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Category Icon   Jan 26, 2004, 05:00 PM
Did ancient celators use magnifying lenses?
Coins
by Bart Lewis

Pages: 1
Words: 1371
Views: 82782
This article first appeared in The Celator, Vol. 11, No. 11, November 1997, p. 40.



The use of magnifying lenses by ancient artists remains an
unresolved question. While scores of ancient glass and crystal lenses are extant
today, no one has yet connected them directly with the crafts of die
cutting and gem engraving. The question has been broached in earlier
Celator articles, with evidence from literary
and archaeological sources suggesting that lenses were used for
magnification. The purpose of this article is to
familiarize the reader with the history of magnifying lenses and to examine
certain aspects of the engravers' art to shed further light on this
mystery. Could such tiny, detailed work have been done with the unaided eye?



Both the telescope and compound microscope are relatively recent
inventions, both occurring in the 17th century. Eyeglasses were most
probably invented in Italy shortly after AD 1286, as they are mentioned in a
sermon by Friar Giordano of Piso delivered in 1306. These lenses were
convex and corrected farsightedness, and could also have served as simple
low-power magnifying lenses. Concave lenses to correct nearsightedness
were apparently not produced for several more
centuries.1



The English monk Roger Bacon, who died in 1292, mentioned that
a medium of crystal or glass placed above small letters rendered
them larger and was useful to the aged and those with weak
eyes.2



The Egyptians and Sumerians
make no references to lenses of any type. In ancient writings the first mention
of lenses (to kindle fires) appears in The
Clouds,
by the Greek dramatist Aristophanes, who died about
380 B.C. "Have you ever seen at the druggist's place that beautiful,
transparent stone with which they kindle fire?"



However, no mention can be found
in ancient Greek writings of
lenses valued as magnifiers. Such a statement first occurs in the writings
of Seneca, the Roman philosopher and politician who died in AD 65.
"Letters, however small and dim, are comparatively large and distinct when
seen through a glass globe filled with
water.3



It is probable that Seneca
thought that the water itself was responsible for this magnification as the
ancients believed that crystal was a form of water, simply being congealed in
a more durable form than ice.4



No one knows how many ancient lenses are actually in existence.
The main problem we face is our inability to differentiate between a
corroded lens and a piece of ancient glass jewelry. There is no doubt that
many museum lenses have been cataloged as gems or bangles because they are
no longer transparent and do not resemble a lens.



>When were lenses first produced?
Approximately 50 lens-shaped crystals were discovered by
Heinrich Schliemann at Troy, one of which was over two inches in
diameter.5 Most of these were perforated in the
center leading contemporary authorities to
>conclude they were ornaments and not lenses. However, a center
perforation would allow an ideal means of carrying the lens and would not
hinder its ability to kindle a fire.



Another early lens has been
dated to ca. 900-700 B.C. and was discovered in Nimrud in 1853. This lens
is plano-convex and 35x41 mm across and 6 mm at its thickest. This lens
was the subject of an article in the British Journal of Physiological Optics
in 1930 (Vol. IV, No. 1).6



Perhaps the most important
discovery was a Roman period magnifying lens discovered in 1854 in the
"House of the Engraver" on the Stabian
Way in Pompeii. It is plano-convex with a corroded, opaque surface and is in
the gem collection at the National Museum in Naples. The fact that such
a lens was discovered in the shop of an ancient engraver is highly
significant.7



Two more lenses were discovered in the house of an artist in
Tanis, Egypt, by Flinders Petrie. He dated the destruction of the house to AD 174.
Again, both lenses are plano-convex and reside at the British Museum.
They are about 2 1/2 inches in diameter and have a focal length of about
3 1/2 inches.8



I personally feel it is most
unrealistic to assume that during the first millennium BC no one would
have looked through a lens or polished gem at a small object and not noticed
its magnifying properties. Rather, it is far more reasonable to assume that
the practical use of such an image magnifier was simply not generally
appreciated or written about.



The total number of ancient
lenses in existence today is not known, although they must number in
the hundreds. Among the museums possessing ancient lenses (which
are recognized as such) are the British Museum, London;
Archaeological Museum, Herakleion (23 lenses on display and more in storage);
National Museum, Naples; Candia Museum, Crete; Lavigerie Museum,
Carthage; Archaeological Museum, Istanbul.



There are two explanations for
the precision obtained by ancient engravers when producing extremely
small details: first, that the work was done with the unaided (but myopic) eye and
second, that simple magnifying lenses were used. Since there is no doubt
that lenses existed in the late Greek and Roman worlds, the only question
concerns their possible use as magnifiers. Pliny, the Roman historian,
mentions that gem engravers complained of considerable eye strain.9 This should
not argue against the use of magnifying lenses but possibly suggest that the
use of such lenses was not universal in ancient times [or that imperfect
lenses created eye-strain, ed.].



Even more challenging than die
engraving is the Roman art of gold-glass portrait medallions. In this art a
portrait would be incised on gold leaf and then sandwiched between two
layers of glass. The detail exhibited is equal to the photographs in this magazine.



George Sines, in his recent
article "Precision in Engraving of
Etruscan and Archaic Greek Gems", has conducted a detailed statistical analysis
of nine engraved Etruscan gems. He found that hatch mark border
spacings on the gems had a median value of 0.048 mm. As a mechanical
engineer himself, Mr. Sines notes that today a skilled machinist can achieve a
precision of only about 0.2 mm with the unaided eye and with a simple
magnifying glass about 0.08 mm.10 The median spacing on the ancient
gems was half this size.



There is no way, of course, that
we can absolutely prove that ancient artists utilized magnifying lenses.
The fact that lenses were discovered in the homes of an ancient engraver and
artist certainly suggests such a use. Also favoring their use is the large
number of extant examples, many misattrib-uted as gems and jewelry.



The only other plausible
explanation is the use of myopic artists. But as L. Natter, a gem engraver in the
18th century noted, the art of engraving in gems is too difficult for a young
man to be able to produce a perfect piece; and when he arrives at a proper age
to excel in it, his eyesight begins to fail. It is therefore highly probable that
the ancients made use of glasses, or microscopes, to supply this
defect."11



The fact that no Greek writings mention the magnifying ability of
a lens is puzzling, as one would assume that such a property would seem
magical to the ancients and thus receive mention. So perhaps we will never
be able to prove conclusively that the ancients used lenses, especially in
any commercial endeavor, for their magnifying properties.



But my denarii say they did.



Notes:


1DeCamp; The Ancient
Engineers,
pp.322.

2Bacon; Opus Majus,
II
, pp. 574-82.

3Seneca; Quaestianes
Naturales
, I, vi 5.

4Anthon; A Dictionary of Greek and
Roman Antiquities,
(1843), pp. 324.

5W. Dörpfeld,
Troja und Illion, Pt. 4 by A. Götze (Athens 1902)
138-39, 374-75.

6W. Gasson, "The Oldest Lens in
the World"
The Opthalmic Optician (9 Dec. 1972).

7Sines and
Sakellearakis, Lens in Antiquity, American Journal of
Archaeology 91 (1987).

8W. M. Flinders Petrie,
Tanis, Pt. 1, (London 1889) 49.

9Pliny, HN 37.60, 200.

10G. Sines, Archeomaterials, Vol. 6,
No, 1 (Winter 1992).

11from (7) quoting L. Natter,
Traite de la méthode antique de graver en
pierres fines, comparée avec la methode
moderne
(Private publication 1754) viii.
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