THE EIGHTEENTH AND NINETEENTH CENTURIES’ ADVANCES, INCLUDING INQUIRIES IN MAGNETISM AND ELECTRICITY
While I. Bernard Cohen’s claim that the eighteenth century was the “age of Newton” has considerable justification, it overlooks other social and cultural changes that were also essential in shaping the important scientific transformations that led up to the enlightenment of the eighteenth century. We have already witnessed the crucial role that previous technological innovations, such as the invention of the telescope, microscope, astrolabe, etc., along with such mechanical models as Kepler’s clockwork universe and Galileo’s microscopic particles culminating in Newton’s corpuscular-mechanistic worldview played in creating modern classical science. In addition, the earlier Renaissance transition in Europe that rejected the medieval outlook and religious authority as bastions of truth also contributed to these scientific developments that evoked a more empirical, rationalistic outlook, yet these changes still were confined largely to contribution of scholars trained at the major universities.
We shall find that other institutions of change in the eighteenth century, the Age of Enlightenment, which were broader in scope and diversified in nature and not confined to the traditional educational regimes of the seventeenth century, also played a major role. So along with the significant influence of Newton there were other cultural changes, such as the impact of the industrial revolution that introduced new technologies like spinning and weaving machines and steam engines that replaced home guilds by factories and transformed agrarian societies into crowded cities with their slums and unsanitary conditions, along with amenities.
The Industrial Revolution also changed the economic system by introducing mass production and an entrepreneurial and capitalistic economy in the industrial cities, along with a new middle class to replace the traditional aristocratic-peasant division of society. Furthermore, there was a marked change in the religious backgrounds of those engaged in the new investigations from those who were Anglicans and had graduated from the usual prestigious preparatory schools such as Eton and universities like Oxford and Cambridge, to those who were often self-taught and learned from their particular trade, along with being educated in what were called “Nonconformist” educational institutions. As I wrote previously:
Underlying this change in background of the new generation of natural philosophers was the shift of the centers of experimental research from Oxbridge to provincial manufacturing towns like Birmingham and Manchester, the latter with its burgeoning textile industry becoming the leading manufacturing and trade center of the world. The advent of the industrial revolution with its large cotton and woolen mills, as well as expanding industries such as coal mining, ironworks, and steel foundries, not only attracted huge numbers of workers and created a new middle class of wealthy families, it rewarded manual skills, engineering inventiveness, and entrepreneurial shrewdness—the type of practical intelligence characteristic of the new breed of natural philosophers.39
As examples, two of the outstanding English chemists of the period were the Unitarian Minister Joseph Priestley who was the son of a cloth shearer and John Dalton a Quaker whose family income came from cottage weaving, along with the American Benjamin Franklin who, despite leaving school at age ten to help his father who was a tallow chandler and soap maker, became a world famous writer, printer, and statesman, as well as attaining international renown for his electrical experiments.
Thus the new experimental inquiries and industrial ventures were largely made by nonconformists like Quakers, Presbyterians, and Unitarians, as well as the sons of craftsmen whose interests or endeavors were not restricted to the traditional classical studies, but motivated by utilitarian interests and needs. Unable to attend the traditional grammar schools and universities because of their lower family backgrounds and inferior religious affiliations, “Dissenting Academies” were created to meet their different educational requirements. In Birmingham such eminent industrialists, inventors, and natural philosophers as Josiah Wedgwood, Joseph Black, Mathew Boulton, John Wilkinson, Erasmus Darwin (grandfather of Charles Darwin), and Joseph Priestley founded the Warrington Academy in 1757, the most famous of the dissenting academies, and the prestigious Lunar Society about 1775.
In the early eighteenth century, owing to Newton’s discussion of electricity and magnetism in his Queries, these subjects attracted some scientific interest. Newton had included them among the important forces of nature that emanated in space, noting that they attracted small particles at a distance, a fact considered by the ancient Greeks, though still unable to explain how they were produced. The Greeks had discovered that rubbed amber, called “electron” in Greek (from which the term “electric” is derived), along with “Heraclean stones” (later called “lodestones” or “magnets”) had these attracting powers. Yet at the time of Newton, because Descartes and most natural philosophers disavowed “occult powers” acting at a distance, believing that the transmission of forces required some material medium or direct physical contact, it was primarily William Gilbert’s book, De Magnete (On the Magnet) published forty-two years before Newton was born, that brought attention to magnetism and electricity owing to their mysterious forces acting at a distance.
