reading stone

English

Noun

reading stone (plural reading stones)

1. A hemisphere of glass used as a magnifier when placed with its flat side against a surface with text.
   • 2013 September-October, Henry Petroski, “The Evolution of Eyeglasses”, in American Scientist:

     The ability of a segment of a glass sphere to magnify whatever is placed before it was known around the year 1000, when the spherical segment was called a reading stone, essentially what today we might term a frameless magnifying glass or plain glass paperweight. Scribes, illuminators, and scholars held such stones directly over manuscript pages as an aid in seeing what was being written, drawn, or read.

Further reading

• reading stone on Wikipedia.Wikipedia