1 The Birth of Science - MSRI

326 11. The Age-Long Recovery
“toys” in reconstructing Alexandrian technology). But when the source
is a nontechnical writer of the imperial age, rather than Euclid or Archimedes,
the effect is unmistakable. The metaphysical ingredient, largely
absent from Galileo, looms large. For already the ancient writer, unable to
make clear demarcations between scientific theory and the reality it models,
tends to frame the discussion in pre-Hellenistic, usually Aristotelian,
concepts: a mix that early modern scientists are wont to contaminate further
with biblical influences (Newton was a passionate commentator of
the Bible).
Plutarch is not the only literary classical source used by Newton. In the
following passage we clearly recognize Seneca as the source, through it is
not explicitly stated:
The Chaldeans, the most learned astronomers of their time, looked
upon the comets (which of ancient times before had been numbered
among the celestial bodies) as a particular sort of planets, which, describing
eccentric orbits, presented themselves to view only by turns,
once in a revolution, when they descended into the lower parts of
their orbits. 127
The same applies to this very significant passage:
Therefore the earth, the sun and all the planets which [are] in our
system, according to the ancients have weight with respect to one
another, and would fall toward each other because of mutual gravity
and coalesce into one mass, if their fall were not prevented by their
circular motions. 128
Where does this lead us?
As we learned in school, the conceptual leap from a purely descriptive
astronomy to a gravitation-based theory lay in taking the sun, the moon page 401
and the planets and realizing — though these bodies are only a handful
and there was no hope of observing others — that their regular motions
did not depend on their “heavenly nature”, but on their having “weight”,
and that these motions could be generalized through a theory that renders
just as regular the motion of anything whatsoever: a stone, an apple
127 Newton, De mundi systemate liber, 1, anonymous translation of 1728 (probably by Motte), as
revised by Cajori. Compare the passages of Seneca quoted on page 271.
128 “Igitur Terra Sol et Planetae omnes qui in nostro systemate ex mente veterum graves sunt in
se mutuo et vi gravitatis mutuae caderent in se invicem & in unam massam coirent nisi descensus
ille a motibus circularibus impediretur” (Classical scholia, folio 271r = [Casini], p. 46 or p. 37). Thus
Newton, who of course was immune to the modern scholarly fear of committing anachronisms by
attributing “Newtonian” notions to ancient authors, provides authoritative corroboration for the
interpretations of Seneca’s passages proposed in Sections 10.5 and 10.9.
Revision: 1.11 Date: 2003/01/06 07:48:20