Vocademy - Learn for Free - Electronics Technology - DC Circuits - A Brief History of the Discovery of Electricity

Let's go way back in time to look at the first electric appliance, the magic lamp. Thousands of years ago, before the invention of the candle, the most common indoor light was the oil lamp. All you needed was a bowl of oil and a cloth wick. Light the wick, and you had a small flame that dimly lit the room. Such open oil lamps evolved into lamps like you have seen depicted as Aladdin's magic lamp, something like an ornate teapot. With the wick in the spout the lamp was carried about by the handle. Such lamps were usually made of clay, but wealthy people often had them made from brass or carved amber. Rub an amber lamp (or bottle, etc.), especially with wool, and it gains magical powers. It attracts dust and chaff. Put your hand near it, and you may feel your hair stand on end. On a dry day, touch the lamp, and you may get a painful "pinprick" with an accompanying clicking sound. Could the story of Aladdin and his magic lamp be based on amber's magical properties? Did amber's properties prompt ancient people to rub amber lamps or bottles and make wishes? History does not say. The earliest historical mention of amber's magical properties was in 600 BC by Thales of Miletus, a Greek mathematician. He noted that amber must be alive because it could make dust and chaff move.

Guericke makes an electric generator

In 1650, Otto von Guericke, a German scientist, inventor, and politician, built an electric generator from a sulfur ball. Placing his hand on the rotating ball would produce electricity just as rubbing amber with wool did. Later it was found that a hollow glass sphere worked as well.

Gilbert names electricity

William Gilbert, an English physician, physicist and natural philosopher, did the earliest modern research on the properties of amber. In 1600 he published a treatise titled On the Magnet and Magnetic Bodies, and On That Great Magnet the Earth. Gilbert noted that the properties of amber were different from the magnetism of lodestones. To differentiate these between the two, he coined the term electricity from the Greek word for amber, elektron. He was also the first to use the term electrical force. The gilbert is an obsolete unit to measure magnetic force.

Gray discovers "electrical fluid"

In 1729, British astronomer Stephen Gray experimented with electricity generated by rubbing a glass tube with silk. He noticed that a cork used to keep the inside of the tube dry and clean became electrified with the glass. Cork could not be electrified by itself. When he stuck a fir stick into the cork, the electricity extended to the end of the stick. He extended the electricity further with a length of oily hemp packing thread. The next day he extended the reach from his balcony to the courtyard below. He found that the electricity would travel around bends and was unaffected by gravity. Since electricity could be made to travel from one place to another, Gray speculated that electricity is a fluid. This gave rise to the term electrical fluid, which was used up to the early 20th century to refer to electricity.

Desaguliers names conductors and insulators

Gray discovered that some materials carried the electricity better than others and some not at all. John Desaguliers, a French-born British natural philosopher, clergyman and engineer�a member of the Royal Society and assistant to Isaac Newton, whom Gray had corresponded with�called these materials conductors and insulators.

Du Fay theorizes two types of electricity

In 1736 Charles Francois du Fay, a French chemist noted that electricity made by rubbing amber with wool appeared to have opposite properties to electricity made by rubbing glass with silk. Two pieces of electrified amber would repel each other. Likewise, two pieces of electrified glass would do the same. However, an electrified piece of amber would be attracted to an electrified piece of glass. He called them resinous and vitreous electricity: resinous because amber is fossilized resin and vitreous because vitrum is Latin for glass.

Von Kleist and Musschenbroek invent the capacitor

In 1745, Ewald Georg von Kleist a German lawyer, Lutheran cleric and physicist, tried to store electrical fluid in a medicine bottle filled with alcohol with a nail through the cork. After attempting to store electricity from a friction generator (such as Guericke's), he received a substantial shock when he touched the nail with one hand while cradling the bottle with the other. Pieter van Musschenbroek, a physics and mathematics professor at the University of Leyden in The Netherlands, tried to repeat von Kleist's results using a glass of beer. He found that it only worked when cradled in his hand, rather than set on an insulating resin block. William Watson, an English physician and scientist, found that wrapping the glass with metal foil worked better than holding it in hand. He substituted water for beer, a jar for the glass and a metal post with a metal ball on top for the nail (the jar would mysteriously lose its electricity if the post had sharp edges). Eventually, the water was replaced by metal foil on the inside of the jar with a metal chain connecting the center metal post to the inner foil. It is called a Leyden jar. Modern versions of this device are called capacitors.

