1 The Birth of Science - MSRI

10.2 Lost Optics 241
subject is Ptolemy’s Optics, where we find an extensive, but unfortunately
truncated, treatment of the phenomenon. 25a Yet refraction had important
and early technological applications, first and foremost to lenses.
The use of lenses to focus sun rays is documented in Greek literature
from at least the fifth century. 26 Theophrastus, among others, mentions
this method of lighting a fire, 27 and Pliny talks of the medical use of converging
lenses for cauterization. 28
Because of a lack of clear literary references, it has often been denied
that classical Antiquity used lenses to magnify images. (Such lenses must
be made of better-quality glass, or else crystal, and require better grinding
techniques, than those used to start fires.) But today it seems very likely
from the archeological evidence that magnifying glasses were indeed in
use. Archeologists have found lenticular objects at many sites, including
Tyre, Pompeii, Cnossos and the Fayyum. 29 Although the finds at Pompeii page 300
(which started coming up in the eighteenth century) and some other sites
have often been interpreted as jewelry, and some others were probably
lenses used for ignition, the especially high quality of some of the lenses
found recently leaves little room for doubt that they were magnifiers. One
of two plano-convex lenses found in Crete in 1983, for instance, magnifies
well at least seven times and still has visible signs of polishing. 30 The
Archeological Museum in Heraklion, Crete, has 23 lenses on display, some
of prime quality, and has others in storage. Some of the finds, such as the
ones from Cnossos, go back to the bronze age and show that lens technology,
though completely lost in early medieval Europe, is in fact very
old.
To accept the idea that magnifying glasses were used in Antiquity we
must account for the scarceness of literary references. We have seen that
literary sources fail to mention other technological products that existed
for sure. Also we can imagine that the use of magnifiers was confined to a
few fortunate souls: probably some professionals to whom they would be
25a
Ptolemy, Optics, V = 223–269 (ed. Lejeune). The work breaks off in the middle of this book V.
See page 56 for a discussion of Ptolemy’s tables of refraction angles.
26
Aristophanes, Clouds, 766–772.
27
Theophrastus, De igne, fr. 73 (Gerke). The fragment actually talks about lighting a fire by converging
sun rays, and it’s not totally clear whether a mirror or a lens is meant; but since both glass
and metals (bronze and silver) are mentioned, Theophrastus probably has in mind both possibilities.
28
Pliny, Naturalis historia, XXXVII, 28–29.
29
See [Beck] for the Cnossos find. The scant literary evidence is discussed in [Kisa], vol. II,
pp. 357–359.
30
[Sines, Sakellarakis]. This article also discusses other recent finds and some older ones.
Revision: 1.11 Date: 2003/01/06 02:20:46