Laser-diode recording process

The invention: Video and audio playback system that uses a lowpower laser to decode information digitally stored on reflective disks. The organization behind the invention: The Philips Corporation, a Dutch electronics firm The Development of Digital Systems Since the advent of the computer age, it has been the goal of many equipment manufacturers to provide reliable digital systems for the storage and retrieval of video and audio programs. A need for such devices was perceived for several reasons. Existing storage media (movie film and 12-inch, vinyl, long-playing records) were relatively large and cumbersome to manipulate and were prone to degradation, breakage, and unwanted noise. Thus, during the late 1960’s, two different methods for storing video programs on disc were invented. A mechanical system was demonstrated by the Telefunken Company, while the Radio Corporation of America (RCA) introduced an electrostatic device (a device that used static electricity). The first commercially successful system, however, was developed during the mid-1970’s by the Philips Corporation. Philips devoted considerable resources to creating a digital video system, read by light beams, which could reproduce an entire feature- length film from one 12-inch videodisc. An integral part of this innovation was the fabrication of a device small enough and fast enough to read the vast amounts of greatly compacted data stored on the 12-inch disc without introducing unwanted noise. Although Philips was aware of the other formats, the company opted to use an optical scanner with a small “semiconductor laser diode” to retrieve the digital information. The laser diode is only a fraction of a millimeter in size, operates quite efficiently with high amplitude and relatively low power (0.1 watt), and can be used continuously. Because this configuration operates at a high frequency, its informationcarrying capacity is quite large.Although the digital videodisc system (called “laservision”) works well, the low level of noise and the clear images offered by this system were masked by the low quality of the conventional television monitors on which they were viewed. Furthermore, the high price of the playback systems and the discs made them noncompetitive with the videocassette recorders (VCRs) that were then capturing the market for home systems. VCRs had the additional advantage that programs could be recorded or copied easily. The Philips Corporation turned its attention to utilizing this technology in an area where low noise levels and high quality would be more readily apparent— audio disc systems. By 1979, they had perfected the basic compact disc (CD) system, which soon revolutionized the world of stereophonic home systems. Reading Digital Discs with Laser Light Digital signals (signals composed of numbers) are stored on discs as “pits” impressed into the plastic disc and then coated with a thin reflective layer of aluminum. A laser beam, manipulated by delicate, fast-moving mirrors, tracks and reads the digital information as changes in light intensity. These data are then converted to a varying electrical signal that contains the video or audio information. The data are then recovered by means of a sophisticated pickup that consists of the semiconductor laser diode, a polarizing beam splitter, an objective lens, a collective lens system, and a photodiode receiver. The beam from the laser diode is focused by a collimator lens (a lens that collects and focuses light) and then passes through the polarizing beam splitter (PBS). This device acts like a one-way mirror mounted at 45 degrees to the light path. Light from the laser passes through the PBS as if it were a window, but the light emerges in a polarized state (which means that the vibration of the light takes place in only one plane). For the beam reflected from the CD surface, however, the PBS acts like a mirror, since the reflected beam has an opposite polarization. The light is thus deflected toward the photodiode detector. The objective lens is needed to focus the light onto the disc surface. On the outer surface of the transparent disc, the main spot of light has a diameter of 0.8 millimeter, which narrows to only 0.0017 millimeter at the reflective surface. At the surface, the spot is about three times the size of the microscopic pits (0.0005 millimeter). The data encoded on the disc determine the relative intensity of the reflected light, on the basis of the presence or absence of pits. When the reflected laser beam enters the photodiode, a modulated light beam is changed into a digital signal that becomes an analog (continuous) audio signal after several stages of signal processing and error correction. Consequences The development of the semiconductor laser diode and associated circuitry for reading stored information has made CD audio systems practical and affordable. These systems can offer the quality of a live musical performance with a clarity that is undisturbed by noise and distortion. Digital systems also offer several other significant advantages over analog devices. The dynamic range (the difference between the softest and the loudest signals that can be stored and reproduced) is considerably greater in digital systems. In addition, digital systems can be copied precisely; the signal is not degraded by copying, as is the case with analog systems. Finally, error-correcting codes can be used to detect and correct errors in transmitted or reproduced digital signals, allowing greater precision and a higher-quality output sound. Besides laser video systems, there are many other applications for laser-read CDs. Compact disc read-only memory (CD-ROM) is used to store computer text. One standard CD can store 500 megabytes of information, which is about twenty times the storage of a hard-disk drive on a typical home computer. Compact disc systems can also be integrated with conventional televisions (called CD-V) to present twenty minutes of sound and five minutes of sound with picture. Finally, CD systems connected with a computer (CD-I) mix audio, video, and computer programming. These devices allow the user to stop at any point in the program, request more information, and receive that information as sound with graphics, film clips, or as text on the screen.

Laser

The invention: Taking its name from the acronym for light amplification by the stimulated emission of radiation, a laser is a beam of electromagnetic radiation that is monochromatic, highly directional, and coherent. Lasers have found multiple applications in electronics, medicine, and other fields. The people behind the invention: Theodore Harold Maiman (1927- ), an American physicist Charles Hard Townes (1915- ), an American physicist who was a cowinner of the 1964 Nobel Prize in Physics Arthur L. Schawlow (1921-1999), an American physicist, cowinner of the 1981 Nobel Prize in Physics Mary Spaeth (1938- ), the American inventor of the tunable laser Coherent Light Laser beams differ from other forms of electromagnetic radiation in being consisting of a single wavelength, being highly directional, and having waves whose crests and troughs are aligned. A laser beam launched from Earth has produced a spot a few kilometers wide on the Moon, nearly 400,000 kilometers away. Ordinary light would have spread much more and produced a spot several times wider than the Moon. Laser light can also be concentrated so as to yield an enormous intensity of energy, more than that of the surface of the Sun, an impossibility with ordinary light. In order to appreciate the difference between laser light and ordinary light, one must examine how light of any kind is produced. An ordinary light bulb contains atoms of gas. For the bulb to light up, these atoms must be excited to a state of energy higher then their normal, or ground, state. This is accomplished by sending a current of electricity through the bulb; the current jolts the atoms into the higher-energy state. This excited state is unstable, however, and the atoms will spontaneously return to their ground state by ridding themselves of excess energy.As these atoms emit energy, light is produced. The light emitted by a lamp full of atoms is disorganized and emitted in all directions randomly. This type of light, common to all ordinary sources, from fluorescent lamps to the Sun, is called “incoherent light.” Laser light is different. The excited atoms in a laser emit their excess energy in a unified, controlled manner. The atoms remain in the excited state until there are a great many excited atoms. Then, they are stimulated to emit energy, not independently, but in an organized fashion, with all their light waves traveling in the same direction, crests and troughs perfectly aligned. This type of light is called “coherent light.” Theory to Reality In 1958, Charles Hard Townes of Columbia University, together with Arthur L. Schawlow, explored the requirements of the laser in a theoretical paper. In the Soviet Union, F. A. Butayeva and V. A. Fabrikant had amplified light in 1957 using mercury; however, their work was not published for two years and was not published in a scientific journal. The work of the Soviet scientists, therefore, received virtually no attention in the Western world. In 1960, Theodore Harold Maiman constructed the first laser in the United States using a single crystal of synthetic pink ruby, shaped into a cylindrical rod about 4 centimeters long and 0.5 centimeter across. The ends, polished flat and made parallel to within about a millionth of a centimeter, were coated with silver to make them mirrors. It is a property of stimulated emission that stimulated light waves will be aligned exactly (crest to crest, trough to trough, and with respect to direction) with the radiation that does the stimulating. From the group of excited atoms, one atom returns to its ground state, emitting light. That light hits one of the other exited atoms and stimulates it to fall to its ground state and emit light. The two light waves are exactly in step. The light from these two atoms hits other excited atoms, which respond in the same way, “amplifying” the total sum of light. If the first atom emits light in a direction parallel to the length of the crystal cylinder, the mirrors at both ends bounce the light waves back and forth, stimulating more light and steadily building up an increasing intensity of light. The mirror at one end of the cylinder is constructed to let through a fraction of the light, enabling the light to emerge as a straight, intense, narrow beam. Consequences When the laser was introduced, it was an immediate sensation. In the eighteen months following Maiman’s announcement that he had succeeded in producing a working laser, about four hundred companies and several government agencies embarked on work involving lasers. Activity centered on improving lasers, as well as on exploring their applications. At the same time, there was equal activity in publicizing the near-miraculous promise of the device, in applications covering the spectrum from “death” rays to sight-saving operations. A popular film in the James Bond series, Goldfinger (1964), showed the hero under threat of being sliced in half by a laser beam—an impossibility at the time the film was made because of the low power-output of the early lasers. In the first decade after Maiman’s laser, there was some disappointment. Successful use of lasers was limited to certain areas of medicine, such as repairing detached retinas, and to scientific applications, particularly in connection with standards: The speed of light was measured with great accuracy, as was the distance to the Moon. By 1990, partly because of advances in other fields, essentially all the laser’s promise had been fulfilled, including the death ray and James Bond’s slicer. Yet the laser continued to find its place in technologies not envisioned at the time of the first laser. For example, lasers are now used in computer printers, in compact disc players, and even in arterial surgery.

