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A reading stone is an approximately hemispherical
A reading stone is an approximately hemispherical lens
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...
that can be placed over text to magnify the letters, making it easier for people with presbyopia
Presbyopia is a physiological insufficiency of optical Accommodation (vertebrate eye), accommodation associated with the aging of the human eye, eye; it results in progressively worsening ability to focus clearly on close objects. Also known as ...
to read. Reading stones were among the earliest common uses of lenses.
The invention of reading stones is often credited to Abbas ibn Firnas
Abū al-Qāsim ʿAbbās ibn Firnās ibn Wardūs al-Tākurnī (; c. 809/810 – 887 CE), known as ʿAbbās ibn Firnās () was an Andalusi polymath: Lynn Townsend White, Jr. (Spring, 1961). "Eilmer of Malmesbury, an Eleventh Century Aviator: A C ...
in the 9th century, although the regular use of reading stones did not begin until around 1000 AD. Early reading stones were made from rock crystal (quartz), beryl
Beryl ( ) is a mineral composed of beryllium aluminium Silicate minerals#Cyclosilicates, silicate with the chemical formula Be3Al2(SiO3)6. Well-known varieties of beryl include emerald and Aquamarine (gem), aquamarine. Naturally occurring Hex ...
and glass, which could be shaped and polished into lenses used for magnification. The Swedish Visby lenses, dating from the 11th or 12th century, may have been early reading stones.
The function of reading stones was replaced by spectacles
Glasses, also known as eyeglasses (American English), spectacles (Commonwealth English), or colloquially as specs, are Visual perception, vision eyewear with clear or tinted lens (optics), lenses mounted in a frame that holds them in front ...
from the late 13th century onwards, but modern versions are still in use. In their contemporary form, they can be found as rod-shaped magnifiers, flat on one side, that magnify a line of text at a time, or as large dome magnifiers which magnify a circular area of a page. Larger Fresnel lens
A Fresnel lens ( ; ; or ) is a type of composite compact lens (optics), lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections.
The simpler Dioptrics, d ...
es can be placed over an entire page. The modern versions are typically made of plastic.
See also
* Dome magnifierReferences