Franklin demonstrates that there is only one type of electricity

Around 1750 Benjamin Franklin, an American statesman and scientist and William Watson noted that when a Leyden jar was electrified (charged as Franklin called it) it contained resinous electricity on the inside and vitreous electricity on the outside or vice versa. When they connected a metal wire from the inside to the outside, both charges would disappear. They thought this would happen if the two types of electricity were the same substance, but with different amounts of "abundance" (Watson labeled the greater abundance positive and the lesser abundance negative). When the inside and outside of the Leyden jar were connected, the electricity flowed like a fluid from the greater abundance to the lesser abundance until they equalized. However, it was impossible to tell with contemporary technology whether the fluid was flowing from the inside to the outside or from the outside to the inside; you could not determine whether vitreous or resinous electricity was the greater abundance.

Franklin proposes an experiment

By this time, it was evident that lightning was electricity (although first proposed by Gilbert). With electricity, you sometimes get small sparks that make a clicking or popping noise. With lightning, you get something that looks an awful lot like a really big spark with an accompanying big boom. Lightning must be huge sparks of electricity. In 1750 Franklin published a proposal for an experiment to extract electricity from clouds by extending a metal pole into the clouds and collecting the electricity in a Leyden jar at the bottom. This would prove that clouds contain electricity and support the observation that lightning appears to be electricity. Once extracted from the cloud you could see if the electricity was vitreous or resinous. This would settle the question as to which was positive and which was negative. Since it appeared that lightning travels from the cloud to the ground, the cloud must contain positive electricity, i.e., the greater abundance.

Dalibard beats Franklin to the punch

In May of 1752 Thomas-Francois Dalibard, a French scientific writer, editor and translator—who had been in communication with Franklin—performed Franklin's experiment. He used a 40-foot-tall (12 neters) metal rod attached to a stone building on a high hill. He successfully extracted electricity from a cloud and stored it in a Leyden jar. Two months later, unaware of Dalibard's success, Franklin also extracted electricity from a cloud with his famous kite experiment. The electricity from the clouds turned out to be vitreous. Therefore, vitreous electricity was the greater abundance and resinous the lesser abundance. From then on vitreous electricity was called positive and resinous electricity was called negative.

Some historians doubt that Franklin performed his kite experiment. However, Joseph Priestley, best known for having discovered oxygen, wrote that Franklin told him that he had done the kite experiment. There are also no contemporary disputes that he did it. The only evidence cited that Franklin did not perform the experiment is that he lived to tell about it. Several people who tried to repeat his experiment didn't. Some historians assume that Franklin did not fly his kite in an actual thunderstorm but into ordinary clouds. I have not been able to find the text of Franklin's proposal, so I don't know if Franklin first proposed performing the experiment during a thunderstorm. I have found quotes where he said a thunderstorm is unnecessary; any cloud will do. However, he made these statements after at least one person was killed trying to repeat the experiment. The Mythbusters, while doing a segment on Franklin's kite experiment, extracted more than 1,000 volts from clear air. This demonstrated that Franklin's experiment would have worked and that the presence of a cloud was not necessary to perform the experiment.

Cavendish almost invents Ohm's Law

In 1781, Henry Cavendish�best known for discovering hydrogen and measuring the density of the earth�expressed the relationship between electrical force and resistance. He experimented with Layden jars and glass tubes of various diameters. He concluded that the flow of electrical fluid is directly proportional to electrical pressure. This is essentially an expression of Ohm's Law. Unfortunately, the Royal Society, the most prestigious body of scientists at the time, did not publish his work on electricity, and he remains virtually unknown in that field.

