Wednesday, July 29, 2009

Interference (wave propagation)

In physics, interference is the addition (superposition) of two or more waves that results in a new wave pattern. Interference usually refers to the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency.

Two non-monochromatic waves are only fully coherent with each other if they both have exactly the same range of wavelengths and the same phase differences at each of the constituent wavelengths.

The total phase difference is derived from the sum of both the path difference and the initial phase difference (if the waves are generated from two or more different sources). It can then be concluded whether the waves reaching a point are in phase (constructive interference) or out of phase (destructive interference).

Theory

Chromatic interference is seen in sea foam, which is made out of plankton. It is an example of the naturally occurring interference.

The principle of superposition of waves states that the resultant displacement at a point is equal to the vector sum of the displacements of different waves at that point. If a crest of a wave meets a crest of another wave at the same point then the crests interfere constructively and the resultant wave amplitude is greater. If a crest of a wave meets a trough of another wave then they interfere destructively, and the overall amplitude is decreased.

This form of interference can occur whenever a wave can propagate from a source to a destination by two or more paths of different length. Two or more sources can only be used to produce interference when there is a fixed phase relation between them, but in this case the interference generated is the same as with a single source; see Huygens' principle.

Experiments

Thomas Young's double-slit experiment showed interference phenomena where two beams of light which are coherent interfere to produce a pattern.

The beams of light both have the same wavelength range and at the center of the interference pattern. They have the same phases at each wavelength, as they both come from the same source.

[edit] Interference patterns

Animation of interference of waves coming from two point sources.

For two coherent sources, the spatial separation between sources is half the wavelength times the number of nodal lines.

Light from any source can be used to obtain interference patterns, for example, Newton's rings can be produced with sunlight. However, in general white light is less suited for producing clear interference patterns, as it is a mix of a full spectrum of colours, that each have different spacing of the interference fringes. Sodium light is close to monochromatic and is thus more suitable for producing interference patterns. The most suitable is laser light because it is almost perfectly monochromatic.

Constructive and destructive interference

Interference pattern produced with a Michelson interferometer. Bright bands are the result of constructive interference while the dark bands are the result of destructive interference.

Consider two waves that are in phase,with amplitudes A1 and A2. Their troughs and peaks line up and the resultant wave will have amplitude A = A1 + A2. This is known as constructive interference.

If the two waves are π radians, or 180°, out of phase, then one wave's crests will coincide with another wave's troughs and so will tend to cancel out. The resultant amplitude is A = |A1A2|. If A1 = A2, the resultant amplitude will be zero. This is known as destructive interference.

When two sinusoidal waves superimpose, the resulting waveform depends on the frequency (or wavelength) amplitude and relative phase of the two waves. If the two waves have the same amplitude A and wavelength the resultant waveform will have an amplitude between 0 and 2A depending on whether the two waves are in phase or out of phase.

combined
waveform
Image:Interference of two waves.png
wave 1
wave 2

Two waves in phase Two waves 180° out
of phase

General quantum interference

Two point interference in a ripple tank.
Quantum mechanics
\Delta x\, \Delta p \ge \frac{\hbar}{2}
Uncertainty principle
Introduction to...

Mathematical formulation of...

[hide]Fundamental concepts
Quantum state · Wave function
Superposition · Entanglement

Measurement · Uncertainty
Exclusion · Duality
Decoherence · Ehrenfest theorem · Tunneling

If a system is in state ψ its wavefunction is described in Dirac or bra-ket notation as:

 |\psi \rang = \sum_i |i\rang \psi_i

where the  |i\rangs specify the different quantum "alternatives" available (technically, they form an eigenvector basis) and the ψi are the probability amplitude coefficients, which are complex numbers.

The probability of observing the system making a transition or quantum leap from state Ψ to a new state Φ is the square of the modulus of the scalar or inner product of the two states:

\operatorname{prob}(\psi \Rightarrow \varphi) = |\lang \psi |\varphi \rang|^2 = |\sum_i\psi^*_i \varphi_i |^2
 = \sum_{ij} \psi^*_i \psi_j \varphi^*_j\varphi_i= \sum_{i} |\psi_i|^2|\varphi_i|^2 + \sum_{ij;i \ne j} \psi^*_i \psi_j \varphi^*_j\varphi_i

where  \psi_i = \lang i|\psi \rang (as defined above) and similarly  \varphi_i = \lang i|\varphi \rang are the coefficients of the final state of the system. * is the complex conjugate so that  \psi_i^* = \lang \psi|i \rang , etc.

Now let's consider the situation classically and imagine that the system transited from |\psi \rang to |\varphi \rang via an intermediate state |i\rang. Then we would classically expect the probability of the two-step transition to be the sum of all the possible intermediate steps. So we would have

\operatorname{prob}(\psi \Rightarrow \varphi) = \sum_i \operatorname{prob}(\psi \Rightarrow i \Rightarrow \varphi)
= \sum_i |\lang \psi |i \rang|^2|\lang i|\varphi \rang|^2 = \sum_i|\psi_i|^2 |\varphi_i|^2.

The classical and quantum derivations for the transition probability differ by the presence, in the quantum case, of the extra terms \sum_{ij;i \ne j} \psi^*_i \psi_j \varphi^*_j\varphi_i; these extra quantum terms represent interference between the different i \ne j intermediate "alternatives". These are consequently known as the quantum interference terms, or cross terms. This is a purely quantum effect and is a consequence of the non-additivity of the probabilities of quantum alternatives.

The interference terms vanish, via the mechanism of quantum decoherence, if the intermediate state  |i\rang is measured or coupled with the environment[1][2].

Examples

A conceptually simple case of interference is a small (compared to wavelength) source – say, a small array of regularly spaced small sources (see diffraction grating).

