Nylon

The invention: A resilient, high-strength polymer with applications

ranging from women’s hose to safety nets used in space flights.

The people behind the invention:Wallace Hume Carothers (1896-1937),

an American organic chemist Charles M. A. Stine (1882-1954), an American chemist

and director of chemical research at Du Pont Elmer Keiser Bolton (1886-1968),

an American industrial chemist Pure Research In the twentieth century,

American corporations created industrial research laboratories.

Their directors became the organizers of inventions,

and their scientists served as the sources of creativity.

The research program of

Nuclear reactor

The invention: 

The first nuclear reactor to produce substantial
quantities of plutonium, making it practical to produce usable
amounts of energy from a chain reaction.

The people behind the invention:

Enrico Fermi (1901-1954), an American physicist
Martin D. Whitaker (1902-1960), the first director of Oak Ridge
National Laboratory
Eugene Paul Wigner (1902-1995), the director of research and
development at Oak Ridge

Nuclear power plant

The invention: 

The first full-scale commercial nuclear power plant, which gave birth to the nuclear power industry.  



The people behind the invention:

Enrico Fermi (1901-1954), an Italian American physicist who
won the 1938 Nobel Prize in Physics
Otto Hahn (1879-1968), a German physical chemist who won the
1944 Nobel Prize in Chemistry
Lise Meitner (1878-1968), an Austrian Swedish physicist
Hyman G. Rickover (1898-1986), a Polish American naval officer

Nuclear magnetic resonance

The invention: 

Procedure that uses hydrogen atoms in the human
body, strong electromagnets, radio waves, and detection equipment
to produce images of sections of the brain.

The people behind the invention:

Raymond Damadian (1936- ), an American physicist and
inventor
Paul C. Lauterbur (1929- ), an American chemist
Peter Mansfield (1933- ), a scientist at the University of
Nottingham, England

Neutrino detector

The invention:Adevice that provided the first direct evidence that the Sun runs on thermonuclear power and challenged existing models of the Sun. The people behind the invention: Raymond Davis, Jr. (1914- ), an American chemist John Norris Bahcall (1934- ), an American astrophysicist Missing Energy In 1871, Hermann von Helmholtz, the German physicist, anatomist, and physiologist, suggested that no ordinary chemical reaction could be responsible for the enormous energy output of the Sun. By the 1920’s, astrophysicists had realized that the energy radiated by the Sun must come from nuclear fusion, in which protons or nuclei combine to form larger nuclei and release energy.

Neoprene

The invention: The first commercially practical synthetic rubber, Neoprene gave a boost to polymer chemistry and the search for new materials. The people behind the invention: Wallace Hume Carothers (1896-1937), an American chemist Arnold Miller Collins (1899- ), an American chemist Elmer Keiser Bolton (1886-1968), an American chemist Julius Arthur Nieuwland (1879-1936), a Belgian American priest, botanist, and chemist Synthetic Rubber: A Mirage? The growing dependence of the industrialized nations upon elastomers (elastic substances) and the shortcomings of natural rubber motivated the twentieth century quest for rubber substitutes. By 1914

Microwave cooking

The invention: System of high-speed cooking that uses microwave radition to agitate liquid molecules to raise temperatures by friction. The people behind the invention: Percy L. Spencer (1894-1970), an American engineer Heinrich Hertz (1857-1894), a German physicist James Clerk Maxwell (1831-1879), a Scottish physicist The Nature of Microwaves Microwaves are electromagnetic waves, as are radio waves, X rays, and visible light. Water waves

Memory metal

Memory metal The invention: Known as nitinol, a metal alloy that returns to its original shape, after being deformed, when it is heated to the proper temperature. The person behind the invention: William Buehler (1923- ), an American metallurgist The Alloy with a Memory In 1960,William Buehler developed an alloy that consisted of 53 to 57 percent nickel (by weight) and the balance titanium. This alloy, which is called nitinol, turned out to have remarkable properties. Nitinol is a “memory metal,” which means that, given the proper conditions, objects made of nitinol can be restored to their original shapes even after they have been radically deformed. The return to the original shape