Volta paves the way for modern electronics

Also in the 1780s, Luigi Aloisio Galvani, an Italian physician, physicist, biologist and philosopher noticed a dead frog's muscles twitching while he dissected it with metal tools. In further experiments, he found that he could extract electricity from the muscles while they were twitching. He thought that the electricity was generated by the muscle and he was extracting it with the metal tools. In 1800 Count Alessandro Volta, an Italian physicist and chemist repeated Galvani's experiments. For the experiment to work, the tools had to be made of different metals. He thought that the electricity might be generated from the salty fluids in the frog's body acting on the dissimilar metals. To test his theory, he constructed a stack of alternating zinc and copper disks. Each pair of disks was separated from the others by heavy paper disks that were soaked in brine. The stack of disks produced electricity.

Volta's pile

As Volta added more disks to the stack, more "electrical force" was produced between the ends of the stack. Today, this force is called electromotive force (emf). It is the result of a greater "abundance" of electricity at one end of the stack than the other end. This acts as a higher pressure on one end of the stack and a lower pressure on the opposite end. If a conductor is connected from one end of the stack to the other, the higher pressure will force electrical "fluid" through the conductor to the lower pressure end. The result is an electrical "current" flowing through the conductor. This "electric pile", as Volta called it, allowed sustained electrical currents instead of the short bursts produced by static electricity.

Volta's invention was a turning point in modern history. Volta's pile allowed Orested to discover the relationship between electricity and magnetism. Only after that could the generator be invented and electricity created and distributed around the world. Today we call Volta's pile a battery. Many historians say that the battery allows us to have portable electronic devices. This is a gross understatement. Without the battery, modern electronics as we know it could not have been developed. Even today, with few exceptions, all electronic equipment requires a battery or simulated battery to operate. Most devices that plug into the electrical mains have power supplies that simulate one or more batteries. Without the battery, electricity would have remained a curiosity suitable for little more than parlor tricks. It would not have ushered in the modern world. The unit of electromotive force, the volt, is named after Volta.

Oersted demonstrates electromagnetism

In 1820, Hans Christian Oersted, a professor at the University of Copenhagen, demonstrated the relationship between electricity and magnetism. During a lecture demonstrating Volta's electric pile, he noticed a nearby compass moving when he completed the circuit. When held near the wire the needle aligned itself perpendicular to the wire. When he reversed the flow of the current, the compass needle flipped. This proved that when an electric current is flowing in a wire, there is a magnetic field surrounding the wire. This discovery led to the invention of the electromagnet, the electric motor and the electric generator. The unit used to measure magnetic field strength is named after Oersted.

Ohm develops Ohm's Law

In 1827, Georg Simon Ohm, a German physicist and mathematician proved the relationship between electrical pressure, current, and resistance. Before Ohm, experimenters, including Andre Ampere, determined that the relationship between voltage, resistance, and current (in modern terms) was non-linear. In other words, if you doubled the voltage across a fixed resistance, the current didn't double.

Ohm found that he got consistent electrical pressure using thermocouples instead of voltaic piles. At first, he used two thermocouples, one submerged in ice water and the other in a steam bath. However, he later found that he could eliminate the thermocouple in the steam bath. He used different lengths of wires to create different resistances. He measured the current with a torsion galvanometer (a needle on a wire suspended in a magnetic field) using a microscope to observe the needle. Still, the current didn't exactly double when the length of the wire was cut precisely in half, etc. Only after adding the resistance of the voltage source--the resistance of the thermocouple in his case--to his calculations was he able to get linear results. This is how Ohm succeeded where others failed. Today the relationship between voltage, current, and resistance is known as Ohm's Law.