Consider the case of a flat boundary (say, between two media with different densities or simply a flat mirror), onto which the plane wave is incident at some angle. In this case of continuous distribution of sources, constructive interference will only be in specular direction – the direction at which angle with the normal is exactly the same as the angle of incidence. Thus, this results in the law of reflection which is simply the result of constructive interference of a plane wave on a plane surface.


Interference of two circular waves – Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). Absolute value snapshots of the (real-valued, scalar) wave field. As time progresses, the wave fronts would move outwards from the two centers, but the dark regions (destructive interference) stay fixed.

Sunday, July 26, 2009

Digital Signal

The term digital signal is used to refer to more than one concept. It can refer to discrete-time signals that have a discrete number of levels, for example a sampled and quantified analog signal, or to the continuous-time waveform signals in a digital system, representing a bit-stream. In the first case, a signal that is generated by means of a digital modulation method is considered as converted to an analog signal, while it is considered as a digital signal in the second case.

Discrete-time signals

Discrete sampled signal
Digital signal

An analog signal is a datum that changes over time—say, the temperature at a given location; the depth of a certain point in a pond; or the amplitude of the voltage at some node in a circuit—that can be represented as a mathematical function, with time as the free variable (abscissa) and the signal itself as the dependent variable (ordinate). A discrete-time signal is a sampled version of an analog signal: the value of the datum is noted at fixed intervals (for example, every microsecond) rather than continuously.

If individual time values of the discrete-time signal, instead of being measured precisely (which would require an infinite number of digits), are approximated to a certain precision—which, therefore, only requires a specific number of digits—then the resultant data stream is termed a digital signal. The process of approximating the precise value within a fixed number of digits, or bits, is called quantization.

In conceptual summary, a digital signal is a quantized discrete-time signal; a discrete-time signal is a sampled analog signal.

In the Digital Revolution, the usage of digital signals has increased significantly. Many modern media devices, especially the ones that connect with computers use digital signals to represent signals that were traditionally represented as continuous-time signals; cell phones, music and video players, personal video recorders, and digital cameras are examples.

In most applications, digital signals are represented as binary numbers, so their precision of quantization is measured in bits. Suppose, for example, that we wish to measure a signal to two significant decimal digits. Since seven bits, or binary digits, can record 128 discrete values (viz., from 0 to 127), those seven bits are more than sufficient to express a range of one hundred values.

Waveforms in digital systems

A digital signal waveform: (1) low level, (2) high level, (3) rising edge, and (4) falling edge.

In computer architecture and other digital systems, a waveform that switches between two voltage levels representing the two states of a Boolean value (0 and 1) is referred to as a digital signal, even though it is an analog voltage waveform, since it is interpreted in terms of only two levels.

The clock signal is a special digital signal that is used to synchronize digital circuits. The image shown can be considered the waveform of a clock signal. Logic changes are triggered either by the rising edge or the falling edge.

The given diagram is an example of the practical pulse and therefore we have introduced two new terms that are:

  • Rising edge: the transition from a low voltage (level 1 in the diagram) to a high voltage (level 2).
  • Falling edge: the transition from a high voltage to a low one.

Although in a highly simplified and idealised model of a digital circuit we may wish for these transitions to occur instantaneously, no real world circuit is purely resistive and therefore no circuit can instantly change voltage levels. This means that during a short, finite transition time the output may not properly reflect the input, and indeed may not correspond to either a logically high or low voltage.

Logic voltage levels

Hobbyist frequency counter circuit built almost entirely of TTL logic chips.

The two states of a wire are usually represented by some measurement of an electrical property: Voltage is the most common, but current is used in some logic families. A threshold is designed for each logic family. When below that threshold, the wire is "low," when above "high." Digital circuits establish a "no man's area" or "exclusion zone" that is wider than the tolerances of the components. The circuits avoid that area, in order to avoid indeterminate results.

It is usual to allow some tolerance in the voltage levels used; for example, 0 to 2 volts might represent logic 0, and 3 to 5 volts logic 1. A voltage of 2 to 3 volts would be invalid, and occur only in a fault condition or during a logic level transition. However, few logic circuits can detect such a condition and most devices will interpret the signal simply as high or low in an undefined or device-specific manner. Some logic devices incorporate schmitt trigger inputs whose behaviour is much better defined in the threshold region, and have increased resilience to small variations in the input voltage.

The levels represent the binary integers or logic levels of 0 and 1. In active-high logic, "low" represents binary 0 and "high" represents binary 1. Active-low logic uses the reverse representation.

Examples of binary logic levels:
Technology L voltage H voltage Notes
CMOS 0V to VCC/2 VCC/2 to VCC VCC = supply voltage
TTL 0V to 0.8V 2V to VCC VCC is 4.75V to 5.25V
ECL -1.175V to -VEE .75V to 0V VEE is about -5.2V VCC=Ground

An Analog or Analogue Signal

An Analog or analogue signal is any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity, i.e analogous to another time varying signal. It differs from a digital signal in that small fluctuations in the signal are meaningful. Analog is usually thought of in an electrical context; however, mechanical, pneumatic, hydraulic, and other systems may also convey analog signals.


An analog signal uses some property of the medium to convey the signal's information. For example, an aneroid barometer uses rotary position as the signal to convey pressure information. Electrically, the property most commonly used is voltage followed closely by frequency, current, and charge.

Any information may be conveyed by an analog signal; often such a signal is a measured response to changes in physical phenomena, such as sound, light, temperature, position, or pressure, and is achieved using a transducer.

For example, in sound recording, fluctuations in air pressure (that is to say, sound) strike the diaphragm of a microphone which causes corresponding fluctuations in a voltage or the current in an electric circuit. The voltage or the current is said to be an "analog" of the sound.

