26 June 2009

Gas-electric car

The invention: 

A hybrid automobile with both an internal combustion engine and an electric motor.

The people behind the invention: 

Victor Wouk -   an American engineer Tom Elliott, executive vice president of
                           American Honda Motor Company
Hiroyuki Yoshino - president and chief executive officer of Honda Motor Company
Fujio Cho              -  president of Toyota Motor Corporation

23 June 2009

Fuel cell

The invention: An electrochemical cell that directly converts energy from reactions between oxidants and fuels, such as liquid hydrogen, into electrical energy. The people behind the invention: Francis Thomas Bacon (1904-1992), an English engineer Sir William Robert Grove (1811-1896), an English inventor Georges Leclanché (1839-1882), a French engineer Alessandro Volta (1745-1827), an Italian physicist The Earth’s Resources Because of the earth’s rapidly increasing population and the dwindling of fossil fuels (natural gas, coal, and petroleum), there is a need to design and develop new ways to obtain energy and to encourage its intelligent use. The burning of fossil fuels to create energy causes a slow buildup of carbon dioxide in the atmosphere, creating pollution that poses many problems for all forms of life on this planet. Chemical and electrical studies can be combined to create electrochemical processes that yield clean energy. Because of their very high rate of efficiency and their nonpolluting nature, fuel cells may provide the solution to the problem of finding sufficient energy sources for humans. The simple reaction of hydrogen and oxygen to form water in such a cell can provide an enormous amount of clean (nonpolluting) energy. Moreover, hydrogen and oxygen are readily available. Studies by Alessandro Volta, Georges Leclanché, and William Grove preceded the work of Bacon in the development of the fuel cell. Bacon became interested in the idea of a hydrogen-oxygen fuel cell in about 1932. His original intent was to develop a fuel cell that could be used in commercial applications. The Fuel Cell Emerges In 1800, the Italian physicist Alessandro Volta experimented with solutions of chemicals and metals that were able to conduct electricity. He found that two pieces of metal and such a solution could be arranged in such a way as to produce an electric current. His creation was the first electrochemical battery, a device that produced energy from a chemical reaction. Studies in this area were continued by various people, and in the late nineteenth century, Georges Leclanché invented the dry cell battery, which is now commonly used. The work of William Grove followed that of Leclanché. His first significant contribution was the Grove cell, an improved form of the cells described above, which became very popular. Grove experimented with various forms of batteries and eventually invented the “gas battery,” which was actually the earliest fuel cell. It is worth noting that his design incorporated separate test tubes of hydrogen and oxygen, which he placed over strips of platinum. After studying the design of Grove’s fuel cell, Bacon decided that, for practical purposes, the use of platinum and other precious metals should be avoided. By 1939, he had constructed a cell in which nickel replaced the platinum used. The theory behind the fuel cell can be described in the following way. If a mixture of hydrogen and oxygen is ignited, energy is released in the form of a violent explosion. In a fuel cell, however, the reaction takes place in a controlled manner. Electrons lost by the hydrogen gas flow out of the fuel cell and return to be taken up by the oxygen in the cell. The electron flow provides electricity to any device that is connected to the fuel cell, and the water that the fuel cell produces can be purified and used for drinking. Bacon’s studies were interrupted byWorldWar II. After the war was over, however, Bacon continued his work. Sir Eric Keightley Rideal of Cambridge University in England supported Bacon’s studies; later, others followed suit. In January, 1954, Bacon wrote an article entitled “Research into the Properties of the Hydrogen/ Oxygen Fuel Cell” for a British journal. He was surprised at the speed with which news of the article spread throughout the scientific world, particularly in the United States. After a series of setbacks, Bacon demonstrated a forty-cell unit that had increased power. This advance showed that the fuel cell was not merely an interesting toy; it had the capacity to do useful work. At this point, the General Electric Company (GE), an American corporation, sent a representative to England to offer employment in the United States to senior members of Bacon’s staff. Three scientists accepted the offer. A high point in Bacon’s career was the announcement that the American Pratt and Whitney Aircraft company had obtained an order to build fuel cells for the Apollo project, which ultimately put two men on the Moon in 1969. Toward the end of his career in 1978, Bacon hoped that commercial applications for his fuel cells would be found.Impact Because they are lighter and more efficient than batteries, fuel cells have proved to be useful in the space program. Beginning with the Gemini 5 spacecraft, alkaline fuel cells (in which a water solution of potassium hydroxide, a basic, or alkaline, chemical, is placed) have been used for more than ten thousand hours in space. The fuel cells used aboard the space shuttle deliver the same amount of power as batteries weighing ten times as much. On a typical seven-day mission, the shuttle’s fuel cells consume 680 kilograms (1,500 pounds) of hydrogen and generate 719 liters (190 gallons) of water that can be used for drinking. Major technical and economic problems must be overcome in order to design fuel cells for practical applications, but some important advancements have been made.Afew test vehicles that use fuel cells as a source of power have been constructed. Fuel cells using hydrogen as a fuel and oxygen to burn the fuel have been used in a van built by General Motors Corporation. Thirty-two fuel cells are installed below the floorboards, and tanks of liquid oxygen are carried in the back of the van. A power plant built in New York City contains stacks of hydrogen-oxygen fuel cells, which can be put on line quickly in response to power needs. The Sanyo Electric Company has developed an electric car that is partially powered by a fuel cell. These tremendous technical advances are the result of the singleminded dedication of Francis Thomas Bacon, who struggled all of his life with an experiment he was convinced would be successful.