Mass spectrograph

The invention: The first device used to measure the mass of atoms, which was found to be the result of the combination of isotopes. The people behind the invention: Francis William Aston (1877-1945), an English physicist who was awarded the 1922 Nobel Prize in Chemistry Sir Joseph John Thomson (1856-1940), an English physicist William Prout (1785-1850), an English biochemist Ernest Rutherford (1871-1937), an English physicist Same Element, Different Weights Isotopes are different forms of a chemical element that act similarly in chemical or physical reactions. Isotopes differ in two ways: They possess different atomic weights and different radioactive transformations. In 1803, John Dalton proposed a new atomic theory of chemistry that claimed that chemical elements in a compound combine by weight in whole number proportions to one another. By 1815, William Prout had taken Dalton’s hypothesis one step further and claimed that the atomic weights of elements were integral (the integers are the positive and negative whole numbers and zero) multiples

Mark I calculator

The invention: Early digital calculator designed to solve differential equations that was a forerunner of modern computers. The people behind the invention: Howard H. Aiken (1900-1973), Harvard University professor and architect of the Mark I Clair D. Lake (1888-1958), a senior engineer at IBM Francis E. Hamilton (1898-1972), an IBM engineer Benjamin M. Durfee (1897-1980), an IBM engineer The Human Computer The physical world can be described by means of mathematics. In principle, one can accurately describe nature down to the smallest detail.

Mammography

The invention: The first X-ray procedure for detecting and diagnosing breast cancer. The people behind the invention: Albert Salomon, the first researcher to use X-ray technology instead of surgery to identify breast cancer Jacob Gershon-Cohen (1899-1971), a breast cancer researcher Studying Breast Cancer Medical researchers have been studying breast cancer for more than a century. At the end of the nineteenth century, however, no one knew how to detect breast cancer until it was quite advanced. Often, by the time it was detected, it was too late for surgery; many patients who did have surgery died. So after X-ray technology first appeared in 1896, cancer researchers were eager to experiment with it. The first scientist to use X-ray techniques in breast cancer experiments was Albert Salomon, a German surgeon. Trying to develop a biopsy technique that could tell which tumors were cancerous and thereby avoid unnecessary surgery, he X-rayed more than three thousand breasts that had been removed from patients during breast cancer surgery. In 1913, he published the results of his experiments, showing that X rays could detect breast cancer. Different types of Xray images, he said, showed different types of cancer. Though Salomon is recognized as the inventor of breast radiology, he never actually used his technique to diagnose breast cancer. In fact, breast cancer radiology, which came to be known as “mammography,” was not taken up quickly by other medical researchers. Those who did try to reproduce his research often found that their results were not conclusive. During the 1920’s, however, more research was conducted in Leipzig, Germany, and in South America. Eventually, the Leipzig researchers, led by Erwin Payr, began to use mammography to diagnose cancer. In the 1930’s, a Leipzig researcher named W. Vogel published a paper that accurately described differences between cancerous and noncancerous tumors as they appeared on X-ray photographs. Researchers in the United States paid little attention to mammography until 1926. That year, a physician in Rochester, New York, was using a fluoroscope to examine heart muscle in a patient and discovered that the fluoroscope could be used to make images of breast tissue as well. The physician, Stafford L. Warren, then developed a stereoscopic technique that he used in examinations before