Gilbert was born in 1540 in Colchester County, Essex England. His background is somewhat uncertain, but he is said to have attended the Grammar School of Colchester and enrolled in St. John’s College, Cambridge where he apparently earned BA, MA, and MD degrees. After those studies he traveled on the continent where he may have acquired the Doctor of Physic Degree. In the biographical memoir to his translation of the De Magnete, P. Fleury Mottelay states:
In 1573, he was elected a Fellow of the Royal College of Physicians, and filled therein many important offices, becoming in turn [omitting the dates] Censor, Treasurer, and President. His skill had already attracted the attention of queen Elizabeth, by whom he was appointed her physician-in-ordinary, and who showed him many marks of her favor . . . .”40
As an indication of how he was regarded at the time, the English historian Henry Hallam wrote that he was
the first in which England produced a remarkable work in Physical Science: but this was one sufficient to raise a lasting reputation for its author. Gilbert, a physician, in his Latin treatise on the Magnet not only collected all the knowledge which others had possessed on the subject, but became at once the father of experimental philosophy in this island, and, by a singular felicity and acuteness of genius, the founder of theories which have been revived after a lapse of ages, and are almost universally received into the creed of science. . . . (p. xii)
When De Magnete was published in 1600 it was highly acclaimed because of its exhaustive summary of the previous investigations into magnetism, as well as Gilbert’s own contributions. Galileo declared Gilbert “great to a degree that is enviable”; Dr. William Whewell, a prominent philosopher of science in the nineteenth century, observed that “Gilbert’s work contains all the fundamental facts of the science, so fully examined . . . that even at this day we have little to add to them”; and Dr. Thomas Thomson said “that De Magnete is one of the finest examples of inductive philosophy that has ever been presented to the world” (pp. xii, xiii).
At the time Gilbert’s De Magnete was thought to contain all that was known about the magnet, including his own discoveries. He detected a magnetic force in numerous substances that he called “electrics” and according to historian of science Sir David Brewster, applied “the term magnetic to all bodies which are acted upon by loadstones and magnets, in the same manner as they act upon each other, and he finds that such bodies contain iron in some state or other” (p. xv). In Gilbert’s study of electricity he is credited with introducing for the first time such terms as “electric force,” “electric emanation,” and “electric attraction” (p. xv). He noted its considerable resemblance to magnetism, yet distinguished between the two based on discovered differences.
He regarded the earth to be a vast magnet attributing to its extremities north and south magnetic poles, “calling south pole the extremity that pointed toward the north, and north pole the extremity pointing toward the south” (p. xv). Noticing the inclination and declination of the magnetic needle, he inferred that at the opposite poles the needle would extend vertically, at the equator horizontally, and in between in intermediate directions. This led to the European perfection of the compass and the designation of latitudes and longitudes by the dips in the needle that vastly improved navigation. He created a globe named ‘terrella’ or little earth that could be used in his experiments to represent the poles and latitudes and longitudes of the earth. He also invented what is called a versorium, known as an electroscope, a device consisting of a rotating iron needle positioned on a movable point so that it could rotate freely enabling him to measure the intensity of electrical discharges (p. 79).
Ironically, despite this acknowledged acclaim at the time and that three Latin editions soon appeared with elaborate title pages, it neither commanded much attention in England nor stimulated continuing research until about three centuries after its publication. As Mottelay writes at the very beginning of his translation, “I FIRST entered upon the translation of this, the earliest known published work treating of both magnetism and electricity, in the beginning of 1889” (p. v). Robert Boyle did publish a brief essay on electricity in 1675 making extensive use of the recently invented vacuum pump and insisting that Gilbert’s “electric effluvium” was composed of minute particles possessing the attractive property, nothing being known yet about its repulsive power.
Thus it was not only Gilbert’s book but the research instigated by Boyle and particularly Newton who, as President of the Royal Society, had incited by his Queries the succeeding tradition of electrical research. One of his first acts on becoming president of the Royal Society was to appoint Francis Hauksbee as Curator of Experiments, despite his lack of a formal education, based on his experimental papers on electricity published in the Society’s Philosophical Transactions, thus illustrating my previous claim regarding the backgrounds of the new researchers. As stated by the Duane and Duane H. D. Roller in The Development of the Concept of Electric Charge:
One may guess that his skill at constructing instruments and his unusual genius for experimentation were what brought him into association with the members of the Royal Society . . . to prepare experiments and was paid for doing so. The facilities and associations afforded Hauksbee by the Society must have been a factor in helping him become “the most active experimentalist of his day.”41
Indeed, at Newton’s very first meeting presiding over the Royal Society Hauksbee demonstrated his perfected instrument crucial for his electrical experiments, the air pump used to created a vacuum. At the time there was considerable interest in streaks of light, called barometric light, that appeared above the mercury inside a barometric tube when shaken. Hauksbee discovered that the flickers of light were only produced when the drops of mercury slid down the glass, never when stationary, and only begun when about half the air was removed, increasing in brightness with the rarification of the air but discontinued entirely when all the air was withdrawn. Apparently surmising that there might be some similarity between these illuminations and electricity, he devised an experiment in which in an evacuated chamber he caused amber to be rubbed against wool that produced similar results, suggesting that the barometric light might be electrical.
