelbach, Olaf Schmidt; Das Fröjel Discovery Programme (German, extensive paper with many illustrations)
- Link to summary of all of 1999 excavation reports at Visby
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