Reading stone
From Wikipedia, the free encyclopedia
A reading stone was an approximately hemispherical transparent object placed on top of text in order to magnify the letters so that people with long-sight could read the text more easily.
They were used in Europe from approximately the 11th century onwards. The function of reading stones was replaced by the use of spectacles from the late 1200s onwards, but modern implementations are still used. In their modern form, they can be found as rod-shaped magnifiers, flat on one side, that magnify a line of text at a time; or as a sheet in the form of a Fresnel lens placed over an entire page. The modern forms are usually made of plastic.
Early reading stones were manufactured from rock crystal (quartz) or beryl as well as glass.
The Visby lenses may have been reading stones.
