Magnetism in the Greco-Roman World


Thales of Miletus, 1875 illustration
The beginning of a manuscript of Lucretius' De Rerum Natura, created in 1563 in Paris. Photo: LegesRomanorum
18th century portrait of Galen

This article was initially published in the February 2017 issue of IEEE-USA InSight

The electromagnetic revolution in the late 19th century profoundly changed technology and society in all aspects of human life. While the mathematical theory and practical use of electrical technologies is a relatively recent event, electrical and magnetic phenomena such as lightning, St. Elmo’s fire, and the shocks of various fishes and eels have been observed by humans since the prehistoric period. With the development of writing and the ability to express and record more complex thoughts, aspects of magnetic phenomena were examined and debated for centuries by several Greek and Roman philosophers throughout the ancient Mediterranean world.

The earliest known Greek to examine the problem of magnetism was Thales of Miletus (c. 624 – 546 BCE), who was regarded as the first Greek philosopher by Aristotle. Though none of Thales’ writings survive, his teachings are preserved by Aristotle’s works. Thales’ observations on the earth and water derive from natural phenomena, rather than supernatural, and his views on magnetism are reflected in Aristotle’s “On the Soul,” which states that “Thales, too, to judge from what is recorded about him, seems to have held soul to be a motive force, since he said that the magnet has a soul in it because it moves the iron.” The use of the word “soul” (psuche) in this case does not necessarily imply the supernatural aspects of the modern connotation, but rather to have “psuche” means to be alive. As living things are capable of independently producing movement, Thales ascribes the attractive forces of the lodestone, a naturally magnetized iron ore, to a living, materialist property.

Expanding on the materialist views of Thales, Empedocles of Akragas (c. 490 – 430 BCE) constructed a theory of magnetism that describes active emanations from iron. While only fragments of his works survive, his writings on magnetism are summarized by Alexander of Aphrodisias (c. 200 CE) who stated that “iron is borne towards the stone by the effluvia emanating from both and because the pores of the stone are fitted to receive the effluvium of the iron.” The idea that iron emits microscopic particles that are congruent with the pores in the lodestone was a common theme expressed among subsequent Greek philosophers who attempted to understand magnetism. Similarly, Democritus (c. 460 – 370 BCE) developed a theory which posited all material was composed of invisible particles called atoms. Despite its superficial similarities to the modern day atomic model, Democritus’ model was crude in comparison. He thought that there were infinite number and sizes of atoms, and attempted to explain magnetism with this theory. Alexander of Aphrodisias wrote that Democritus believed lodestone and iron contained similar atoms, but those of the stone are smaller and rarer, and contains more void. Due to their atomic similarity, the atoms of the lodestone permeate through the pores of the iron, disturbing its atoms, causing them to stream outside towards the stone. This cycle of movement of atoms between stone and iron is what Democritus believed to cause the physical movement between the two. Empedocles’ and Democritus’ ideas were influential, yet not universally embraced by the Greek philosophical schools. Aristotle (384 – 322 BCE) in particular rejected both the idea of atomic theory and Thales’ idea that the soul causes magnetic movement. However, the idea of atomic emanation persisted and was reflected in the works of Epicurus (341 – 270 BCE). Lucretius (99 – 55 BCE), a Roman poet and Epicurean, wrote a poem in approximately 60 BCE called "De rerum natura" (“On the Nature of Things”), which describes the magnetic attraction:

First, stream there must from off the lode-stone seeds

Innumerable, a very tide, which smites

By blows that air asunder lying betwixt

The stone and iron. And when is emptied out

This space, and a large place between the two

Is made a void, forthwith the primal germs

Of iron, headlong slipping, fall conjoined

Into the vacuum, and the ring itself

By reason thereof doth follow after and go

Thuswise with all its body.

Lucretius goes on to mention loose iron filings which “seethe furiously” when influenced by the magnetic, suggesting observation of attraction in the shape of a field. Historian and biographer Plutarch (46 – 120 CE) elaborates on this idea, stating that lodestone emits matter, reflecting circumambient air, and forming a void. The circumambient air is expelled in a circle around the void, returning to the lodestone and moving any iron in its path. Plutarch explains that non-iron objects like wood are not moved, as pores of the iron bear a likeness to the particles of the vortex, which are not found in non-magnetic materials like wood. Electrical attraction of amber is described in a similar fashion, except that amber must first be rubbed in order to release the exhalations from its pores.

