The Pull of History

Human Understanding of Magnetism and Gravity through the Ages

Yoshitaka Yamamoto

• Publisher: WSPC
• Year: 2017
• ISBN:
  9789813223783
• Topic: Ciencias físicas
• Subtopic: Física

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This book seeks to understand what bring to pass the birth of modern physics by focusing upon the formation of the concept of force. This would be the first book to note the important role magnetism has played in this process. Indeed, the force between celestial bodies, before the introduction of the Isaac Newtonian gravitational force, is first introduced by Johannes Kepler by analogy with the magnetic force. Moreover, this book, by concentrating our attention on the magnetism, fully describes the developments and the recognition of the force concept during the Middle Ages. The detailed description of the Middle Ages and the Renaissance is a strong point of this book. By discussing and emphasizing on the role accomplished by the magnetic force, this book makes clear the connection between the natural magic and the modern experimental physics. This book will open up a new aspect of the birth of modern physics.

--> Contents:

• Preface
• Introduction
• Antiquity and the Middle Ages:
  • Ancient Greece: The Science of Magnetism is Born
  • The Hellenistic Age
  • The Days of the Roman Empire
  • Christianity in the Middle Ages
  • The Discovery of Magnetic Directionality
  • Thomas Aquinas and His Understanding of Magnetism
  • Roger Bacon and the Propagation of Magnetic Force
  • Petrus Peregrinus and His Letter Concerning the Magnet
• Renaissance:
  • Nicolaus Cusanus and the Quantification of Magnetic Force
  • The Rediscovery of Things Ancient: Magic in the Early Renaissance Period
  • The Age of Exploration and the Discovery of Magnetic Declination
  • Robert Norman and The Newe Attractive
  • Mining and the Continued Peculiarity of Magnetism
  • Paracelsus and Magnet Therapy
  • Changes in Magical Thought during the Late Renaissance
  • Della Porta's Investigations into Magnetism
• The Dawn of the Modern Age:
  • William Gilbert's On the Magnet
  • Johannes Kepler and the Magnetical Philosophy
  • Seventeenth-century Mechanism and Notions of Force
  • Robert Boyle and the Transformation of Mechanism in Britain
  • Magnetism and Gravity: Hooke and Newton
  • Epilogue: Ascertaining the Laws of Magnetic Force
• Notes
• Bibliography

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--> Readership: History students, philosophy students, general public. -->
Keywords:History;Magnetism;Philosophy;Greek;Modern PhysicsReview:0

Part 1

Antiquity and the Middle Ages

Chapter 1

Ancient Greece: The Science of Magnetism is Born

Section 1—Early Attempts to Explain Magnetism

Tradition has it that the first ancient Greek scholar ever to discuss the magnet was Thales (c. 624–546 B.C.) of Miletus, a flourishing port city in Ionia on the Aegean Sea. In fact, none of Thales’s writings were preserved, so whatever we claim to know about him has come down to us from scholars of later generations. About two hundred years after the time of Thales, for example, Aristotle (384–322 B.C.) noted in On the Soul 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.¹

In Lives of Eminent Philosophers, Diogenes Laertius, writing a further five centuries later, in the third century A.D., corroborates the traditional claim regarding magnets:

Aristotle and Hippias affirm that, arguing from the magnet and from amber, [Thales] attributed a soul or life even to inanimate objects.²

We cannot actually confirm whether or not Thales knew of amber’s power to attract (due to static electricity), because the writings of Hippias, too, have been lost; nor does Aristotle mention amber in any of his extant works.

According to both Aristotle and Diogenes Laertius, Thales referred to magnets only to explain the action of the soul, mentioning them only in the course of defending his claim that everything has a soul. Nowhere do they suggest that Thales explained what magnets were, nor, certainly, that he claimed magnets as a new discovery of his own. To the contrary, their writings suggest that, by Thales’s time, magnets and their action were already well known. Incidentally, both the Greek word for “soul” (psuche) and the Latin equivalent (anima) are actually much broader in meaning than is conveyed by the modern English word “soul.” Psuche spans all the nuances of “soul,” “life,” and “mind”; it refers to all things lifelike and to the principle of life itself³. Thales was a proponent of hylozoism—the belief that all material things have life—and, for him, the magnet gave a straightforward demonstration of this doctrine.

