The First Scientific American

by Joyce Chaplin

  An illustration within an electric treatise of 1748 showed some of these experiments. At the bottom right-hand corner, an assistant rotates a wheel connected to a glass globe, which spins against an experimenter’s hand. The consequent electrostatic charge travels through a metal rod, or conductor. A man standing on an insulating platform grasps the end of the conductor and conveys the charge into his upraised sword, with which he ignites spirits of alcohol that a woman, who is grounded, holds in a spoon. Above them, two children are demonstrating electricity’s effects on chaff. The boy, insulated on a disk of pitch or wax, holds the end of the conductor. He proffers a plate with the chaff in his other hand. The girl, who is grounded, holds another plate above, and the chaff is mysteriously suspended in midair.

  The invention of the Leyden jar in 1746 made electrical experiments even more exciting—and dangerous. This jar was usually a glass container coated with metal plate or foil and filled with water or small pieces of metal shot. (The jar, or sometimes bottle, showed investigators’ conviction that electricity was a fluid.) The apparatus dramatically condensed an electrical charge. With the Leyden jar, “electricians” could see what a stronger electrical force did to the array of materials they had already been testing.80

  Electrical demonstrators reexamined many of the questions about fluids and particles that Franklin had already considered. It was particularly puzzling that electricity exhibited both attraction and repulsion, the two concepts Newton had used to explain gravity. Before he died in 1727, Newton had made many and not always matching statements about electricity. Some of those statements asserted that electricity showed how attraction and repulsion could occur in the same substance, but others were not convinced. Some investigators concluded that there were, in fact, two electrical fluids: electrical attraction and repulsion lay in separate, if related, substances. And Newton’s posthumous critics used electricity to attack his theories. French Cartesians, above all the Abbé Jean-Antoine Nollet (soon to be Franklin’s nemesis), insisted that explanations of electricity should stick to mechanical causes, not unseen forces. Nollet proposed that there was only one electrical substance but that it had two streams, outgoing (“effluent”) and incoming (“affluent”), depending on the material that generated them.81

  Electrical amusements. William Watson, Expériences et observations . . . [sur] l’électricité (1748). HARVARD COLLEGE LIBRARY.

  All of this serious electrical work coexisted with extremely popular feats of autoexperimentation and audience participation. One trick, the Venus Electrificata, ran a light charge over a lady, who could then “repulse” any gentleman bold enough to “salute” her with a kiss. Demonstrations of Leyden jars knocked children backward, stunned trusting assistants, killed small animals, and sent charges through astonishing numbers of hand-holding people. In 1746, Nollet reported that he made 200 monks jump and yelp. No wonder Franklin had been entranced when he saw Spencer reveal the electrical fire in Boston. No wonder he jumped at the chance to play with fire himself.82

  But this kind of experiment was more complicated than anything Franklin had done with his Pennsylvania fireplace. For the new experiments, he would need collaborators, special equipment, an experimental space, and patronage. It was extremely fortunate that he had already managed to guarantee his access to all four.

  Fairy godmothers give glass slippers; Peter Collinson, the English patron of the Library Company, gave his American godchildren a glass “electric tube.” Collinson was, of course, in the habit of sending books and equipment to the library. The glass cylinder he now sent would, when rotated against hands or padding, generate static electricity. The tube arrived early in 1747 and was probably intended for general use. But it was Franklin who, in March, wrote the note thanking Collinson for his “kind present” and “directions for using it.” This is the first extant letter between the two men, initiating a correspondence in which Franklin documented his electrical experiments—and made himself Collinson’s most important American client. Soon after, in July, Thomas Penn, the proprietor of the colony, sent an apparatus, probably one in which the tube could be mounted and rotated. “I never was before engaged in any study,” Franklin reported, “that so totally engrossed my attention and my time.”83