Next he evacuated a sealed glass globe and found that in rotating it by rubbing it with his hands flashes of light again appeared in the evacuated interior. He then found that a nonevacuated globe when rotated with his hands produced electrification on the surface of the globe, not in the interior. He next discovered that this “charged” glass globe could attract or repel a brass leaf and that when held to his face produced a sensation like an “electric wind.” While detecting that an electric globe electrified a neutral one, he did not realize that this was an example of induced electrification believing instead, based on his effluvial theory, that it was due to the attrition of the effluvial material.
In another ingenious experiment showing how important experimentation was becoming in trying to solve technical problems, he surrounded a central globe with a semicircular wire from which he hung a line of threads above the surface of the globe. He found that with an uncharged spinning globe the movement of the air aligned the threads in the same direction as the air, but that a sufficiently charged globe attracted the threads in the direction of the central globe overcoming the force of the air. Then, pointing his finger at the loose ends of the circular band of threads facing the globe, he found they were repelled, but if directed to the top loop of the threads they were attracted, though he did not recognize the difference between attractive and repulsive forces, thus showing how difficult it is to break with tradition. In summary, while
Hauksbee’s experiments linked barometric light with electric effects, introduced the triboelectric generator, demonstrated the occurrence of electrical influence, and provided evidence of electrical repulsion as well as attraction, his attempts at explaining the phenomena in terms of a material effluvium [perhaps a precursor of Newton’s Æthereal medium] were week, illustrating the importance for scientific progress of theorizing as well as ingenious experimentation.42 (brackets added)
Little is known about the early background of the next contributor, Stephen Gray (1666–1736), other than that he lived as a “poor brethren” in the charterhouse and therefore also was unable to acquire a formal education. To convey an idea of life at the time, the Charterhouse was founded to provide schooling for boys who were “gentlemen by descent and in poverty” and a living for poor brethren who were preferably “soldiers that had borne arms by sea or land, merchants decayed by piracy or shipwreck, or servants in household to the King or Queen’s Majesty” (p. 571). As with Hauksbee, what we know about Gray is limited to his communications with the Royal Society, although how he became involved in electrical experiments is unknown.
Gray’s initial published paper on electricity appeared in the Philosophical Transactions in 1720, then nine years later he divulged to Dr. John Theophilus Desaguliers (Newton’s assistant) and others his discovery that the “electric virtue” of a rubbed glass tube could be conducted by a “packthread” over great distances, more than 650 feet, detecting what is now called “electrical conduction” (p. 330). He also found that the success of the conduction depended upon the nature of the connecting material and anticipated the distinction between “electrical per se” and “non-electrical” noting that rubbing could create the former but that the latter could not be produced by rubbing but only by coming in contact with an electrified body (p. 330).
Anticipating Benjamin Franklin, he also found that when a metal rod with a pointed tip was brought to an electrified object it attracted the electricity in a smooth and silent manner, while a blunt tipped rod produced a bright flash with a sharp snap. But his most important contribution was the discovery that whatever the nature of the “electric virtue” or “electric fluid,” as the electricity was then called, when created it exists independently of the charged source and thus constitutes a separate entity, like gravity, magnetism, and heat. This was reinforced by finding that an unelectrified object can be electrified by bringing it close to an electrified object without touching it, suggesting that the electric virtue by itself existed between the two objects. Again anticipating Franklin, he suggested that this “electric fire” resembles thunder and lightening. For his exemplary research in 1732 he was made a Fellow of the Royal Society (FRS), twelve years after his first submission to the Royal Society (p. 331).
The next contributor not only benefited from the previous electrical research of Hauksbee and Gray, but also from a better education becoming a member of the French Academy of Sciences and a Fellow of the Royal Society. His extended French name, Charles François de Cisternay du Fay has been abbreviated simply to Dufay. Having studied Gray’s experiments eight months earlier, by December 1733 he was able to submit to the Royal Society a summary of his own experiments under seven headings, the first five of which were an extension of the previous research while the sixth presented the discovery of a simple but significance principle of electrification that holds true today. “This principle is that an electrified body attracts all those that are not themselves electrified, and repels them as soon as they become electrified by . . . [conduction from] the electrified body” (p. 331).
