1 The Birth of Science - MSRI

270 10. Lost Science
have cropped up more than once. Therefore it seems likely that Dionysius’
statement is taken from Posidonius, who might have had in mind
(given among other things his astronomical interests) the same dynamical
analogy between the earth and a sling that Plutarch brings up. 133
Strabo, in the Geography, is clearly referring to the whole earth when page 336
he makes the ground assumption (“hypothesis”) that the ge is spheroidal
(¦). 134 This term is usually interpreted to mean “exactly like a
sphere”. Thus H. L. Jones, who adds for good measure: “The spheroidicity
[non-sphericalness] of the earth was apparently not suspected until
the seventeenth century.” 135 Strabo’s use of the term can certainly bear
that interpretation. But Strabo says he borrows his ground assumptions
from the scientific treatises on the subject; therefore one cannot exclude
the possibility that the word here has its (Hellenistic!) scientific sense, now
generally borne by the expression “ellipsoid of revolution”. 136 The suspicion
that Strabo’s sources declared the earth to be ellipsoidal finds some
support in a passage of Diodorus Siculus about the genesis of our world,
to the effect that the early earth, still fluid, was shaped by gravity and its
own continual rotation. 137
Diogenes Laertius reports that “the Stoics” gave not only the earth but
also heavenly bodies a spheroidal shape. 138 Elsewhere he talks of heavenly
bodies being spheroidal in certain cases and ovoidal in others, 139 saying
this was the Epicurean belief. Aetius attributes to Cleanthes the opinion
that heavenly bodies have a conoidal shape. 140 The introduction in a technical
sense of terms that were previously in common use must perforce
have led to confusion after the notion of linguistic conventionalism was
lost. 141
The ellipsoidal shape of the earth was “suspected” in the seventeenth
century, as Jones says. Remarkably, this suspicion predates any measure-
133 See quotation and discussion starting on page 245. An echo of the original meaning may perhaps
still be seen in Dionysius’ verses: he writes that the (earth or land) is
¦ (Dionysius Periegetes, Oikoumenes periegesis, v. 6–7 =
[GGM], vol. II, pp. 104–105).
134 Strabo, Geography, I, i, 20, and again at II, v, 5.
135
[Strabo/Jones], vol. 1, p. 40, note 2.
136
See the Archimedes quotation on page 156 and note 28a immediately thereafter.
137
Diodorus Siculus, Bibliotheca historica, I, vii, 2. Note that when Archimedes proves in the first
book of On floating bodies that the spherical shape of the oceans follows from gravity, he specifies
that this is true “in rest conditions”.
138
Diogenes Laertius, Vitae philosophorum, VII, 145.
139
Diogenes Laertius, Vitae philosophorum, X, 74.
140
[DG], 344, 2.
141
Thus in the passage just cited, as in others such as [DG], 312b, 22–23 and 329a, 1–2, the doxographer’s
statements that certain authors gave objects a conical or conoidal shape might have arisen
from a misunderstanding of references to conics.
Revision: 1.11 Date: 2003/01/06 02:20:46
page 337