by Isaac Asimov
The earliest matches smoked horribly, produced a stench, and made use of chemicals that were dangerously poisonous. Matches became really safe to use in 1845, when the Austrian chemist Anton Ritter von Schrotter made use of red phosphorus for the purpose. Eventually safety matches were developed in which the red phosphorus is put on a rough strip somewhere on the box or container that holds the matches, while the match itself has the other necessary chemicals in its head. Neither match nor strip can alone burst into flame, but if rubbed on the strip, the match catches fire.
There was also a return to flint and steel, with crucial improvements. In place of the steel is Mischmetal, a mixture of metals (principally cerium) which, on being scraped by a little wheel, yields particularly hot sparks. In place of tinder is easily inflammable lighter fluid. The result is the cigarette lighter.
ELECTRIC LIGHT
Open flames of one sort or another flicker and are a constant fire hazard. Something totally new was needed, and it had long been noted that electricity could yield light. Leyden jars produced sparks when discharged; electric currents sometimes made wires glow upon passing through them. Both systems have been used for lighting.
In 1805, Humphry Davy forced an electric discharge across the air space between two conductors. By maintaining the current, the discharge was continuous, and he had an electric arc. As electricity became cheaper, it became possible to use arc lamps for lighting. In the 1870s the streets of Paris and some other cities had such lamps. The light was harsh, flickering, and open, however—and still a fire hazard.
It would be better to have an electric current heat a thin wire, or filament, till it glowed. Naturally, the filament had to be made to glow in the absence of oxygen, or it would not last long before being oxidized. The first attempts to remove oxygen involved the straightforward route of removing air. By 1875, Crookes (in connection with his work on cathode rays; see chapter 7) had devised methods for producing a good enough vacuum for this purpose, and with sufficient speed and economy. Nevertheless, the filaments used remained unsatisfactory, breaking too easily. In 1878, Thomas Edison, fresh from his triumph in creating the phonograph, announced that he would tackle the problem. He was only thirty-one, but such was his reputation as an inventor that his announcement caused the stocks of gas companies to tumble on the New York and London stock exchanges.
After hundreds of experiments and fabulous frustrations, Edison finally found a material that would serve as the filament—a scorched cotton thread. On 21 October 1879, he lit his bulb. It burned for 40 continuous hours. On the following New Year’s Eve, Edison put his lamps on triumphant public display by lighting up the main street of Menlo Park, New Jersey, where his laboratory was located. He quickly patented his lamp and began to produce it in quantity.
Yet Edison was not the sole inventor of the incandescent lamp. At least one other inventor had about an equal claim—Joseph Swan of England, who exhibited a carbon-filament lamp at a meeting of the Newcastle-on-Tyne Chemical Society on 18 December 1878, but did not get his lamp into production until 1881.
Edison proceeded to work on the problem of providing houses with a steady and sufficient supply of electricity for his lamps—a task that took as much ingenuity as the invention of the lamp itself. Two major improvements were later made in the lamp. In 1910, William David Coolidge of the General Electric Company adopted heat-resisting metal tungsten as the material for the filament (figure 9.7); and, in 1913, Irving Langmuir introduced the inert gas nitrogen in the lamp to prevent the evaporation and breaking of the filament that occurs in a vacuum.
Figure 9.7. Incandescent lamp.
Argon (use of which was introduced in 1920) serves the purpose even better than nitrogen, for argon is completely inert. Krypton, another inert gas, is still more efficient, allowing a lamp filament to reach higher temperatures and burn more brightly without loss of life.
For half a century, the clear glass of the light-bulb made the glowing filament within harsh and as difficult to look at as the sun. A chemical engineer, Marvin Pipkin, devised a practical method of etching the glass of the bulb within (on the outside, etching served to collect dust and darken the light). The use of frosted bulbs finally produced a soft and pleasant, steady light.
The coming of the electric light had the potential for banishing all open flames from lighting and thus making fires very much a thing of the past. Unfortunately, there are still open flames and probably always will be—in fireplaces, in gas stoves, in gas and oil furnaces. Particularly unfortunate is the fact that hundreds of millions of addicts carry with them open flames in the form of lit cigarettes and frequently used cigarette lighters. The loss of property and of life resulting from cigarette-induced fires (forest fires and brush fires, as well as building fires) is difficult to overestimate.