Laminated glass

The invention: Double sheets of glass separated by a thin layer of plastic sandwiched between them. The people behind the invention: Edouard Benedictus (1879-1930), a French artist Katherine Burr Blodgett (1898-1979), an American physicist The Quest for Unbreakable Glass People have been fascinated for centuries by the delicate transparency of glass and the glitter of crystals. They have also been frustrated by the brittleness and fragility of glass. When glass breaks, it forms sharp pieces that can cut people severely. During the 1800’s and early 1900’s, a number of people demonstrated ways to make “unbreakable” glass. In 1855 in England, the first “unbreakable” glass panes were made by embedding thin wires in the glass. The embedded wire grid held the glass together when it was struck or subjected to the intense heat of a fire.Wire glass is still used in windows that must be fire resistant. The concept of embedding the wire within a glass sheet so that the glass would not shatter was a predecessor of the concept of laminated glass. A series of inventors in Europe and the United States worked on the idea of using a durable, transparent inner layer of plastic between two sheets of glass to prevent the glass from shattering when it was dropped or struck by an impact. In 1899, Charles E.Wade of Scranton, Pennsylvania, obtained a patent for a kind of glass that had a sheet or netting of mica fused within it to bind it. In 1902, Earnest E. G. Street of Paris, France, proposed coating glass battery jars with pyroxylin plastic (celluloid) so that they would hold together if they cracked. In Swindon, England, in 1905, John Crewe Wood applied for a patent for a material that would prevent automobile windshields from shattering and injuring people when they broke. He proposed cementing a sheet of material such as celluloid between two sheets of glass. When the window was broken, the inner material would hold the glass splinters together so that they would not cut anyone.Remembering a Fortuitous Fall In his patent application, Edouard Benedictus described himself as an artist and painter. He was also a poet, musician, and philosopher who was descended from the philosopher Baruch Benedictus Spinoza; he seemed an unlikely contributor to the progress of glass manufacture. In 1903, Benedictus was cleaning his laboratory when he dropped a glass bottle that held a nitrocellulose solution. The solvents, which had evaporated during the years that the bottle had sat on a shelf, had left a strong celluloid coating on the glass. When Benedictus picked up the bottle, he was surprised to see that it had not shattered: It was starred, but all the glass fragments had been held together by the internal celluloid coating. He looked at the bottle closely, labeled it with the date (November, 1903) and the height from which it had fallen, and put it back on the shelf. One day some years later (the date is uncertain), Benedictus became aware of vehicular collisions in which two young women received serious lacerations from broken glass. He wrote a poetic account of a daydream he had while he was thinking intently about the two women. He described a vision in which the faintly illuminated bottle that had fallen some years before but had not shattered appeared to float down to him from the shelf. He got up, went into his laboratory, and began to work on an idea that originated with his thoughts of the bottle that would not splinter. Benedictus found the old bottle and devised a series of experiments that he carried out until the next evening. By the time he had finished, he had made the first sheet of Triplex glass, for which he applied for a patent in 1909. He also founded the Société du Verre Triplex (The Triplex Glass Society) in that year. In 1912, the Triplex Safety Glass Company was established in England. The company sold its products for military equipment in World War I, which began two years later. Triplex glass was the predecessor of laminated glass. Laminated glass is composed of two or more sheets of glass with a thin layer of plastic (usually polyvinyl butyral, although Benedictus used pyroxylin) laminated between the glass sheets using pressure and heat. The plastic layer will yield rather than rupture when subjected to loads and stresses. This prevents the glass from shattering into sharp pieces. Because of this property, laminated glass is also known as “safety glass.” Impact Even after the protective value of laminated glass was known,the product was not widely used for some years. There were a number of technical difficulties that had to be solved, such as the discoloring of the plastic layer when it was exposed to sunlight; the relatively high cost; and the cloudiness of the plastic layer, which obscured vision—especially at night. Nevertheless, the expanding automobile industry and the corresponding increase in the number of accidents provided the impetus for improving the qualities and manufacturing processes of laminated glass. In the early part of the century, almost two-thirds of all injuries suffered in automobile accidents involved broken glass. Laminated glass is used in many applications in which safety is important. It is typically used in all windows in cars, trucks, ships, and aircraft. Thick sheets of bullet-resistant laminated glass are used in banks, jewelry displays, and military installations. Thinner sheets of laminated glass are used as security glass in museums, libraries, and other areas where resistance to break-in attempts is needed. Many buildings have large ceiling skylights that are made of laminated glass; if the glass is damaged, it will not shatter, fall, and hurt people below. Laminated glass is used in airports, hotels, and apartments in noisy areas and in recording studios to reduce the amount of noise that is transmitted. It is also used in safety goggles and in viewing ports at industrial plants and test chambers. Edouard Benedictus’s recollection of the bottle that fell but did not shatter has thus helped make many situations in which glass is used safer for everyone.

Iron lung

The invention: Amechanical respirator that saved the lives of victims of poliomyelitis. The people behind the invention: Philip Drinker (1894-1972), an engineer who made many contributions to medicine Louis Shaw (1886-1940), a respiratory physiologist who assisted Drinker Charles F. McKhann III (1898-1988), a pediatrician and founding member of the American Board of Pediatrics A Terrifying Disease Poliomyelitis (polio, or infantile paralysis) is an infectious viral disease that damages the central nervous system, causing paralysis in many cases. Its effect results from the destruction of neurons (nerve cells) in the spinal cord. In many cases, the disease produces crippled limbs and the wasting away of muscles. In others, polio results in the fatal paralysis of the respiratory muscles. It is fortunate that use of the Salk and Sabin vaccines beginning in the 1950’s has virtually eradicated the disease. In the 1920’s, poliomyelitis was a terrifying disease. Paralysis of the respiratory muscles caused rapid death by suffocation, often within only a few hours after the first signs of respiratory distress had appeared. In 1929, Philip Drinker and Louis Shaw, both of Harvard University, reported the development of a mechanical respirator that would keep those afflicted with the disease alive for indefinite periods of time. This device, soon nicknamed the “iron lung,” helped thousands of people who suffered from respiratory paralysis as a result of poliomyelitis or other diseases. Development of the iron lung arose after Drinker, then an assistant professor in Harvard’s Department of Industrial Hygiene, was appointed to a Rockefeller Institute commission formed to improve methods for resuscitating victims of electric shock. The best-known use of the iron lung—treatment of poliomyelitis—was a result of numerous epidemics of the disease that occurred from 1898 until the 1920’s, each leaving thousands of Americans paralyzed. The concept of the iron lung reportedly arose from Drinker’s observation of physiological experiments carried out by Shaw and Drinker’s brother, Cecil. The experiments involved the placement of a cat inside an airtight box—a body plethysmograph—with the cat’s head protruding from an airtight collar. Shaw and Cecil Drinker then measured the volume changes in the plethysmograph to identify normal breathing patterns. Philip Drinker then placed cats paralyzed by curare inside plethysmographies and showed that they could be kept breathing artificially by use of air from a hypodermic syringe connected to the device. Next, they proceeded to build a human-sized plethysmographlike machine, with a five-hundred-dollar grant from the New York Consolidated Gas Company. This was done by a tinsmith and the Harvard Medical School machine shop. Breath for Paralyzed Lungs The first machine was tested on Drinker and Shaw, and after several modifications were made, a workable iron lung was made available for clinical use. This machine consisted of a metal cylinder large enough to hold a human being. One end of the cylinder, which contained a rubber collar, slid out on casters along with a stretcher on which the patient was placed. Once the patient was in position and the collar was fitted around the patient’s neck, the stretcher was pushed back into the cylinder and the iron lung was made airtight. The iron lung then “breathed” for the patient by using an electric blower to remove and replace air alternatively inside the machine. In the human chest, inhalation occurs when the diaphragm contracts and powerful muscles (which are paralyzed in poliomyelitis sufferers) expand the rib cage. This lowers the air pressure in the lungs and allows inhalation to occur. In exhalation, the diaphragm and chest muscles relax, and air is expelled as the chest cavity returns to its normal size. In cases of respiratory paralysis treated with an iron lung, the air coming into or leaving the iron lung alternately compressed the patient’s chest, producing artificial exhalation, and the allowed it to expand to so that the chest could fill with air. In this way, iron lungs “breathed” for the patients using them.Careful examination of each patient was required to allow technicians to adjust the rate of operation of the machine. Acooling system and ports for drainage lines, intravenous lines, and the other apparatus needed to maintain a wide variety of patients were included in the machine. The first person treated in an iron lung was an eight-year-old girl afflicted with respiratory paralysis resulting from poliomyelitis. The iron lung kept her alive for five days. Unfortunately, she died from heart failure as a result of pneumonia. The next iron lung patient, a Harvard University student, was confined to the machine for several weeks and later recovered enough to resume a normal life.