surgery. Warren published his findings in 1930; his article also described changes in breast tissue that occurred because of pregnancy, lactation (milk production), menstruation, and breast disease. Yet Stafford’s technique was complicated and required equipment that most physicians of the time did not have. Eventually, he lost interest in mammography and went on to other research. Using the Technique In the late 1930’s, Jacob Gershon-Cohen became the first clinician to advocate regular mammography for all women to detect breast cancer before it became a major problem. Mammography was not very expensive, he pointed out, and it was already quite accurate. A milestone in breast cancer research came in 1956, when Gershon- Cohen and others began a five-year study of more than 1,300 women to test the accuracy of mammography for detecting breast cancer. Each woman studied was screened once every six months. Of the 1,055 women who finished the study, 92 were diagnosed with benign tumors and 23 with malignant tumors. Remarkably, out of all these, only one diagnosis turned out to be wrong. During the same period, Robert Egan of Houston began tracking breast cancer X rays. Over a span of three years, one thousand X-ray photographs were used to make diagnoses. When these diagnoses were compared to the results of surgical biopsies, it was confirmed that mammography had produced 238 correct diagnoses of cancer, out of 240 cases. Egan therefore joined the crusade for regular breast cancer screening. Once mammography was finally accepted by doctors in the late 1950’s and early 1960’s, researchers realized that they needed a way to teach mammography quickly and effectively to those who would use it. A study was done, and it showed that any radiologist could conduct the procedure with only five days of training.In the early 1970’s, the American Cancer Society and the National Cancer Institute joined forces on a nationwide breast cancer screening program called the “Breast Cancer Detection Demonstration Project.” Its goal in 1971 was to screen more than 250,000 women over the age of thirty-five. Since the 1960’s, however, some people had argued that mammography was dangerous because it used radiation on patients. In 1976, Ralph Nader, a consumer advocate, stated that women who were to undergo mammography should be given consent forms that would list the dangers of radiation. In the years that followed, mammography was refined to reduced the amount of radiation needed to detect cancer. It became a standard tool for diagnosis, and doctors recommended that women have a mammogram every two or three years after the age of forty. Impact Radiology is not a science that concerns only breast cancer screening. While it does provide the technical facilities necessary to practice mammography, the photographic images obtained must be interpreted by general practitioners, as well as by specialists. Once Gershon-Cohen had demonstrated the viability of the technique, a means of training was devised that made it fairly easy for clinicians to learn how to practice mammography successfully. Once all these factors—accuracy, safety, simplicity—were in place, mammography became an important factor in the fight against breast cancer. The progress made in mammography during the twentieth century was a major improvement in the effort to keep more women from dying of breast cancer. The disease has always been one of the primary contributors to the number of female cancer deaths that occur annually in the United States and around the world. This high figure stems from the fact that women had no way of detecting the disease until tumors were in an advanced state. Once Salomon’s procedure was utilized, physicians had a means by which they could look inside breast tissue without engaging in exploratory surgery, thus giving women a screening technique that was simple and inexpensive. By 1971, a quarter million women over age thirty-five had been screened. Twenty years later, that number was in the millions.