The invention: 

Method for preserving foods and other organic matter by freezing them and using a vacuum to remove their water content without damaging their solid matter.

The people behind the invention:

Earl W. Flosdorf (1904- ), an American physician
Ronald I. N. Greaves (1908- ), an English pathologist
Jacques Arsène d’Arsonval (1851-1940), a French physicist

FORTRAN programming language

The invention: The first major computer programming language, FORTRAN supported programming in a mathematical language that was natural to scientists and engineers and achieved unsurpassed success in scientific computation. The people behind the invention: John Backus (1924- ), an American software engineer and manager John W. Mauchly (1907-1980), an American physicist and engineer Herman Heine Goldstine (1913- ), a mathematician and computer scientist John von Neumann (1903-1957), a Hungarian American mathematician and physicist Talking to Machines Formula Translation, or FORTRAN—the first widely accepted high-level computer language—was completed by John Backus and his coworkers at the International Business Machines (IBM) Corporation in April, 1957. Designed to support programming in a mathematical language that was natural to scientists and engineers, FORTRAN achieved unsurpassed success in scientific computation. Computer languages are means of specifying the instructions that a computer should execute and the order of those instructions. Computer languages can be divided into categories of progressively higher degrees of abstraction. At the lowest level is binary code, or machine code: Binary digits, or “bits,” specify in complete detail every instruction that the machine will execute. This was the only language available in the early days of computers, when such machines as the ENIAC (Electronic Numerical Integrator and Calculator) required hand-operated switches and plugboard connections. All higher levels of language are implemented by having a program translate instructions written in the higher language into binary machine language (also called “object code”). High-level languages (also called “programming languages”) are largely or entirely independent of the underlying machine structure. FORTRAN was the first language of this type to win widespread acceptance. The emergence of machine-independent programming languages was a gradual process that spanned the first decade of electronic computation. One of the earliest developments was the invention of “flowcharts,” or “flow diagrams,” by Herman Heine Goldstine and John von Neumann in 1947. Flowcharting became the most influential software methodology during the first twenty years of computing. Short Code was the first language to be implemented that contained some high-level features, such as the ability to use mathematical equations. The idea came from JohnW. Mauchly, and it was implemented on the BINAC (Binary Automatic Computer) in 1949 with an “interpreter”; later, it was carried over to the UNIVAC (Universal Automatic Computer) I. Interpreters are programs that do not translate commands into a series of object-code instructions; instead, they directly execute (interpret) those commands. Every time the interpreter encounters a command, that command must be interpreted again. “Compilers,” however, convert the entire command into object code before it is executed. Much early effort went into creating ways to handle commonly encountered problems—particularly scientific mathematical calculations. A number of interpretive languages arose to support these features. As long as such complex operations had to be performed by software (computer programs), however, scientific