Any measured analog signal must theoretically have noise and a finite slew rate. Therefore, both analog and digital systems are subject to limitations in resolution and bandwidth. In practice, as analog systems become more complex, effects such as non-linearity and noise ultimately degrade analog resolution to such extent that the performance of digital systems may surpass it. In analog systems, it is difficult to detect when such degradation occurs. However, in digital systems, degradation can not only be detected but corrected as well.

Advantages

The main advantage is the fine definition of the analog signal which has the potential for an infinite amount of signal resolution.[1] Compared to digital signals, analog signals are of higher density.[2].

Another advantage with analog signals is that their processing may be achieved more simply than with the digital equivalent. An analog signal may be processed directly by analog components,[3] though some processes aren't available except in digital form.

Disadvantages

The primary disadvantage of analog signaling is that any system has noise – i.e., random unwanted variation. As the signal is copied and re-copied, or transmitted over long distances, these apparently random variations become dominant. Electrically, these losses can be diminished by shielding, good connections, and several cable types such as coaxial or twisted pair.

The effects of noise create signal loss and distortion. This is impossible to recover, since amplifying the signal to recover attenuated parts of the signal amplifies the noise (distortion/interference) as well. Even if the resolution of an analog signal is higher than a comparable digital signal, in many cases, the difference is overshadowed by the noise in the signal.

Modulation

Another method of conveying an analog signal is to use modulation. In this, some base signal (e.g., a sinusoidal carrier wave) has one of its properties modulated: amplitude modulation involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation changes the frequency. Other techniques, such as changing the phase of the base signal also work.

Analog circuits do not involve quantisation of information into digital format. The concept being measured over the circuit, whether sound, light, pressure, temperature, or an exceeded limit, remains from end to end.

See digital for a discussion of digital vs. analog.

Sources: Parts of an earlier version of this article were originally taken from Federal Standard 1037C in support of MIL-STD-188.


Thomas Alva Edison

Thomas Alva Edison (February 11, 1847 – October 18, 1931) was an American inventor, scientist and businessman who developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. Dubbed "The Wizard of Menlo Park" by a newspaper reporter, he was one of the first inventors to apply the principles of mass production and large teamwork to the process of invention, and therefore is often credited with the creation of the first industrial research laboratory.

Edison is considered one of the most prolific inventors in history, holding 1,093 U.S. patents in his name, as well as many patents in the United Kingdom, France and Germany. He is credited with numerous inventions that contributed to mass communication and, in particular, telecommunications. His advanced work in these fields was an outgrowth of his early career as a telegraph operator. Edison originated the concept and implementation of electric-power generation and distribution to homes, businesses, and factories - a crucial development in the modern industrialized world. His first power plant was on Manhattan Island, New York.

Early life

Birthplace of Thomas Edison
Historical marker of Edison's birthplace in Milan, Ohio
Thomas Edison as a boy

Thomas Edison was born in Milan, Ohio, and grew up in Port Huron, Michigan. He was the seventh and last child of Samuel "The Iron Shovel" Edison, Jr. (1804–1896) (born in Marshalltown, Nova Scotia, Canada) and Nancy Matthews Elliott (1810–1871). He considered himself to be of Dutch ancestry.[1] In school, the young Edison's mind often wandered, and his teacher, the Reverend Engle, was overheard calling him "addled." This ended Edison's three months of official schooling. Edison recalled later, "My mother was the making of me. She was so true, so sure of me; and I felt I had something to live for, someone I must not disappoint." His mother then home schooled him.[2] Much of his education came from reading R.G. Parker's School of Natural Philosophy and The Cooper Union. Edison developed hearing problems at an early age. The cause of his deafness has been attributed to a bout of scarlet fever during childhood and recurring untreated middle ear infections. Around the middle of his career Edison attributed the hearing loss to being struck on the ears by a train conductor when his chemical laboratory in a boxcar caught fire and he was thrown off the train in Smiths Creek, Michigan, along with his apparatus and chemicals. In his later years he modified the story to say the injury occurred when the conductor, in helping him onto a moving train, lifted him by the ears.[3][4] Edison's family was forced to move to Port Huron, Michigan, when the railroad bypassed Milan in 1854,[5] but his life there was bittersweet. He sold candy and newspapers on trains running from Port Huron to Detroit, as well as vegetables that he sold to supplement his income. This began Edison's long streak of entrepreneurial ventures as he discovered his talents as a businessman. These talents eventually led him to found 14 companies, including General Electric, which is still in existence, and one of the largest publicly traded companies in the world.[6]

Telegrapher

Edison became a telegraph operator after he saved three-year-old Jimmie MacKenzie from being struck by a runaway train. Jimmie's father, station agent J.U. MacKenzie of Mount Clemens, Michigan, was so grateful that he trained Edison as a telegraph operator. Edison's first telegraphy job away from Port Huron was at Stratford Junction, Ontario, on the Grand Trunk Railway.[7] In 1866, at the age of 19, Thomas Edison moved to Louisville, Kentucky, where, as an employee of Western Union, he worked the Associated Press bureau news wire. Edison requested the night shift, which allowed him plenty of time to spend at his two favorite pastimes—reading and experimenting. Eventually, the latter pre-occupation cost him his job. One night in 1867, he was working with a battery when he spilled sulfuric acid onto the floor. It ran between the floorboards and onto his boss's desk below. The next morning Edison was fired.[8]

One of his mentors during those early years was a fellow telegrapher and inventor named Franklin Leonard Pope, who allowed the impoverished youth to live and work in the basement of his Elizabeth, New Jersey home. Some of Edison's earliest inventions were related to telegraphy, including a stock ticker. His first patent was for the electric vote recorder, (U. S. Patent 90,646),[9] which was granted on June 1, 1869.[10]

