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was removed, increasing in brightness with the rarification of the air but discontinued entirely when all the air was withdrawn.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,’ i
n 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.
Three Scientific Revolutions: How They Transformed Our Conceptions of Reality Page 10
