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.