Then, due to his asking the acute question of whether the repulsion was restricted just to bodies electrified in the same manner or also applied to those that had been electrified differently, he discovered that when rubbed glass was brought in contact with an electrified resinous substance such as copal, it was not repelled as expected but attracted. Thus his seventh discovery consisted of finding that there
are two distinct electricities, very different from each other: one of these I call vitreous electricity, the other, resinous electricity. The first is that of [rubbed] glass, rock crystal, precious stones, hair of animals, wool, and many other bodies. The second is that of [rubbed] amber, copal, gum, lac, silk, thread, paper, and a vast number of substances].” (p. 333; italics and brackets in original)
It was not then known that the type of electrification produced depends not only on the material of the electrified objects, but also on the nature of the material used in the rubbing: wool, silk, or cat’s fur producing vitreous electricity while rabbit’s fur creates resinous electricity.
Thus Dufay made the important discovery that the same kinds of electrics will repel each other while the opposite kinds will attract. In addition he found that neutral or unelectrified objects, if they can be electrified, can be electrified by either kind of electricity. Though he normally did not speculate about the nature of electrification, instead of accepting an effluvium surrounding the electrified objects he introduced an atmosphère particulière, an “electric fluid” (analogous to the release of caloric fluid or phlogiston in explaining combustion), as the source of the peculiar manifestations when electricity is transmitted from one electric object to another. He also surmised that neutral objects contain an equal amount of the different kinds of electrical fluids (“vitrious” and “resinous”) and that when two objects with different amounts of electricity come in contact, the one with the greater amount will transmit its excess to the lesser one until equilibrium is reached (pp. 333–34).
In Europe the concept of electricity as a fluid produced a flurry of experiments related to its being contained and transmitted like a fluid. Though somewhat different, the concept of an electric “charge” was also introduced based on the analogy of “charging” armaments with gun powder. The term “electric charge” is still retained. A number of experiments, highly dangerous, were performed to show how the electric fluid could be contained and the quantity measured.
Another experimenter was a Pomeranian clergyman named E. G. von Kleist. In 1745 Kleist, an amateur experimenter, performed an experiment with dramatic results showing how electricity could be contained. Using a bottle containing water with a very narrow neck enclosing a nail, while continuing to hold the bottle he electrified the nail and then bringing it in contact with an unelectrified object it produced an intense spark. Still holding the bottle, he touched the nail with his other hand experiencing such a severe shock that “it stuns my arms and shoulders.” If the bottle were removed from other objects it remained charged for some time, showing that it retained the electrification (pp. 334–35).
In 1746 Dutch professor Pieter van Musschenbroek, in another shocking experiment, conveyed the results to the French Academy warning others not to try it. He suspended the barrel of a gun by two long silk threads at each end. Electrifying one end of the barrel from the other he hung a brass wire extending into a glass flask, partially filled with water. “This flask I held in my right hand, while with my left I attempted to draw sparks from the gun barrel. Suddenly my right hand was struck so violently that all my body was affected as if it had been struck by lightning. . . . The arm and all the body were affected in a terrible way that I cannot describe: in a word, I thought it was all up with me . . .” (pp. 334–35). Because of the notoriety of the experiment and since Musschenbroek was a professor at the University of Leiden, it became known as the Leiden experiment and the flask, named the “Leyden jar,” was used in chemistry laboratories when I was a student and is still used today.
Performing electrical experiments had become so popular by the mid eighteenth century that they were conducted by amateurs as well as natural philosophers and were described in popular magazines as well as scholarly journals. The interest was so extensive that it even reached the North American colonies, coming to the attention of Benjamin Franklin, known to many as “America’s first great man of science.” Despite leaving school at age ten to assist his father in his workshop, Franklin became famous as a writer, printer, diplomat, and experimental physicist. Like those in Manchester and Birmingham, he was instrumental in organizing the American Philosophical Society (the first society in the colonies for the discussion of scientific topics); helped establish the Library Company, the earliest lending library in America; and was one of the founders of the Philadelphia Academy and College that later became the University of Pennsylvania.
He was in his late thirties when, in 1743, having attended lectures in Boston by Dr. Spencer from Scotland, he became interested in electrical experiments. Receiving a present of a glass tube from Peter Collinson, a Fellow of the Royal Society, he wrote in his autobiography, “I eagerly seized the opportunity of repeating what I had seen in Boston, and, by much practice, acquir’d great readiness in performing those also which we had an account of from England, adding a number of new ones” (p. 337).
Having achieved financial independence, he was able to devote full time to his experiments and purchase any equipment needed for his research, including the newly invented Leyden jar. In subsequent communications with Collinson in which he describes his initial experiments and in turn receiving reports of electrical experiments abroad, Franklin presents in some detail an experiment on how electrical fluid, or as he called it “fire,” was variously conducted among a number of persons standing on wax insulators.
