1 The Birth of Science - MSRI

10.12 Atoms, Gases and Heat 277
based on its weight and its collisions with other atoms. 177 (Naturally, the
idea that atomic motion is subject to intrinsic stochastic fluctuations has
gained renewed interest due to the establishment of quantum mechanics.)
In contrast, the Stoics reiterated the general validity of determinism, explaining
the apparent randomness of many events through our inability
to follow causal chains that are too complex. 178 Chrysippus, in particular, page 345
criticized the Epicurean hypothesis of unmotivated motion and explained
that in every case, even that of a die that lands on a particular face, there
is always a hidden cause. 179
10.12 Atoms, Gases and Heat
Some Hellenistic scientific ideas about thermal phenomena have come
down to us through Plutarch and other sources. One interesting remark is
that wool clothing makes us warm because of its insulating power rather
than because of inherent heat, as demonstrated for example by the use
of wool to keep snow from melting. 180 Plutarch also discusses — and exaggerates
— the effects of temperature on the density of water. 181 In the
context of pneumatics, thermal dilation was also well known and put to
use, as shown by Philo of Byzantium’s description of a device, nowadays
called a thermoscope, showing how air expands when it is heated. 182 Such
studies were closely connected with the development of ideas on atomic
motion: Philo in fact observes that expansion of the gas is owed to the
increase in interatomic distances, which cannot be observed directly. Unfortunately,
in his extant works Philo makes only a bare mention of these
theoretical ideas, referring the reader to another work of his that has perished,
titled De mirabilibus arbitriis in the Latin manuscripts of the Pneumatica.
183
Epicurus distinguished two types of atomic motion: the vibration of
atoms around a fixed position (in solids) and the free movement of atoms
177
This idea does not appear in any of the letters of Epicurus that have come down to us. The
earliest author who reports it is Lucretius (De rerum natura, II, 216–260).
178
Plutarch, De animae procreatione in Timaeo, 1015 B–C. See also [SVF], II, texts 965–973.
179
Plutarch, De stoicorum repugnantiis, 1045B–F.
180
Plutarch, Quaestionum convivalium libri vi, 691C–692A.
181
Plutarch, Quaestiones naturales, 914A; see also note 25 on page 25.
182
Philo of Byzantium, Pneumatica, vii. See also the chapters of Heron’s Pneumatics mentioned on
pages 115–116.
183
Philo of Byzantium, Pneumatica, iii = [Philo/Prager], p. 129. Several authors have interpreted
arbitria as an Arabic-mediated corruption of “automata” or “organs”, assuming perhaps that these
are the only wonder-evoking (mirabilia) entities in pneumatics. But, as noted by Prager (loc. cit.,
note 409), the context shows clearly that the reference is not to automata or organs, but to a discussion
of the motion of atoms in the void.
Revision: 1.11 Date: 2003/01/06 02:20:46