Layard/Nimrud lens
History
The Layard/Nimrud lens, also known as the Nimrud lens, is a 3000-year-old piece of rock crystal, which was unearthed by Austen Henry Layard at the Assyrian palace of Nimrud, in modern-day Iraq. It has been dated to between 750 and 710 BC. The lens is slightly oval, and was roughly ground, perhaps on a lapidary wheel. It has a focal point about 11 centimetres from the flat side, and a focal length of about 12 cm. This would make it equivalent to a 3x magnifying glass (combined with another lens, it could achieve much higher magnification). The surface of the lens has twelve cavities that were opened during grinding, which would have contained naptha or some other fluid trapped in the raw crystal.
Purpose and Use
The actual use of the lens is not clear, with some speculating that it was used as a magnifying glass, or as a burning-glass to start fires by concentrating sunlight, while others have proposed that it was used as part of a telescope. However, the optical properties of the lens and the fact that it was found in the same area as Assyrian astronomical texts have led some to suggest that it may have been used as part of a telescope, possibly explaining the Assyrians' detailed knowledge of astronomy. The latter theory is supported by the 1st century Roman author Pliny the Elder, who makes a reference to a lens of this kind being used by the Assyrians.
Significance
The discovery of the Layard/Nimrud lens has prompted speculation on the technological capabilities of ancient cultures. Some have proposed that the lens could have been used in conjunction with other lenses to form a telescope, which could explain the detailed astronomical knowledge of the Assyrians. If true, this would predate the invention of the telescope by over a thousand years. However, this theory remains speculative and is not widely accepted by the scientific community.