Without going into the details of the experiments, I shall just relate what he and his collaborators contributed that included the significant introduction of the terms “positive” or “plus” and “negative” or “minus” electrics. As he states:
Hence have arisen some new terms among us. We say B (and bodies like circumstanced) is electrized positively; A, negatively. Or rather, B is electrized plus; A, minus. And we daily in our experiments electrized [objects] plus or minus, as we think proper. To electrize plus or minus, no more needs to be known than this: that the parts of the [glass] tube or sphere which are rubbed do, in the instant of the friction, attract the electrical fire, and therefore take it from the thing rubbing; the same parts immediately, as the friction upon them ceases, are disposed to give the fire they have received to any body that has less. (pp. 340–41; brackets in original)
Despite the fact that Franklin and his associates benefited from the research of others in England and Europe, that in less than four years they were able to formulate a conceptual framework that generally accounted for the experimental results was a remarkable achievement, especially its quantifiability. This was illustrated in their explanation of the function of the Leyden jar. Because on their theory the total electrification was conserved, they showed experimentally that when the inner coating of the jar was positively electrified the outer coating was equally charged negatively, the flow always going from the greater to the lesser amount of electrification, but if connected by a wire equilibrium was instantly established.
Then, in seeking a more fundamental explanation, in a paper entitled “Opinions and Conjectures Concerning the Properties and Effects of the Electric Matter, arising from Experiments and Observations made at Philadelphia, 1749,” he attempted to explain the “electric matter” or “fluid” as consisting of very subtle particles since it penetrated all substances including hard metals. Moreover, if these particles are pliable and repel each other, then the repelling effect can be attributed to them. But while normally repellent, if they come in contact with a neutral object they will be distributed uniformly to maintain the neutrality, while if a conductor loses particles by their being attracted by another object, the remaining particles will attract additional particles to maintain equilibrium.
In answer to a criticism as to how objects can acquire an excess of electric matter if they can retain only a quantity equal to their own particles, Franklin claimed that “in common matter there is as much electric matter as it can contain; therefore, if more be added it can not enter the body but collects on its surface to form an ‘electric atmosphere,’ in which case the body ‘is said to be electrified.’”43 Yet there was a remaining objection. While it was obvious why two positively electrified objects repel each other, when it was discovered that two negatively charged objects also repel, there was no immediate explanation. Why should two bodies possessing less electricity resist sharing some electricity?
As usual when one encounters an anomaly in a theoretical explanation something either has to give or be added. In this case it was German natural philosopher Franz V. T. Æpinus who introduced a resolving assumption.
The revolutionary idea of Æpinus was that in solids, liquids, and gases the particles of what Franklin called “common matter” repel one another just like the particles of the electric fluid in Franklin’s theory. Æpinus’s revision introduced a complete duality. The particles of common matter and of electric matter each have the property of repelling particles of their own kind while each kind of particle has the additional property of attracting particles of the other kind. (p. 343)
Attributing additional electrical charges to the natural particles of a body came to be known as the “two fluid system” analogous to Dufay’s earlier hypothesis of two electric fluids, one vitreous and the other resinous.
However, as usually occurs with scientific explanations, while Æpinus’s resolution explained the anomaly of negatively charged bodies repelling each other despite having fewer electrically charged particles, this explanation raised a further problem, as Æpinus realized. If the particles of common matter also repel each other this conflicts with Newton’s universal law of gravitation that all material objects exert a gravitational attractive force on each other. How could the repulsive force of the negatively charged common particles generate the attractive gravitational forces? Æpinus proposed a counter-explanation to no avail; the resolution was beyond an explanation at the time that would have to await the discovery in atomic physics of variously charged particles.
But despite the theoretical impasse there was sufficient truth in Franklin’s conception of electricity that he was able to draw practical consequences from it that enhanced his international acclaim. Although he was not the first to suggest that there was an affinity between electricity and lightning, he was the first to establish their identity. In an entry in his “experimental notebook” he indicated that there were twelve ways the “Electric fluid agrees with lightning:”
(1) giving light; (2) color of the light; (3) crooked direction; (4) swift motion; (5) being conducted by metals; (6) crack or noise in exploding; (7) subsisting in water or ice; (8) rending bodies it passes through; (9) destroying animals [he has killed fowls by the discharge of several Leyden jars connected together]; (10) melting metals; (11) firing inflammable substances; (12) sulfurous smell.44
In the essay on “Opinions and Conjectures Concerning the Properties and Effects of the Electric Matter” mentioned earlier, he had indicated that pointed objects attract an electrical force at a greater distance and with greater ease than a blunt object. He also expressed his belief that clouds were electrified as seen in bolts of lightning. But never satisfied with just conjectures, these combined documents led him to devise means of testing whether lightning was truly electrical and that clouds too were electrified, along with inventing ways of avoiding being struck by them.