  It was quite an operation: collaborative, sociable, and located in the heart of public life. Franklin named his fellow experimenters, about whom we know quite a bit, but was unhelpfully vague on the place of the experiments, which, as it turns out, has since been demolished. Franklin’s three collaborators were Thomas Hopkinson, Philip Syng, and Ebenezer Kinnersley. Hopkinson was a lawyer, Syng a silversmith (and Junto founder), and Kinnersley a Baptist minister and itinerant electrical demonstrator. Together, the four “electricians” embodied head and hands professions, the sciences, and religion.84

  The Library Company still lacked its own building. Only later would its members use rooms at Philadelphia’s Carpenter’s Hall and, still later, build the group’s current house. In the meantime, the company convened in the west wing of the State House (where the assembly met), on its second floor. The house’s two wing buildings were pulled down in the early nineteenth century; early twentieth-century reproductions now sit where they once did. The second floor of the west wing measured about fifty by twenty-two feet and was divided into two rooms. The best estimate of the size of the room where electricity snapped in the 1740s is that it was perhaps twenty by ten feet. The room would have accommodated a table to hold the electrostatic equipment, half a dozen or so active people who could comfortably move about the table, and spectators who could stand or sit along the walls. Thus, in the colony’s center of government, Philadelphians could perform and witness experimental philosophy in action.85

  In the very first experiments, the ones Franklin described in his first substantial letter to Collinson, he and Hopkinson made their first distinctive observation of “the wonderful Effect of Points [pointed bodies] both in drawing off and throwing off the Electrical Fire.” The Library Company men discovered this effect when they placed a piece of iron shot, three or four inches in size, “on the Mouth of a clean dry Glass Bottle.” Then, attaching a silk thread to the ceiling, they suspended a marble-sized “Cork Ball” to rest on the side of the shot. They electrified the shot and saw the cork jerk back four or five inches, “more or less according to the Quantity of Electricity.”86

  Then someone extended “a long, slender, sharp Bodkin,” or metal pin, within six or eight inches of the piece of shot: “The Repellency is instantly destroy’d, and the Cork flies to” the shot. (In the dark, the bodkin glowed as it approached.) A “blunt Body” had to be placed “within an Inch, and draw a Spark to produce the same Effect.” Moreover, a metal conductor had no effect unless it was attached to some other substance, such as wood, that was a nonconductor. 87

  The Philadelphians discovered other ways to break the charge around an electrified object. They breathed on the air around the shot, sifted sand over it, waved woodsmoke toward it, plunged it in darkness, and lighted it with a candle—all of these did seem to weaken the charge. But sunlight thrown off a mirror had no effect. And smoke from rosin did not affect the repulsion “but [was] attracted by both the Shot and the Cork-ball, forming proportionable Atmospheres round them,” as in diagrams of the planets “in Burnets or Whiston’s Theory of the Earth.”88

  The point of the experiments was to visualize electricity, the invisible fluid—fleeting even when it flashed in the dark. The experimenters sought their quarry by exposing it to different conditions, seeing its reactions, and then assigning it traits. The American experimenters had to verify experiments done in Europe (the directions Collinson had sent with the electric tube had described previous experiments and their terminology, electrify and electrise). And they needed to show that electricity had universal properties; stones had to fall in America as they did in Europe. The Philadelphia experiments were important in confirming that electricity exhibited repulsion, the size and strength of which could b
e manipulated (as when a bodkin approached an electrified object). They also revealed which materials were conductors or nonconductors of electricity.

  But Franklin’s group had also revealed two new properties of electricity: the significance of pointed objects and the importance of nonconductors. Each finding established greater experimental precision. Yes, metal conducted electricity, but a metal point probed the subtle fluid more subtly: the smaller the conductor, the greater its effect on electricity. And the probe performed best when it was itself grounded, placed within a nonconducting substance. Earlier experiments had established that metal conducted electricity and wood did not; the Library Company experimenters helped show that the shape and interaction of these materials were relevant, too.