computation would be relatively slow. Therefore, Backus lobbied successfully for a direct hardware implementation of these operations on IBM’s new scientific computer, the 704. Backus then started the Programming Research Group at IBM in order to develop a compiler that would allow programs to be written in a mathematically oriented language rather than a machine-oriented language. In November of 1954, the group defined an initial version of FORTRAN.A More Accessible Language Before FORTRAN was developed, a computer had to perform a whole series of tasks to make certain types of mathematical calculations. FORTRAN made it possible for the same calculations to be performed much more easily. In general, FORTRAN supported constructs with which scientists were already acquainted, such as functions and multidimensional arrays. In defining a powerful notation that was accessible to scientists and engineers, FORTRAN opened up programming to a much wider community. Backus’s success in getting the IBM 704’s hardware to support scientific computation directly, however, posed a major challenge: Because such computation would be much faster, the object code produced by FORTRAN would also have to be much faster. The lower-level compilers preceding FORTRAN produced programs that were usually five to ten times slower than their hand-coded counterparts; therefore, efficiency became the primary design objective for Backus. The highly publicized claims for FORTRAN met with widespread skepticism among programmers. Much of the team’s efforts, therefore, went into discovering ways to produce the most efficient object code. The efficiency of the compiler produced by Backus, combined with its clarity and ease of use, guaranteed the system’s success. By 1959, many IBM 704 users programmed exclusively in FORTRAN. By 1963, virtually every computer manufacturer either had delivered or had promised a version of FORTRAN. Incompatibilities among manufacturers were minimized by the popularity of IBM’s version of FORTRAN; every company wanted to be able to support IBM programs on its own equipment. Nevertheless, there was sufficient interest in obtaining a standard for FORTRAN that the American National Standards Institute adopted a formal standard for it in 1966. Arevised standard was adopted in 1978, yielding FORTRAN 77. Consequences In demonstrating the feasibility of efficient high-level languages, FORTRAN inaugurated a period of great proliferation of programming languages. Most of these languages attempted to provide similar or better high-level programming constructs oriented toward a different, nonscientific programming environment. COBOL, for example, stands for “Common Business Oriented Language.” FORTRAN, while remaining the dominant language for scientific programming, has not found general acceptance among nonscientists. An IBM project established in 1963 to extend FORTRAN found the task too unwieldy and instead ended up producing an entirely different language, PL/I, which was delivered in 1966. In the beginning, Backus and his coworkers believed that their revolutionary language would virtually eliminate the burdens of coding and debugging. Instead, FORTRAN launched software as a field of study and an industry in its own right. In addition to stimulating the introduction of new languages, FORTRAN encouraged the development of operating systems. Programming languages had already grown into simple operating systems called “monitors.” Operating systems since then have been greatly improved so that they support, for example, simultaneously active programs (multiprogramming) and the networking (combining) of multiple computers.