Thus with the help of his son he undertook his famous kite experiment to prove that lightning was indeed a form of electricity. After attaching a wire as the detector to the front of a kite, he then tied to it a long kemp cord that reached the ground on the end of which was fastened a key and a silk ribbon for insulation. At the outbreak of a storm they raised the kite and ran into a shed after allowing the cord to become wet to increase its conductivity. Holding the kite by the dry silk ribbon so as not to be electrified, as expected a bolt of lightning from a passing cloud struck the wire detector and was transmitted through the cord to the key where it was then collected into a Leyden jar as proof of its electrical nature.
In another variation of the experiment, attaching a pointed metal rod to the peak of his roof he hung from it a long wire descending from the side of the house to a metal frame holding two iron bells with metal clappers. As before, when lightning struck the electrical discharge it was transmitted to the rod down the wire to the iron bells which produced a clanging sound. Owing to these experiments, lightning rods were installed on the tops of buildings and church spires to deflect lightning from striking them and causing a fire. Although others had thought of the possibility of such experiments and protective devises Franklin was unique in actualizing them.
In conclusion, as stated by Duane and Duane H. D. Roller in the book cited previously:
By 1757 the public demands on Franklin’s time had become so great that he ceased completely the experimentation that had already earned him the reputation of the foremost electrical scientist of his day.
By this time he had received the Copley Gold Medal, which is the highest distinction that the Royal Society can bestow, and had also been elected a Fellow of the Society. In 1773, the French Academy of Sciences made him a “foreign associate,” an unusual honor and one that was not to be accorded to another American scientist until a century later. (p. 607)
The growing confidence in the progress of science due to acquired scientific explanations confirmable by experimental evidence and expressed in the language of mathematics, as proposed by Galileo and Newton, having been reinforced by the electrical investigations, especially Franklin’s quantification of electrical phenomena, there followed an attempt to ascertain whether one could discover electrical laws comparable to Newton’s universal laws of gravitation. Based on the analogy with Newton’s law that gravity is a function of mass, distance, and gravitational forces, perhaps electricity can be measured in terms of mass, distance, and electrical forces.
In fact the Swiss physicist Daniel Bernoulli invented an electrometer that directly measured the strength of “the electric force between two charged metal disks when they were at known distances apart,” the measurements indicating that “the force varies inversely as the square of the distance between the plates,” conforming to Newton’s gravitational law (p. 610). In another experiment Joseph Priestley, the identifier of oxygen, also confirmed that the strength of the electric force agreed with Newton’s inverse square law. Then French physicist Charles Coulomb devised an “electrical torsion balance” that proved so accurate that he could measure “with the greatest exactitude the electrical force exerted by a body, however slightly the body is charged” (p. 617), confirming that the strength of the repulsive force between two equally electrified bodies varies inversely with the square of the distance.
Again, according to Duane and Duane H. D. Roller, since Newton’s law applies to the attractive force between two objects this also had to be confirmed, as Coulomb succeeded in doing with an “electric raised torsion pendulum” that he also invented (p. 620). The question then was whether the other portion of Newton’s law also applied, that the gravitational force was proportional to the product of the masses (density per volume). Though the concepts of “electric fire” or “electric fluid” would not seem amenable to such a confirmation, Franklin’s hypothesis of bodies being composed of two kinds of particles (a kind of matter) that exert opposite forces, negative for electric and positive for natural matter, suggested that there was the possibility of a determination if one substituted electric mass” for “gravitational mass.”
Believing it was possible, Coulomb declared that the “electrical force between two electrified objects is proportional to the inverse square law of the distance between them and to the product P of their electrical masses, or f µ P/ d2” (p. 621), again conforming to Newton’s law of gravitation and that became known as “Coulomb’s law.” As Duane and Duane H. D. Roller state:
With this quantification of electrical science, it becomes possible to bring to bear upon its further study the entire weight of mathematical techniques. Eighteenth-century mathematics had to a very large degree developed along lines applicable to Newtonian mechanics, and with the formulation of electrical science in quantitative terms so analogous to mechanics, electricity became thoroughly amenable to mathematical treatment, with striking results in the nineteenth century. (pp. 621–22)
Turning next to the investigation of light, throughout history fire, sun, and sunlight have been of intense interest. The sun was deified as Helios and Sol respectively by the ancient Greeks and the Romans. The Pythagoreans placed fire in the center of the cosmos calling it the “Hearth of the World” and the “Throne of Zeus.” Plato in the Republic declared that “of all the divinities of the skies the sun is the most glorious because it not only . . . gives to the objects of vision their power of being seen, but also their nourishment and existence.”45 It was partly due to its exalted position that Copernicus and Kepler ceded to the sun its central place in the universe, though little was known then about the nature of light and its transmission.