The Internet

The invention: 

A worldwide network of interlocking computer
systems, developed out of a U.S. government project to improve
military preparedness.

The people behind the invention:

Paul Baran, a researcher for the RAND corporation
Vinton G. Cerf (1943- ), an American computer scientist
regarded as the “father of the Internet”

Internal combustion engine

The invention: The most common type of engine in automobiles and many other vehicles, the internal combusion engine is characterized by the fact that it burns its liquid fuelly internally—in contrast to engines, such as the steam engine, that burn fuel in external furnaces. The people behind the invention: Sir Harry Ralph Ricardo (1885-1974), an English engineer Oliver Thornycroft (1885-1956), an engineer and works manager Sir David Randall Pye (1886-1960), an engineer and administrator Sir Robert Waley Cohen (1877-1952), a scientist and industrialist The Internal Combustion Engine: 1900-1916 By the beginning of the twentieth century, internal combustion engines were almost everywhere. City streets in Berlin, London, and New York were filled with automobile and truck traffic; gasoline- and diesel-powered boat engines were replacing sails; stationary steam engines for electrical generation were being edged out by internal combustion engines. Even aircraft use was at hand: To progress from theWright brothers’ first manned flight in 1903 to the fighting planes ofWorldWar I took only a little more than a decade. The internal combustion engines of the time, however, were primitive in design. They were heavy (10 to 15 pounds per output horsepower, as opposed to 1 to 2 pounds today), slow (typically 1,000 or fewer revolutions per minute or less, as opposed to 2,000 to 5,000 today), and extremely inefficient in extracting the energy content of their fuel. These were not major drawbacks for stationary applications, or even for road traffic that rarely went faster than 30 or 40 miles per hour, but the advent of military aircraft and tanks demanded that engines be made more efficient.Engine and Fuel Design Harry Ricardo, son of an architect and grandson (on his mother’s side) of an engineer, was a central figure in the necessary redesign of internal combustion engines. As a schoolboy, he built a coal-fired steam engine for his bicycle, and at Cambridge University he produced a single-cylinder gasoline motorcycle, incorporating many of his own ideas, which won a fuel-economy competition when it traveled almost 40 miles on a quart of gasoline. He also began development of a two-cycle engine called the “Dolphin,” which later was produced for use in fishing boats and automobiles. In fact, in 1911, Ricardo took his new bride on their honeymoon trip in a Dolphinpowered car. The impetus that led to major engine research came in 1916 when Ricardo was an engineer in his family’s firm. The British government asked for newly designed tank engines, which had to operate in the dirt and mud of battle, at a tilt of up to 35 degrees, and could not give off telltale clouds of blue oil smoke. Ricardo solved the problem with a special piston design and with air circulation around the carburetor and within the engine to keep the oil cool. Design work on the tank engines turned Ricardo into a fullfledged research engineer. In 1917, he founded his own company, and a remarkable series of discoveries quickly followed. He investigated the problem of detonation of the fuel-air mixture in the internal combustion cylinder. The mixture is supposed to be ignited by the spark plug at the top of the compression stroke, with a controlled flame front spreading at a rate about equal to the speed of the piston head as it moves downward in the power stroke. Some fuels, however, detonated (ignited spontaneously throughout the entire fuel-air mixture) as a result of the compression itself, causing loss of fuel efficiency and damage to the engine. With the cooperation of RobertWaley Cohen of Shell Petroleum, Ricardo evaluated chemical mixtures of fuels and found that paraffins (such as n-heptane, the current low-octane standard) detonated readily, but aromatics such as toluene were nearly immune to detonation. He established a “toluene number” rating to describe the tendency of various fuels to detonate; this number was replaced in the 1920’s by the “octane number” devised by Thomas Midgley at the Delco laboratories in Dayton, Ohio. The fuel work was carried out in an experimental engine designed by Ricardo that allowed direct observation of the flame front as it spread and permitted changes in compression ratio while the engine was running. Three principles emerged from the investigation: the fuel-air mixture should be admitted with as much turbulence as possible, for thorough mixing and efficient combustion; the spark plug should be centrally located to prevent distant pockets of the mixture from detonating before the flame front reaches them; and the mixture should be kept as cool as possible to prevent detonation. These principles were then applied in the first truly efficient sidevalve (“L-head”) engine—that is, an engine with the valves in a chamber at the side of the cylinder, in the engine block, rather than overhead, in the engine head. Ricardo patented this design, and after winning a patent dispute in court in 1932, he received royalties or consulting fees for it from engine manufacturers all over the world.Impact The side-valve engine was the workhorse design for automobile and marine engines until after World War II. With its valves actuated directly by a camshaft in the crankcase, it is simple, rugged, and easy to manufacture. Overhead valves with overhead camshafts are the standard in automobile engines today, but the sidevalve engine is still found in marine applications and in small engines for lawn mowers, home generator systems, and the like. In its widespread use and its decades of employment, the side-valve engine represents a scientific and technological breakthrough in the twentieth century. Ricardo and his colleagues, Oliver Thornycroft and D. R. Pye, went on to create other engine designs—notably, the sleeve-valve aircraft engine that was the basic pattern for most of the great British planes of World War II and early versions of the aircraft jet engine. For his technical advances and service to the government, Ricardo was elected a Fellow of the Royal Society in 1929, and he was knighted in 1948.

Interchangeable parts

The invention: 

A key idea in the late Industrial Revolution, the
interchangeability of parts made possible mass production of
identical products.


The people behind the invention:

Henry M. Leland (1843-1932), president of Cadillac Motor Car
Company in 1908, known as a master of precision
Frederick Bennett, the British agent for Cadillac Motor Car
Company who convinced the Royal Automobile Club to run
the standardization test at Brooklands, England
Henry Ford (1863-1947), founder of Ford Motor Company who
introduced the moving assembly line into the automobile
industry in 1913

Instant photography

The invention: Popularly known by its Polaroid tradename, a camera capable of producing finished photographs immediately after its film was exposed. The people behind the invention: Edwin Herbert Land (1909-1991), an American physicist and chemist Howard G. Rogers (1915- ), a senior researcher at Polaroid and Land’s collaborator William J. McCune (1915- ), an engineer and head of the Polaroid team Ansel Adams (1902-1984), an American photographer and Land’s technical consultant The Daughter of Invention Because he was a chemist and physicist interested primarily in research relating to light and vision, and to the materials that affect them, it was inevitable that Edwin Herbert Land should be drawn into the field of photography. Land founded the Polaroid Corporation in 1929. During the summer of 1943, while Land and his wife were vacationing in Santa Fe, New Mexico, with their three-yearold daughter, Land stopped to take a picture of the child. After the picture was taken, his daughter asked to see it. When she was told she could not see the picture immediately, she asked how long it would be. Within an hour after his daughter’s question, Land had conceived a preliminary plan for designing the camera, the film, and the physical chemistry of what would become the instant camera. Such a device would, he hoped, produce a picture immediately after exposure. Within six months, Land had solved most of the essential problems of the instant photography system. He and a small group of associates at Polaroid secretly worked on the project. Howard G. Rogers was Land’s collaborator in the laboratory. Land conferred the responsibility for the engineering and mechanical phase of the project on William J. McCune, who led the team that eventually designed the original camera and the machinery that produced both the camera and Land’s new film. The first Polaroid Land camera—the Model 95—produced photographs measuring 8.25 by 10.8 centimeters; there were eight pictures to a roll. Rather than being black-and-white, the original Polaroid prints were sepia-toned (producing a warm, reddish-brown color). The reasons for the sepia coloration were chemical rather than aesthetic; as soon as Land’s researchers could devise a workable formula for sharp black-and-white prints (about ten months after the camera was introduced commercially), they replaced the sepia film. A Sophisticated Chemical Reaction Although the mechanical process involved in the first demonstration camera was relatively simple, this process was merely the means by which a highly sophisticated chemical reaction— the diffusion transfer process—was produced. In the basic diffusion transfer process, when an exposed negative image is developed, the undeveloped portion corresponds to the opposite aspect of the image, the positive. Almost all selfprocessing instant photography materials operate according to three phases—negative development, diffusion transfer, and positive development. These occur simultaneously, so that positive image formation begins instantly. With black-and-white materials, the positive was originally completed in about sixty seconds; with color materials (introduced later), the process took somewhat longer. The basic phenomenon of silver in solution diffusing from one emulsion to another was first observed in the 1850’s, but no practical use of this action was made until 1939. The photographic use of diffusion transfer for producing normal-continuous-tone images was investigated actively from the early 1940’s by Land and his associates. The instant camera using this method was demonstrated in 1947 and marketed in 1948. The fundamentals of photographic diffusion transfer are simplest in a black-and-white peel-apart film. The negative sheet is exposed in the camera in the normal way. It is then pulled out of the camera, or film pack holder, by a paper tab. Next, it passes through a set of rollers, which press it face-to-face with a sheet of receiving material included in the film pack. Simultaneously, the rollers rupture a pod of reagent chemicals that are spread evenly by the rollers between the two layers. The reagent contains a strong alkali and a silver halide solvent, both of which diffuse into the negative emulsion. There the alkali activates the developing agent, which immediately reduces the exposed halides to a negative image. At the same time, the solvent dissolves the unexposed halides. The silver in the dissolved halides forms the positive image. Impact The Polaroid Land camera had a tremendous impact on the photographic industry as well as on the amateur and professional photographer. Ansel Adams, who was known for his monumental, ultrasharp black-and-white panoramas of the American West, suggested to Land ways in which the tonal value of Polaroid film could be enhanced, as well as new applications for Polaroid photographic technology. Soon after it was introduced, Polaroid photography became part of the American way of life and changed the face of amateur photography forever. By the 1950’s, Americans had become accustomed to the world of recorded visual information through films, magazines, and newspapers; they also had become enthusiastic picturetakers as a result of the growing trend for simpler and more convenient cameras. By allowing these photographers not only to record their perceptions but also to see the results almost immediately, Polaroid brought people closer to the creative process.

