§41. Blood and Iron

William Gilbert, a prominent physician, published an experimental study of magnetism, De magnete, in 1600. The work has been called “the first learned book on experimental physics.” In his “Preface to the Candid Reader,” Gilbert says his work is a “new sort of philosophizing,” one that does not abide in the library but ranges abroad in nature, seeking its phenomena.

Gilbert's De magnete swallows whole the work of the same name by Petrus Maricourt (§27), as well as other authorities whom scholars had been citing to each other about magnetism for centuries. But Gilbert does not stop there. What makes his voice different is to have learned deeply from technical, ar­tisanal, and navigational literature and technology. He investigated mining, metallurgy, navigation, nautical instruments, astronomy, and the medical effects of magnetism, and personally manufactured the wrought iron used in his experiments, some of which simply repeat the processes of contem­porary iron manufacture. He tried to translate all of this experience into the language of scholars on behalf of a new, experimental direction in natural philosophy.

De magnete is a work of self-consciously experimental natural philosophy from a time before such research absorbed the mechanical ideas that would become the signature of seventeenth-century experimentalism in Galileo, Torricelli, Boyle, Hooke, and Newton.

The first report of the experiment is by Robert Norman in The Newe Attractive (1581), a work on magnetism that was important for Gilbert. Norman was a maritime instrument maker and self-t rained mathemati­cian and experimentalist. There were no few such men in England at that time, mathematical mechanists, untrained by the universities, practical men working in navigation, instrument-making, cartography, and surveying. Mastery of sometimes complex and precise instruments was central to their art. For them, instruments like the astrolabe were problem-solving devices, not tools of investigation. They also sustained vernacular textbook traditions in astronomy, geometry, arithmetic, surveying, navigation, cartography, fortifications, and gunnery.

The working philosophy of these “mechanics” was that mathematics is the basis of all their advances. It is widely applicable and its application can be tested and advanced though trials facilitated by instruments. These math­ematical practitioners independently established their own experimental method of investigating. Norman emphasized their experimental norm in The Newe Attractive, where he strikes the very note that Gilbert will in his preface. He builds on “exacte triall, and perfect experiments,” and criticizes those working on the problem of magnetic inclination who “have more followed their bookes than experience in that matter.”¹⁴⁰

There is a reason why Gilbert, a physician, turned to work on magnetism.

Gilbert’s originality was first to have the audacity to imagine that the whole earth could be a magnet, then to appreciate that experimental techniques gleaned from Petrus and Robert Norman would allow him to demonstrate that proposition, and finally to propose the result as a solution to the problem in Copernicus. The earth is a giant loadstone, and experiments confirm that spherical magnets rotate. Given that the earth is such a magnet, it is capable of spontaneous circular motion about its axis and of keeping itself in a par­ticular orientation, as Copernicus postulates. Circular motion “is innate in the terrestrial globe and natural to it.” That is why all of Gilbert’s lodestones were spherical, though he knew a bar magnet displays the same phenomena. He wanted readers never to forget the analogy with the earth, even calling his spherical magnets terrellae, little earths, and attributing the phenomenon of terrestrial gravity, the earth’s constant orientation in space, and its daily rota­tion to planetary magnetism.¹⁴¹

Tradition attributes to Thales the argument that self-movement in lodestones proves they are alive. The conclusion still looks right to Gilbert. “The magnetic force is animated or is similar to the soul.” The earth, being a magnet, is alive, and like everything alive its movement is purposeful.

The ontology of Aristotle’s physics is refuted; the earth is a magnet, and cannot be reduced to elemental earthy qualities. Gilbert says of the four elem­ents and primary qualities, “We may leave them for cockroaches and moths to prey upon.” His natural philosophy promotes a universe in which space is isotropic; celestial and terrestrial regions are uniform in materials and laws, with a single element at once magnetic and vital, and planets moving in a Copernican way through a vacuum.¹⁴²

Twenty-eight years after Gilbert’s De magnete, William Harvey, a Padua- trained doctor and physician to James I and Charles I, published his exper­imental work On the Motion of the Heart and Blood in Animals (1628). The work established once and for all that blood circulates in distinct systems of veins and arteries. “It is absolutely necessary to conclude that the blood in the animal body is impelled in a circle, and is in a state of ceaseless motion.” This had still not been cleared up. Erasistratus, in Alexandria in the third cen­tury bce, demonstrated the operation of cardiac valves, but was baffled by his discovery. He thought pulse was a contraction of the arterial walls and that arteries, filled not with blood but colorless pneuma, were a distinct system from the veins. What were valves for? Galen refuted the bloodless artery, but the rest remained the state of cardiology to Harvey’s time.¹⁴³

Galen believed that the heart is not a muscle. It expands forcefully but does not contract, rising up with a vigorous motion, then relaxing, changing shape but not size, a motion natural, vital, but not muscular.

