§21. Mechanics in Antiquity

The natural philosophy of Democritus and Epicurus has been described as “mechanical” merely because it is atomistic. However, the connection be­tween atomism and mechanism is new in the seventeenth century, and nothing is properly mechanical about ancient atomism.

Aristotle says of the atomists, chiefly Democritus, that they “believe the automatic (tautomaton) to be the cause even of the heavens above us and indeed of all the worlds; for they say that the whirl (dine) and the motion which separated and arranged the whole in this order are produced auto­matically.” Despite the suggestive language of the translation, these are not allusions to mechanism. For Aristotle, “automatic” describes what happens ateleologically, without purpose. What happens by chance is something that might have been purposive, even though it was not. I purposefully visit the market, and by chance encounter a debtor who repays me (I might have purposefully sought him out). When Aristotle says the atomist world is au­tomatic he means it is without purpose, undesigned, unmeasured, and there­fore far from mechanical.¹⁶⁷

Aristotle is no stranger to mechanisms or the science of mechanics.

Greek mechanics emerged as a developed mathematical discipline in the late fourth century bce. As the accomplishments sank in, postclassical thinkers began to draw analogies to mechanical devices in the investiga­tion of nature. Mechane is the ancient Greek word for a device or stratagem. Amechane, human helplessness before the gods, contrasts with Odysseus's ingenious polumechania. Aeschylus describes the robe with which Klytemnestra entangled and killed her husband as a mechanema, a device for implementing a purpose. In Aesop, an old lion too weak to feed itself is reduced to living by tricks, mechanikos. The word is not a catch-all for tools or technics, distinctly if vaguely referring to artifacts with which to accomplish what no single person could do unaided. Primarily that means devices for lifting weights or moving fluids or ballistic devices for throwing projectiles, but also traps for killing husbands.

Ancient tradition credits Archytas, a Pythagorean associate of Plato, with the first system of ta mechanika on mathematical principles. However, the oldest extant treatise is the Aristotelian Mechanica. Nothing precludes au­thorship by Aristotle, although the theory of the work has few echoes else­where in his writings. An ancient tradition attributes the work to Strato of Lampsacus, who followed Theophrastus as the second successor at Aristotle’s Lyceum. The work defines its subject as belonging to theoremata. The treatise concerns the principles of the class of machines that move heavy bodies for human benefit. These are worthy of investigation because “it seems strange that a great weight can be moved by a small force.” That is the wonder with which Aristotle said philosophy began. The central instances of mechanics according to this treatment are balance and lever, pulley, wheel, wedge, steering oar, forceps, and masts. Historian of science Pierre Duhem found striking how the treatise unifies these several devices under a simple analysis and offers a mathematical account of their action. The balance reduces to circles, the lever to a balance, and all the other machines to levers.¹⁷⁰

There were important contributions to mechanics in later antiquity, no­tably by Archimedes, prince of ancient mathematicians, and Philo of Byzantium, whose experimental ballistics I discuss later (§24). The expe­rience with machines revealed new and unexpected powers in matter. For instance, mechanists spoke of the power of the void, referring to the power of compression and recoil and the principle of the piston. Phenomena of elasticity were newly pondered. Epicurus left atomic collision pretty vague. Atoms contain no void. Are they then perfectly rigid? What is their behavior in collision? It is only from the third century bce that Greeks begin to tackle these thorny questions that still troubled Leibniz.

This is the time of the first experiments in introducing mechanics into nat­ural philosophy, seeking an alternative to atomism or hylomorphism. Heron of Alexandria, whose Mechanics (first century ce) was one of several math­ematical works of late antiquity Galileo studied in the new editions of the sixteenth century, makes the proposal explicit. Mechanists have to be natural philosophers too. “It is now absolutely necessary for those who occupy them­selves with the science of mechanics to know the causes that are in effect in the use of each motion.... Anyone who wants to find the causes thoroughly, necessarily has to apply natural principles, either one or more, and has to link everything that he researches with them.”¹⁷¹ Rule-of-thumb empiricism is not enough anymore; the engineer has to study natural philosophy. “It is quite clearly necessary that those who are learning about mechanical arts should understand the nature of the center of gravity and gravity itself.”

Ancient mechanics survived Roman collapse by a tenuous thread. Fundamental texts were fortuitously preserved through the Middle Ages, and their study taken up in the sixteenth century pretty much where the Greeks left it. The Aristotelian Mechanics was taught at Padua, where Galileo encountered it, and new Latin translations of mechanical works by Heron and Archimedes were immensely popular, especially in Italy. By the seven­teenth century, “mechanical” and its cognates in European languages had three principal connotations:

(1) Mathematical application of a science of mechanics to bodies in motion.

(2) Mutual contact and pressure of bodies solid or fluid.

(3) Explanations modeled on working machines or automata.

For Hobbes, (2) is primary, (1) secondary, and (3) irrelevant. Mechanism does not have to be empirical, as Hobbes showed by his indifference to ver­ification (§47). For Boyle, (2) is also primary and (1) not much considered. Boyle is, however, enthusiastic about the analogy between nature and the most complex machine of his day, the mechanical clock.

In this great automaton, the world (as in a watch or clock), the materials it consists of being left to themselves could never at the first convene into so curious an engine: and yet, when the skillful artist has once made and set it a-going, the phenomena it exhibits are to be accounted for by the number, bigness, proportion, shape, motion (or endeavour), rest, coaptation, and other mechanical affections, of the springs, wheels, pillars, and other parts it is made up of.¹⁷²

For Leibniz, (1) is primary, while (2) is a means or guarantee of (1). He all but equates mechanical and mathematical. “Everything happens me­chanically in nature, that is, according to certain mathematical laws.” Mathematicians “reduce everything as far as possible to mechanical laws.” “How can we hope to explain the causes of such things except by mechanical laws, that is, by concrete mathematics of geometry applied to motion?”¹⁷³

Mechanics matters to our themes of experience and empiricism because the Greek experience with mechanics prompted innovation in natural phi­losophy, and when this mechanics restarts in the sixteenth century it lends itself, especially with Galileo, to an emerging experimental natural philos­ophy. We can draw a line from the experience of mechanics in antiquity to the experimental mechanics of the seventeenth century.