Electricity means the presence or motion of electrical charge. When the charge is moving from its source (origin) to sink (destination), it's called electrical current. Electrical charge that simply dwells on an object is referred to as static electricity.
We will explain electricity by drawing an analogy to water in a pipe.
Charge is like the drops of water inside the pipe; it describes a quantity of energy. Charge is proportional to electrical energy and can be positive or negative. The most familiar charged particles are protons and electrons. Protons have a positive electrical charge (+), and electrons have a negative charge (-). Batteries and capacitors can both store electrical charge. It's measured in coulombs, named for Charles-Augustin de Coulomb, and its SI unit is abbreviated as Q.
Current is the motion of electrical charge from higher voltage to lower voltage. Completing or closing a circuit creates an electrical connection that allows current to flow. Magnetic fields can cause or induce electrical current to flow in nearby wires. Electrical power is the amount of electrical energy transferred from source to sink per unit time. A common unit of electrical power is the watt, abbreviated W. Electrical current is measured in amperes, named for André-Marie Ampère, and the SI unit for electrical current is I (from the French intensité du courant).
Resistance opposes the motion of electrical charge. Materials with high intrinsic resistance that don't like to conduct electrical charge are called insulators. High resistance works against the conduction of electrical charge like a valve or choke works against the motion of water through a pipe. The SI unit for resistance is the ohm, named for Georg Ohm and abbreviated with the Greek letter Ω (uppercase omega).
Voltage, sometimes referred to as electrical pressure, is the electrical potential energy embodied in electricity. Electrons flow spontaneously from higher voltage to lower voltage, like water always flows downhill. The SI unit for voltage is the volt, named for Alessandro Volta and abbreviated V.
When electricity seeks a path to lower voltage, as with a bolt of lightning, it is sometimes known as seeking a path to ground. Houses and buildings are built with an electrical connection to the earth, meant to harmlessly dissipate the energy of a lightning strike or power surge. Air is an insulator. However, under high enough pressure, water will force itself through solid rock. Fluids can be compressed, it just takes a titanic amount of energy to force the molecules of a liquid closer together. Similarly, enough electrical pressure will force electrical charge to seek a path to ground through things that are normally not conductive, such as air, fresh water, church steeples, or even the human body. This is why high-voltage power lines are dangerous, requiring special insulators to prevent the electricity in the wires from grounding itself out by traveling down the tower into the earth.
When Was Electricity Invented?
Our words for electricity and electrical energy derive directly from ἤλεκτρον (elektron), the Greek word for "amber." Thales of Miletus, one of the Seven Sages of ancient Greece, recorded observations on the electrical properties of amber in ca. 600 BCE, some six hundred years before the birth of Christ. Rubbed against hair or animal fur, amber acquires a static electrical charge that attracts dust particles. (This is called the triboelectric effect, and it's the reason electrostatic dust filters work. It's also the reason flour sometimes jumps up onto the wall of a mixing bowl, in apparent defiance of gravity.) If you touch the amber, the electrical charge that has built up in the amber suddenly has a path to a lower-energy state, and in equalizing it delivers that energy to your fingertip in the form of a tiny electrical shock.
The philosopher Democritus suggested that all the matter in the universe, however complex, was ultimately composed of tiny, irreducible particles he called atomos. ("A-" denotes the absence or opposite of a thing, while the Greek suffix τόμος or -tómos has the same root word as an -otomy medical procedure in which something is cut.) This school of thought saw atoms as solid objects that interacted with other atoms via mechanical connections, such as a ball and socket or a hook and eye. More than two thousand years after Thales and Democritus, English scientist William Gilbert coined the term electricus in his own work, referring to the triboelectric effect.
Atoms and electrons are discrete and quantized, and electrical charge is quantized for the same reason. In that sense, Democritus and Stephen Hawking agree on the nature of the atom. What Democritus didn't know was that electrical energy is entirely enough to hold things together with as much force as a mechanical linkage; the electromagnetic force is second in strength only to the strong nuclear force. The electrostatic repulsion between two electrons is 10⁴² times as strong as their mutual gravitational attraction.
Humans were aware of electrical energy for thousands of years before anyone understood what electrons or electricity are, which we know because they wrote about electric fish. For example, the electric catfish of the Nile, when full-grown and mature, is capable of delivering a painful 350-volt shock to an assailant or prospective prey: enough to stun an adult human. Ancient Egyptian papyri discuss electric fishes of the Nile basin, such as the electric catfish and the aba aba or African knifefish, calling them "Thunderers of the Nile" and revering them as protectors of all other fish.
Electric catfish appeared in Egyptian murals ca. 3100 BCE, around the time of Narmer, a predynastic Egyptian ruler and attested founder of the First Dynasty. Narmer's very name may refer to the electric catfish. However, some sources give a wholly different use for the electric catfish's powers. Doctors of the day are reputed to have used smaller, immature fish—only capable of using a small fraction of their full electrical potential—to treat arthritis and gout, like a kind of living TENS unit.