Ohm's testing apparatus

Henry and Faraday discover induction, invent the telegraph

In the early 1830s, Joseph Henry, an American physicist who served as the first Secretary of the Smithsonian Institution and Michael Faraday, an English scientist, experimented with electromagnets. An electromagnet is a coil of wire wrapped around an iron bar. When the wire is connected across a battery, the resulting magnetic field is concentrated because the coils are close together. The presence of the iron magnefies the magnetic field. Henry found that when he broke the circuit, a spark would jump across the gap between the switch contacts. He first proposed that the electrical current in the wire had momentum, like a train in motion that would be hard to stop, and this would force the electricity across the gap. Later he realized that when he broke the circuit, the collapsing magnetic field around the coil of wire induced its own current in the wire. It was this self-induced current (self-induction) that forced the electricity to jump the gap. Around the same time, Michael Faraday also experimented with coils of wire. He placed two coils next to each other (or wound one on top of the other) and passed current through one. He discovered that when he broke the circuit, stopping the flow of current in one coil, a galvanometer attached to the other coil would briefly show some current flow. Once again, it was the moving magnetic field produced by the first coil that induced the current in the second. This phenomenon is called mutual induction. In reality, Henry and Faraday both discovered self-induction and mutual induction at about the same time. After essentially flipping a coin, the scientific community gave credit for the discovery of self-induction to Henry and mutual induction to Faraday.

Most historians now credit Henry with inventing the electric telegraph. Henry's telegraph consisted of a battery, a switch and an electromagnet that moved a clapper to ring a bell. He used it to send signals from his office to his home while he was a professor at Princeton. The unit of inductance is named after Henry and the unit of capacitance, the farad, is named after Faraday.

Morse's telegraph

By 1837 electric telegraphs were being built in Europe. These were all sorts of devices that used electromagnets to move pointers to letters of the alphabet. The operator at the transmitter would move his pointer to a letter and the receiver would mimic the transmitter. That year, Samuel Morse, an American painter, developed a system using a cumbersome mechanism with long and short notches cut into a piece of wood. This was drawn over a switch, closing and opening the circuit for long and short times. The receiving end had an electromagnet that pushed an inked wheel against a strip of paper when the circuit was closed, making dots and dashes on the paper. Morse and Alfred Vail, his machinist assistant, developed a code of dots and dashes to use with the apparatus to send messages.

Kirchhoff's Laws

Swan, Edison, et al. invent the light bulb

The main problem to overcome was that the glowing wire, depending on what it was made of, would either quickly melt or burn up. By 1878 Joseph Swan, a British physicist and chemist, and Thomas Edison had both developed practical electric lights. Both used wires made of metals that melt at very high temperatures and encased the wire in a glass bulb. They removed the air from inside the bulb with a vacuum pump to prevent the wire from oxidizing. Edison eventually used a carbon-paper filiment and invented a bulb design that could be mass produced.

Maxwell proposes the existence of radio waves

Around 1862, James Clerk Maxwell, a Scottish scientist proposed that light consists of coupled waves of electricity and magnetism (electromagnetic waves). In 1864 he mathematically predicted the existence of invisible light waves that were of much longer wavelengths than visible light. Like the visible light emitted from an electric spark, he proposed that such a spark should also emit invisible waves. The Royal Society accepted Maxwell's theory of the electromagnetic nature of light but did not accept his invisible light theories. The unit used to measure magnetic field density is named after Maxwell. Braun invents first solid-state devices In 1874 German scientist Karl Ferdinand Braun discovered that certain crystals would conduct electrical current in only one direction. This works if one of the metal contacts to the crystal has an imperfect connection.

Braun invents first solid state devices

Hughes invents the microphone

Bell and Watson invent the telephone

In 1876 Alexander Bell patented a liquid-based microphone as part of a device for transmitting voice over telegraph wires. Part of Bell's patent application was written at the "last minute" and looked suspiciously like a patent application that Elisha Gray filed the same day (the clerk at the patent office later admitted to selling Gray's drawings to Bell's attorney). Bell's assistant, Thomas Watson accidentally discovered that Bell's receiver—a diaphragm connected to an electromagnet; this vibrated in response to variations of current in the wires—also acted as a microphone.