Infrared photography

The invention: The first application of color to infrared photography, which performs tasks not possible for ordinary photography. The person behind the invention: Sir William Herschel (1738-1822), a pioneering English astronomer Invisible Light Photography developed rapidly in the nineteenth century when it became possible to record the colors and shades of visible light on sensitive materials. Visible light is a form of radiation that consists of electromagnetic waves, which also make up other forms of radiation such as X rays and radio waves. Visible light occupies the range of wavelengths from about 400 nanometers (1 nanometer is 1 billionth of a meter) to about 700 nanometers in the electromagnetic spectrum. Infrared radiation occupies the range fromabout 700 nanometers to about 1,350 nanometers in the electromagnetic spectrum. Infrared rays cannot be seen by the human eye, but they behave in the same way that rays of visible light behave; they can be reflected, diffracted (broken), and refracted (bent). Sir William Herschel, a British astronomer, discovered infrared rays in 1800 by calculating the temperature of the heat that they produced. The term “infrared,” which was probably first used in 1800, was used to indicate rays that had wavelengths that were longer than those on the red end (the high end) of the spectrum of visible light but shorter than those of the microwaves, which appear higher on the electromagnetic spectrum. Infrared film is therefore sensitive to the infrared radiation that the human eye cannot see or record. Dyes that were sensitive to infrared radiation were discovered early in the twentieth century, but they were not widely used until the 1930’s. Because these dyes produced only black-and-white images, their usefulness to artists and researchers was limited. After 1930, however, a tidal wave of infrared photographic applications appeared.The Development of Color-Sensitive Infrared Film In the early 1940’s, military intelligence used infrared viewers for night operations and for gathering information about the enemy. One device that was commonly used for such purposes was called a “snooper scope.” Aerial photography with black-and-white infrared film was used to locate enemy hiding places and equipment. The images that were produced, however, often lacked clear definition. The development in 1942 of the first color-sensitive infrared film, Ektachrome Aero Film, became possible when researchers at the Eastman Kodak Company’s laboratories solved some complex chemical and physical problems that had hampered the development of color infrared film up to that point. Regular color film is sensitive to all visible colors of the spectrum; infrared color film is sensitive to violet, blue, and red light as well as to infrared radiation. Typical color film has three layers of emulsion, which are sensitized to blue, green, and red. Infrared color film, however, has its three emulsion layers sensitized to green, red, and infrared. Infrared wavelengths are recorded as reds of varying densities, depending on the intensity of the infrared radiation. The more infrared radiation there is, the darker the color of the red that is recorded. In infrared photography, a filter is placed over the camera lens to block the unwanted rays of visible light. The filter blocks visible and ultraviolet rays but allows infrared radiation to pass. All three layers of infrared film are sensitive to blue, so a yellow filter is used. All blue radiation is absorbed by this filter. In regular photography, color film consists of three basic layers: the top layer is sensitive to blue light, the middle layer is sensitive to green, and the third layer is sensitive to red. Exposing the film to light causes a latent image to be formed in the silver halide crystals that make up each of the three layers. In infrared photography, color film consists of a top layer that is sensitive to infrared radiation, a middle layer sensitive to green, and a bottom layer sensitive to red. “Reversal processing” produces blue in the infrared-sensitive layer, yellow in the green-sensitive layer, and magenta in the red-sensitive layer. The blue, yellow, and magenta layers of the film produce the “false colors” that accentuate the various levels of infrared radiation shown as red in a color transparency, slide, or print.relationship to the color of light to which the layer is sensitive. If the relationship is not complementary, the resulting colors will be false. This means that objects whose colors appear to be similar to the human eye will not necessarily be recorded as similar colors on infrared film. A red rose with healthy green leaves will appear on infrared color film as being yellow with red leaves, because the chlorophyll contained in the plant leaf reflects infrared radiation and causes the green leaves to be recorded as red. Infrared radiation from about 700 nanometers to about 900 nanometers on the electromagnetic spectrum can be recorded by infrared color film. Above 900 nanometers, infrared radiation exists as heat patterns that must be recorded by nonphotographic means. Impact Infrared photography has proved to be valuable in many of the sciences and the arts. It has been used to create artistic images that are often unexpected visual explosions of everyday views. Because infrared radiation penetrates haze easily, infrared films are often used in mapping areas or determining vegetation types. Many cloud-covered tropical areas would be impossible to map without infrared photography. False-color infrared film can differentiate between healthy and unhealthy plants, so it is widely used to study insect and disease problems in plants. Medical research uses infrared photography to trace blood flow, detect and monitor tumor growth, and to study many other physiological functions that are invisible to the human eye. Some forms of cancer can be detected by infrared analysis before any other tests are able to perceive them. Infrared film is used in criminology to photograph illegal activities in the dark and to study evidence at crime scenes. Powder burns around a bullet hole, which are often invisible to the eye, show clearly on infrared film. In addition, forgeries in documents and works of art can often be seen clearly when photographed on infrared film. Archaeologists have used infrared film to locate ancient sites that are invisible in daylight. Wildlife biologists also document the behavior of animals at night with infrared equipment.