By the time of Newton the two dominant theories of the transmission of light were Descartes’s view that light as seen was the physiological effect on our senses of the “instantaneous pression” of the contiguous motionless particles comprising the fluid vortices of the universe while the other was the wave theory of light held by Robert Hooke, Christiaan Huygens, and others. Yet for reasons presented in our previous discussion of the Opticks, Newton rejected both theories based on his prismatic experiments and corpuscular theory of light. So just as Newton’s Queries in the Opticks stimulated research into the theories of an ethereal medium, gravity, particles, magnetism, and electricity, in the eighteenth century, his Queries from 21 to 31 discussing the properties and transmission of light, especially that it consists of rays composed of corpuscles, encouraged investigations into optics and light.
Though his theory had gained ascendance by the early eighteenth century, it was challenged by Thomas Young in a paper entitled “Outlines of Experiments and Inquiries Respecting Sound and Light” published in the Royal Society’s Philosophical Transactions in 1800. Drawing an analogy with the transmission of sound, Young rejected the particle theory of light in favor of the wave theory that depicted light, like sound, as the undulations of an underlying stationary medium.
Young presented several objections to the corpuscular theory before providing the main evidence in favor of the wave theory. The first was that if light were composed of material particles they would be attracted by gravitational forces so that their velocities would vary with the strength of the gravitational force of the emitting body, yet light seems to travel with an invariant velocity; however, this objection does not apply to waves which, if propagated in an aetherial medium, are not affected by gravity. Second, Young believed that Newton’s explanation that the light and dark rings of light, known as “Newton’s rings,” are caused by the partial reflection and transmission of the light particles when directed through two lenses separated by a film of air, described as “Fits of easy Reflection and easy Transmission,” could more reasonably be explained by the refraction of alternating light and dark waves.
As additional support he found that when monochromatic light is projected on a screen that has a circular opening the diameter of which is larger than the wavelength of the light passing through, it produces a circular image on the screen behind it. But if the diameter of the opening is about equal to the wave length of the light then a series of alternating light and dark bands indicative of the interference of waves appear on the posterior screen. He found that the latter effect is produced also when two holes very small and close together are cut in the screen and a beam of monochromatic light strikes the screen midway between the two points. In an essay titled “On the Theory of Light and Colors,” published in 1802, he described these bands as being “constructive (in phase) and destructive (out of phase) interference.”46
Despite the nearly incontrovertible evidence, as an indication of how strong Newton’s influence was at the time and how difficult it is for even some scientists to question or reject their theories, Henry Brougham described Young’s paper as “destitute of every species of merit . . .” (p. 19). However, Young’s conclusions did resonate in the thinking of a gifted French engineer, Augustine Jean Fresnel, who rejected the corpuscular explanation of diffraction declaring that it had been refuted experimentally. When, in defense of the corpuscular theory, the supporters maintained that the diffraction patterns in Young’s experiment were produced by the edges of the circular holes deflecting the particles passing through, Fresnel tested the explanation by altering the shape and the mass of the holes and finding that it had no effect at all, the diffraction pattern depending only on the relative sizes of the apertures and the wave lengths of the monochromatic waves.
He then supplemented Young’s experiments by attributing mathematical dimensions to the properties of the diffracted waves. As we now know, the properties of particles and waves are the converse of each other: particles having a discrete location in space with various shapes and sizes, possess mass and momentum along with the energy of motion, and interact by deflection with a loss of energy. In contrast, waves are defined by their lengths, frequencies, amplitudes, and intensities, are diffused in space as wave trains, and interact to reinforce if in phase or destruct if out of phase. As described by Peter Achinstein:
[Fresnel’s] account is much more sophisticated than Young’s, not only because it is quantitative, but also because in determining the resulting vibration . . . Fresnel derives mathematical expressions for the amplitude of the vibration at any point behind the diffractor, and for the light intensity at that point. From these he infers the positions and intensities of the diffraction bands—inferences that were confirmed experimenally. (p. 21)
Fresnel was awarded a prize when he sent his results in a “Memoir on the Diffraction of Light” to the Paris Academy in 1819.
As optical investigations continued further evidence was discovered to support the wave theory. The initial inability of the wave theory to explain the polarization of light emerging from Iceland spar due to the assumption that light waves were transmitted longitudinally, running lengthwise like sound percussions, was surmounted when they were discovered to be produced by transversal vibrations (up and down) perpendicular to their direction of movement. Because of being transversal when they are reflected through Iceland crystal the latter’s internal structure separates the vibration into perpendicular directions, thus the emerging light is polarized at right angles to each other.