  Franklin next tackled the biggest question of all: What kind of matter was the electrical fluid? To answer this, he modified an experiment described in the text Collinson had sent. In that trial, the experimenters had stood a man on a nonconducting layer of pitch and then electrified him; anyone who tried to lay a finger on him felt a painful charge. The experiment established that electricity could be artificially concentrated in something as ordinary as a human body. But that did not reveal what it was or where it came from. Did the machine generate it? Or did it already lurk within the air, floor, walls, or experimenters?

  Franklin and his associates did the experiment again. They stood their electrified man on a slab of wax and got the same results. But then they put two men on two wax slabs. One man put his hands against the rotating electric tube, and the other took the “fire” from the machine’s conductor. Surprise! They carried different charges. Each of the two was electrified—a third person felt a painful shock on trying to touch either—but they could also shock each other.89

  Franklin’s Leyden jar experiment. Benjamin Franklin, New Experiments and Observations on Electricity (1754). HOUGHTON LIBRARY, HARVARD UNIVERSITY.

  From this experiment, Franklin argued that electrical matter was present everywhere yet in two different quantities, negative and positive. The man who rubbed the electric tube was “electrised . . . negatively” because he had given his “fire” to the tube; conversely, the man who received the charge from the conductor was “electrised positively”—he had an excess. Two humans had divided the fluid and then brought it back together, with a snap, when they touched. Positive and negative charges were also revealed when these two people approached a third person insulated on wax, who had the usual (meaning equally mixed) distribution of charge—more snaps.90

  Franklin illustrated these principles in a demonstration with a Leyden jar. He placed ajar on a nonconducting base, ran a wire up from its outside bottom, charged the water inside, and then ran a second wire from inside and through its stopper. He let a suspended bit of cork play between the two wires and their different charges, carrying the positive charge from top to bottom until the “Equilibrium” was restored and the cork rested.91

  From this experiment, Franklin argued that electricity’s two states could exist anywhere and were necessary to create an equilibrium, meaning the usual form of electricity itself. “If the Persons standing on Wax touch one another during the exciting of the Tube, neither of them will appear to be electrised” because both were: “The Equality is never destroyed, the Fire only circulating” from tube to human. In electricity itself, the “plus and minus [were] combined and ballanced”; if separated, the charges returned to “Equilibrium” or “the original Equality.” Here is where the concept of fluid circulation helped Franklin visualize electricity, as something that did not change or vanish but simply moved in streams. As well, he stressed that an “Atmosphere” existed around an electrified body and governed its reactions to other bodies that might disrupt this equilibrium. His earlier experiments with heat (which also circulated, formed equilibria, and generated atmospheres) had clearly prepared him to see electricity in these particular ways.92

  Above all, Franklin thought his experiments helped establish knowledge about all matter. Those pointed bodkins confirmed that the electric fluid (and other matter) was composed of particles. The points, because of their narrowed ends, drew electricity “Particle by Particle,” whereas a blunt instrument had the opposite effect. The electric fluid was a perfect example of an imponderable, that is, a weightless, elastic substance. Yet it was distinctive because it had particles that were mutually repellent, hence its positive and negative qualities. And electricity was opposed to solid, or “ponderable,” matter. Each attracted the other—“common Matter is a Kind of a Spunge to the Electrical Fluid.” The latter’s material was “extreamly subtile” and therefore able, like heat, to “permeate common Matter.” A doubter could be convinced by receiving, in the common matter of his or her flesh, “a shock from an electrified Glass Jar.”93