In vitro plant culture

The invention: Method for propagating plants in artificial media that has revolutionized agriculture. The people behind the invention: Georges Michel Morel (1916-1973), a French physiologist Philip Cleaver White (1913- ), an American chemist Plant Tissue Grows “In Glass” In the mid-1800’s, biologists began pondering whether a cell isolated from a multicellular organism could live separately if it were provided with the proper environment. In 1902, with this question in mind, the German plant physiologist Gottlieb Haberlandt attempted to culture (grow) isolated plant cells under sterile conditions on an artificial growth medium. Although his cultured cells never underwent cell division under these “in vitro” (in glass) conditions, Haberlandt is credited with originating the concept of cell culture. Subsequently, scientists attempted to culture plant tissues and organs rather than individual cells and tried to determine the medium components necessary for the growth of plant tissue in vitro. In 1934, Philip White grew the first organ culture, using tomato roots. The discovery of plant hormones, which are compounds that regulate growth and development, was crucial to the successful culture of plant tissues; in 1939, Roger Gautheret, P. Nobécourt, and White independently reported the successful culture of plant callus tissue. “Callus” is an irregular mass of dividing cells that often results from the wounding of plant tissue. Plant scientists were fascinated by the perpetual growth of such tissue in culture and spent years establishing optimal growth conditions and exploring the nutritional and hormonal requirements of plant tissue. Plants by the Millions A lull in botanical research occurred during World War II, but immediately afterward there was a resurgence of interest in applying tissue culture techniques to plant research. Georges Morel, a plant physiologist at the National Institute for Agronomic Research in France, was one of many scientists during this time who had become interested in the formation of tumors in plants as well as in studying various pathogens such as fungi and viruses that cause plant disease. To further these studies, Morel adapted existing techniques in order to grow tissue from a wider variety of plant types in culture, and he continued to try to identify factors that affected the normal growth and development of plants. Morel was successful in culturing tissue from ferns and was the first to culture monocot plants. Monocots have certain features that distinguish them fromthe other classes of seed-bearing plants, especially with respect to seed structure. More important, the monocots include the economically important species of grasses (the major plants of range and pasture) and cereals. For these cultures, Morel utilized a small piece of the growing tip of a plant shoot (the shoot apex) as the starting tissue material. This tissue was placed in a glass tube, supplied with a medium containing specific nutrients, vitamins, and plant hormones, and allowed to grow in the light. Under these conditions, the apex tissue grew roots and buds and eventually developed into a complete plant. Morel was able to generate whole plants from pieces of the shoot apex that were only 100 to 250 micrometers in length. Morel also investigated the growth of parasites such as fungi and viruses in dual culture with host-plant tissue. Using results from these studies and culture techniques that he had mastered, Morel and his colleague Claude Martin regenerated virus-free plants from tissue that had been taken from virally infected plants. Tissues from certain tropical species, dahlias, and potato plants were used for the original experiments, but after Morel adapted the methods for the generation of virus-free orchids, plants that had previously been difficult to propagate by any means, the true significance of his work was recognized. Morel was the first to recognize the potential of the in vitro culture methods for the mass propagation of plants. He estimated that several million plants could be obtained in one year from a single small piece of shoot-apex tissue. Plants generated in this manner were clonal (genetically identical organisms prepared from a single plant).With other methods of plant propagation, there is often a great variation in the traits of the plants produced, but as a result of Morel’s ideas, breeders could select for some desirable trait in a particular plant and then produce multiple clonal plants, all of which expressed the desired trait. The methodology also allowed for the production of virus-free plant material, which minimized both the spread of potential pathogens during shipping and losses caused by disease. Consequences Variations on Morel’s methods are used to propagate plants used for human food consumption; plants that are sources of fiber, oil, and livestock feed; forest trees; and plants used in landscaping and in the floral industry. In vitro stocks are preserved under deepfreeze conditions, and disease-free plants can be proliferated quickly at any time of the year after shipping or storage. The in vitro multiplication of plants has been especially useful for species such as coconut and certain palms that cannot be propagated by other methods, such as by sowing seeds or grafting, and has also become important in the preservation and propagation of rare plant species that might otherwise have become extinct. Many of these plants are sources of pharmaceuticals, oils, fragrances, and other valuable products. The capability of regenerating plants from tissue culture has also been crucial in basic scientific research. Plant cells grown in culture can be studied more easily than can intact plants, and scientists have gained an in-depth understanding of plant physiology and biochemistry by using this method. This information and the methods of Morel and others have made possible the genetic engineering and propagation of crop plants that are resistant to disease or disastrous environmental conditions such as drought and freezing. In vitro techniques have truly revolutionized agriculture.

IBM Model 1401 Computer

The invention: A relatively small, simple, and inexpensive computer that is often credited with having launched the personal computer age. The people behind the invention: Howard H. Aiken (1900-1973), an American mathematician Charles Babbage (1792-1871), an English mathematician and inventor Herman Hollerith (1860-1929), an American inventor Computers: From the Beginning Computers evolved into their modern form over a period of thousands of years as a result of humanity’s efforts to simplify the process of counting. Two counting devices that are considered to be very simple, early computers are the abacus and the slide rule. These calculating devices are representative of digital and analog computers, respectively, because an abacus counts numbers of things, while the slide rule calculates length measurements. The first modern computer, which was planned by Charles Babbage in 1833, was never built. It was intended to perform complex calculations with a data processing/memory unit that was controlled by punched cards. In 1944, Harvard University’s Howard H. Aiken and the International Business Machines (IBM) Corporation built such a computer—the huge, punched-tape-controlled Automatic Sequence Controlled Calculator, or Mark I ASCC, which could perform complex mathematical operations in seconds. During the next fifteen years, computer advances produced digital computers that used binary arithmetic for calculation, incorporated simplified components that decreased the sizes of computers, had much faster calculating speeds, and were transistorized. Although practical computers had become much faster than they had been only a few years earlier, they were still huge and extremely expensive. In 1959, however, IBM introduced the Model 1401 computer. Smaller, simpler, and much cheaper than the multimillion-dollar computers that were available, the IBM Model 1401 computer was also relatively easy to program and use. Its low cost, simplicity of operation, and very wide use have led many experts to view the IBM Model 1401 computer as beginning the age of the personal computer. Computer Operation and IBM’s Model 1401 Modern computers are essentially very fast calculating machines that are capable of sorting, comparing, analyzing, and outputting information, as well as storing it for future use. Many sources credit Aiken’s Mark I ASCC as being the first modern computer to be built. This huge, five-ton machine used thousands of relays to perform complex mathematical calculations in seconds. Soon after its introduction, other companies produced computers that were faster and more versatile than the Mark I. The computer development race was on. All these early computers utilized the decimal system for calculations until it was found that binary arithmetic, whose numbers are combinations of the binary digits 1 and 0, was much more suitable for the purpose. The advantage of the binary system is that the electronic switches that make up a computer (tubes, transistors, or chips) can be either on or off; in the binary system, the on state can be represented by the digit 1, the off state by the digit 0. Strung together correctly, binary numbers, or digits, can be inputted rapidly and used for high-speed computations. In fact, the computer term bit is a contraction of the phrase “binary digit.” A computer consists of input and output devices, a storage device (memory), arithmetic and logic units, and a control unit. In most cases, a central processing unit (CPU) combines the logic, arithmetic, memory, and control aspects. Instructions are loaded into the memory via an input device, processed, and stored. Then, the CPU issues commands to the other parts of the system to carry out computations or other functions and output the data as needed. Most output is printed as hard copy or displayed on cathode-ray tube monitors, or screens. The early modern computers—such as the Mark I ASCC—were huge because their information circuits were large relays or tubes. Computers became smaller and smaller as the tubes were replaced first with transistors, then with simple integrated circuits, and then with silicon chips. Each technological changeover also produced more powerful, more cost-effective computers. In the 1950’s, with reliable transistors available, IBM began the development of two types of computers that were completed by about 1959. The larger version was the Stretch computer, which was advertised as the most powerful computer of its day. Customized for each individual purchaser (for example, the Atomic Energy Commission), a Stretch computer cost $10 million or more. Some innovations in Stretch computers included semiconductor circuits, new switching systems that quickly converted various kinds of data into one language that was understood by the CPU, rapid data readers, and devices that seemed to anticipate future operations. Consequences The IBM Model 1401 was the first computer sold in very large numbers. It led IBM and other companies to seek to develop less expensive, more versatile, smaller computers that would be sold to small businesses and to individuals. Six years after the development of the Model 1401, other IBM models—and those made by other companies—became available that were more compact and had larger memories. The search for compactness and versatility continued. A major development was the invention of integrated circuits by Jack S. Kilby of Texas Instruments; these integrated circuits became available by the mid-1960’s. They were followed by even smaller “microprocessors” (computer chips) that became available in the 1970’s. Computers continued to become smaller and more powerful. Input and storage devices also decreased rapidly in size. At first, the punched cards invented by Herman Hollerith, founder of the Tabulation Machine Company (which later became IBM), were read by bulky readers. In time, less bulky magnetic tapes and more compact readers were developed, after which magnetic disks and compact disc drives were introduced. Many other advances have been made. Modern computers can talk, create art and graphics, compose music, play games, and operate robots. Further advancement is expected as societal needs change. Many experts believe that it was the sale of large numbers of IBM Model 1401 computers that began the trend.