Fresnel was even able to rebut the main optical evidence that had convinced Newton of the superiority of the corpuscular theory: the sharp outline of shadows cast by large objects when deflected by light. Fresnel argued that one can explain the sharp outline as due to the large object’s obstruction of certain waves at the edge of their propagation, but if one reduces the size of the object to the magnitude of the light wave then the light bends around the object as sound waves do. Finally another crucial test could be made based on the change of the velocity of light when passing through a lesser to a denser medium.
Newton had predicted that on the corpuscular theory the greater gravitational attraction of the denser medium would cause an acceleration of the light particles while on the wave theory the diffraction of the light would cause a retardation of the velocity. In a series of ingenious experiments now cited as experimentum crucis (critical experiments) begun in 1850, by French physicist Jean Léon Foucault confirmed that water or glass impedes the velocity of light in accordance with the wave theory. Then, based on these results, another French physicist named Hippolyte Louis Fizeau determined the velocity of light to be 300,000 kilometers per second, or 186,281 miles per second.
Illustrating how the correct paradigm of scientific inquiry leads to the determination of the relative truth of hypotheses, along with opening up new vistas of discovery, by the middle of the nineteenth century, Huygens’s wave theory of light had superseded Newton’s corpuscular theory, although radically new interpretations were yet to come, including the discovery that light was a form of electromagnetism, and the twentieth-century discovery that it can exhibit either wave or particle properties depending on the experimental conditions.
As for the discovery of electromagnetism, since ancient times electricity and magnetism were considered separate phenomena. But then in the winter of 1819–1820 Hans Christian Oersted (1777–1851), professor of natural philosophy in Copenhagen, during a course of lectures wondered if an electric current might have an effect on a magnetic needle. To test the supposition he placed an electrified wire at a right angle to the north south axis of a compass to no effect. Deciding to align the electrified wire parallel to the N-S axis he was surprised to find it produced a pronounced deflection of the needle, showing a relation between electricity and magnetism.
This was supported by Michael Faraday (1791–1867), a bookbinder’s journeyman who apprenticed at age thirteen and therefore had little formal education but became an outstanding scientist, again showing the more common backgrounds of these later scientists. Attracted to science, he began attending the lectures by Sir Humphrey Davy at the Royal Institution in London becoming a member in 1823 and then a fellow of the Royal Society the following year. In 1833 he attained the position of Fullerian Professor of Chemistry at the Royal Institution. By then his reputation was such that he was offered knighthood and the presidency of the Royal Society but declined both. He is especially noted for his discovery of electromagnetic induction.
It had long been known that when iron filings were spread on a sheet of paper and a magnet placed underneath, the filings became aligned in a curved pattern around the magnet that, according to Sir Edmund Whittaker, “suggested to Faraday the idea of lines of magnetic force; or curves whose direction at every point coincides with the direction of the magnetic intensity at that point. . . .”47 He then discovered that a moving magnet brought near an electric circuit induced a current, just as Oersted had found that an electric current changed the magnetic direction of the compass needle. As Whittaker continues:
Faraday found that a current is induced in a circuit either when the strength of an adjacent current is altered, or when a magnet is brought near to the circuit, or when the circuit itself is moved about in presence of another current or a magnet. He saw from the first that in all cases the induction depends on the relative motion of the circuit and the lines of magnetic force in its vicinity. The precise nature of this dependence was the subject of long-continued further experiments. (p. 172)
Faraday’s realization that a magnetic field can induce an electric current combined with Hans Christian Oersted’s complementary discovery led to the conception of an independently existing electromagnetism either as a field or a current due to the interactions, replacing the previous conception that they were fluids. Reinforcing again the importance of mathematics in modern science, James Clerk Maxwell (1831–1879), based on these experimental discoveries, formulated intriguing equations describing the structure of electromagnetic fields and how they change in time due to the interactions. It was Maxwell’s equations that implied that the velocity of the propagation of the waves of the electric field is identical to that of light indicating that light too is a form of electromagnetism.
This was confirmed towards the end of the nineteenth century when Heinrich Hertz (1857–1894) experimentally proved the existence of electromagnetic waves having the same velocity as that of light. Because electromagnetism involves the interaction of contiguous fields rather than forces emanated by discrete physical bodies in space as in Newtonian science, the conceptual framework of electromagnetism represents the beginning of the third scientific revolution that transformed our conception of reality. In their book The Evolution of Physics, Albert Einstein and Leopold Infeld declared that the “theoretical discovery of an electromagnetic wave spreading with the speed of light is one of the greatest achievements in the history of science.”48 Indeed, it was these developments that made possible the later introduction of radar, electric power, telegraphy, radio, television, the internet, and so forth. As Carl Sagan states in The Demon-Haunted World: Science as a Candle in the Dark, this “has done more to shape our civilization than any ten recent presidents and prime ministers” (p. 390).