Marriages and children

Mina Edison in 1906

On December 25, 1871, Edison married 16-year-old Mary Stilwell, whom he had met two months earlier as she was an employee at one of his shops. They had three children:

  • Marion Estelle Edison (1873–1965), nicknamed "Dot"[citation needed]
  • Thomas Alva Edison, Jr. (1876–1935), nicknamed "Dash"[citation needed]
  • William Leslie Edison (1878–1937)[11]

Mary Edison died on August 9, 1884, possibly from a brain tumor.[12]

On February 24, 1886, at the age of thirty nine, Edison married 20-year-old Mina Miller in Akron, Ohio.[13] She was the daughter of inventor Lewis Miller, co-founder of the Chautauqua Institution and a benefactor of Methodist charities. They also had three children:

  • Madeleine Edison (1888–1979), who married John Eyre Sloane.[14][15]
  • Charles Edison (1890–1969), who took over the company upon his father's death and who later was elected Governor of New Jersey.[16] He also took charge of his father's experimental laboratories in West Orange.
  • Theodore Edison (1898–1992), the only family member to get a college degree (MIT Physics 1923), and had over 80 patents to his credit.

Mina outlived Thomas Edison, dying on August 24, 1947.[17][18]

Beginning his career

Photograph of Edison with his phonograph, taken by Mathew Brady in 1877

Thomas Edison began his career as an inventor in Newark, New Jersey, with the automatic repeater and his other improved telegraphic devices, but the invention which first gained him fame was the phonograph in 1877. This accomplishment was so unexpected by the public at large as to appear almost magical. Edison became known as "The Wizard of Menlo Park," New Jersey, where he lived. His first phonograph recorded on tinfoil around a grooved cylinder and had poor sound quality. The tinfoil recordings could only be replayed a few times. In the 1880s, a redesigned model using wax-coated cardboard cylinders was produced by Alexander Graham Bell, Chichester Bell, and Charles Tainter. This was one reason that Thomas Edison continued work on his own "Perfected Phonograph."

Menlo Park (1876-1881)

Edison's Menlo Park Laboratory, removed to Greenfield Village in Dearborn, Michigan. (Note the organ against the back wall)
Thomas Edison's first successful light bulb model, used in public demonstration at Menlo Park, December 1879
U.S. Patent#223898: Electric-Lamp. Issued January 27, 1880.

Edison's major innovation was the first industrial research lab, which was built in Menlo Park, New Jersey. It was built with the funds from the sale of Edison's quadruplex telegraph. After his demonstration of the telegraph, Edison was not sure that his original plan to sell it for $4,000 to $5,000 was right, so he asked Western Union to make a bid. He was surprised to hear them offer $10,000,[citation needed] which he gratefully accepted. The quadruplex telegraph was Edison's first big financial success, and Menlo Park became the first institution set up with the specific purpose of producing constant technological innovation and improvement. Edison was legally attributed with most of the inventions produced there, though many employees carried out research and development work under his direction. His staff was generally told to carry out his directions in conducting research, and he drove them hard to produce results. The large research group, which included engineers and other workers, based much of their research on work done by others before them.

William J. Hammer, a consulting electrical engineer, began his duties as a laboratory assistant to Edison in December 1879. He assisted in experiments on the telephone, phonograph, electric railway, iron ore separator, electric lighting, and other developing inventions. However, Hammer worked primarily on the incandescent electric lamp and was put in charge of tests and records on that device. In 1880, he was appointed chief engineer of the Edison Lamp Works. In his first year, the plant under General Manager Francis Robbins Upton turned out 50,000 lamps. According to Edison, Hammer was "a pioneer of incandescent electric lighting".

Nearly all of Edison's patents were utility patents, which were protected for a 17-year period and included inventions or processes that are electrical, mechanical, or chemical in nature. About a dozen were design patents, which protect an ornamental design for up to a 14-year period. Like most patents, the inventions he described were improvements over prior art. The phonograph patent, on the other hand, was unprecedented as the first device to record and reproduce sounds.[19] Edison did not invent the first electric light bulb, but instead invented the first commercially practical incandescent light. Several designs had already been developed by earlier inventors including the patent he purchased from Henry Woodward and Mathew Evans, Moses G. Farmer,[20] Joseph Swan, James Bowman Lindsay, William E. Sawyer, Sir Humphry Davy, and Heinrich Göbel. Some of these early bulbs had such flaws as an extremely short life, high expense to produce, and high electric current drawn, making them difficult to apply on a large scale commercially. In 1878, Edison applied the term filament to the element of glowing wire carrying the current, although the English inventor Joseph Swan had used the term prior to this. Edison took the features of these earlier designs and set his workers to the task of creating longer-lasting bulbs. By 1879, he had produced a new concept: a high resistance lamp in a very high vacuum, which would burn for hundreds of hours. While the earlier inventors had produced electric lighting in laboratory conditions, dating back to a demonstration of a glowing wire by Alessandro Volta in 1800, Edison concentrated on commercial application, and was able to sell the concept to homes and businesses by mass-producing relatively long-lasting light bulbs and creating a complete system for the generation and distribution of electricity.

In just over a decade Edison's Menlo Park laboratory had expanded to occupy two city blocks. Edison said he wanted the lab to have "a stock of almost every conceivable material". A newspaper article printed in 1887 reveals the seriousness of his claim, stating the lab contained "eight thousand kinds of chemicals, every kind of screw made, every size of needle, every kind of cord or wire, hair of humans, horses, hogs, cows, rabbits, goats, minx, camels ...silk in every texture, cocoons, various kinds of hoofs, shark's teeth, deer horns, tortoise shell ...cork, resin, varnish and oil, ostrich feathers, a peacock's tail, jet, amber, rubber, all ores ..." and the list goes on.[21]

Over his desk, Edison displayed a placard with Sir Joshua Reynolds' famous quote: "There is no expedient to which a man will not resort to avoid the real labor of thinking."[22] This slogan was reputedly posted at several other locations throughout the facility.