Hydrogen bomb

The invention: Popularly known as the “H-Bomb,” the hydrogen bomb differs from the original atomic bomb in using fusion, rather than fission, to create a thermonuclear explosion almost a thousand times more powerful. The people behind the invention: Edward Teller (1908- ), a Hungarian-born theoretical physicist Stanislaw Ulam (1909-1984), a Polish-born mathematician Crash Development Afew months before the 1942 creation of the Manhattan Project, the United States-led effort to build the atomic (fission) bomb, physicist Enrico Fermi suggested to Edward Teller that such a bomb could release more energy by the process of heating a mass of the hydrogen isotope deuterium and igniting the fusion of hydrogen into helium. Fusion is the process whereby two atoms come together to form a larger atom, and this process usually occurs only in stars, such as the Sun. Physicists Hans Bethe, George Gamow, and Teller had been studying fusion since 1934 and knew of the tremendous energy than could be released by this process—even more energy than the fission (atom-splitting) process that would create the atomic bomb. Initially, Teller dismissed Fermi’s idea, but later in 1942, in collaboration with Emil Konopinski, he concluded that a hydrogen bomb, or superbomb, could be made. For practical considerations, it was decided that the design of the superbomb would have to wait until after the war. In 1946, a secret conference on the superbomb was held in Los Alamos, New Mexico, that was attended by, among other Manhattan Project veterans, Stanislaw Ulam and Klaus Emil Julius Fuchs. Supporting the investigation of Teller’s concept, the conferees requested a more complete mathematical analysis of his own admittedly crude calculations on the dynamics of the fusion reaction. In 1947, Teller believed that these calculations might take years. Two years later, however,the Soviet explosion of an atomic bomb convinced Teller that America’s ColdWar adversary was hard at work on its own superbomb. Even when new calculations cast further doubt on his designs, Teller began a vigorous campaign for crash development of the hydrogen bomb, or H-bomb. The Superbomb Scientists knew that fusion reactions could be induced by the explosion of an atomic bomb. The basic problem was simple and formidable: How could fusion fuel be heated and compressed long enough to achieve significant thermonuclear burning before the atomic fission explosion blew the assembly apart? A major part of the solution came from Ulam in 1951. He proposed using the energy from an exploding atomic bomb to induce significant thermonuclear reactions in adjacent fusion fuel components. This arrangement, in which the A-bomb (the primary) is physically separated from the H-bomb’s (the secondary’s) fusion fuel, became known as the “Teller-Ulam configuration.” All H-bombs are cylindrical, with an atomic device at one end and the other components filling the remaining space. Energy from the exploding primary could be transported by X rays and would therefore affect the fusion fuel at near light speed—before the arrival of the explosion. Frederick de Hoffman’s work verified and enriched the new concept. In the revised method, moderated X rays from the primary irradiate a reactive plastic medium surrounding concentric and generally cylindrical layers of fusion and fission fuel in the secondary. Instantly, the plastic becomes a hot plasma that compresses and heats the inner layer of fusion fuel, which in turn compresses a central core of fissile plutonium to supercriticality. Thus compressed, and bombarded by fusion-produced, high-energy neutrons, the fission element expands rapidly in a chain reaction from the inside out, further compressing and heating the surrounding fusion fuel, releasing more energy and more neutrons that induce fission in a fuel casing-tamper made of normally stable uranium 238. With its equipment to refrigerate the hydrogen isotopes, the device created to test Teller’s new concept weighed more than sixty tons. During Operation Ivy, it was tested at Elugelab in the Marshall Islands on November 1, 1952. Exceeding the expectations of all concerned and vaporizing the island, the explosion equaled 10.4 million tons of trinitrotoluene (TNT), which meant that it was about seven hundred times more powerful than the atomic bomb dropped on Hiroshima, Japan, in 1945. A version of this device weighing about 20 tons was prepared for delivery by specially modified Air Force B-36 bombers in the event of an emergency during wartime. In development at Los Alamos before the 1952 test was a device weighing only about 4 tons, a “dry bomb” that did not require refrigeration equipment or liquid fusion fuel; when sufficiently compressed and heated in its molded-powder form, the new fusion fuel component, lithium-6 deutride, instantly produced tritium, an isotope of hydrogen. This concept was tested during Operation Castle at Bikini atoll in 1954 and produced a yield of 15 million tons of TNT, the largest-ever nuclear explosion created by the United States. Consequences Teller was not alone in believing that the world could produce thermonuclear devices capable of causing great destruction. Months before Fermi suggested to Teller the possibility of explosive thermonuclear reactions on Earth, Japanese physicist Tokutaro Hagiwara had proposed that a uranium 235 bomb could ignite significant fusion reactions in hydrogen. The Soviet Union successfully tested an H-bomb dropped from an airplane in 1955, one year before the United States did so. Teller became the scientific adviser on nuclear affairs of many presidents, from Dwight D. Eisenhower to Ronald Reagan. The widespread blast and fallout effects of H-bombs assured the mutual destruction of the users of such weapons. During the Cold War (from about 1947 to 1981), both the United States and the Soviet Union possessed H-bombs. “Testing” these bombs made each side aware of how powerful the other side was. Everyone wanted to avoid nuclear war. It was thought that no one would try to start a war that would end in the world’s destruction. This theory was called deterrence: The United States wanted to let the Soviet Union know that it had just as many bombs, or more, than it did, so that the leaders of the Sovet Union would be deterred from starting a war.Teller knew that the availability of H-bombs on both sides was not enough to guarantee that such weapons would never be used. It was also necessary to make the Soviet Union aware of the existence of the bombs through testing. He consistently advised against U.S. participation with the Soviet Union in a moratorium (period of waiting) on nuclear weapons testing. Largely based on Teller’s urging that underground testing be continued, the United States rejected a total moratorium in favor of the 1963 Atmospheric Test Ban Treaty. During the 1980’s, Teller, among others, convinced President Reagan to embrace the Strategic Defense Initiative (SDI). Teller argued that SDI components, such as the space-based “Excalibur,” a nuclear bomb-powered X-ray laser weapon proposed by the Lawrence- Livermore National Laboratory, would make thermonuclear war not unimaginable, but theoretically impossible.

Hovercraft

The invention: A vehicle requiring no surface contact for traction that moves freely over a variety of surfaces—particularly water—while supported on a self-generated cushion of air. The people behind the invention: Christopher Sydney Cockerell (1910- ), a British engineer who built the first hovercraft Ronald A. Shaw (1910- ), an early pioneer in aerodynamics who experimented with hovercraft Sir John Isaac Thornycroft (1843-1928), a Royal Navy architect who was the first to experiment with air-cushion theory Air-Cushion Travel The air-cushion vehicle was first conceived by Sir John Isaac Thornycroft of Great Britain in the 1870’s. He theorized that if a ship had a plenum chamber (a box open at the bottom) for a hull and it were pumped full of air, the ship would rise out of the water and move faster, because there would be less drag. The main problem was keeping the air from escaping from under the craft. In the early 1950’s, Christopher Sydney Cockerell was experimenting with ways to reduce both the wave-making and frictional resistance that craft had to water. In 1953, he constructed a punt with a fan that supplied air to the bottom of the craft, which could thus glide over the surface with very little friction. The air was contained under the craft by specially constructed side walls. In 1955, the first true “hovercraft,” as Cockerell called it, was constructed of balsa wood. It weighed only 127 grams and traveled over water at a speed of 13 kilometers per hour. On November 16, 1956, Cockerell successfully demonstrated his model hovercraft at the patent agent’s office in London. It was immediately placed on the “secret” list, and Saunders-Roe Ltd. was given the first contract to build hovercraft in 1957. The first experimental piloted hovercraft, the SR.N1, which had a weight of 3,400 kilograms and could carry three people at the speed of 25 knots, was completed on May 28, 1959, and publicly demonstrated on June 11, 1959. Ground Effect Phenomenon In a hovercraft, a jet airstream is directed downward through a hole in a metal disk, which forces the disk to rise. The jet of air has a reverse effect of its own that forces the disk away from the surface. Some of the air hitting the ground bounces back against the disk to add further lift. This is called the “ground effect.” The ground effect is such that the greater the under-surface area of the hovercraft, the greater the reverse thrust of the air that bounces back. This makes the hovercraft a mechanically efficient machine because it provides three functions. First, the ground effect reduces friction between the craft and the earth’s surface. Second, it acts as a spring suspension to reduce some of the vertical acceleration effects that arise from travel over an uneven surface. Third, it provides a safe and comfortable ride at high speed, whatever the operating environment. The air cushion can distribute the weight of the hovercraft over almost its entire area so that the cushion pressure is low. The basic elements of the air-cushion vehicle are a hull, a propulsion system, and a lift system. The hull, which accommodates the crew, passengers, and freight, contains both the propulsion and lift systems. The propulsion and lift systems can be driven by the same power plant or by separate power plants. Early designs used only one unit, but this proved to be a problem when adequate power was not achieved for movement and lift. Better results are achieved when two units are used, since far more power is used to lift the vehicle than to propel it. For lift, high-speed centrifugal fans are used to drive the air through jets that are located under the craft. A redesigned aircraft propeller is used for propulsion. Rudderlike fins and an air fan that can be swiveled to provide direction are placed at the rear of the craft. Several different air systems can be used, depending on whether a skirt system is used in the lift process. The plenum chamber system, the peripheral jet system, and several types of recirculating air systems have all been successfully tried without skirting. Avariety of rigid and flexible skirts have also proved to be satisfactory, depending on the use of the vehicle. Skirts are used to hold the air for lift. Skirts were once hung like curtains around hovercraft. Instead of simple curtains to contain the air, there are now complicated designs that contain the cushion, duct the air, and even provide a secondary suspension. The materials used in the skirting have also changed from a rubberized fabric to pure rubber and nylon and, finally, to neoprene, a lamination of nylon and plastic. The three basic types of hovercraft are the amphibious, nonamphibious, and semiamphibious models. The amphibious type can travel over water and land, whereas the nonamphibious type is restricted to water travel. The semiamphibious model is also restricted to water travel but may terminate travel by nosing up on a prepared ramp or beach. All hovercraft contain built-in buoyancy tanks in the side skirting as a safety measure in the event that a hovercraft must settle on the water. Most hovercraft are equipped with gas turbines and use either propellers or water-jet propulsion. Impact Hovercraft are used primarily for short passenger ferry services. Great Britain was the only nation to produce a large number of hovercraft. The British built larger and faster craft and pioneered their successful use as ferries across the English Channel, where they could reach speeds of 111 kilometers per hour (160 knots) and carry more than four hundred passengers and almost one hundred vehicles. France and the former Soviet Union have also effectively demonstrated hovercraft river travel, and the Soviets have experimented with military applications as well. The military adaptations of hovercraft have been more diversified. Beach landings have been performed effectively, and the United States used hovercraft for river patrols during the Vietnam War. Other uses also exist for hovercraft. They can be used as harbor pilot vessels and for patrolling shores in a variety of police-and customs- related duties. Hovercraft can also serve as flood-rescue craft and fire-fighting vehicles. Even a hoverfreighter is being considered. The air-cushion theory in transport systems is rapidly developing. It has spread to trains and smaller people movers in many countries. Their smooth, rapid, clean, and efficient operation makes hovercraft attractive to transportation designers around the world.