We do not know what else Thales may have said about magnets or magnetism, but we do know that he was the first to explain matter in terms of an original substance and was, in this sense, the first to explain natural phenomena in scientific terms. He is said to have claimed that “everything is made of water,” thereby positing water as a substance whose existence preceded everything else and that could be relied on to remain the same, whatever the vicissitudes of nature. Yet if the original substance is unchanging, why then do objects exist in different states, and how can things undergo change? The first attempt at resolving these questions came—to the best of our knowledge—from a fellow native of Miletus, Anaximenes (c. mid-sixth century B.C.). He held air to be the original substance and believed that changes in its density were responsible for changes seen in all other substances:

As it [i.e., air] is condensed and rarefied it appears different: when it is diffused into a more rarefied condition it becomes fire; wind, again, is air moderately condensed; cloud is produced from air by compression; when it is yet more condensed it is water, and then earth; and when it is as dense as possible it is stones.⁴

This idea, presumably, came from the everyday experience of seeing water turn to ice when cooled and to vapor when heated. The positing by Heraclitus (c. 540–480 B.C.) of fire as the original substance can be seen as an extension of the same thinking. In any case, Thales’s water, Anaximenes’s air, and Heraclitus’s fire were all lifelike existences with souls. We can surmise that these three substances were all singled out because of their obvious importance in the sustenance of human life. During this period in history, the universe as a whole was thought to be alive. And magnets were seen as “living proof,” so to speak, of the life to be found in all natural objects, including those that appeared to be inanimate.

The Milesian philosophers thus accepted the world as it was—that is, as they were able to apprehend it via the senses. But in the first half of the fifth century B.C., across the water in Elea, southern Italy, Parmenides (c. 515–445 B.C.) believed otherwise. He held that reason (logos) alone was to be trusted and that the senses deceived. With this deliberate protest against the status quo, Parmenides elevated pure thought, for the first time, to a position of supremacy over sensory perception, counterposing rationalism to empiricism. He argued that it was irrational to discuss the existence of “things that are not” and that therefore there could be no such thing as change or movement: to say that something has changed or moved, we must assume the existence of that which no longer exists (at least not in its former state or at its former position). For this reason, he believed, not only qualitative change but also creation and disappearance as such were mere illusions. The philosophers who came after Parmenides faced the urgent task of determining how to respond to this radical notion of the negation of change.

Those who wished to unseat Parmenides in the latter half of the century included Empedocles (c. 495–c. 435 B.C.), a native of Sicily; Leucippus of Miletus (c. 480–? B.C.); and Democritus of Thracia (460–c. 370 B.C.). While Empedocles originated the so-called four-element theory of matter and Leucippus and Democritus advanced a competing theory called atomism, in fact both camps were attempting to refute Parmenides by advancing a basic strategy, if you will, for understanding nature as something that was ever-changing yet still orderly. Theirs were two separate attempts to establish harmony between, on the one hand, Thales’s idea of a changeless original substance as a first principle in explaining natural phenomenon and, on the other, the diversity and ceaseless mutability of objects seen in everyday life. Empedocles parted company with the idea of a single original substance and instead believed that four elements—earth, water, air, and fire—were the roots of all substances. In contrast, the atoms, or particles, spoken of by Leucippus and Democritus were of varied shapes and sizes, but all were formed from a single substance. In this respect, atomism differed from the four-element theory in its interpretation of Thales’s basic tenet, yet both theories were alike in being reductionist: both held that all the complexity of the natural world, with all the bewildering change and diversity known to man through the evidence of the senses, could and should be explained by just one substance or, at any rate, a very small number of substances.

Where, then, does the magnet fit into all of this? The first attempts to provide a rational explanation for magnetism came, in fact, from both Empedocles and Democritus, and also from Diogenes of Apollonia (c. 450 B.C.), who believed that air was primordial.

In Empedocles’s context, the words “earth,” “water,” and “air” had much broader meanings than they do in modern times, referring, respectively, to solids, liquids, and gases in general. “Fire,” too, denoted not what we would normally think of but rather something akin to what we today would call “energy.” Moreover, for Empedocles these elements did not represent different states, or modes, with the possibility of solids or gases turning to liquid and vice versa. Instead, these were elements in the literal sense of the term: they could be neither created nor destroyed, all substances could be reduced to them, and they themselves could be reduced no further. The four elements did not undergo change, but were combined by “love” and separated by “strife” and thus were mixed in various proportions to form the different substances found in nature. While Empedocles’s terminology strikes the modern ear as a somewhat bizarre example of anthropomorphism, it is more important to realize that his introduction of the concept of “proportion” made an enormous contribution to the later development of the theory of matter.

But in what manner did Empedocles explain magnets? An answer to this question comes to us through Alexander of Aphrodisias (fl. c. 200), who is best known as a commentator on the works of Aristotle. In Quaestiones, Alexander attributes the following explanation of magnetism to Empedocles:

The iron is carried towards the magnet by the effluences from both and the pores of the magnet which are commensurate with the [effluences] from the iron.… For the effluences from [the magnet] push away the air on the pores of the iron and move [the air] which rests on them like a lid; and when this is removed the iron follows the effluence which flows all together. And the effluences from [the iron] travel to the pores of the magnet, and because they are commensurate with them and fit into them, the iron too follows the effluences and is carried [along].⁵