Long-distance telephone

The invention: System for conveying voice signals via wires over long distances. The people behind the invention: Alexander Graham Bell (1847-1922), a Scottish American inventor Thomas A. Watson (1854-1934), an American electrical engineer The Problem of Distance The telephone may be the most important invention of the nineteenth century. The device developed by Alexander Graham Bell and Thomas A. Watson opened a new era in communication and made it possible for people to converse over long distances for the first time. During the last two decades of the nineteenth century and the first decade of the twentieth century, the American Telephone and Telegraph (AT&T) Company continued to refine and upgrade telephone facilities, introducing such innovations as automatic dialing and long-distance service. One of the greatest challenges faced by Bell engineers was to develop a way of maintaining signal quality over long distances. Telephone wires were susceptible to interference from electrical storms and other natural phenomena, and electrical resistance and radiation caused a fairly rapid drop-off in signal strength, which made long-distance conversations barely audible or unintelligible. By 1900, Bell engineers had discovered that signal strength could be improved somewhat by wrapping the main wire conductor with thinner wires called “loading coils” at prescribed intervals along the length of the cable. Using this procedure, Bell extended longdistance service from New York to Denver, Colorado, which was then considered the farthest point that could be reached with acceptable quality. The result, however, was still unsatisfactory, and Bell engineers realized that some form of signal amplification would be necessary to improve the quality of the signal.A breakthrough came in 1906, when Lee de Forest invented the “audion tube,” which could send and amplify radio waves. Bell scientists immediately recognized the potential of the new device for long-distance telephony and began building amplifiers that would be placed strategically along the long-distance wire network. Work progressed so quickly that by 1909, Bell officials were predicting that the first transcontinental long-distance telephone service, between New York and San Francisco, was imminent. In that year, Bell president Theodore N. Vail went so far as to promise the organizers of the Panama-Pacific Exposition, scheduled to open in San Francisco in 1914, that Bell would offer a demonstration at the exposition. The promise was risky, because certain technical problems associated with sending a telephone signal over a 4,800- kilometer wire had not yet been solved. De Forest’s audion tube was a crude device, but progress was being made. Two more breakthroughs came in 1912, when de Forest improved on his original concept and Bell engineer Harold D. Arnold improved it further. Bell bought the rights to de Forest’s vacuumtube patents in 1913 and completed the construction of the New York-San Francisco circuit. The last connection was made at the Utah-Nevada border on June 17, 1914. Success Leads to Further Improvements Bell’s long-distance network was tested successfully on June 29, 1914, but the official demonstration was postponed until January 25, 1915, to accommodate the Panama-Pacific Exposition, which had also been postponed. On that date, a connection was established between Jekyll Island, Georgia, where Theodore Vail was recuperating from an illness, and New York City, where Alexander Graham Bell was standing by to talk to his former associate Thomas Watson, who was in San Francisco. When everything was in place, the following conversation took place. Bell: “Hoy! Hoy! Mr. Watson? Are you there? Do you hear me?”Watson: “Yes, Dr. Bell, I hear you perfectly. Do you hear me well?” Bell: “Yes, your voice is perfectly distinct. It is as clear as if you were here in New York.” The first transcontinental telephone conversation transmitted by wire was followed quickly by another that was transmitted via radio. Although the Bell company was slow to recognize the potential of radio wave amplification for the “wireless” transmission of telephone conversations, by 1909 the company had made a significant commitment to conduct research in radio telephony. On April 4, 1915, a wireless signal was transmitted by Bell technicians from Montauk Point on Long Island, New York, to Wilmington, Delaware, a distance of more than 320 kilometers. Shortly thereafter, a similar test was conducted between New York City and Brunswick, Georgia, via a relay station at Montauk Point. The total distance of the transmission was more than 1,600 kilometers. Finally, in September, 1915, Vail placed a successful transcontinental radiotelephone call from his office in New York to Bell engineering chief J. J. Carty in San Francisco. Only a month later, the first telephone transmission across the Atlantic Ocean was accomplished via radio from Arlington, Virginia, to the Eiffel Tower in Paris, France. The signal was detectable, although its quality was poor. It would be ten years before true transatlantic radio-telephone service would begin. The Bell company recognized that creating a nationwide longdistance network would increase the volume of telephone calls simply by increasing the number of destinations that could be reached from any single telephone station. As the network expanded, each subscriber would have more reason to use the telephone more often, thereby increasing Bell’s revenues. Thus, the company’s strategy became one of tying local and regional networks together to create one large system. Impact Just as the railroads had interconnected centers of commerce, industry, and agriculture all across the continental United States in the nineteenth century, the telephone promised to bring a new kind of interconnection to the country in the twentieth century: instantaneous voice communication. During the first quarter century after the invention of the telephone and during its subsequent commercialization, the emphasis of telephone companies was to set up central office switches that would provide interconnections among subscribers within a fairly limited geographical area. Large cities were wired quickly, and by the beginning of the twentieth century most were served by telephone switches that could accommodate thousands of subscribers. The development of intercontinental telephone service was a milestone in the history of telephony for two reasons. First, it was a practical demonstration of the almost limitless applications of this innovative technology. Second, for the first time in its brief history, the telephone network took on a national character. It became clear that large central office networks, even in large cities such as New York, Chicago, and Baltimore, were merely small parts of a much larger, universally accessible communication network that spanned a continent. The next step would be to look abroad, to Europe and beyond.