Edison reinvents the carbon microphone

In 1877 Thomas Edison patented the carbon microphone even though Hughes had already invented it (proving that the U.S. Patent Office was no better in 1877 than it is today). The carbon microphone was adapted to Bell's telephone. The carbon microphone was many times more sensitive than bell's transceiver and made the telephone practical. Bell's transceiver (now used just as a receiver) coupled to a carbon microphone acted as an amplifier. Before the invention of vacuum tube amplifiers (and later transistor amplifiers), this made it possible to relay telephone conversations over much longer distances.

Hughes discovers radio waves

Hertz proves radio waves exist

Laming and Stoney discover and name the electron

Marconi develops commercially viable radio broadcasting

Tesla and Westinghouse design and build the first hydroelectric power station

The advantage of alternating current is that it can be stepped up to extremely high voltages efficiently through transformers (Invented by Henry and Faraday). They are just coils of wire wrapped around each other and iron cores. The high voltage can deliver power over long distances efficiently where it is stepped back down to safer voltages through more transformers. This was the beginning of modern electrical power distribution. The unit used to measure magnetic field strength is named after Tesla.

Thomson isolates the electron, shows the direction of electrical current

In 1897 Joseph John Thomson, an English physicist used high voltages to pass electricity through evacuated glass tubes called Crooke's tubes. When the electricity struck the end of the tube, the glass glowed a pale green color. By blocking the flow of electricity with metal barriers, he was able to show which direction the electricity was flowing.

A Crooke's tube, showing a Maltese Cross and its shadow. The electrons are coming from the small end of the tube toward you and to your left. The positive electrode is below the cross. The electrons streaming from the cathode (negative electrode) cannot make the turn to the anode (positive electrode) and strike the cross and the end of the tube. The electrons that miss the cross strike the glass, causing the glass at the large end to glow.

Contrary to everyone's educated guess, Thomson showed that electricity flowed from the negative side to the positive side. By this time the labels of positive and negative electricity were firmly ingrained in the scientific lexicon. Thompson showed that electricity flows from negative to positive rather than from positive to negative as previously thought. Thompson also showed that the electrical flow could be restricted to the point that individual particles could be detected. Not knowing that these particles had already been predicted to exist and had already been named "electrons" (by Laming and Stoney), Thompson called these particles electric corpuscles.

Fleming invents the vacuum tube (electric valve)

A metal cylinder, called the plate, surrounds the glowing filament. If a high voltage is placed between the filament and the plate—negative to the filament and positive to the plate—electrons will flow from the filament to the plate. However, if the voltage is reversed, electrons are repelled from the plate back to the filament and there is no electrical flow. Like Braun's crystal rectifier, the diode acts like a check valve allowing electrical flow in only one direction.

Alexanderson vastly improves on Marconi's radio transmitters

These had a significant advantage over Marconi's transmitters in that they produced oscillations (variations of voltage or current at regular intervals) at a single frequency. Marconi's transmitters produced radio noise of many frequencies at once.

We can use light to illustrate how Marconi's and Alexanderson's transmitters differed. Marconi's transmitters produced the equivalent of white light. Remember, from elementary school science, that white light contains all the colors of the visible spectrum. You can look at white light through different colored filters, and you will still see the light, except tinted to the color of the filter. If you look at white light through a red filter, you will see red light. If you look at the same white light through a green filter, you will see green light. If you send a message, by flashing the light (using Morse code), you will get the same message through either filter.

Alexanderson's transmitters produced the equivalent of a single color. Let's say one transmitter produces only red light, another only green light, yet another only blue light, etc. Now let's say we want to send messages to different people in a room by flashing theses colored lights (using Morse code as above). Just to complicate things, let's say has their backs are to the lights, so they can't look at the individual lights. All they can see is the light bouncing off the walls and ceiling. We also need to send all the messages at the same time. Can you see the problem? It will be impossible for anyone to distinguish his or her message from the chaos of flashing colors.

Now let's say that the people who are to receive the message from the red light have red filters. Looking through the red filters, they will see only the red light. Likewise, the people receiving the green message have green filters. The others have blue filters. Distinguishing the messages is now easy. Electronic filters can separate radio waves in the same manner.

