1 The Birth of Science - MSRI

3.5 Pneumatics 69
air in motion; 84 this simple meaning of the term may have been sharpened
precisely through the development of pneumatics.
Although the total loss of Ctesibius’ works and the corruption of Philo’s
text greatly limit our knowledge of theoretic aspects of Hellenistic pneumatics,
we do have some insight on one important methodological char- page 104
acteristic of it. The objects described in the early, and reputedly authentic,
chapters of Philo’s works are intended neither to amaze nor, for the most
part, to perform useful functions; they are simple experimental devices
designed to demonstrate particular phenomena, such as those related to
the syphon principle. Some of Philo’s demonstrative experiments are still
used in school today to teach the experimental method: for example, the
effect that burning a candle inside a submerged dome has on the water
level inside the dome. 85 Heron, most probably drawing from Ctesibius or
Strato of Lampsacus, devotes the entire introduction of his Pneumatica to
arguing that macroscopic regions of vacuum cannot exist in nature, but
can be approximated artificially — as in fact he demonstrates later in the
work on several occasions. In particular, Heron explains that the natural
distribution of particles and void in air can be changed in both directions
under the application of external forces, although the air opposes such
changes with an elastic reaction. 86 The elastic properties of air had already
been described and used by Ctesibius, as we know from Philo. 86a
Pneumatics, appearing from its foundation as a theory of phenomena
that can only be caused artificially, lies very far from natural philosophy
and certainly from Aristotelian philosophy. 87 This provides corroborative
evidence for the revolution in thought illustrated in Section 1.4 with examples
from mechanics.
533; II, 450–454, 543, 546). The reference [Sambursky: PS] may be useful in connection with Stoic
physics.
84
Heron, Pneumatica, I, proem = [Heron: OO], vol. I, 6, 6–7.
85
Philo of Byzantium, Pneumatica, viii = [Philo/Prager], p. 136. Even Philo’s explanation for the
rise (some of the air “perishes” and is replaced by water), though now known to be incomplete,
continues to be offered in different language by many textbooks as if it were the whole story. In
this the books follow an uninterrupted tradition over two thousand years old. We will return to
Philo’s explanation at the end of Section 5.7.
86
Heron, Pneumatica, I, proem = [Heron: OO], vol. I, 24, 20 ff.
86a
Belopoeica, 77–78 = [Marsden: TT], pp. 152–154.
87
Aristotle gave several “demonstrations” of the impossibility of the vacuum (Physica, IV, 6–9,
213a–217b). Like Archimedes with the ship (page 19), Ctesibius overcomes Aristotle’s objections
by designing machines that create phenomena not observable in nature. It was once thought that
Heron offered the impossibility of a vacuum as an explanation for why syphons work (Pneumatica,
I, ii = [Heron: OO], vol. I, 36, 8–18). This view turns out to be based on the emendation of a question
mark into a colon by philologists eager to shoehorn Heron into the confines of Aristotelian orthodoxy.
This at least is what Prager concluded after comparing the edited text with the Biblioteca
Marciana codex of the Pneumatica ([Philo/Prager], p. 21).
Revision: 1.13 Date: 2002/10/16 19:04:00