Long-distance radiotelephony

The invention: The first radio transmissions fromthe United States to Europe opened a new era in telecommunications. The people behind the invention: Guglielmo Marconi (1874-1937), Italian inventor of transatlantic telegraphy Reginald Aubrey Fessenden (1866-1932), an American radio engineer Lee de Forest (1873-1961), an American inventor Harold D. Arnold (1883-1933), an American physicist John J. Carty (1861-1932), an American electrical engineer An Accidental Broadcast The idea of commercial transatlantic communication was first conceived by Italian physicist and inventor Guglielmo Marconi, the pioneer of wireless telegraphy. Marconi used a spark transmitter to generate radio waves that were interrupted, or modulated, to form the dots and dashes of Morse code. The rapid generation of sparks created an electromagnetic disturbance that sent radio waves of different frequencies into the air—a broad, noisy transmission that was difficult to tune and detect. The inventor Reginald Aubrey Fessenden produced an alternative method that became the basis of radio technology in the twentieth century. His continuous radio waves kept to one frequency, making them much easier to detect at long distances. Furthermore, the continuous waves could be modulated by an audio signal, making it possible to transmit the sound of speech. Fessenden used an alternator to generate electromagnetic waves at the high frequencies required in radio transmission. It was specially constructed at the laboratories of the General Electric Company. The machine was shipped to Brant Rock, Massachusetts, in 1906 for testing. Radio messages were sent to a boat cruising offshore, and the feasibility of radiotelephony was thus demonstrated. Fessenden followed this success with a broadcast of messages and music between Brant Rock and a receiving station constructed at Plymouth, Massachusetts. The equipment installed at Brant Rock had a range of about 160 kilometers. The transmission distance was determined by the strength of the electric power delivered by the alternator, which was measured in watts. Fessenden’s alternator was rated at 500 watts, but it usually delivered much less power. Yet this was sufficient to send a radio message across the Atlantic. Fessenden had built a receiving station at Machrihanish, Scotland, to test the operation of a large rotary spark transmitter that he had constructed. An operator at this station picked up the voice of an engineer at Brant Rock who was sending instructions to Plymouth. Thus, the first radiotelephone message had been sent across the Atlantic by accident. Fessenden, however, decided not to make this startling development public. The station at Machrihanish was destroyed in a storm, making it impossible to carry out further tests. The successful transmission undoubtedly had been the result of exceptionally clear atmospheric conditions that might never again favor the inventor. One of the parties following the development of the experiments in radio telephony was the American Telephone and Telegraph (AT&T) Company. Fessenden entered into negotiations to sell his system to the telephone company, but, because of the financial panic of 1907, the sale was never made. Virginia to Paris and Hawaii The English physicist John Ambrose Fleming had invented a twoelement (diode) vacuum tube in 1904 that could be used to generate and detect radio waves. Two years later, the American inventor Lee de Forest added a third element to the diode to produce his “audion” (triode), which was a more sensitive detector. John J. Carty, head of a research and development effort at AT&T, examined these new devices carefully. He became convinced that