Holography

The invention: A lensless system of three-dimensional photography that was one of the most important developments in twentieth century optical science. The people behind the invention: Dennis Gabor (1900-1979), a Hungarian-born inventor and physicist who was awarded the 1971 Nobel Prize in Physics Emmett Leith (1927- ), a radar researcher who, with Juris Upatnieks, produced the first laser holograms Juris Upatnieks (1936- ), a radar researcher who, with Emmett Leith, produced the first laser holograms Easter Inspiration The development of photography in the early 1900’s made possible the recording of events and information in ways unknown before the twentieth century: the photographing of star clusters, the recording of the emission spectra of heated elements, the storing of data in the form of small recorded images (for example, microfilm), and the photographing of microscopic specimens, among other things. Because of its vast importance to the scientist, the science of photography has developed steadily. An understanding of the photographic and holographic processes requires some knowledge of the wave behavior of light. Light is an electromagnetic wave that, like a water wave, has an amplitude and a phase. The amplitude corresponds to the wave height, while the phase indicates which part of the wave is passing a given point at a given time. A cork floating in a pond bobs up and down as waves pass under it. The position of the cork at any time depends on both amplitude and phase: The phase determines on which part of the wave the cork is floating at any given time, and the amplitude determines how high or low the cork can be moved. Waves from more than one source arriving at the cork combine in ways that depend on their relative phases. If the waves meet in the same phase, they add and produce a large amplitude; if they arrive out of phase, they subtract and produce a small amplitude. The total amplitude, or intensity, depends on the phases of the combining waves. Dennis Gabor, the inventor of holography, was intrigued by the way in which the photographic image of an object was stored by a photographic plate but was unable to devote any consistent research effort to the question until the 1940’s. At that time, Gabor was involved in the development of the electron microscope. On Easter morning in 1947, as Gabor was pondering the problem of how to improve the electron microscope, the solution came to him. He would attempt to take a poor electron picture and then correct it optically. The process would require coherent electron beams—that is, electron waves with a definite phase. This two-stage method was inspired by the work of Lawrence Bragg. Bragg had formed the image of a crystal lattice by diffracting the photographic X-ray diffraction pattern of the original lattice. This double diffraction process is the basis of the holographic process. Bragg’s method was limited because of his inability to record the phase information of the X-ray photograph. Therefore, he could study only those crystals for which the phase relationship of the reflected waves could be predicted. Waiting for the Laser Gabor devised a way of capturing the phase information after he realized that adding coherent background to the wave reflected from an object would make it possible to produce an interference pattern on the photographic plate. When the phases of the two waves are identical, a maximum intensity will be recorded; when they are out of phase, a minimum intensity is recorded. Therefore, what is recorded in a hologram is not an image of the object but rather the interference pattern of the two coherent waves. This pattern looks like a collection of swirls and blank spots. The hologram (or photograph) is then illuminated by the reference beam, and part of the transmitted light is a replica of the original object wave. When viewing this object wave, one sees an exact replica of the original object. The major impediment at the time in making holograms using any form of radiation was a lack of coherent sources. For example, the coherence of the mercury lamp used by Gabor and his assistant IvorWilliams was so short that they were able to make holograms of only about a centimeter in diameter. The early results were rather poor in terms of image quality and also had a double image. For this reason, there was little interest in holography, and the subject lay almost untouched for more than ten years. Interest in the field was rekindled after the laser (light amplification by stimulated emission of radiation) was developed in 1962. Emmett Leith and Juris Upatnieks, who were conducting radar research at the University of Michigan, published the first laser holographs in 1963. The laser was an intense light source with a very long coherence length. Its monochromatic nature improved the resolution of the images greatly. Also, there was no longer any restriction on the size of the object to be photographed. The availability of the laser allowed Leith and Upatnieks to propose another improvement in holographic technique. Before 1964, holograms were made of only thin transparent objects. A small region of the hologram bore a one-to-one correspondence to a region of the object. Only a small portion of the image could be viewed at one time without the aid of additional optical components. Illuminating the transparency diffusely allowed the whole image to be seen at one time. This development also made it possible to record holograms of diffusely reflected three-dimensional objects. Gabor had seen from the beginning that this should make it possible to create three-dimensional images. After the early 1960’s, the field of holography developed very quickly. Because holography is different from conventional photography, the two techniques often complement each other. Gabor saw his idea blossom into a very important technique in optical science. Impact The development of the laser and the publication of the first laser holograms in 1963 caused a blossoming of the new technique in many fields. Soon, techniques were developed that allowed holograms to be viewed with white light. It also became possible for holograms to reconstruct multicolored images. Holographic methods have been used to map terrain with radar waves and to conduct surveillance in the fields of forestry, agriculture, and meteorology.By the 1990’s, holography had become a multimillion-dollar industry, finding applications in advertising, as an art form, and in security devices on credit cards, as well as in scientific fields. An alternate form of holography, also suggested by Gabor, uses sound waves. Acoustical imaging is useful whenever the medium around the object to be viewed is opaque to light rays—for example, in medical diagnosis. Holography has affected many areas of science, technology, and culture.

Heat pump

The invention:

A device that warms and cools buildings efficiently
and cheaply by moving heat from one area to another.

The people behind the invention:

T. G. N. Haldane, a British engineer
Lord Kelvin (William Thomson, 1824-1907), a British
mathematician, scientist, and engineer
Sadi Carnot (1796-1832), a French physicist and
thermodynamicist