  The glass of that jar itself hinted at matter’s construction. A rotating glass tube could generate an electrostatic charge, but a residual charge would remain in the glass. Franklin demonstrated this by charging a Leyden jar and then pouring its water into another glass vessel. Which was now electrified? Not the one with the water but the original, emptied of the visible fluid but not the invisible fluid of electricity. It was not, after all, the water that contained the electricity. Franklin pondered the implications. “If that due Quantity of Electrical Fire so obstinately retained by Glass, could be separated from it, [perhaps] it would no longer be Glass,” he speculated. If, somehow, electricity could be poured out of all other matter, material reality might alter. There was no way to do that experiment, but it was quite an idea! Lacking a divine ability to drain electrical matter from the universe, Franklin simply observed that a battery need not be shaped like a jar or bottle. In a rare moment of agreement with Nollet, Franklin stated that electricity was a fluid that could exist within planes, as with sheets of glass and metal sandwiched together.94

  From bits of cork, metal, and glass, using their own breath and hands, Franklin and the other Library Company experimenters made some astonishingly assured claims about the nature of matter. Newton had hypothesized that electricity was a great force running through the cosmos, perhaps even unifying the other forces he examined, light and gravity. Franklin had defined protocols for investigating these possibilities—he had made electrical experimentation into a science. The sciences still revealed the wonderful nature of Creation, but the wonders apparently could be controlled and measured. And Franklin had proposed an elegant way to understand electricity—as one fluid with two qualities, negative and positive, that were beautifully balanced in nature. The theory needed neither multiple fluids nor the Cartesian hypothesis of differently configured particles in order to explain electricity’s effects on other forms of matter.

  Yet again, Franklin had discovered an equilibrium. Money, heat, electricity—all circulated, and all returned to a state of balance. A flow of analogical reasoning had brought Franklin to his definitions of positive and negative charges. Because his theory passed from his era to ours—it survived him—we now think of electrical circuits and of positive and negative charges as natural, as simply the way electricity occurs. But these explanations of electricity were highly contingent. Circulation and equilibrium had not always existed as concepts within natural philosophy. Yet they emerged in time for Franklin to use them to describe electricity. Moreover, he had already tested those concepts in his economic writings and his work with heating systems.

  If electricity had been more thoroughly investigated earlier or if its accepted definitions had come later, maybe we would now be thinking that other concepts were “natural” explanations of it—the four humors, perhaps, or capital accumulation. Franklin’s contribution was brilliant because it immediately made sense to his contemporaries, who were likewise weaned on Harvey, Petty, Sanctorius, and Newton—not because he invented concepts specifically for electricity.

  As well as brilliant, the Philadelphia experiments were highly sociable. The tests needed a cast of characters: thinkers to design and modify the exper
iments, standers to perch on wax, rotaters to turn the glass tube, and observers to point out what the nervous and excited experimenters might be missing. And everything depended on a transatlantic economy—note the variety of imported commodities, the electric tube especially but also the silk, cork, mirror, and glass bottle. (To lessen the experimenters’ dependence on imports, Franklin encouraged a local glassmaker, Caspar Wistar, to make glass electric globes.) Unlike in electrical experimentation in Europe, men dominated the Philadelphia experiments. An occasional Venus Electrificata did, however, help show that the Philadelphians could “encrease the Force of the electrical Kiss vastly.”95

  There was no shortage of electrical standers or kissers. People came “continually in crouds” to see the experiments, which spilled over into Franklin’s house. His letters to Collinson used plural pronouns—“us” and “we”—to describe his efforts. Thus, it is impossible for us to know exactly who did what. (Did Franklin stand on a slab of wax? Did his collaborators shock him and laugh?) But the anonymous plural pronouns assured Collinson (and others) that many people saw and believed the American demonstrations. Even when he performed some experiments “alone,” Franklin made a point of “repeating them to my Friends and Acquaintance,” all of whom appeared in Franklin’s communications to Collinson: “We fire Spirits with the Wire of the Phial. We light Candles just blown out, by drawing a Spark.... We represent Lightning.... We electrise a Person. . . . We encrease the Force.” Even in his first letter to Collinson, Franklin had remarked that the electric tube had “put several of us on making electrical experiments, in which we have observed some particular phaenomena that we look upon to be new.”96