an electronic amplifier, incorporating the triode into its design, could be used to increase the strength of telephone signals and to long distances. On Carty’s advice, AT&T purchased the rights to de Forest’s audion. A team of about twenty-five researchers, under the leadership of physicist Harold D. Arnold, were assigned the job of perfecting the triode and turning it into a reliable amplifier. The improved triode was responsible for the success of transcontinental cable telephone service, which was introduced in January, 1915. The triode was also the basis of AT&T’s foray into radio telephony. Carty’s research plan called for a system with three components: an oscillator to generate the radio waves, a modulator to add the audio signals to the waves, and an amplifier to transmit the radio waves. The total power output of the system was 7,500 watts, enough to send the radio waves over thousands of kilometers.The apparatus was installed in the U.S. Navy’s radio tower in Arlington, Virginia, in 1915. Radio messages from Arlington were picked up at a receiving station in California, a distance of 4,000 kilometers, then at a station in Pearl Harbor, Hawaii, which was 7,200 kilometers from Arlington. AT&T’s engineers had succeeded in joining the company telephone lines with the radio transmitter at Arlington; therefore, the president of AT&T, Theodore Vail, could pick up his telephone and talk directly with someone in California. The next experiment was to send a radio message fromArlington to a receiving station set up in the Eiffel Tower in Paris. After several unsuccessful attempts, the telephone engineers in the Eiffel Tower finally heard Arlington’s messages on October 21, 1915. The AT&T receiving station in Hawaii also picked up the messages. The two receiving stations had to send their reply by telegraph to the United States because both stations were set up to receive only. Two-way radio communication was still years in the future. Impact The announcement that messages had been received in Paris was front-page news and brought about an outburst of national pride in the United States. The demonstration of transatlantic radio telephony was more important as publicity for AT&T than as a scientific advance. All the credit went to AT&T and to Carty’s laboratory. Both Fessenden and de Forest attempted to draw attention to their contributions to long-distance radio telephony, but to no avail. The Arlington-to-Paris transmission was a triumph for corporate public relations and corporate research. The development of the triode had been achieved with large teams of highly trained scientists—in contrast to the small-scale efforts of Fessenden and de Forest, who had little formal scientific training. Carty’s laboratory was an example of the new type of industrial research that was to dominate the twentieth century. The golden days of the lone inventor, in the mold of Thomas Edison or Alexander Graham Bell, were gone. In the years that followed the first transatlantic radio telephone messages, little was done by AT&T to advance the technology or to develop a commercial service. The equipment used in the 1915 demonstration was more a makeshift laboratory apparatus than a prototype for a new radio technology. The messages sent were short and faint. There was a great gulf between hearing “hello” and “goodbye” amid the static. The many predictions of a direct telephone connection between New York and other major cities overseas were premature. It was not until 1927 that a transatlantic radio circuit was opened for public use. By that time, a new technological direction had been taken, and the method used in 1915 had been superseded by shortwave radio communication.

