The Natural Philosophy of William Gilbert and His Predecessors

In Short

W. James King’s historical essay re-evaluates De magnete (1600), the celebrated treatise by Elizabethan physician William Gilbert. By contrasting Gilbert’s explanations of magnetism and electricity with those of ancient Greek thinkers, scholastic philosophers like St. Thomas Aquinas, and Renaissance scholars, King demonstrates that Gilbert was not a sudden, modern revolutionary. Instead, he acted as a modifier of medieval Aristotelian traditions. Through biological analogies, material effluvia, and formal powers, Gilbert synthesized empirical observations from craftspeople and scholars into a comprehensive "magnetic philosophy" that treated the Earth itself as a giant loadstone.

The Story

King’s narrative re-evaluates the origin story of modern physical science. It opens with the long-held tradition crediting William Gilbert’s 1600 work, De magnete, as the foundational breakthrough for the modern study of electricity and magnetism. King sets out to test this assumption by examining Gilbert’s actual debts to his predecessors. The arc begins in antiquity and the Middle Ages, where early thinkers attempted to explain why a loadstone moves iron. Thales and Plato invoked animistic souls inside the stone, while scholastic philosophers, led by St. Thomas Aquinas, incorporated the loadstone into an Aristotelian framework. Aquinas viewed magnetic attraction as an "occult power" driven by substantial forms and celestial influences, acting through alteration and proximity rather than pure mechanical force.

As the narrative moves toward the Renaissance, King shows how practical craftspeople—such as hydrographer Robert Norman, who discovered magnetic dip—began gathering empirical measurements of compass behavior. Gilbert drew directly on these findings, but his primary ambition was not merely collecting raw data; it was constructing a new physiology, or comprehensive philosophy of nature. Gilbert posited that iron and loadstones are true, primary components of the Earth's core. From this, he made a major conceptual leap: because loadstones possess verticity and alignment, the Earth itself must be a giant loadstone, endowing all its fragments with an innate magnetic nature.

To ground this system, Gilbert systematically separated magnetic forces from electric ones. He argued that rubbed electrics, such as amber, emit a material, vaporous "spiritus" or effluvium derived from internal moisture, which physically reaches out, enfolds nearby light bodies, and draws them back. Magnetic attraction, by contrast, is not a one-way mechanical pull by a material vapor. Gilbert defined it as coition—a mutual, concerted action ("conactus") where both bodies act, react, and move together toward formal unity within a surrounding sphere of influence, the orbis virtutis.

King closes his study by tracing how Gilbert’s contemporary and subsequent readers received his grand cosmological vision. Francis Bacon dismissed Gilbert’s magnetic philosophy as an overextended system built from a single narrow study—an "Idol of the Cave." Later XVII-century experimenters like Robert Boyle and Sir Thomas Browne largely bypassed Gilbert’s qualitative forms in favor of corpuscular theories. Yet, two primary architects of the scientific revolution found immense value in his work: Galileo used Gilbert’s turning Earth-magnet to support Copernicanism, while Kepler adapted the loadstone’s directional power into a physical framework for planetary motion. Ultimately, King reveals that Gilbert was not a fully modern physicist born out of time, but a masterful bridge between medieval scholasticism and early modern science.

How It Unfolds

The medieval inheritance Scholastic philosophers interpret magnetic attraction through Aristotelian concepts of matter, substantial form, and celestial influence. St. Thomas Aquinas treats the loadstone's ability to draw iron as an innate, occult quality imparted by the heavens.

The empirical shift Navigators, chartmakers, and instrument makers, including Robert Norman, begin measuring the physical behaviors of magnetic needles. Gilbert draws upon these practical observations to construct a unified theory of the loadstone.

The Earth as a loadstone Gilbert argues that iron and loadstones represent the uncorrupted matter of the terrestrial interior. He concludes that the Earth itself is a giant magnet whose primary form governs its axial orientation and internal cohesion.

Distinguishing electricity from magnetism Gilbert classifies attractions into two distinct categories: electric and magnetic. Electric attraction relies on physical, vaporous effluvia emitted by rubbed, moist substances, while magnetic coition operates through a shared formal energy.