Confronting these standard views, Harvey showed that blood emerges from the heart with force and in quantity. A combination of calculation and experiment convinced him that in a relatively brief period the whole of the blood contained in the body must pass through the heart. Where did it go? Why did the arteries not burst? Baffling, unless possibly “the blood did pass back again... and return into the right ventricle of the heart. I began to be­think myself if it might not have a circular motion.” That will be his famous conclusion, but circulation does not rely on the mechanical idea of a pump, which Harvey criticizes. The heart’s movement is an effect of an innate power of the blood itself; the blood moves the heart, not vice versa. Harvey says we must not suppose “that the blood has... motion or heat as the gift of the heart.... I hold that the innate heat [i.e., blood] is the first cause of di­lation and that the primary dilation is in the blood itself.” In his Anatomical Exercises, he draws attention to the movement of the heart. “This motion [cardiac distension, diastole] proceeds from the blood... provoked [irritari] to the motion of contraction by the distending blood.”¹⁴⁴

Blood is not for Harvey what it was for Aristotle, who considered it to be the final stage of material nutriment for the body. For Harvey, blood is the first unity of body and soul and constitutes an organism. Innate heat is present in the blood in its first appearance in the egg. Imitating a famous passage in Aristotle’s Generation of Animals, Harvey writes, “In the blood there inheres spirit or some power acting beyond the powers of the element (most con­spicuous in the nutrition and preservation of each particular part of the an­imal), a nature, nay a very soul, in that spirit and blood, which corresponds to the element of the stars.” Blood possesses both sense and motion: “Now that both senses and motion are in the blood is obvious from many indications, although Aristotle denies the fact” “The blood perceives things that tend to injure by irritating, or to benefit by cherishing it”¹⁴⁵

Like Gilbert he feels he is doing something new in natural philosophy.

The idea of circulation was not universally admired among his medical peers. Some thought it was the sort of “hypothesis” that Hippocrates urged physicians to eschew. It must be said that Harvey made no effort to explain the medical significance of circulation and seemed indifferent to the criticism of medical irrelevance. He sees his conclusions as philosophical, not medical. Renaissance anatomist Fabricius, Harvey's teacher at Padua, trained students to view anatomy as natural philosophy, not an adjunct to medicine, which to Harvey meant that anatomy must be comparative. He scorns anatomists who study “one animal only, namely man—and that one dead” Harvey dis­sected anything he could get, even insects. His work on the motion of the heart is a systematic interpretation of circulatory phenomena in all animals. Structures are observed to vary in different organisms or under different conditions; hypotheses are formed on the cause; then predictions deduced and falsification pursued either by experiment or further comparison.¹⁴⁷

Galen thought that careful observation allowed the anatomist not only to visualize an organ clearly and distinctly, but also to appreciate its pur­pose and the divine wisdom it expresses. Like a medical empiricist, Harvey dismisses that as superfluous theory. No observation will reveal why the blood circulates. These final causes are difficult if not impossible and therefore irrelevant, not just for medical practice but for physiology and nat­ural philosophy. That is a new idea. The medical empiricists of antiquity did not say the rationalists’ theories were wrong, only that they were irrelevant to healing. Harvey transposes this attitude from medicine to physiology. What makes no difference to experiments and observations has no claim to scien­tific credibility.¹⁴⁸

For Aristotle, perception cannot produce understanding until a universal forms in the mind. Unconsciously retracing Ockham on intuitive cognition, Harvey turns this thinking on its head. The observations are unimpeachable, but as we retreat from observation into memory, concepts, and universals, we deal with abstractions of diminishing cognitive qualification. “It behooves him, whoever is desirous to learn, to see anything which is in question, if it be obvious to sense, and sight, whether it be so or no, or else be bound to believe those that have made trial, for by no other clearer or more evident certainty can he learn or be taught.”¹⁴⁹

Aristotle thought we had to activate the epagogic power of nous to discover the universal in observations. For Harvey (as for Bacon), we have to struggle to keep observation free of the obstacles an undisciplined mind is susceptible to. He repeats Democritus’s argument for the superiority of sensations. “That which we discover by the senses is more clear and more manifest to us than that which we discover by the mind, because the latter springs from these sensible perceptions and is illuminated by them.” He draws Bacon’s conclu­sion, which was also Galileo’s, and Galen’s before them all: “Without the right verdict of the senses controlled by frequent observations and valid experi­ence, we make judgments entirely on phantasms and apparitions inhabiting our minds.”¹⁵⁰

Harvey became the “English Democritus.” He was selected for the epithet by physicians seeking an alternative between medical quackery and dog­matic orthodoxy. It was easy for university graduates to deride the empirical investigation of new therapies (for instance, vaccination), but it was also easy for egregious empirics to cheat the public. The usefulness of experiments must be affirmed against the dogmatic followers of school authority, and the best vigilance against quackery is to make medicine a branch of experimental natural philosophy, a program thought to require a better medical ancestor than Hippocrates. The favorite was Democritus.

By the mid-seventeenth century the Abderian’s name had acquired a nimbus of wisdom and sober morality that gave it greater authority than that of Epicurus, still despised for atheism. Dante left Democritus in limbo but consigned Epicurus to the sixth circle of Hell. Hippocrates is rightly praised for attention to empirical observation, but physicians are urged to natural in­vestigation, which was the greatness of Democritus. He became an image for the right combination of scrupulous observation and experimental method grounded in a corpuscular natural philosophy. Walter Charleton, a physi­cian and atomist in natural philosophy, described the London College of Physicians as “genuine sons of Democritus,” who with “admirable dexterity and skill anatomize without confusion of the smallest organ, and instantly explore the proper office of each Organical part” Harvey embodied this Democritean physician (“our Democritus Londinensis”), who uses experi­ment to inquire into principles of nature, deriving benefit for both the art of medicine and the improvement of natural philosophy.¹⁵¹