Laser vaporization

The invention: Technique using laser light beams to vaporize the plaque that clogs arteries. The people behind the invention: Albert Einstein (1879-1955), a theoretical American physicist Theodore Harold Maiman (1927- ), inventor of the laser Light, Lasers, and Coronary Arteries Visible light, a type of electromagnetic radiation, is actually a form of energy. The fact that the light beams produced by a light bulb can warm an object demonstrates that this is the case. Light beams are radiated in all directions by a light bulb. In contrast, the device called the “laser” produces light that travels in the form of a “coherent” unidirectional beam. Coherent light beams can be focused on very small areas, generating sufficient heat to melt steel. The term “laser” was invented in 1957 by R. Gordon Gould of Columbia University. It stands for light amplification by stimulated emission of radiation, the means by which laser light beams are made. Many different materials—including solid ruby gemstones, liquid dye solutions, and mixtures of gases—can produce such beams in a process called “lasing.” The different types of lasers yield light beams of different colors that have many uses in science, industry, and medicine. For example, ruby lasers, which were developed in 1960, are widely used in eye surgery. In 1983, a group of physicians in Toulouse, France, used a laser for cardiovascular treatment. They used the laser to vaporize the “atheroma” material that clogs the arteries in the condition called “atherosclerosis.” The technique that they used is known as “laser vaporization surgery.” Laser Operation, Welding, and Surgery Lasers are electronic devices that emit intense beams of light when a process called “stimulated emission” occurs. The principles of laser operation, including stimulated emission, were established by Albert Einstein and other scientists in the first third of the twentieth century. In 1960, Theodore H. Maiman of the Hughes Research Center in Malibu, California, built the first laser, using a ruby crystal to produce a laser beam composed of red light. All lasers are made up of three main components. The first of these, the laser’s “active medium,” is a solid (like Maiman’s ruby crystal), a liquid, or a gas that can be made to lase. The second component is a flash lamp or some other light energy source that puts light into the active medium. The third component is a pair of mirrors that are situated on both sides of the active medium and are designed in such a way that one mirror transmits part of the energy that strikes it, yielding the light beam that leaves the laser. Lasers can produce energy because light is one of many forms of energy that are called, collectively, electromagnetic radiation (among the other forms of electromagnetic radiation are X rays and radio waves). These forms of electromagnetic radiation have different wavelengths; the smaller the wavelength, the higher the energy level. The energy level is measured in units called “quanta.” The emission of light quanta from atoms that are said to be in the “excited state” produces energy, and the absorption of quanta by unexcited atoms— atoms said to be in the “ground state”—excites those atoms. The familiar light bulb spontaneously and haphazardly emits light of many wavelengths from excited atoms. This emission occurs in all directions and at widely varying times. In contrast, the light reflection between the mirrors at the ends of a laser causes all of the many excited atoms present in the active medium simultaneously to emit light waves of the same wavelength. This process is called “stimulated emission.” Stimulated emission ultimately causes a laser to yield a beam of coherent light, which means that the wavelength, emission time, and direction of all the waves in the laser beam are the same. The use of focusing devices makes it possible to convert an emitted laser beam into a point source that can be as small as a few thousandths of an inch in diameter. Such focused beams are very hot, and they can be used for such diverse functions as cutting or welding metal objects and performing delicate surgery. The nature of the active medium used in a laser determines the wavelength of its emitted light beam; this in turn dictates both the energy of the emitted quanta and the appropriate uses for the laser.Maiman’s ruby laser, for example, has been used since the 1960’s in eye surgery to reattach detached retinas. This is done by focusing the laser on the tiny retinal tear that causes a retina to become detached. The very hot, high-intensity light beam then “welds” the retina back into place, bloodlessly, by burning it to produce scar tissue. The burning process has no effect on nearby tissues. Other types of lasers have been used in surgeries on the digestive tract and the uterus since the 1970’s. In 1983, a group of physicians began using lasers to treat cardiovascular disease. The original work, which was carried out by a number of physicians in Toulouse, France, involved the vaporization of atheroma deposits (atherosclerotic plaque) in a human artery. This very exciting event added a new method to medical science’s arsenal of life-saving techniques. Consequences Since their discovery, lasers have been used for many purposes in science and industry. Such uses include the study of the laws of chemistry and physics, photography, communications, and surveying. Lasers have been utilized in surgery since the mid-1960’s, and their use has had a tremendous impact on medicine. The first type of laser surgery to be conducted was the repair of detached retinas via ruby lasers. This technique has become the method of choice for such eye surgery because it takes only minutes to perform rather than the hours required for conventional surgical methods. It is also beneficial because the lasing of the surgical site cauterizes that site, preventing bleeding. In the late 1970’s, the use of other lasers for abdominal cancer surgery and uterine surgery began and flourished. In these forms of surgery, more powerful lasers are used. In the 1980’s, laser vaporization surgery (LVS) began to be used to clear atherosclerotic plaque (atheromas) from clogged arteries. This methodology gives cardiologists a useful new tool. Before LVS was available, surgeons dislodged atheromas by means of “transluminal angioplasty,” which involved pushing small, fluoroscopeguided inflatable balloons through clogged arteries.