With Menlo Park, Edison had created the first industrial laboratory concerned with creating knowledge and then controlling its application.

Carbon telephone transmitter

In 1877–1878, Edison invented and developed the carbon microphone used in all telephones along with the Bell receiver until the 1980s. After protracted patent litigation, in 1892 a federal court ruled that Edison—and not Emile Berliner—was the inventor of the carbon microphone. The carbon microphone was also used in radio broadcasting and public address work through the 1920s.

Electric light

Edison in 1878
Edison speech, 1920s.ogg
Video clip of Thomas Edison talking about the invention of the light bulb, late 1920s

After many experiments with platinum and other metal filaments, Edison returned to a carbon filament. The first successful test was on October 22, 1879,[23] and lasted 40 hours. Edison continued to improve this design and by November 4, 1879, filed for U.S. patent 223,898 (granted on January 27, 1880) for an electric lamp using "a carbon filament or strip coiled and connected to platina contact wires".[24] Although the patent described several ways of creating the carbon filament including "cotton and linen thread, wood splints, papers coiled in various ways",[24] it was not until several months after the patent was granted that Edison and his team discovered a carbonized bamboo filament that could last over 1,200 hours.

Edison allegedly bought light bulb U.S. patent 181,613 of Henry Woodward that was issued August 29, 1876 and obtained an exclusive license to Woodward's Canadian patent. These patents covered a carbon rod in a nitrogen filled glass cylinder, and differed substantially from the first commercially practical bulb invented by Edison.[citation needed]

In 1878, Edison formed the Edison Electric Light Company in New York City with several financiers, including J. P. Morgan and the members of the Vanderbilt family. Edison made the first public demonstration of his incandescent light bulb on December 31, 1879, in Menlo Park. It was during this time that he said: "We will make electricity so cheap that only the rich will burn candles."[25]

George Westinghouse's company bought Philip Diehl's competing induction lamp patent rights (1882) for $25,000, forcing the holders of the Edison patent to charge a more reasonable rate for the use of the Edison patent rights and lowering the price of the electric lamp.[26]

On October 8, 1883, the U.S. patent office ruled that Edison's patent was based on the work of William Sawyer and was therefore invalid. Litigation continued for nearly six years, until October 6, 1889, when a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid. To avoid a possible court battle with Joseph Swan, whose British patent had been awarded a year before Edison's, he and Swan formed a joint company called Ediswan to manufacture and market the invention in Britain.

Mahen Theatre in Brno in what is now the Czech Republic, was the first public building in the world to use Edison's electric lamps, with the installation supervised by Edison's assistant in the invention of the lamp, Francis Jehl.[27]

Electric power distribution

Edison patented an electric distribution system in 1880, which was essential to capitalize on the invention of the electric lamp. On December 17, 1880, Edison founded the Edison Electric Illuminating Company. The company established the first investor-owned electric utility in 1882 on Pearl Street Station, New York City. It was on September 4, 1882, that Edison switched on his Pearl Street generating station's electrical power distribution system, which provided 110 volts direct current (DC) to 59 customers in lower Manhattan.

Earlier in the year, in January 1882 he had switched on the first steam generating power station at Holborn Viaduct in London. The DC supply system provided electricity supplies to street lamps and several private dwellings within a short distance of the station. On January 19, 1883, the first standardized incandescent electric lighting system employing overhead wires began service in Roselle, New Jersey.

War of currents

Extravagant displays of electric lights quickly became a feature of public events, as this picture from the 1897 Tennessee Centennial Exposition shows.

Edison's true success, like that of his friend Henry Ford, was in his ability to maximize profits through establishment of mass-production systems and intellectual property rights. This dampened the success of less profitable work by others who were focused on inventing longer-lasting high-efficiency technology.[28][29] George Westinghouse and Edison became adversaries because of Edison's promotion of direct current for electric power distribution instead of the more easily transmitted alternating current (AC) system invented by Nikola Tesla and promoted by Westinghouse. Unlike DC, AC could be stepped up to very high voltages with transformers, sent over thinner and cheaper wires, and stepped down again at the destination for distribution to users.

In 1887 there were 121 Edison power stations in the United States delivering DC electricity to customers. When the limitations of Direct Current (DC) were discussed by the public, Edison launched a propaganda campaign to convince people that Alternating Current (AC) was far too dangerous to use. The problem with DC was that the power plants could only economically deliver DC electricity to customers about one and a half miles from the generating station, so it was only suitable for central business districts. When George Westinghouse suggested using high-voltage AC instead, as it could carry electricity hundreds of miles with marginal loss of power, Edison waged a "War of Currents" to prevent AC from being adopted.

Despite Edison's contempt for capital punishment, the war against AC led him to become involved in the development and promotion of the electric chair as a demonstration of AC's greater lethal potential versus the "safer" DC. Edison went on to carry out a brief but intense campaign to ban the use of AC or to limit the allowable voltage for safety purposes. As part of this campaign, Edison's employees publicly electrocuted animals to demonstrate the dangers of AC;[30][31] AC electric currents, particularly near 60 Hz frequency, have a markedly greater potential for inducing fatal “Cardiac Fibrillation” than do DC currents.[32] On one of the more notable occasions, in 1903, Edison's workers electrocuted Topsy the elephant at Luna Park, near Coney Island, after she had killed several men and her owners wanted her put to death.[33] His company filmed the electrocution.