Heart-lung machine

The invention: The first artificial device to oxygenate and circulate blood during surgery, the heart-lung machine began the era of open-heart surgery. The people behind the invention: John H. Gibbon, Jr. (1903-1974), a cardiovascular surgeon Mary Hopkinson Gibbon (1905- ), a research technician Thomas J. Watson (1874-1956), chairman of the board of IBM T. L. Stokes and J. B. Flick, researchers in Gibbon’s laboratory Bernard J. Miller (1918- ), a cardiovascular surgeon and research associate Cecelia Bavolek, the first human to undergo open-heart surgery successfully using the heart-lung machine A Young Woman’s Death In the first half of the twentieth century, cardiovascular medicine had many triumphs. Effective anesthesia, antiseptic conditions, and antibiotics made surgery safer. Blood-typing, anti-clotting agents, and blood preservatives made blood transfusion practical. Cardiac catheterization (feeding a tube into the heart), electrocardiography, and fluoroscopy (visualizing living tissues with an X-ray machine) made the nonsurgical diagnosis of cardiovascular problems possible. As of 1950, however, there was no safe way to treat damage or defects within the heart. To make such a correction, this vital organ’s function had to be interrupted. The problem was to keep the body’s tissues alive while working on the heart. While some surgeons practiced so-called blind surgery, in which they inserted a finger into the heart through a small incision without observing what they were attempting to correct, others tried to reduce the body’s need for circulation by slowly chilling the patient until the heart stopped. Still other surgeons used “cross-circulation,” in which the patient’s circulation was connected to a donor’s circulation. All these approaches carried profound risks of hemorrhage, tissue damage, and death. In February of 1931, Gibbon witnessed the death of a young woman whose lung circulation was blocked by a blood clot. Because her blood could not pass through her lungs, she slowly lost consciousness from lack of oxygen. As he monitored her pulse and breathing, Gibbon thought about ways to circumvent the obstructed lungs and straining heart and provide the oxygen required. Because surgery to remove such a blood clot was often fatal, the woman’s surgeons operated only as a last resort. Though the surgery took only six and one-half minutes, she never regained consciousness. This experience prompted Gibbon to pursue what few people then considered a practical line of research: a way to circulate and oxygenate blood outside the body. A Woman’s Life Restored Gibbon began the project in earnest in 1934, when he returned to the laboratory of Edward D. Churchill at Massachusetts General Hospital for his second surgical research fellowship. He was assisted by Mary Hopkinson Gibbon. Together, they developed, using cats, a surgical technique for removing blood froma vein, supplying the blood with oxygen, and returning it to an artery using tubes inserted into the blood vessels. Their objective was to create a device that would keep the blood moving, spread it over a very thin layer to pick up oxygen efficiently and remove carbon dioxide, and avoid both clotting and damaging blood cells. In 1939, they reported that prolonged survival after heart-lung bypass was possible in experimental animals. WorldWar II (1939-1945) interrupted the progress of this work; it was resumed by Gibbon at Jefferson Medical College in 1944. Shortly thereafter, he attracted the interest of Thomas J.Watson, chairman of the board of the International Business Machines (IBM) Corporation, who provided the services of IBM’s experimental physics laboratory and model machine shop as well as the assistance of staff engineers. IBM constructed and modified two experimental machines over the next seven years, and IBM engineers contributed significantly to the evolution of a machine that would be practical in humans. Gibbon’s first attempt to use the pump-oxygenator in a human being was in a fifteen-month-old baby. This attempt failed, not because of a malfunction or a surgical mistake but because of a misdiagnosis. The child died following surgery because the real problem had not been corrected by the surgery. On May 6, 1953, the heart-lung machine was first used successfully on Cecelia Bavolek. In the six months before surgery, Bavolek had been hospitalized three times for symptoms of heart failure when she tried to engage in normal activity. While her circulation was connected to the heart-lung machine for forty-five minutes, the surgical team headed by Gibbon was able to close an opening between her atria and establish normal heart function. Two months later, an examination of the defect revealed that it was fully closed; Bavolek resumed a normal life. The age of open-heart surgery had begun. Consequences The heart-lung bypass technique alone could not make openheart surgery truly practical. When it was possible to keep tissues alive by diverting blood around the heart and oxygenating it, other questions already under investigation became even more critical: how to prolong the survival of bloodless organs, how to measure oxygen and carbon dioxide levels in the blood, and how to prolong anesthesia during complicated surgery. Thus, following the first successful use of the heart-lung machine, surgeons continued to refine the methods of open-heart surgery. The heart-lung apparatus set the stage for the advent of “replacement parts” for many types of cardiovascular problems. Cardiac valve replacement was first successfully accomplished in 1960 by placing an artificial ball valve between the left atrium and ventricle. In 1957, doctors performed the first coronary bypass surgery, grafting sections of a leg vein into the heart’s circulation system to divert blood around clogged coronary arteries. Likewise, the first successful heart transplant (1967) and the controversial Jarvik-7 artificial heart implantation (1982) required the ability to stop the heart and keep the body’s tissues alive during time-consuming and delicate surgical procedures. Gibbon’s heart-lung machine paved the way for all these developments.

Hearing aid

The invention: Miniaturized electronic amplifier worn inside the ears of hearing-impaired persons. The organization behind the invention: Bell Labs, the research and development arm of the American Telephone and Telegraph Company Trapped in Silence Until the middle of the twentieth century, people who experienced hearing loss had little hope of being able to hear sounds without the use of large, awkward, heavy appliances. For many years, the only hearing aids available were devices known as ear trumpets. The ear trumpet tried to compensate for hearing loss by increasing the number of sound waves funneled into the ear canal. A wide, bell-like mouth similar to the bell of a musical trumpet narrowed to a tube that the user placed in his or her ear. Ear trumpets helped a little, but they could not truly increase the volume of the sounds heard. Beginning in the nineteenth century, inventors tried to develop electrical devices that would serve as hearing aids. The telephone was actually a by-product of Alexander Graham Bell’s efforts to make a hearing aid. Following the invention of the telephone, electrical engineers designed hearing aids that employed telephone technology, but those hearing aids were only a slight improvement over the old ear trumpets. They required large, heavy battery packs and used a carbon microphone similar to the receiver in a telephone. More sensitive than purely physical devices such as the ear trumpet, they could transmit a wider range of sounds but could not amplify them as effectively as electronic hearing aids now do. Transistors Make Miniaturization Possible Two types of hearing aids exist: body-worn and head-worn. Body-worn hearing aids permit the widest range of sounds to be heard, but because of the devices’ larger size, many hearing impaired persons do not like to wear them. Head-worn hearing aids, especially those worn completely in the ear, are much less conspicuous. In addition to in-ear aids, the category of head-worn hearing aids includes both hearing aids mounted in eyeglass frames and those worn behind the ear. All hearing aids, whether head-worn or body-worn, consist of four parts: a microphone to pick up sounds, an amplifier, a receiver, and a power source. The microphone gathers sound waves and converts them to electrical signals; the amplifier boosts, or increases, those signals; and the receiver then converts the signals back into sound waves. In effect, the hearing aid is a miniature radio. After the receiver converts the signals back to sound waves, those waves are directed into the ear canal through an earpiece or ear mold. The ear mold generally is made of plastic and is custom fitted from an impression taken from the prospective user’s ear. Effective head-worn hearing aids could not be built until the electronic circuit was developed in the early 1950’s. The same invention— the transistor—that led to small portable radios and tape players allowed engineers to create miniaturized, inconspicuous hearing aids. Depending on the degree of amplification required, the amplifier in a hearing aid contains three or more transistors. Transistors first replaced vacuum tubes in devices such as radios and phonographs, and then engineers realized that they could be used in devices for the hearing-impaired. The research at Bell Labs that led to the invention of the transistor rose out of military research duringWorldWar II. The vacuum tubes used in, for example, radar installations to amplify the strength of electronic signals were big, were fragile because they were made of blown glass, and gave off high levels of heat when they were used. Transistors, however, made it possible to build solid-state, integrated circuits. These are made from crystals of metals such as germanium or arsenic alloys and therefore are much less fragile than glass. They are also extremely small (in fact, some integrated circuits are barely visible to the naked eye) and give off no heat during use. The number of transistors in a hearing aid varies depending upon the amount of amplification required. The first transistor is the most important for the listener in terms of the quality of sound heard. If the frequency response is set too high—that is, if the device is too sensitive—the listener will be bothered by distracting background noise. Theoretically, there is no limit on the amount of amplification that a hearing aid can be designed to provide, but there are practical limits. The higher the amplification, the more power is required to operate the hearing aid. This is why body-worn hearing aids can convey a wider range of sounds than head-worn devices can. It is the power source—not the electronic components—that is the limiting factor. A body-worn hearing aid includes a larger battery pack than can be used with a head-worn device. Indeed, despite advances in battery technology, the power requirements of a head-worn hearing aid are such that a 1.4-volt battery that could power a wristwatch for several years will last only a few days in a hearing aid. Consequences The invention of the electronic hearing aid made it possible for many hearing-impaired persons to participate in a hearing world. Prior to the invention of the hearing aid, hearing-impaired children often were unable to participate in routine school activities or function effectively in mainstream society. Instead of being able to live at home with their families and enjoy the same experiences that were available to other children their age, often they were forced to attend special schools operated by the state or by charities. Hearing-impaired people were singled out as being different and were limited in their choice of occupations. Although not every hearing-impaired person can be helped to hear with a hearing aid— particularly in cases of total hearing loss—the electronic hearing aid has ended restrictions for many hearing-impaired people. Hearingimpaired children are now included in public school classes, and hearing-impaired adults can now pursue occupations from which they were once excluded. Today, many deaf and hearing-impaired persons have chosen to live without the help of a hearing aid. They believe that they are not disabled but simply different, and they point out that their “disability” often allows them to appreciate and participate in life in unique and positive ways. For them, the use of hearing aids is a choice, not a necessity. For those who choose, hearing aids make it possible to participate in the hearing world.