1 The Birth of Science - MSRI

240 10. Lost Science
a convenient fraction of the meridian, just as with the meter’s definition page 298
in the eighteenth century.
10.2 Lost Optics
Only two sizable works of ancient optics are extant. Authored by Euclid
and Ptolemy, they stand almost five hundred years apart. Euclid’s Optics
represents an early stage of the science, which was then developed in lost
treatises by some of the greatest scientists of antiquity, including Archimedes,
Apollonius and Hipparchus, and finally hit a crisis like all other
scientific disciplines. We have several reasons to think that Ptolemy’s book
is more of a partial recovery of earlier stages than an improvement on
them. Ptolemy discusses only plane and spherical mirrors, without ever
applying to mirrors the theory of conics, but Diocles’ short work On burning
mirrors shows that such applications, later taken up by the Arabs,
were very much older than Ptolemy. Ptolemy’s Optics is the only surviving
work that includes a theory of binocular vision, but certain testimonia
imply that such a theory had already been developed by Hipparchus. 19
The state of the sources leaves us in the dark about many areas of physical
optics. For example, we know very little about research on colors 20 and
on dispersion (the dependence of refraction on the color of light, which
gives rise to the rainbow and allows the separation of colors through a
prism). But interest in these subjects is demonstrated by many references
found in the literature: for example, in Diogenes Laertius, 21 Plutarch, 22
Lucretius 23 and Seneca, who talks about glass objects “with many angles”
that, when hit by sunlight, give back the colors of the rainbow. 24 Apuleius page 299
says that Archimedes too studied the rainbow phenomenon. 25
It would be particularly valuable to know what the state of knowledge
on refraction was. Among extant scientific works, the first to discuss the
19
Plutarch mentions a theory of binocular vision (Quaestionum convivalium libri vi, 625E–626E).
Aetius attributed such a theory to Hipparchus (in Stobaeus, Eclogae, II, lii, 18 = [DG], 404, 9).
20
A very interesting passage in Ptolemy’s Optics (II, 96 = 60, 11–19, ed. Lejeune) discusses spinning
disks with sections of different colors — the kind later called Newton’s disks. As Lejeune
remarks, they appear here “as a true experimental instrument”.
21
Diogenes Laertius, Vitae philosophorum, VI, 152.
22
For example, De facie quae in orbe lunae apparet, 921A; De Iside et Osiride, 358F–359A.
23
Lucretius, De rerum natura, II, 799–800.
24
Seneca, Naturales quaestiones, I, vii, 1. The passage mentions a glass virgula, a term that is usually
translated “little rod”. But virga, besides rod, is also the name of the mini-rainbow that arises as a
result of dispersion, and which Seneca discusses in the continuation of the passage cited. Thus
virgula vitrea could have been, in Seneca’s source, a small straight rainbow obtained with a glass
object. As to the “many angles”, it is possible that Seneca’s source did not refer to objects with
particularly many facets, but to the refraction angles of the various colors.
25
Apuleius, Apologia, xvi.
Revision: 1.11 Date: 2003/01/06 02:20:46