AC replaced DC in most instances of generation and power distribution, enormously extending the range and improving the efficiency of power distribution. Though widespread use of DC ultimately lost favor for distribution, it exists today primarily in long-distance high-voltage direct current (HVDC) transmission systems. Low voltage DC distribution continued to be used in high density downtown areas for many years but was replaced by AC low voltage network distribution in many central business districts. DC had the advantage that large battery banks could maintain continuous power through brief interruptions of the electric supply from generators and the transmission system. Utilities such as Commonwealth Edison in Chicago had rotary converters, also known as motor-generator sets , which could change DC to AC and AC to various frequencies in the early to mid-20th century. Utilities supplied rectifiers to convert the low voltage AC to DC for such DC loads as elevators, fans and pumps. There were still 1,600 DC customers in downtown New York City as of 2005, and service was only finally discontinued on November 14, 2007.[34] Most subway systems still are powered by direct current.

Fluoroscopy

Edison is credited with designing and producing the first commercially available fluoroscope, the machine that takes radiographs (colloquially known as "X-rays"). Until Edison discovered that calcium tungstate fluoroscopy screens produced brighter images than the barium platinocyanide screens originally used by Wilhelm Röntgen, the technology was only capable of producing very faint images. The fundamental design of Edison's fluoroscope is still in use today, despite the fact that Edison himself abandoned the project after nearly losing his own eyesight and seriously maiming his assistant, Clarence Dally. Dally had made himself an enthusiastic human guinea pig for the fluoroscopy project and in the process been exposed to a poisonous dose of radiation. He later died of injuries related to the exposure. In 1903, a shaken Edison said "Don't talk to me about X-rays, I am afraid of them."[35]

Work relations

Frank J. Sprague, a competent mathematician and former naval officer, was recruited by Edward H. Johnson and joined the Edison organization in 1883. One of Sprague's significant contributions to the Edison Laboratory at Menlo Park was to expand Edison's mathematical methods. Despite the common belief that Edison did not use mathematics, analysis of his notebooks reveal that he was an astute user of mathematical analysis conducted by his assistants such as Francis Upton, for example, determining the critical parameters of his electric lighting system including lamp resistance by a sophisticated analysis of Ohm's Law, Joule's Law and economics.[36]

Another of Edison's assistants was Nikola Tesla, who claimed that Edison promised him $50,000 if he succeeded in making improvements to his DC generation plants. Tesla claimed that several months later, when he had finished the work and asked to be paid, Edison said, "When you become a full-fledged American you will appreciate an American joke."[37] Tesla immediately resigned. With Tesla's salary of $18 per week, the payment would have amounted to over 53 years pay and the amount was equal to the initial capital of the company. Tesla resigned when he was refused a raise to $25 per week.[38] Although Tesla accepted an Edison Medal later in life and professed a high opinion of Edison as an inventor and engineer, this and other negative series of events concerning Edison remained with Tesla. The day after Edison died, the New York Times contained extensive coverage of Edison's life, with the only negative opinion coming from Tesla who was quoted as saying, "He had no hobby, cared for no sort of amusement of any kind and lived in utter disregard of the most elementary rules of hygiene" and that, "His method was inefficient in the extreme, for an immense ground had to be covered to get anything at all unless blind chance intervened and, at first, I was almost a sorry witness of his doings, knowing that just a little theory and calculation would have saved him 90% of the labour. But he had a veritable contempt for book learning and mathematical knowledge, trusting himself entirely to his inventor's instinct and practical American sense." When Edison was a very old man and close to death, he said, in looking back, that the biggest mistake he had made was that he never respected Tesla or his work.[39]

There were 28 men recognized as Edison Pioneers.

Media inventions

The key to Edison's fortunes was telegraphy. With knowledge gained from years of working as a telegraph operator, he learned the basics of electricity. This allowed him to make his early fortune with the stock ticker, the first electricity-based broadcast system. Edison patented the sound recording and reproducing phonograph in 1878. Edison was also granted a patent for the motion picture camera or "Kinetograph". He did the electromechanical design, while his employee W.K.L. Dickson, a photographer, worked on the photographic and optical development. Much of the credit for the invention belongs to Dickson.[23] In 1891, Thomas Edison built a Kinetoscope, or peep-hole viewer. This device was installed in penny arcades, where people could watch short, simple films. The kinetograph and kinetoscope were both first publicly exhibited May 20, 1891.[40]

On August 9, 1892, Edison received a patent for a two-way telegraph. In April 1896, Thomas Armat's Vitascope, manufactured by the Edison factory and marketed in Edison's name, was used to project motion pictures in public screenings in New York City. Later he exhibited motion pictures with voice soundtrack on cylinder recordings, mechanically synchronized with the film.

Officially the kinetoscope entered in Europe when the rich American Businessman Irving T. Bush (1869–1948) bought from the Continental Commerce Company of Franck Z. Maguire and Joseph D. Bachus a dozen machines. Bush placed from October 17, 1894 on the first kinetoscopes in London. At the same time the French company Kinétoscope Edison Michel et Alexis Werner bought these machines for the market in France. In the last three months of 1894 The Continental Commerce Company sold hundreds of kinetoscopes in Europe (i.e. the Netherlands and Italy). In Germany and in Austria-Hungary the kinetoscope was introduced by the Deutsche-österreichische-Edison-Kinetoscop Gesellschaft, founded by the Ludwig Stollwerck[41] of the Schokoladen-Süsswarenfabrik Stollwerck & Co of Cologne. The first kinetoscopes arrived in Belgium at the Fairs in early 1895. The Edison's Kinétoscope Français, a Belgian company, was founded in Brussels on January 15, 1895 with the rights to sell the kinetoscopes in Monaco, France and the French colonies. The main investors in this company were Belgian industrialists. On May 14, 1895 the Edison's Kinétoscope Belge was founded in Brussels. The businessman Ladislas-Victor Lewitzki, living in London but active in Belgium and France, took the initiative in starting this business. He had contacts with Leon Gaumont and the American Mutoscope and Biograph Co. In 1898 he also became shareholder of the Biograph and Mutoscope Company for France.[42]

In 1901, he visited the Sudbury area as a mining prospector, and is credited with the original discovery of the Falconbridge ore body. His attempts to actually mine the ore body were not successful, however, and he abandoned his mining claim in 1903.[43] A street in Falconbridge, as well as the Edison Building, which served as the head office of Falconbridge Mines, are named for him.