Much of science during the Roman Empire was influenced by Epicurean philosophy. Pliny the Elder’s (23 – 79 CE) Naturalis Historia was an early encyclopedia which attempted to describe all ancient knowledge. The sections on amber and lodestone expand on the brief text “On Stones,” written by Theophrastus around 300 BCE. Here Pliny described magnetism in a similar fashion to Lucretius, and unlike many classical Greek philosophers, did not seem to be concerned with the rationalizing underlying theory of attraction, but instead with describing its properties that are immediately visible. Pliny also provides a possible origin of the word “magnet,” of which he wrote “Nicander is our authority for believing that it was called Magnes, from the man who first found it on Mount Ida, and he is said to have discovered it when the nails in his shoes and the ferrule of his staff adhered to it, as he was pasturing his herds.” A more plausible origin of the word “magnet” is derived from the Greek “magnes lithos”, or “stone of Magnesia”, an ancient city whose ruins are located near the village of Tekin in Türkiye.

The materialist explanation of magnetism fell out of favor with the Christian era, and in particular was rejected by Galen (129 – 200 CE). Instead of the Epicurean philosophy, Galen argued in favor of a Christian theistic philosophy, which attributed all actions to divinity. Galen had rejected the Epicurean view of magnetism on the account that it did not sufficiently explain the phenomena of magnetic induction. Though not referred to such in the ancient world, the basic principles of magnetic induction were known and referenced as early as the 5th century BCE. A lost play by Euripides (480 – 406 BCE), Oeneus, is referenced by Socrates in Plato’s Ion, which included the line that “this stone not only attracts iron rings, but also imparts to them a similar power of attracting other rings”. Galen’s work “On the Natural Faculties” used a similar example to criticize the Epicurean view of magnetic attraction through atomic particles. He stated the Epicurean “principle will not explain the fact that, when the iron has another piece brought in contact with it, this becomes attached to it... as a matter of fact, I have seen five writing-stylets of iron attached to one another in a line, only the first one being in contact with the lodestone, and the power being transmitted through it to the others.” As Epicurean model could not adequately account for induction, Galen saw this as firm proof that the materialistic theory was incorrect, and instead suggested that the attractive power of the magnet is divine.

The idea of an immaterial force, though not necessary a divine one, is present in the writings of Alexander of Aphrodisias, a philosopher who taught between 198 and 209 CE. Much of his surviving work was commentary on Aristotle, and is the primary source for most of what we know regarding ancient Greek materialist magnetic theory. His commentaries on magnetism are possibly the first scientific analysis of magnetism in the method of Aristotle. He summarized and rejected Empedocles and Democritus, and advanced an immaterial theory of attraction, that the magnet possesses something that iron does not. This idea is later described by Simplicius (490 – 560 CE) as attraction by an incorporeal force, the immaterialist theory being the dominant viewpoint throughout the Middle Ages.

While the intellectual problems of magnetism attracted many philosophers, the ancient Greeks and Romans found very little engineering use for magnetism. Some ancient authors have provided anecdotes of magnetism being used in architecture, but it is unlikely these were more than legend. In particular, Pliny describes an attempt to construct a levitating statue in Arsinoë IV’s tomb. Arsinoë was executed by Mark Antony in 41 BCE under Cleopatra’s order, and the architect Timochares began to construct a magnetic tomb in which the statue of Arsinoë could be suspended in mid-air. The concept of polarity was not known to the ancient world, and magnetic lodestone was understood as having attractive properties. While evidence exists that magnetic repulsion was observed, Pliny suggests that repulsive magnets were a completely different stone, referred to as “theamedes.” As such, Timochares’ solution to magnetic suspension was not repulsive magnetic material in the floor of the tomb, but rather a vaulted ceiling made from magnetic materials that evenly counterbalanced the statue’s weight. The forces required to pull the statue in the air, however, are significantly greater than found in naturally occurring materials. While Pliny noted that Timochares died before the project was completed, later writers including Ausonius, St. Augustine, St. Isidore and Cedrinus affirmed that the statue was not only completed, but functioned as intended.

Discounting these outlying curiosities, widespread practical use of magnetism is not reliably documented until several centuries after the collapse of the Roman Empire. The earliest known account of magnetic declination comes from the Chinese text Kuan Shih Ti Li Chih Meng (“Mr. Kuan's Geomantic Instructor”), which dates to around 880 CE, and a mathematical understanding of magnetism was not developed until the 19th century. While the ancient Greeks and Romans lacked much of the understanding we have today, their attempts to analyze problems through reason and logic form the building blocks of humanity’s legacy of science, engineering and technology.

References and Further Reading