In 1853, Sir David Brewster (1781-1868) presented a lens to the British Association for the Advancement of Science that had been found in excavations by Austen Henry Layard (1817-1894) at Nineveh (Kuyunjik, Iraq). It had been found in deposits dated around 600 BCE and although its provenance was not in question, doubts were raised about its function. Whilst it clearly works as a lens, it was thought to have been used as a decoration in a piece of jewellery, although Brewster himself believed it to have been a true optical lens.
With this object, we can see how contemporary perceptions of form and function may not always be correct. The ‘obvious’ interpretation of a ground oval crystal with a biconvex cross-section as an optical lens is not a guide to its original function. What would be the context for such a piece in the ancient Near East? Had it been part of a piece of optical equipment, there ought to be other evidence for such equipment. If, say, it were part of an astronomical telescope, then elements of the telescopes and their mountings ought to be found. If part of a pair of spectacles, then some sort of frame should be found from time to time. The absence of this type of material makes the lens explanation rely on special pleading and the use of irrelevant evidence (such as the ability of pre-Columbian Americans to make tiny gold beads, as quoted by Berlitz). As part of an item of jewellery, its accidental magnifying properties could have made it more curious and valuable.