To the best of our knowledge, this was the first theory of magnetism in history to be based on micromechanics, and actually it went much further than just magnetism. According to Theophrastus (c. 372–c. 288 B.C.), a disciple of Aristotle’s, Empedocles described all sensory perception in the same way, theorizing that perception occurred when a substance released some kind of effluence that matched the pores of a particular sensory organ.⁶ In other words, every function or action, whether physical or physiological, could be explained equally in terms of mechanics. We must remember, though, that to some extent Empedocles was a product of his times: in the ancient Mediterranean, there was no clear boundary between the physical and the physiological, between the inanimate and the animate. Empedocles thus believed that all objects had tiny, invisible pores and that all actions with respect to any object—including the process of a living thing perceiving the object via its sensory organs—involved stimulation by invisible fluids or solid particles entering and leaving these pores. Until fairly recent times, this theory served as the definitive model used by mechanists and atomists to explain a wide range of actions.

In his commentary, just after the passage quoted above, Alexander points out that, even if we accept the existence of hypothetical effluences, Empedocles’s theory of how magnets work does not explain why it is only iron that flows toward the magnet—that is, “why … the magnet does not follow its own proper effluences and is [not] moved towards the iron.” Implicit in his critique was the premise that magnets themselves were always stationary.

This premise, in fact, was held during the time of Empedocles as well, almost 650 years earlier. Diogenes of Apollonia was, roughly speaking, a contemporary of Empedocles’s. According to biographer Diogenes Laertius, Diogenes of Apollonia (like the earlier Anaximenes) subscribed to monism:

Air [claimed Diogenes of Apollonia] is the universal element … Air by condensation and rarefaction generates the worlds.⁷

In this respect Diogenes of Apollonia differed from Empedocles, but the two had similar notions about magnetism; the former also hypothesized the existence of something similar to effluences in an attempt to explain why magnets and iron did not exert reciprocal force upon one another. His theory, as described by Alexander, was that

all the things that are malleable both naturally emit a certain moisture from themselves and attract it from outside, some more and some less, but that bronze and iron emit most, a sign of which is both that something is burnt off and consumed from them in fire, and also that when they are smeared with vinegar and olive-oil they rust; they are affected in this way because the vinegar attracts the moisture out of them.… The iron both attracts and emits more moisture; the magnet, being rarer and more earthy than the iron, attracts more moisture from the adjacent air than it emits. Well, it admits into itself that [moisture] which it attracts that is akin to it, but rejects that which is not. The iron is akin to it, and for this reason it attracts [the moisture] from [the iron] and admits it into itself, and through its attracting of this it draws the iron too [towards itself], on account of the continual attraction of the moisture in it. The iron does not also attract the magnet, because the iron is not so rare as to be able to admit the moisture from it all together.⁸

Essentially, the two men’s theories are very similar, except for Diogenes’s explicit statement that the attractive force between the iron and the magnet is not reciprocal and his use of the word “moisture” instead of “effluence.” Whatever his success, or lack thereof, in addressing the nonreciprocity issue, we can be sure that Diogenes’s theory was among those that came to serve as a prototype to explain magnetic phenomena in mechanistic terms.

Others, such as Democritus, had theories of their own that were different and yet still mechanistic. First, a little background on Democritus: As mentioned earlier, he, along with Leucippus, founded atomism around 400 B.C. Democritus accepted the existence of the void, a concept that had until then been rejected, and he assumed the indivisible atom to be the building block of all existence and to have the properties of impenetrability and extension. He believed that the world was comprised of the void (empty space) and solid atoms, which moved around in the void. He further described atoms as being particles made of a single, homogeneous substance and varying only in size and shape. He held the diversity of what we perceive with the senses to be due to differences in the shape, position, and arrangement of the component atoms. He believed that “each of the shapes when arranged in a different compound produces a different condition,” and further postulated that atoms in sweet things were round and of moderate size, while those in sour things were large, rough, and angular.⁹ Aristotle commented that Democritus “reduces Savours to the atomic figures,”¹⁰ and it was precisely this reductionism—which insists that all characteristics perceived by the senses be explained by the geometrical shape, position, or combination of atoms themselves devoid of such characteristics—that later became the foundation of the atomistic and mechanistic theories that persisted to modern times.

Returning to magnetism, it is said that Democritus produced a work entitled Concerning the Magnet¹¹. This, unfortunately, has been lost to history, so all we can do is to catch a glimpse of its contents through references made by those who came after him.

According to the commentator Simplicius (c. 490–560), Democritus stated that “by nature like is moved by like and things of the same kind are carried towards one another.”¹² Originally, the general belief that like attracts like was most probably a product of hylozoism, with scholars projecting onto the world of inanimate objects their experience of seeing animals...

Table of contents

• Cover Page
• Title
• Copyright
• Preface
• Introduction
• Contents
• Part 1 Antiquity and the Middle Ages
• Part 2 Renaissance
• Part 3 The Dawn of the Modern Age
• Notes
• Bibliography