21 June 2009

Food freezing

The invention: It was long known that low temperatures helped to protect food against spoiling; the invention that made frozen food practical was a method of freezing items quickly. Clarence Birdseye’s quick-freezing technique made possible a revolution in food preparation, storage, and distribution. The people behind the invention: Clarence Birdseye (1886-1956), a scientist and inventor Donald K. Tressler (1894-1981), a researcher at Cornell University Amanda Theodosia Jones (1835-1914), a food-preservation pioneer Feeding the Family In 1917, Clarence Birdseye developed a means of quick-freezing meat, fish, vegetables, and fruit without substantially changing their original taste. His system of freezing was called by Fortune magazine “one of the most exciting and revolutionary ideas in the history of food.” Birdseye went on to refine and perfect his method and to promote the frozen foods industry until it became a commercial success nationwide. It was during a trip to Labrador, where he worked as a fur trader, that Birdseye was inspired by this idea. Birdseye’s new wife and five-week-old baby had accompanied him there. In order to keep his family well fed, he placed barrels of fresh cabbages in salt water and then exposed the vegetables to freezing winds. Successful at preserving vegetables, he went on to freeze a winter’s supply of ducks, caribou, and rabbit meat. In the following years, Birdseye experimented with many freezing techniques. His equipment was crude: an electric fan, ice, and salt water. His earliest experiments were on fish and rabbits, which he froze and packed in old candy boxes. By 1924, he had borrowed money against his life insurance and was lucky enough to find three partners willing to invest in his new General Seafoods Company (later renamed General Foods), located in Gloucester, Massachusetts. Although it was Birdseye’s genius that put the principles of quick-freezing to work, he did not actually invent quick-freezing. The scientific principles involved had been known for some time. As early as 1842, a patent for freezing fish had been issued in England. Nevertheless, the commercial exploitation of the freezing process could not have happened until the end of the 1800’s, when mechanical refrigeration was invented. Even then, Birdseye had to overcome major obstacles. Finding a Niche By the 1920’s, there still were few mechanical refrigerators in American homes. It would take years before adequate facilities for food freezing and retail distribution would be established across the United States. By the late 1930’s, frozen foods had, indeed, found its role in commerce but still could not compete with canned or fresh foods. Birdseye had to work tirelessly to promote the industry, writing and delivering numerous lectures and articles to advance its popularity. His efforts were helped by scientific research conducted at Cornell University by Donald K. Tressler and by C. R. Fellers of what was then Massachusetts State College. Also, during World War II (1939-1945), more Americans began to accept the idea: Rationing, combined with a shortage of canned foods, contributed to the demand for frozen foods. The armed forces made large purchases of these items as well. General Foods was the first to use a system of extremely rapid freezing of perishable foods in packages. Under the Birdseye system, fresh foods, such as berries or lobster, were packaged snugly in convenient square containers. Then, the packages were pressed between refrigerated metal plates under pressure at 50 degrees below zero. Two types of freezing machines were used. The “double belt” freezer consisted of two metal belts that moved through a 15-meter freezing tunnel, while a special salt solution was sprayed on the surfaces of the belts. This double-belt freezer was used only in permanent installations and was soon replaced by the “multiplate” freezer, which was portable and required only 11.5 square meters of floor space compared to the double belt’s 152 square meters.The multiplate freezer also made it possible to apply the technique of quick-freezing to seasonal crops. People were able to transport these freezers easily from one harvesting field to another, where they were used to freeze crops such as peas fresh off the vine. The handy multiplate freezer consisted of an insulated cabinet equipped with refrigerated metal plates. Stacked one above the other, these plates were capable of being opened and closed to receive food products and to compress them with evenly distributed pressure. Each aluminum plate had internal passages through which ammonia flowed and expanded at a temperature of -3.8 degrees Celsius, thus causing the foods to freeze. A major benefit of the new frozen foods was that their taste and vitamin content were not lost. Ordinarily, when food is frozen slowly, ice crystals form, which slowly rupture food cells, thus altering the taste of the food. With quick-freezing, however, the food looks, tastes, and smells like fresh food. Quick-freezing also cuts down on bacteria. Impact During the months between one food harvest and the next, humankind requires trillions of pounds of food to survive. In many parts of the world, an adequate supply of food is available; elsewhere, much food goes to waste and many go hungry. Methods of food preservation such as those developed by Birdseye have done much to help those who cannot obtain proper fresh foods. Preserving perishable foods also means that they will be available in greater quantity and variety all year-round. In all parts of the world, both tropical and arctic delicacies can be eaten in any season of the year. With the rise in popularity of frozen “fast” foods, nutritionists began to study their effect on the human body. Research has shown that fresh is the most beneficial. In an industrial nation with many people, the distribution of fresh commodities is, however, difficult. It may be many decades before scientists know the long-term effects on generations raised primarily on frozen foods.