The dynamics of coition Rather than viewing magnetism as a passive object pulled by an active agent, Gilbert introduces "coition" as a mutual effort. Magnetized bodies enter an alliance within their surrounding orbis virtutis to restore formal unity.

The legacy weighed While later mechanical philosophers like Robert Boyle reject Gilbert's organic explanations, Kepler and Galileo adapt his concept of a magnetic Earth to explain planetary movements and defend the Copernican system.

The People

William Gilbert The Elizabethan physician and natural philosopher at the center of the book. Gilbert seeks to organize scattered empirical data on loadstones into a complete, grand "magnetic philosophy." He aims to prove that the Earth is a giant magnet possessing a living, primary form, though his reliance on organic analogies ultimately ties his thought to the very scholastic tradition he sought to modify.

St. Thomas Aquinas The key medieval theologian whose Aristotelian framework established the baseline for pre-modern science. Aquinas seeks to explain how non-tangible forces operate without violating the principle that change requires contact. He treats magnetic pull as a secondary quality, showing how the loadstone alters the nature of iron through an occult power derived from celestial bodies.

Robert Norman An Elizabethan hydrographer and instrument maker whose practical discoveries provide crucial empirical groundwork. Norman seeks to understand navigation instruments, leading him to discover the magnetic dip of the compass needle. His observational work directly stimulates Gilbert to begin his own exhaustive study of loadstones.

Johannes Kepler and Galileo Galilei The XVII-century astronomers who serve as Gilbert’s most significant intellectual heirs. Both seek physical models to explain a moving, heliocentric universe. While critiquing the looseness of Gilbert's philosophical proofs, they adapt his concepts of the terrella and planetary magnetic virtue to support Copernican astronomy.

In Its Own Voice

"From this comparison it appears that Gilbert can best be understood by considering him not so much a herald of the new science as a modifier of the old."

— King introduces his main thesis, challenging the traditional view that Gilbert created modern magnetism out of nothing.

"Instead of an agent and a patient in coition, one has 'conactus.' Coition, as the Latin origin of the term denoted, is always a concerted action."

— The author explains how Gilbert replaced traditional one-way mechanical attraction with a mutual interaction between two magnetic bodies.

"One does not find in De magnete a prototype of modern physical science in the same sense one can in the writings of Galileo and Kepler."

— The book concludes by defining Gilbert's true historical value as an exemplar of Renaissance philosophy rather than modern physics.

What It's Really About

King’s essay explores how scientific revolutions actually occur, arguing against the myth of sudden intellectual breaks with the past. By placing De magnete alongside medieval treatises, King demonstrates that groundbreaking discoveries often remain deeply wrapped in the terminology, assumptions, and worldviews of the eras that preceded them. The text investigates the tension between empirical craft knowledge—gleaned from sailors and instrument makers—and the formal, philosophical frameworks used to explain it.

At its core, the work examines how concepts evolve across generations: Gilbert's anthropomorphic "primary forms" and qualitative "spheres of virtue" were not modern physics, yet they provided the necessary conceptual stepping stones that later thinkers transformed into quantitative fields of force and universal laws of motion.

Why Read It Today

This concise study is an ideal read for readers interested in the history of ideas, the evolution of scientific thought, and the true intellectual climate of the Renaissance. King writes with clarity and restraint, cutting through historical hype to offer a grounded look at how scientific concepts are reshaped over time.

The reader should be prepared for dense conceptual terrain. King quotes medieval Latin passages from St. Thomas Aquinas, Petrus Peregrinus, and Gilbert himself, while grappling with scholastic philosophy, formal causes, and early modern definitions of "effluvia" and "substance." Yet this technical density is precisely what makes the essay so rewarding. It places the reader directly inside the mindset of late XVI-century natural philosophy, where magnetism was viewed through biological analogies of growth, decay, and bodily humors. What lingers after finishing King’s essay is a richer appreciation for the messy, continuous nature of discovery—showing that even our most revolutionary ideas are built using the language and tools of the past.