The same electric fish that caught our attention so long ago catapulted electricity back into the public eye in 1775, with two scientific papers on the shocks delivered by the electric eel, as well as the anatomy and physiology of its electric organs. Shortly thereafter, physicist Luigi Galvani literally and figuratively galvanized the field when he demonstrated, with his experiments on frogs' legs, that neurons carry electrical impulses that control muscles.
Charles-Augustin de Coulomb discovered, in his experiments with friction, that like charges repel while unlike charges attract. Rubbing two lightweight glass or metal balls with charged amber, de Coulomb demonstrated, made the balls move away from one another, just as rubbing them with a charged glass rod caused them to repel one another—but rubbing one with amber and the other with glass caused the balls to attract one another.
Mathematics also contributed much to what we understand about electricity. Carl Friedrich Gauss was a student of mathematician Leonhard Euler, who popularized the concept of pi. Euler's sense of cycles informed the work Gauss did with electromagnetism, periodicity, and noise: work that would one day underlie the calculation of electrical phases that made alternating current possible. Not long afterward, Georg Ohm published a mathematical analysis of the electrical circuit so precise that one of the major laws of electricity now bears his name.
Fifty years of revelations like these touched off a century of explosively rapid research and development in electrical engineering. In 1820, Hans Christian Ørsted published his discovery that a compass needle could be deflected away from magnetic north just by holding an electrified wire near it—without touching the compass at all. Within two years, Michael Faraday made history with the invention of the electric motor. Soon, entrepreneurs like Edison, Brush, Ferraris, von Siemens, Tesla, and Westinghouse were making headlines.
By the turn of the twentieth century, the race to bring electricity into the home was well underway. But what form would it take? The desire to see their own vision for electrification take hold spurred a three-way industrial knock-down-drag-out between Edison, Westinghouse, and the Thomson-Houston Electric company, a saga we now refer to as the war of the currents.
The War of the Currents
The broad strokes go like this: Edison had invented a low-voltage direct current (DC) electrical system that worked very well in dense commercial and residential areas. However, DC has very limited range and high line losses, so using it for long-distance power transmission was impractical. Nikola Tesla, who started out working for Edison, favored alternating current (AC) because of smaller line losses. AC required higher voltages and more insulation, but Tesla believed that the ease of converting AC between higher and lower voltages made it ultimately the superior technology.
Edison didn't see things that way. He may or may not have sincerely believed that AC power was more dangerous than his own low-voltage DC, but he saw the threat it posed to his business interests in the crowded DC space. But Tesla's AC patents had caught the attention of George Westinghouse, an inventor and railroad baron who sought an inexpensive way to power the far-flung switches and signals that coordinated his company's trains. Westinghouse licensed Tesla's patents for $2.50 per AC horsepower, soon introducing high-voltage AC systems for residential and business use thanks to the invention of a far more efficient step-down transformer.
In response, the Edison Electric Light Company distributed an 80+ page pamphlet of propaganda warning customers that both Westinghouse and Thomson-Houston (another competitor building AC and DC systems) were in violation of relevant patents and likely putting their customers and the general public at risk if they dared to install electrical systems built by either company.
Getting 'Westinghoused'
The danger of alternating current wasn't something Edison dreamed up just to slander his competitors. AC lines carrying as much as 6,000 volts stretched across New York City. Many of these lines weren't built to the safety standards of the 1890s, a time when "safety standards" cheerfully allowed companies to sell heroin in children's cough syrups. Downed AC power lines and repair mistakes had killed people, felling their victims by instantly stopping their hearts, and the public was primed to think of AC power as more dangerous than DC.
And thus, we arrive at the electric chair.
Just before the turn of the century, scientists were looking for a more humane and reliable way to kill prisoners. New York settled on the idea of using electricity after a string of botched hangings. Still, the scientists on the recommendation committee had a problem: They didn't know how many volts they needed to use to kill a person, and they weren't sure what type of current would do the job most effectively. Edison wanted nothing to do with the matter but seized the opportunity to paint AC as dangerous. Initially, the first execution by electricity was to be carried out using Thomson-Houston generators. The company got wind of this and brought three Westinghouse generators. These were installed instead. Westinghouse appears to have paid for a lawyer for the defendant in question, William Kemmler, in the hopes that the court would find the electric chair to be cruel and unusual punishment.
Spoiler: The Court did not so find. Kemmler was executed, the execution was a botched horror show, and the term "Westinghoused" was briefly put forward to describe what we now call "electrocution."
How did it all end? In the most anticlimactic way you can think of. Edison left his company, and his anti-AC attitude went with him. Four years after Westinghouse poached Tesla, the Edison Electric Light Company merged with Thomson-Houston to form General Electric. The Edison Illuminating Company would be purchased by Consolidated Gas in 1901 before changing its name to Consolidated Edison, or ConEd. After a few intense years of public spectacle and tit-for-tat patent trolling, the war was over. AC had won.
