• From the Scientific Revolution to Volta and Galvani

Scientific thought dating back to Aristotle was heavily focused on reasoning and thought experiments; hence the name “natural philosophy.” The scientific method as we know it today did not exist until thinkers like Immanuel Kant, David Hume, Sir Francis Bacon and Roger Bacon outlined its steps. Natural philosophy advanced to the scientific method known today with the advent of empiricism; the process of observing a problem, hypothesizing an answer and conducting experiments to test the hypothesis finally allowed science to move beyond its medieval stagnation.

In 1600, during the very beginning of the Age of Enlightenment, an Englishman named William Gilbert made a breakthrough on the topic of electricity.

Gilbert, who later became court physician to Queen Elizabeth I, wrote a work that outlined his theories of magnetism and electricity; the treatise, called De Magnete for short, has been described as the “beginning of the science of electricity” (Baigrie 10). Gilbert explained magnetism through his belief that the earth was a giant magnet, or terrella. Importantly, he coined the term “electricity” to explain the force of attraction in “electrics”—his term for electrified objects. He was the first to include objects other than amber in the list of objects that could be electrified. He outlined a theory of electricity that would last for centuries: the force behind electric attraction was an invisible liquid, or effluvium, that responded to electrical charge by pushing the “electrics” together or apart. He describes effluvia as more like a force than a physical substance.

The mathematician and philosopher René Descartes was responsible for the next evolution in electrical theory.

Descartes believed that all natural phenomena could be explained through physical, mechanical effects; he rejected the idea of unseen forces, a component of the effluvia theory in his era, as scientifically inadequate. In 1644, Descartes published a piece asserting that magnetism is caused by mechanical actions, not unseen forces. His explanation of magnetism involved the movement of minute particles, but had many complicated and contradictory aspects.

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Robert Boyle (1627-1681), who is best known for Boyle’s law of gases, was inspired by Descartes’s theory of the “mechanization of matter.” He elaborated on and refined Gilbert’s theories of electric attraction in results he published in 1675.

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-The first electrostatic generator was invented in 1660 by Otto von Guericke (1602-1686). The generator consisted of a quickly rotating shaft with a sulphur ball on the end; it was difficult to use and therefore did not gain popularity. Guericke was the first to observe that charge could travel through a linen thread (the principle of electric conduction) and that similarly electrified bodies repelled one another, but he did not follow up on these observations. Guericke is best known for his work with vacuums, which helped to discredit Aristotle’s idea that “nature abhors a vacuum.”

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In 1687, Sir Isaac Newton’s monumental work Principia Mathematica changed existing theories of physics and mathematics. Although Newton (1643-1727) was instrumental in changing scientific thinking in his age, his experiments into electricity were modest—he trapped bits of paper under glass and charged the glass through rubbing, causing the paper bits to move. He concluded that glass could be an electric, and that “effluvia” could penetrate it effectively.

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The first precursor to the electric lightbulb can be dated to 1709, when Francis Hauksbee (1660-1713), a student of Robert Boyle, built a machine for rotating amber on wool in an air-evacuated vessel. At first he rubbed an air-evacuated ball containing mercury, but later experimented with the ball without mercury. By applying high-speed friction to the evacuated glass ball, he produced a glow within the ball bright enough to read words written in capital letters. It would be 200 years before Thomas Alva Edison made the first commercially-viable lightbulb.

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English scientist Stephen Gray (1666-1736) shook up the effluvia theory by discovering conductivity. When conducting experiments in static electricity with a glass jar, Gray noticed that the cork in its mouth was attracting bits of lint and dust. Gray wondered if the attraction power could be extended beyond the cork. Within a few days of experimentation, he found that he could transmit electricity 765 feet through a packthread and 850 through a wire. He also found that he needed to insulate the conductors from ground contact, and noticed that bends in the conductor made no difference in the transmission. He also dropped the thread off of a tower and noticed that gravity made no difference in the transmission of electricity.

Before Gray’s experiments, it had been thought that the effluvia were inseparably connected to objects, but Gray had shown that electricity could be transmitted long distances. Charles François de Cisternay Dufay (1698-1739) repeated Gray’s experiments and decided that there were two kinds of electricity: vitreous, which came from glass objects; and resinous, which came from objects such as silk, sealing wax and paper. Additionally, Dufay beat Gray’s record by conducting electricity a distance of 1,256 feet on wet packing thread.

