1 The Birth of Science - MSRI

3.6 Aristarchus, Heliocentrism, and Relative Motion 73
medes’ planetarium was of this type has an important source of support
in the main testimonium about the issue, from Cicero:
Archimedes’ invention is admirable in that he figured out a way to
make a single conversio reproduce the diverse and various trajectories,
in motions that contrast among themselves. 101
The word conversio can mean rotation, inversion, reversal. It would cer- page 109
tainly be an appropriate term for a hinge allowing the production of retrograde
motion. In any case this emphasis on the singleness of the mechanism
on which the various contrasting motions depend would be inconsistent
with a mechanical model based on a Ptolemaic-type algorithm.
We are told of other moving planetaria from antiquity in a passage of
Pappus 102 to the effect that some were built that were powered by a hydraulic
mechanism, and again by Cicero, 103 who mentions a planetarium
constructed by Posidonius in the first century B.C. While we do not know
that anyone ever managed to build a Ptolemaic-type mechanism capable
of representing planetary motion, after the “Copernican revolution” the
construction of moving planetaria — obviously of heliocentric type — became
possible again.
Thus the history of planetaria suggests that the heliocentric theory may
not have been abandoned immediately after Aristarchus, as has generally
been claimed, 104 but during the interruption in scientific activities that succeeded
Hipparchus. We will return to this point in Chapter 10.
Nor was Aristarchus the first person to say that the earth moved. Already
Heraclides of Pontus, in the fourth century B.C., asserted the daily page 110
101
“. . . in eo admirandum esse inventum Archimedi, quod excogitasset, quem ad modum in dissimillimis
motibus inaequabiles et varios cursus servaret una conversio” (Cicero, De re publica, I,
xiv, 22). Cicero is relaying observations contained in a lost work of Sulpicius Gallus, who saw the
Archimedean planetarium at the home of his coconsul Marcus Marcellus, who in turn had inherited
it from his grandfather, the Marcellus who sacked Syracuse. Cicero brings up elsewhere the
same idea of a single conversio on which all the motions depend (Tusculanae disputationes, I, xxv, 63).
102
Pappus, Collectio, VIII, 1026, 2–4 (ed. Hultsch).
103
Cicero, De natura deorum, II, xxxiv, 88.
104
Support for the idea that Aristarchus was too far ahead of his time to have had a lasting influence
on the course of science is generally found in the oft-mentioned accusation of impiety leveled
at him because of his heliocentrism. Our source for this episode is the same passage in Plutarch
already discussed (De facie. . . , 923A). In fact, the belief that Aristarchus was accused of impiety
originates with the seventeenth century philologist G. Ménage, who, obviously influenced by the
prosecutions of Giordano Bruno and Galileo, distorted the meaning of the passage by emending an
accusative into a nominative and vice versa. Later editors, perhaps regarding as inevitable the link
between heliocentrism and impiety, have almost without exception accepted the emendation to
Plutarch’s text, which became canonical in Ménage’s “modernized” version. For more information
on this enlightening episode, see [Russo, Medaglia].
Revision: 1.13 Date: 2002/10/16 19:04:00