Laser eye surgery

The invention: The first significant clinical ophthalmic application of any laser system was the treatment of retinal tears with a pulsed ruby laser. The people behind the invention: Charles J. Campbell (1926- ), an ophthalmologist H. Christian Zweng (1925- ), an ophthalmologist Milton M. Zaret (1927- ), an ophthalmologist Theodore Harold Maiman (1927- ), the physicist who developed the first laser Monkeys and Rabbits The term “laser” is an acronym for light amplification by the stimulated emission of radiation. The development of the laser for ophthalmic (eye surgery) surgery arose from the initial concentration of conventional light by magnifying lenses. Within a laser, atoms are highly energized. When one of these atoms loses its energy in the form of light, it stimulates other atoms to emit light of the same frequency and in the same direction. A cascade of these identical light waves is soon produced, which then oscillate back and forth between the mirrors in the laser cavity. One mirror is only partially reflective, allowing some of the laser light to pass through. This light can be concentrated further into a small burst of high intensity. On July 7, 1960, Theodore Harold Maiman made public his discovery of the first laser—a ruby laser. Shortly thereafter, ophthalmologists began using ruby lasers for medical purposes. The first significant medical uses of the ruby laser occurred in 1961, with experiments on animals conducted by Charles J. Campbell in New York, H. Christian Zweng, and Milton M. Zaret. Zaret and his colleagues produced photocoagulation (a thickening or drawing together of substances by use of light) of the eyes of rabbits by flashes froma ruby laser. Sufficient energy was delivered to cause immediate thermal injury to the retina and iris of the rabbit. The beam also was directed to the interior of the rabbit eye, resulting in retinal coagulations. The team examined the retinal lesions and pointed out both the possible advantages of laser as a tool for therapeutic photocoagulation and the potential applications in medical research. In 1962, Zweng, along with several of his associates, began experimenting with laser photocoagulation on the eyes of monkeys and rabbits in order to establish parameters for the use of lasers on the human eye. Reflected by Blood The vitreous humor, a transparent jelly that usually fills the vitreous cavity of the eyes of younger individuals, commonly shrinks with age, with myopia, or with certain pathologic conditions. As these conditions occur, the vitreous humor begins to separate from the adjacent retina. In some patients, the separating vitreous humor produces a traction (pulling), causing a retinal tear to form. Through this opening in the retina, liquefied vitreous humor can pass to a site underneath the retina, producing retinal detachment and loss of vision. Alaser can be used to cause photocoagulation of a retinal tear. As a result, an adhesive scar forms between the retina surrounding the tear and the underlying layers so that, despite traction, the retina does not detach. If more than a small area of retina has detached, the laser often is ineffective and major retinal detachment surgery must be performed. Thus, in the experiments of Campbell and Zweng, the ruby laser was used to prevent, rather than treat, retinal detachment. In subsequent experiments with humans, all patients were treated with the experimental laser photocoagulator without anesthesia. Although usually no attempt was made to seal holes or tears, the diseased portions of the retina were walled off satisfactorily so that no detachments occurred. One problem that arose involved microaneurysms. A“microaneurysm” is a tiny aneurysm, or blood-filled bubble extending from the wall of a blood vessel. When attempts to obliterate microaneurysms were unsuccessful, the researchers postulated that the color of the ruby pulse so resembled the red of blood that the light was reflected rather than absorbed. They believed that another lasing material emitting light in another part of the spectrum might have performed more successfully.Previously, xenon-arc lamp photocoagulators had been used to treat retinal tears. The long exposure time required of these systems, combined with their broad spectral range emission (versus the single wavelength output of a laser), however, made the retinal spot on which the xenon-arc could be focused too large for many applications. Focused laser spots on the retina could be as small as 50 microns. Consequences The first laser in ophthalmic use by Campbell, Zweng, and Zaret, among others, was a solid laser—Maiman’s ruby laser. While the results they achieved with this laser were more impressive than with the previously used xenon-arc, in the decades following these experiments, argon gas replaced ruby as the most frequently used material in treating retinal tears. Argon laser energy is delivered to the area around the retinal tear through a slit lamp or by using an intraocular probe introduced directly into the eye. The argon wavelength is transmitted through the clear structures of the eye, such as the cornea, lens, and vitreous. This beam is composed of blue-green light that can be effectively aimed at the desired portion of the eye. Nevertheless, the beam can be absorbed by cataracts and by vitreous or retinal blood, decreasing its effectiveness. Moreover, while the ruby laser was found to be highly effective in producing an adhesive scar, it was not useful in the treatment of vascular diseases of the eye. Aseries of laser sources, each with different characteristics, was considered, investigated, and used clinically for various durations during the period that followed Campbell and Zweng’s experiments. Other laser types that are being adapted for use in ophthalmology are carbon dioxide lasers for scleral surgery (surgery on the tough, white, fibrous membrane covering the entire eyeball except the area covered by the cornea) and eye wall resection, dye lasers to kill or slow the growth of tumors, eximer lasers for their ability to break down corneal tissue without heating, and pulsed erbium lasers used to cut intraocular membranes.

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.