Two Marconi transmitters cannot operate anywhere near each other at the same time. You cannot separate one signal from another. Multiple Alexanderson transmitters can be used near each other as long as they rotate at different speeds, thus creating radio signals at different frequencies.

Fessenden transmits voice over radio

Rutherford and Bohr develop a new model of the atom

De Forest invents amplifying vacuum tube

All-electronic radio transmitter (no moving parts)

Sometime around 1910 multiple researchers made vacuum tube amplifiers and fed some of the output back to the input in various ways. When just enough of the signal is fed back at just the right time, the amplifier will oscillate, meaning the output voltage varies up and down in an orderly repetitious manner. Soon these oscillators were used as the basis of radio transmitters since they were a superior way of making pure radio waves to Ernst Alexanderson's electromechanical transmitters.

Armstrong invents modern radio receiver

In 1918 Edwin Armstrong, an American electrical engineer and inventor of the Armstrong oscillator, invented the superheterodyne receiver. The heart of this receiver is a circuit that converts a high frequency to a lower frequency. This allowed reception of radio signals with frequencies too high for circuits of the time. More importantly, it allowed a receiver design that is precision-tuned once to a single frequency. To receive frequency other than the one to which the receiver is tuned, the desired frequency is converted to the frequency of the pre-tuned circuit. Before this, tuning a receiver to a particular frequency was quite fiddly and time-consuming. Converting another signal to the frequency of your already-tuned receiver is as simple as changing one capacitor or inductor. This superheterodyne receiver is still the basis for virtually all radio receivers today.

Farnsworth invents all-electronic television (no moving parts)

The intensity of the beam would be varied to "paint" an electronically produced picture on a layer of material that glowed when hit by the electrons. He demonstrated the first all-electronic television, with no mechanical spinning disks or oscillating mirrors, in 1927. Vladimir Zworykin is often credited with inventing electronic television for RCA. However, Farnsworth had demonstrated his system to Zworykin while negotiating with RCA to license his inventions. When Farnsworth refused to sell his inventions to RCA for a flat fee, Zworykin copied much of Farnsworth's system. Patent interference suits brought by RCA against Farnsworth were found in favor of Farnsworth.

Armstrong invents FM radio

In 1933 Edwin Armstrong invented a radio transmitter that varied the output frequency rather than the power amplitude. This frequency modulation (FM) radio had the advantage that it didn't respond to noise (unwanted signals), either natural or man-made. Noise tends to change the amplitude of the signal and does not affect the frequency.

Bardeen and Brattain invent the transistor

In 1947, John Bardeen and Walter Brattain at AT&T's Bell Laboratories made a device with two gold contacts on a germanium crystal. It was essentially one of Karl Braun's point contact diodes with two contacts very close together. A small change in electrical current from one contact to the crystal caused a large change in the current from the other contact to the crystal. This solid-state device (a single piece of material, not containing a vacuum) became known as the transistor. It amplified electrical signals like the vacuum tube triode but had many advantages over it (i.e., no hot filament, no high voltage, smaller, cheaper to mass produce). William Shockley is often credited with inventing the transistor. However, he participated little in the development other than being Bardeen's and Brattain's boss.

Fairchild Co. invents the integrated circuit

Biard and Holonyak invent the light emitting diode (LED)

In 1961, James R. Biard and Gary Pittman discovered near-infrared light coming from a tunnel diode. They developed this into an efficient infrared emitting diode. In 1962, Nick Holonyak Jr. invented a visible red LED while working for General Electric. These solid state light are very efficient and long-lasting. Early LEDs were best suited as indicator lights. Red and Green LEDs were available for many years before Shuji Nakamura invented high brightness blue LEDs in 1994.

Any color of the visible spectrum can be created with red, green and blue LEDs. Most white LEDs use a deep violet LED to illuminate a phosphor that converts the violet light into white light. The cost of high wattage white LEDs has dropped dramatically in recent years and they are becoming the choice for area illumination.

This history is certainly incomplete, but it covers the basic principles and inventions that are the basis for most electronic equipment today.

A Brief History of the Discovery of Electricity

Ancient beginnings