In Egitto le lenti più antiche mai conosciute

Segnalo questo articolo del prof. J.M.Enoch,illustre oftalmologo nonchè esperto di optometria, secondo il quale queste "lastrine" in cristallo di rocca o cristallo di quarzo (durezza scala di Mohs 7), appaione nel 2620 AC. fino al 2400 AC. circa , quando furono trascurate per riapparire 700 anni dopo ed essere poi abbandonate d inuovo.
Il minerale è lavorato in modo raffinato per la concavita o convessità simile alla cornea e si sostiene che la curvatura sia frutto di studio e non di casualità.
Altri studiosi, tuttora riconoscendo la particolarità di queste lenti, si chiedono se già potessero essere usate, magari montate su telaietti, per effettuare lavori di precisione come incisioni su piccolissimi oggetti.

"The earliest known lenses had their origin in Egypt at the beginning
of the Fourth Dynasty when they were employed in Egyptian statuary.
These lenses were of amazing quality and complexity with no known
precursors. The first lenses in this group are dated (about) 2620 BCE.
These were constructed of fine grade rock crystal or crystalline quartz
(#7 on the Mohs hardness scale). Examples of these lenses were used
until about 2400 BCE, after which they disappeared. Oddly, they
reappeared briefly about seven hundred years later during the Twelfth
Dynasty, after which they were gone forever in this form. Today, they
can be seen in Egyptian statues in museums in Cairo, Paris and Leipzig.
The lenses had a front (rather flat) convex surface simulating the cornea
of the associated "virtual" or schematic eye, and they were parts of
distinguished funerary statues. The same optical elements also had a
small high power concave lens ground into the middle of the flat rear
lens surface located in the plane of the aperture of the pupil. Associated
with these lenses was a strong optical illusion causing the eye to appear
to follow the viewer as he/she moves about the statue in any direction.
This illusion has been characterized (and now measured) by the
author. Two lenses in this series at the Louvre (the right eye of Le
Scribe Accroupi, E3023, and Reserve eye, E3009) were recently
optically assessed by him and coworkers."

Prof. Enoch published on the subject in:

"First known lenses originating in Egypt about 4600 years ago,"
Documenta Ophthalmologica 99, no. 3 (November, 1999): 303-314,
revised and corrected July 2006.