FM radio

The invention: A method of broadcasting radio signals by modulating the frequency, rather than the amplitude, of radio waves, FM radio greatly improved the quality of sound transmission. The people behind the invention: Edwin H. Armstrong (1890-1954), the inventor of FM radio broadcasting David Sarnoff (1891-1971), the founder of RCA An Entirely New System Because early radio broadcasts used amplitude modulation (AM) to transmit their sounds, they were subject to a sizable amount of interference and static. Since goodAMreception relies on the amount of energy transmitted, energy sources in the atmosphere between the station and the receiver can distort or weaken the original signal. This is particularly irritating for the transmission of music. Edwin H. Armstrong provided a solution to this technological constraint. A graduate of Columbia University, Armstrong made a significant contribution to the development of radio with his basic inventions for circuits for AM receivers. (Indeed, the monies Armstrong received from his earlier inventions financed the development of the frequency modulation, or FM, system.) Armstrong was one among many contributors to AM radio. For FM broadcasting, however, Armstrong must be ranked as the most important inventor. During the 1920’s, Armstrong established his own research laboratory in Alpine, New Jersey, across the Hudson River from New York City. With a small staff of dedicated assistants, he carried out research on radio circuitry and systems for nearly three decades. At that time, Armstrong also began to teach electrical engineering at Columbia University. From 1928 to 1933, Armstrong worked diligently at his private laboratory at Columbia University to construct a working model of an FM radio broadcasting system. With the primitive limitations then imposed on the state of vacuum tube technology, a number of Armstrong’s experimental circuits required as many as one hundred tubes. Between July, 1930, and January, 1933, Armstrong filed four basic FM patent applications. All were granted simultaneously on December 26, 1933. Armstrong sought to perfectFMradio broadcasting, not to offer radio listeners better musical reception but to create an entirely new radio broadcasting system. On November 5, 1935, Armstrong made his first public demonstration of FM broadcasting in New York City to an audience of radio engineers. An amateur station based in suburban Yonkers, New York, transmitted these first signals. The scientific world began to consider the advantages and disadvantages of Armstrong’s system; other laboratories began to craft their own FM systems. Corporate Conniving Because Armstrong had no desire to become a manufacturer or broadcaster, he approached David Sarnoff, head of the Radio Corporation of America (RCA). As the owner of the top manufacturer of radio sets and the top radio broadcasting network, Sarnoff was interested in all advances of radio technology. Armstrong first demonstrated FM radio broadcasting for Sarnoff in December, 1933. This was followed by visits from RCA engineers, who were sufficiently impressed to recommend to Sarnoff that the company conduct field tests of the Armstrong system. In 1934, Armstrong, with the cooperation of RCA, set up a test transmitter at the top of the Empire State Building, sharing facilities with the experimental RCAtelevision transmitter. From 1934 through 1935, tests were conducted using the Empire State facility, to mixed reactions of RCA’s best engineers. AM radio broadcasting already had a performance record of nearly two decades. The engineers wondered if this new technology could replace something that had worked so well. This less-than-enthusiastic evaluation fueled the skepticism of RCA lawyers and salespeople. RCA had too much invested in the AM system, both as a leading manufacturer and as the dominant owner of the major radio network of the time, the National Broadcasting Company (NBC). Sarnoff was in no rush to adopt FM. To change systems would risk the millions of dollars RCAwas making as America emerged from the Great Depression. In 1935, Sarnoff advised Armstrong that RCA would cease any further research and development activity in FM radio broadcasting. (Still, engineers at RCA laboratories continued to work on FM to protect the corporate patent position.) Sarnoff declared to the press that his company would push the frontiers of broadcasting by concentrating on research and development of radio with pictures, that is, television. As a tangible sign, Sarnoff ordered that Armstrong’s FM radio broadcasting tower be removed from the top of the Empire State Building. Armstrong was outraged. By the mid-1930’s, the development of FM radio broadcasting had become a mission for Armstrong. For the remainder of his life, Armstrong devoted his considerable talents to the promotion of FM radio broadcasting. Impact After the break with Sarnoff, Armstrong proceeded with plans to develop his own FM operation. Allied with two of RCA’s biggest manufacturing competitors, Zenith and General Electric, Armstrong pressed ahead. In June of 1936, at a Federal Communications Commission (FCC) hearing, Armstrong proclaimed that FM broadcasting was the only static-free, noise-free, and uniform system—both day and night—available. He argued, correctly, thatAMradio broadcasting had none of these qualities. During World War II (1939-1945), Armstrong gave the military permission to use FM with no compensation. That patriotic gesture cost Armstrong millions of dollars when the military soon became all FM. It did, however, expand interest in FM radio broadcasting. World War II had provided a field test of equipment and use. By the 1970’s, FM radio broadcasting had grown tremendously. By 1972, one in three radio listeners tuned into an FM station some time during the day. Advertisers began to use FM radio stations to reach the young and affluent audiences that were turning to FM stations in greater numbers. By the late 1970’s, FM radio stations were outnumberingAMstations. By 1980, nearly half of radio listeners tuned into FM stations on a regular basis. Adecade later, FM radio listening accounted for more than two-thirds of audience time. Armstrong’s predictions that listeners would prefer the clear, static-free sounds offered by FM radio broadcasting had come to pass by the mid-1980’s, nearly fifty years after Armstrong had commenced his struggle to make FM radio broadcasting a part of commercial radio.