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In 1745 the invention of the Leyden jar, the first capacitor, stimulated interest in scientists throughout the world. Dutch scientist Pietr van Muscchenbroek is usually credited with inventing the Leyden jar, although German scientist Ewald G. von Kleist independently created a similar device in the same year. (The device was named after the University of Leyden in the Netherlands, where Musschenbroek was a professor.) During Musschenbroek’s experiments attempting to isolate and trap the static electrical charge, Musschenbroek placed a wire in a cork on a jar of water, then hung the jar from a gun barrel. The gun barrel, which hung suspended from silk threads, received charge from a nearby static electricity generator. When Musschenbroek touched the jar with one hand and the jar with the other, he was surprised by a powerful electric shock.

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Musschenbroek improved the Leyden jar with later experiments by using thinner glass jars and covering both the inside and outside of the jars with tinfoil. He switched the original wire and cork to a stronger brass wire attached to a lid made from a brass knob and varnished wood. He half-filled the jar with water and inserted a wire that had been charged by an electricity generator. Under ideal conditions, the jar could store an electric charge for several days. Musschenbroek also found that by placing multiple charged jars in a metal pan, he could increase their effects.

The Leyden jar experiments inspired scientists around the world to make further experiments in electricity. French scientist Jean-Antoine Abbe Nollet (1700-1770) tested the effects of Leyden jars on animals and plants, improving the design of the jars over the course of the experiments. But the advances in electrical theory made by American founding father Benjamin Franklin (1706-1790) were more significant.

Franklin was fascinated by the Leyden jars, but in America, he was isolated from recent European discoveries. However, his isolation may have helped him develop his independent theories on the nature of electricity. Franklin and his co-experimenters built a hand-cranked electrical generator and acquired a Leyden jar in 1747, and experimented with the effectiveness of a blunt-ended conductor versus a pointed conductor in drawing a charge across a gap. Franklin and his colleagues soon determined that a spark would leap much farther to reach a pointed conductor than a blunt-ended one. This result would later guide Franklin’s invention of the lightning rod.

Franklin developed a new theory of electricity based on his experiments: he hypothesized that there was only one form of electricity. All of objects contained a quantity of “electrical fire” which was activated when an object was rubbed. He called objects that give off electrical fire “electrically negative,” since they lose electrical fire, and objects that gained it “electrically positive.” Today we use the opposite terminology—charged objects are positive and objects receiving charge are negative.

Through further experimentation with Leyden jars, Franklin noticed similarities of behavior between the electrical sparks they produced and lightning. Eager to compare lightning to the flashes within the Leyden jars, he prepared a silk kite with an iron key attached, and during a thunderstorm in July 1752, he performed his famous kite experiment. First, he observed that the kite string’s fibers were standing apart if charged; he then touched the iron key and observed the spark that flew from it. It looked exactly like the charges within the Leyden jars. He brought a Leyden jar up to the key and was able to charge it, showing that the energy within the skies and within the generator used to charge the Leyden jars was the same—it was electricity.

In 1748, Franklin was the first to use the term “battery” to describe a series of Leyden jars. (A battery that is believed to have been owned by Franklin can be seen at the Ben Franklin Tercentenary collection here.) In addition to this important contribution, Franklin invented a series of electrified novelties, such as a toy spider that jiggled its legs when brought close to a Leyden jar and a portrait of King George with an electrified crown that produced a “high-treason” shock when touched. In one grand gesture, he held a picnic in which he butchered turkeys through an electrical shock from a large battery.

While Franklin’s single-fluid theory of electricity resolved some inconsistencies within electrical theory, it left other questions unanswered. For example, why are two objects with the same charge repelled from one another? French engineer Charles-Augustin de Coulomb (1736-1806) built a machine that quantified the strength of this repulsion. Coulomb’s torsion balance experiments allowed him to formulate Coulomb’s law, a key element of electrical theory to the present day. It states that the force of electrostatic attraction or repulsion is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them. (Coulomb was unaware that the reclusive English scientist Henry Cavendish (1731-1810) had independently discovered Coulomb’s inverse square law, but his work would not be published until a century later, through the efforts of Scottish scientist James Clerk Maxwell. Cavendish also anticipated Ohm’s law, among many other findings.)

To explain the existence of the opposing or repelling forces, which Franklin’s theory left unanswered, Coulomb reverted to the two fluid-theory of electricity. However, his findings were rejected in England, America and, importantly, in Italy, where two of the fathers of the battery were at work: Luigi Galvani and Alessandro Volta.