In 1902, agents of Thomas Edison bribed a theater owner in London for a copy of A Trip to the Moon by Georges Méliès. Edison then made hundreds of copies and showed them in New York City. Méliès received no compensation. He was counting on taking the film to US and recapture the huge cost of it by showing it throughout the US when he realized it has already been showing in the US by Edison. This bankrupted Méliès.[44] Other exhibitors similarly routinely copied and exhibited each others films.[45] To better protect the copyrights on his films, Edison deposited prints of them on long strips of photographic paper with the U.S. copyright office. Many of these paper prints survived longer and in better condition than the actual films of that era.[46]

Edison's favourite movie was The Birth of a Nation. He thought that talkies had "spoiled everything" for him. "There isn't any good acting on the screen. They concentrate on the voice now and have forgotten how to act. I can sense it more than you because I am deaf."[47]

In 1908, Edison started the Motion Picture Patents Company, which was a conglomerate of nine major film studios (commonly known as the Edison Trust). Thomas Edison was the first honorary fellow of the Acoustical Society of America, which was founded in 1929.

West Orange and Fort Myers (1886-1931)

Edison moved from Menlo Park after the death of Mary Stilwell and purchased a home known as "Glenmont" in 1886 as a wedding gift for Mina in Llewellyn Park in West Orange, New Jersey. In 1885, Thomas Edison bought property in Fort Myers, Florida, and built what was later called Seminole Lodge as a winter retreat. Edison and his wife Mina spent many winters in Fort Myers where they recreated and Edison tried to find a domestic source of natural rubber.

Henry Ford, the automobile magnate, later lived a few hundred feet away from Edison at his winter retreat in Fort Myers, Florida. Edison even contributed technology to the automobile. They were friends until Edison's death.

Thomas A. Edison Industries Exhibit, Primary Battery section, 1915
Henry Ford, Thomas Edison, Harvey Firestone—the fathers of modernity. Ft. Myers, Florida, February 11, 1929.

In 1928, Edison joined the Fort Myers Civitan Club. He believed strongly in the organization, writing that "The Civitan Club is doing things--big things--for the community, state, and nation, and I certainly consider it an honor to be numbered in its ranks."[48] He was an active member in the club until his death, sometimes bringing Henry Ford to the club's meetings.

The final years

Edison was active in business right up to the end. Just months before his death in 1931, the Lackawanna Railroad implemented electric trains in suburban service from Hoboken to Gladstone, Montclair and Dover in New Jersey. Transmission was by means of an overhead catenary system, with the entire project under Edison's guidance. To the surprise of many, he was at the throttle of the very first MU (Multiple-Unit) train to depart Lackawanna Terminal in Hoboken, driving the train all the way to Dover. As another tribute to his lasting legacy, the same fleet of cars Edison deployed on the Lackawanna in 1931 served commuters until their retirement in 1984, when some of them were purchased by the Berkshire Scenic Railway Museum in Lenox, MA. A special plaque commemorating the joint achievement of both the railway and Edison, can be seen today in the waiting room of Lackawanna Terminal in Hoboken, presently operated by New Jersey Transit.[49]

Edison was said to have been influenced by a fad diet that was popular in the day to that in his last few years "the only liquid he consumed was a pint of milk every three hours".[23] He is reported to have believed this diet would restore his health. However, this tale is doubtful. In 1930, the year before Edison died, Mina said in an interview about him that "Correct eating is one of his greatest hobbies." She also said that during one of his periodic "great scientific adventures", Edison would be up at 7:00, have breakfast at 8:00, and be rarely home for lunch or dinner, implying that he continued to have all three.[47]

Edison became the owner of his Milan, Ohio, birthplace in 1906. On his last visit, in 1923, he was shocked to find his old home still lit by lamps and candles.

Thomas Edison died of complications of diabetes on October 18, 1931, in his home, "Glenmont" in Llewellyn Park in West Orange, New Jersey, which he had purchased in 1886 as a wedding gift for Mina. He is buried behind the home.[50][51]

Mina died in 1947. Edison's last breath is reportedly contained in a test tube at the Henry Ford Museum. Ford reportedly convinced Charles Edison to seal a test tube of air in the inventor's room shortly after his death, as a memento. A plaster death mask was also made.[52]

Views on politics, religion and metaphysics

Historian Paul Israel has characterized Edison as a "freethinker".[23] Edison was heavily influenced by Thomas Paine's The Age of Reason.[23] Edison defended Paine's "scientific deism", saying, "He has been called an atheist, but atheist he was not. Paine believed in a supreme intelligence, as representing the idea which other men often express by the name of deity."[23] In an October 2, 1910 interview in the New York Times Magazine, Edison stated:

Nature is what we know. We do not know the gods of religions. And nature is not kind, or merciful, or loving. If God made me – the fabled God of the three qualities of which I spoke: mercy, kindness, love – He also made the fish I catch and eat. And where do His mercy, kindness, and love for that fish come in? No; nature made us – nature did it all – not the gods of the religions.[53]