Fluorescent lighting

lighting The invention: A form of electrical lighting that uses a glass tube coated with phosphor that gives off a cool bluish light and emits ultraviolet radiation. The people behind the invention: Vincenzo Cascariolo (1571-1624), an Italian alchemist and shoemaker Heinrich Geissler (1814-1879), a German glassblower Peter Cooper Hewitt (1861-1921), an American electrical engineer Celebrating the “Twelve Greatest Inventors” On the night of November 23, 1936, more than one thousand industrialists, patent attorneys, and scientists assembled in the main ballroom of the Mayflower Hotel in Washington, D.C., to celebrate the one hundredth anniversary of the U.S. Patent Office.Atransport liner over the city radioed the names chosen by the Patent Office as America’s “Twelve Greatest Inventors,” and, as the distinguished group strained to hear those names, “the room was flooded for a moment by the most brilliant light yet used to illuminate a space that size.” Thus did The New York Times summarize the commercial introduction of the fluorescent lamp. The twelve inventors present were Thomas Alva Edison, Robert Fulton, Charles Goodyear, Charles Hall, Elias Howe, Cyrus Hall McCormick, Ottmar Mergenthaler, Samuel F. B. Morse, George Westinghouse, Wilbur Wright, and Eli Whitney. There was, however, no name to bear the honor for inventing fluorescent lighting. That honor is shared by many who participated in a very long series of discoveries. The fluorescent lamp operates as a low-pressure, electric discharge inside a glass tube that contains a droplet of mercury and a gas, commonly argon. The inside of the glass tube is coated with fine particles of phosphor. When electricity is applied to the gas, the mercury gives off a bluish light and emits ultraviolet radiation.When bathed in the strong ultraviolet radiation emitted by the mercury, the phosphor fluoresces (emits light). The setting for the introduction of the fluorescent lamp began at the beginning of the 1600’s, when Vincenzo Cascariolo, an Italian shoemaker and alchemist, discovered a substance that gave off a bluish glow in the dark after exposure to strong sunlight. The fluorescent substance was apparently barium sulfide and was so unusual for that time and so valuable that its formulation was kept secret for a long time. Gradually, however, scholars became aware of the preparation secrets of the substance and studied it and other luminescent materials. Further studies in fluorescent lighting were made by the German physicist Johann Wilhelm Ritter. He observed the luminescence of phosphors that were exposed to various “exciting” lights. In 1801, he noted that some phosphors shone brightly when illuminated by light that the eye could not see (ultraviolet light). Ritter thus discovered the ultraviolet region of the light spectrum. The use of phosphors to transform ultraviolet light into visible light was an important step in the continuing development of the fluorescent lamp. Further studies in fluorescent lighting were made by the German physicist Johann Wilhelm Ritter. He observed the luminescence of phosphors that were exposed to various “exciting” lights. In 1801, he noted that some phosphors shone brightly when illuminated by light that the eye could not see (ultraviolet light). Ritter thus discovered the ultraviolet region of the light spectrum. The use of phosphors to transform ultraviolet light into visible light was an important step in the continuing development of the fluorescent lamp. The