- Sylvia Berryman
A branch of the ancient Greek mechanical art, roughly concerned with the movement of fluids and the ways that its properties could be used to produce effects, whether lifting water, holding it suspended, or producing surprise effects that imitate the motions of living beings in theatrical displays. Water-driven timepieces and a steam-powered turbine are included in this branch.
A number of early experiments in this area were aimed at establishing the corporeality of air—Anaxagoras, for instance, is credited with a test involving the lowering of a tube closed at its upper end into water, to show that the water’s entrance into the tube is somehow blocked by the air contained in the tube (DK 59A69). Many other such early investigations by natural philosophers were concerned with the explanation of biological phenomena such as respiration and the propulsion of fluids through the body, often by analogy with other more readily visible processes such as the operation of the water clock or klepsydra (see clocks), which features in the Empedoclean account of the mechanics of respiration (DK 31B100; see empedocles). In some later physiological theories, pneumatic motion is invoked to explain the phenomena of pulsation and fluid dynamics generally, (e.g., by Erasistratus), as well as the activities of the motor nerves (perhaps by Herophilus, although the evidence is not secure).
It is unclear exactly when pneumatics came to be thought of as a subject in its own right. Its traditional founder was Ctesibius of Alexandria, who worked in the early 3rd century bce and invented a number of mechanical toys operated by air, water, and steam under pressure. None of his work survives intact, but the fifth book of Philon (2) of Byzantium’s Mechanical Syntaxis (probably composed in the mid-3rd century bce, and existing now only in Arabic and Latin translations) is thought to draw heavily on Ctesibius’ theoretical and practical work, as does book 10 of Vitruvius’ On Architecture. The earliest surviving work in Greek is Hero of Alexandria’s Pneumatica, which was probably composed in the 1st century ce. In the preface to this work, the author is keen to acknowledge his debt to early philosophers as well as mechanics.
The central theoretical problem, however, concerned the nature of the void and its role in the dynamics of fluid motion. Pneumatic motion was explained in a number of different ways depending on how the status of void was viewed: explanations making vague references to “because of the void” or “because there can’t be a void” might be connected to more specific theories. Those like the atomists and Plato, who denied the existence of void explained the “tendency to refill” of emptier spaces by circular mutual replacement, or the pressure of particles in denser regions pushing from behind. Peripatetic writers ascribe a kind of “continuity” to matter that leads it to follow along continuously with exiting matter to prevent gaps forming. Some theorists apparently thought that the void itself “attracts” materials into it. Hero—who jumbles together all known explanations in the Introduction to his collection of pneumatic devices— seems to have thought that close-packed particles in contact could deform under pressure into interstitial voids and pack even closer, but would rebound to their original size. This account, because it ascribes the property of elasticity to the particles of matter themselves, would not have been endorsed by traditional atomism and would likely post-date Ctesibius’ demonstration of the elasticity of air.
While the bulk of the tradition concerning the forces operating on liquids was produced with a view to the making of mechanical devices, a unique text is that by Archimedes, On Floating Bodies. Mostly engaged with the forces acting on solids immersed in a liquid, the treatise also derives, on pure mathematical principles, the sphericity of the liquid surrounding the earth taken as a whole.
The term pneuma could refer to wind, breath, or a technical substance that was variously conceived; Aristotle refers to it as the analogue of the fifth element that composes the heavens. Stoic theory saw pneuma not as a localized substance but as a pervasive principle diffused throughout all matter; the theory seems to have had little connection with the development of pneumatics as a technical field. In medicine, it seems likely that the development of complex pneumatic devices distributing fluids “automatically” contributed to the notion that the fluid systems of organic bodies worked like pneumatic devices.
- Berryman, Sylvia. The Mechanical Hypothesis in Ancient Greek Natural Philosophy. Cambridge, UK: Cambridge University Press, 2009.
- Drachmann, A. G. The Mechanical Technology of Greek and Roman Antiquity. Copenhagen: Munksgaard, 1963.
- Hall, Marie Boas, ed. The Pneumatics of Hero of Alexandria. London: Macdonald, 1971.
- Keyser, Paul T. “A New Look at Heron’s Steam Engine,” Archive for History of the Exact Sciences 44 (1992): 107–124.
- Prager, Frank David. Philo of Byzantium Pneumatica: The First Treatise on Experimental Physics: Western Version and Eastern Version. Wiesbaden, Germany: L. Reichert, 1974.
- Oleson, John Peter. Greek and Roman Mechanical Water-Lifting Devices: The History of a Technology. Toronto: Springer, 1984.
- Schmidt, Wilhem. Heronis Alexandrini Opera, 1. Leipzig: Teubner, 1899.
- Vallance, J. T. The Lost Theory of Asclepiades of Bithynia. Oxford: Clarendon Press, 1990.
- Woodcroft, Bennet. The Pneumatics of Hero of Alexandria. London: Printed by Charles Whittingham, 1851.