Edison was called an atheist for those remarks, and although he did not allow himself to be drawn into the controversy publicly, he clarified himself in a private letter: "You have misunderstood the whole article, because you jumped to the conclusion that it denies the existence of God. There is no such denial, what you call God I call Nature, the Supreme intelligence that rules matter. All the article states is that it is doubtful in my opinion if our intelligence or soul or whatever one may call it lives hereafter as an entity or disperses back again from whence it came, scattered amongst the cells of which we are made."[23]

Nonviolence was key to Edison's moral views, and when asked to serve as a naval consultant for World War I, specified he would only work on defensive weapons and later noted, "I am proud of the fact that I never invented weapons to kill." Edison's philosophy of nonviolence extended to animals as well, about which he stated: "Nonviolence leads to the highest ethics, which is the goal of all evolution. Until we stop harming all other living beings, we are still savages."[54]

Tributes

Places named for Edison

Several places have been named after Edison, most notably the town of Edison, New Jersey. Thomas Edison State College, a nationally-known college for adult learners, is in Trenton, New Jersey. Two community colleges are named for him: Edison State College in Fort Myers, Florida, and Edison Community College in Piqua, Ohio.[55] There are numerous high schools named after Edison; see Edison High School.

The City Hotel, in Sunbury, Pennsylvania, was the first building to be lit with Edison's three-wire system. The hotel was re-named The Hotel Edison, and retains that name today.

Three bridges around the United States have been named in his honor (see Edison Bridge).

Museums and memorials

In West Orange, New Jersey, the 13.5 acre (5.5 ha) Glenmont estate is maintained and operated by the National Park Service as the Edison National Historic Site.[citation needed] The Thomas Alva Edison Memorial Tower and Museum is in the town of Edison, New Jersey.[citation needed] In Beaumont, Texas, there is an Edison Museum, though Edison never visited there.[citation needed] The Port Huron Museum, in Port Huron, Michigan, restored the original depot that Thomas Edison worked out of as a young newsbutcher. The depot has been named the Thomas Edison Depot Museum.[citation needed] The town has many Edison historical landmarks, including the graves of Edison's parents, and a monument along the Saint Clair River. Edison's influence can be seen throughout this city of 32,000. In Detroit, the Edison Memorial Fountain in Grand Circus Park was created to honor his achievements. The limestone fountain was dedicated October 21, 1929.[citation needed]

Companies bearing Edison's name

Awards named in honor of Edison

The Edison Medal was created on February 11, 1904, by a group of Edison's friends and associates. Four years later the American Institute of Electrical Engineers (AIEE), later IEEE, entered into an agreement with the group to present the medal as its highest award. The first medal was presented in 1909 to Elihu Thomson and, in a twist of fate, was awarded to Nikola Tesla in 1917. It is the oldest award in the area of electrical and electronics engineering, and is presented annually "for a career of meritorious achievement in electrical science, electrical engineering or the electrical arts."

In the Netherlands, the major music awards are named the Edison Award after him.

The American Society of Mechanical Engineers concedes the Thomas A. Edison Patent Award to individual patents since 2000.[56]

Honors and awards given to Edison

In 1887, Edison won the Matteucci Medal. In 1890, he was elected a member of the Royal Swedish Academy of Sciences.

He was ranked thirty-fifth on Michael H. Hart's 1978 book The 100, a list of the most influential figures in history. Life magazine (USA), in a special double issue in 1997, placed Edison first in the list of the "100 Most Important People in the Last 1000 Years", noting that the light bulb he promoted "lit up the world". In the 2005 television series The Greatest American, he was voted by viewers as the fifteenth-greatest.

In 1983, the United States Congress, pursuant to Senate Joint Resolution 140 (Public Law 97 - 198), designated February 11, Edison's birthday, as National Inventor's Day.

Other items named after Edison

The United States Navy named the USS Edison (DD-439), a Gleaves class destroyer, in his honor in 1940. The ship was decommissioned a few months after the end of World War II. In 1962, the Navy commissioned USS Thomas A. Edison (SSBN-610), a fleet ballistic missile nuclear-powered submarine. Decommissioned on December 1, 1983, Thomas A. Edison was stricken from the Naval Vessel Register on April 30, 1986. She went through the Navy’s Nuclear Powered Ship and Submarine Recycling Program at Bremerton, Washington, beginning on October 1, 1996. When she finished the program on December 1, 1997, she ceased to exist as a complete ship and was listed as scrapped.

In popular culture

Thomas Edison has appeared in popular culture as a character in novels, films, comics and video games. His prolific inventing helped make him an icon and he has made appearances in popular culture during his lifetime down to the present day. His history with Nikola Tesla has also provided dramatic tension and is a theme returned to numerous times.

Thomas Alva Edison

"Genius is one percent inspiration, ninety-nine percent perspiration."
- Thomas Alva Edison, Harper's Monthly (September 1932)
Born February 11, 1847(1847-02-11)
Milan, Ohio
Died October 18, 1931 (aged 84)
West Orange, New Jersey
Occupation inventor, scientist, businessman
Religious beliefs Deist
Spouse(s) Mary Stilwell (m. 1871–1884) «start: (1871)–end+1: (1885)»"Marriage: Mary Stilwell to Thomas Edison" Location: (linkback:http://en.wikipedia.org/wiki/Thomas_Edison)
Mina Edison (m. 1886–1931) «start: (1886)–end+1: (1932)»"Marriage: Mina Edison to Thomas Edison" Location: (linkback:http://en.wikipedia.org/wiki/Thomas_Edison)
Children Marion Estelle Edison (1873–1965)
Thomas Alva Edison Jr. (1876–1935)
William Leslie Edison (1878–1937)
Madeleine Edison (1888–1979)
Charles Edison (1890–1969)
Theodore Miller Edison (1898–1992)
Parents Samuel Ogden Edison, Jr. (1804–1896)
Nancy Matthews Elliott (1810–1871)
Relatives Lewis Miller (father-in-law)