From ancient times, people were familiar with four types of phenomena that today would all be explained using the concept of electric charge: (a)
lightning, (b) the
torpedo fish (or electric ray), (c)
St Elmo's Fire, and (d) that
amber rubbed with
fur would attract small, light objects. The first account of the is often attributed to the ancient Greek mathematician
Thales of Miletus, who lived from c. 624 to c. 546 BC, but there are doubts about whether Thales left any writings; his account about amber is known from an account from early 200s. In other words, there was no indication of any conception of electric charge. More generally, the ancient Greeks did not understand the connections among these four kinds of phenomena. The Greeks observed that the charged amber buttons could attract light objects such as
hair. They also found that if they rubbed the amber for long enough, they could even get an
electric spark to jump, but there is also a claim that no mention of electric sparks appeared until late 17th century. This property derives from the
triboelectric effect. In late 1100s, the substance
jet, a compacted form of coal, was noted to have an amber effect, and in the middle of the 1500s,
Girolamo Fracastoro, discovered that
diamond also showed this effect. Some efforts were made by Fracastoro and others, especially
Gerolamo Cardano to develop explanations for this phenomenon. In contrast to
astronomy,
mechanics, and
optics, which had been studied quantitatively since antiquity, the start of ongoing qualitative and quantitative research into electrical phenomena can be marked with the publication of
De Magnete by the English scientist
William Gilbert in 1600. In this book, there was a small section where Gilbert returned to the amber effect (as he called it) in addressing many of the earlier theories, Gilbert is also credited with the term
electrical, while the term
electricity came later, first attributed to Sir
Thomas Browne in his
Pseudodoxia Epidemica from 1646. (For more linguistic details see
Etymology of electricity.) Gilbert hypothesized that this amber effect could be explained by an effluvium (a small stream of particles that flows from the electric object, without diminishing its bulk or weight) that acts on other objects. This idea of a material electrical effluvium was influential in the 17th and 18th centuries. It was a precursor to ideas developed in the 18th century about "electric fluid" (Dufay, Nollet, Franklin) and "electric charge". Around 1663
Otto von Guericke invented what was probably the first
electrostatic generator, but he did not recognize it primarily as an electrical device and only conducted minimal electrical experiments with it. Other European pioneers were
Robert Boyle, who in 1675 published the first book in English that was devoted solely to electrical phenomena. His work was largely a repetition of Gilbert's studies, but he also identified several more "electrics", and noted mutual attraction between two bodies. Through these experiments, Gray discovered the importance of different materials, which facilitated or hindered the conduction of electrical effluvia.
John Theophilus Desaguliers, who repeated many of Gray's experiments, is credited with coining the terms
conductors and
insulators to refer to the effects of different materials in these experiments. He attempted to explain this phenomenon with the idea of electrical effluvia. Gray's discoveries introduced an important shift in the historical development of knowledge about electric charge. The fact that electrical effluvia could be transferred from one object to another, opened the theoretical possibility that this property was not inseparably connected to the bodies that were electrified by rubbing. In 1733
Charles François de Cisternay du Fay, inspired by Gray's work, made a series of experiments (reported in ''Mémoires de l'
Académie Royale des Sciences''), showing that more or less all substances could be 'electrified' by rubbing, except for metals and fluids and proposed that electricity comes in two varieties that cancel each other, which he expressed in terms of a two-fluid theory. When
glass was rubbed with
silk, du Fay said that the glass was charged with
vitreous electricity, and, when amber was rubbed with fur, the amber was charged with
resinous electricity. In contemporary understanding, positive charge is now defined as the charge of a glass rod after being rubbed with a silk cloth, but it is arbitrary which type of charge is called positive and which is called negative. Another important two-fluid theory from this time was proposed by
Jean-Antoine Nollet (1745). Up until about 1745, the main explanation for electrical attraction and repulsion was the idea that electrified bodies gave off an effluvium.
Benjamin Franklin started electrical experiments in late 1746, and by 1750 had developed a one-
fluid theory of electricity, based on an experiment that showed that a rubbed glass received the same, but opposite, charge strength as the cloth used to rub the glass. Franklin imagined electricity as being a type of invisible fluid present in all matter and coined the term itself (as well as
battery and some others); for example, he believed that it was the
glass in a
Leyden jar that held the accumulated charge. He posited that rubbing insulating surfaces together caused this fluid to change location, and that a flow of this fluid constitutes an electric current. He also posited that when matter contained an excess of the fluid it was charged and when it had a deficit it was charged. He identified the term with vitreous electricity and with resinous electricity after performing an experiment with a glass tube he had received from his overseas colleague Peter Collinson. The experiment had participant A charge the glass tube and participant B receive a shock to the knuckle from the charged tube. Franklin identified participant B to be positively charged after having been shocked by the tube. There is some ambiguity about whether
William Watson independently arrived at the same one-fluid explanation around the same time (1747). Watson, after seeing Franklin's letter to Collinson, claims that he had presented the same explanation as Franklin in spring 1747. Franklin had studied some of Watson's works prior to making his own experiments and analysis, which was probably significant for Franklin's own theorizing. One physicist suggests that Watson first proposed a one-fluid theory, which Franklin then elaborated further and more influentially. A historian of science argues that Watson missed a subtle difference between his ideas and Franklin's, so that Watson misinterpreted his ideas as being similar to Franklin's. In any case, there was no animosity between Watson and Franklin, and the Franklin model of electrical action, formulated in early 1747, eventually became widely accepted at that time. It is now known that the Franklin model was fundamentally correct. There is only one kind of electrical charge, and only one variable is required to keep track of the amount of charge. Until 1800 it was only possible to study conduction of electric charge by using an electrostatic discharge. In 1800
Alessandro Volta was the first to show that charge could be maintained in continuous motion through a closed path. In 1833,
Michael Faraday sought to remove any doubt that electricity is identical, regardless of the source by which it is produced. He discussed a variety of known forms, which he characterized as common electricity (e.g.,
static electricity,
piezoelectricity,
magnetic induction), voltaic electricity (e.g.,
electric current from a
voltaic pile), and animal electricity (e.g.,
bioelectricity). In 1838, Faraday raised a question about whether electricity was a fluid or fluids or a property of matter, like gravity. He investigated whether matter could be charged with one kind of charge independently of the other. He came to the conclusion that electric charge was a relation between two or more bodies, because he could not charge one body without having an opposite charge in another body. In 1838, Faraday also put forth a theoretical explanation of electric force, while expressing neutrality about whether it originates from one, two, or no fluids. He focused on the idea that the normal state of particles is to be nonpolarized, and that when polarized, they seek to return to their natural, nonpolarized state. In developing a field theory approach to electrodynamics (starting in the mid-1850s),
James Clerk Maxwell stops considering electric charge as a special substance that accumulates in objects, and starts to understand electric charge as a consequence of the transformation of energy in the field. This pre-quantum understanding considered magnitude of electric charge to be a continuous quantity, even at the microscopic level. == Role of charge in static electricity ==