British mathematician and physicist Sir George Gabriel Stokes studied the phenomenon as well. It was he who, in 1852, termed the afterglow “fluorescence.” Geissler Tubes While these advances were being made, other workers were trying to produce a practical form of electric light. In 1706, the English physicist Francis Hauksbee devised an electrostatic generator, which is used to accelerate charged particles to very high levels of electrical energy. He then connected the device to a glass “jar,” used a vacuum pump to evacuate the jar to a low pressure, and tested his generator. In so doing, Hauksbee obtained the first human-made electrical glow discharge by “capturing lightning” in a jar. In 1854, Heinrich Geissler, a glassblower and apparatus maker, opened his shop in Bonn, Germany, to make scientific instruments; in 1855, he produced a vacuum pump that used liquid mercury as an evacuation fluid. That same year, Geissler made the first gaseous conduction lamps while working in collaboration with the German scientist Julius Plücker. Plücker referred to these lamps as “Geissler tubes.” Geissler was able to create red light with neon gas filling a lamp and light of nearly all colors by using certain types of gas within each of the lamps. Thus, both the neon sign business and the science of spectroscopy were born. Geissler tubes were studied extensively by a variety of workers. At the beginning of the twentieth century, the practical American engineer Peter Cooper Hewitt put these studies to use by marketing the first low-pressure mercury vapor lamps. The lamps were quite successful, although they required high voltage for operation, emitted an eerie blue-green, and shone dimly by comparison with their eventual successor, the fluorescent lamp. At about the same time, systematic studies of phosphors had finally begun. By the 1920’s, a number of investigators had discovered that the low-pressure mercury vapor discharge marketed by Hewitt was an extremely efficient method for producing ultraviolet light, if the mercury and rare gas pressures were properly adjusted. With a phosphor to convert the ultraviolet light back to visible light, the Hewitt lamp made an excellent light source. Impact The introduction of fluorescent lighting in 1936 presented the public with a completely new form of lighting that had enormous advantages of high efficiency, long life, and relatively low cost. By 1938, production of fluorescent lamps was well under way. By April, 1938, four sizes of fluorescent lamps in various colors had been offered to the public and more than two hundred thousand lamps had been sold. During 1939 and 1940, two great expositions—the New York World’s Fair and the San Francisco International Exposition— helped popularize fluorescent lighting. Thousands of tubular fluorescent lamps formed a great spiral in the “motor display salon,” the car showroom of the General Motors exhibit at the New York World’s Fair. Fluorescent lamps lit the Polish Restaurant and hung in vertical clusters on the flagpoles along theAvenue of the Flags at the fair, while two-meter-long, upright fluorescent tubes illuminated buildings at the San Francisco International Exposition. When the United States entered World War II (1939-1945), the demand for efficient factory lighting soared. In 1941, more than twenty-one million fluorescent lamps were sold. Technical advances continued to improve the fluorescent lamp. By the 1990’s, this type of lamp supplied most of the world’s artificial lighting.