The glowing filament of the light-bulb (incandescent light, since it is induced by sheer heat of the filament as it resists the flow of the electric current) is not the only way of turning electricity into light. For instance, the so-called neon lights (introduced by the French chemist Georges Claude in 1910) are tubes in which an electric discharge excites atoms of neon gas to emit a bright, red glow. The sun lamp contains mercury vapor which, when excited by a discharge, yields radiation rich in ultraviolet light; this can be used not only to produce a tan but also to kill bacteria or generate fluorescence. And the latter, in turn, leads to fluorescent lighting, introduced in its contemporary form in 1939 at the New York World’s Fair. Here the ultraviolet light from mercury vapor excites fluorescence in a phosphor coating the inside of the tube (figure 9.8). Since this cool light wastes little energy in heat, it consumes less electric power.
Figure 9.8. Fluorescent lamp. A discharge of electrons from the filament excites the mercury vapor in the tube, producing ultraviolet radiation. The ultraviolet makes the phosphor glow.
A 40-watt fluorescent tube supplies as much light, and far less heat, than a 150-watt incandescent light. Since the Second World War, therefore, there has been a massive swing toward the fluorescent. The first fluorescent tubes made use of beryllium salts as phosphors, which resulted in cases of serious poisoning (berylliosis) induced by breathing dusts containing these salts or by introducing the substance through cuts caused by broken tubes. After 1949, other far less dangerous phosphors were used.
The latest promising development is a method that converts electricity directly into light without the prior formation of ultraviolet light. In 1936, the French physicist Georges Destriau discovered that an intense alternating current could make a phosphor, such as zinc sulfide, glow. Electrical engineers are now distributing the phosphor through plastic or glass and are using this phenomenon, called electroluminescence, to develop glowing panels. Thus, a luminescent wall or ceiling can light a room, bathing it in a soft, colored glow. The efficiency of electroluminescence is still too low, however, to allow it to compete with other forms of electrical lighting.
PHOTOGRAPHY
Probably no invention involving light has given mankind more enjoyment than photography. This had its earliest beginnings in the observation that light, passing through a pinhole into a small dark chamber (camera obscuta in Latin), will form a dim, inverted image of the scene outside the chamber. Such a device was constructed about 1550 by an Italian alchemist, Giambattista della Porta. This is the pinhole camera.
In a pinhole camera, the amount of light entering is very small. If, however, a lens is substituted for the pinhole, a considerable quantity of light can be brought to a focus, and the image is then much brighter. With that accomplished, it was necessary to find some chemical reaction that will respond to light. A number of men labored in this cause, including, most notably, the Frenchmen Joseph Nicephore Niepce and Louis Jacques Mande Daguerre and the Englishman William Henry Fox Talbot. Niepce tried to make sunlight darken silver chloride in a proper pattern and produced the first primitive photograph in 1822, but an 8-hour exposure was required.
Daguerre went into partnership with Ni
epce before the latter died, and went on to improve the process. Having had sunlight darken silver salts, he dissolved the unchanged salts in sodium thiosulfate, a process suggested by the scientist John Herschel (the son of William Herschel). By 1839, Daguerre was producing daguerrotypes, the first practical photographs, with exposures requiring no more than 20 minutes.
Talbot improved the process still further, producing negatives in which the places where light strikes are darkened so that dark remains light while light becomes dark. From such negatives any number of positives can be developed, in which the light undergoes another reversal so that light is light and dark, dark, as they should be. In 1844, Talbot published the first book illustrated with photographs.
Photography went on to prove its value in human documentation when, in the 1850s, the British photographed Crimean war scenes and when, in the next decade, the American photographer Matthew Brady, with what we would now consider impossibly primitive equipment, took classic photographs of the American Civil War in action.
For nearly half a century, the wet plate had to be used in photography. This consisted of a glass plate, which was smeared with an emulsion of chemical that had to be made up on the spot. The picture had to be taken before the emulsion dried. As long as there was no solution to this limitation, photographs could be taken only by skillful professionals.
In 1878, however, an American inventor, George Eastman, discovered how to mix the emulsion with gelatin, smear it on the plate, and let it dry into a firm gel that would keep for long periods of time. In 1884, he patented photographic film in which the gel was smeared first on paper and then, in 1889, on celluloid. In 1888, he invented the Kodak, a camera that would take photographs at the press of a button. The exposed film could then be given away to be developed. Now photography became a popular hobby. As ever more sensitive emulsions came into use, pictures could be taken in a flash of light, and there was no need for a sitter to pose for long periods of time with glazed, unnatural expressions.
One would not suppose that things could be made any simpler, but in 1947, the American inventor Edwin Herbert Land devised a camera with a double roll of film, an ordinary negative film and a positive paper, with sealed containers of chemicals between. The chemicals are released at the proper moment and develop the positive print automatically. A few minutes after you have snapped the camera, you have the completed photograph in your hand.
Throughout the nineteenth century, photographs were black and white, lacking in color. In the early twentieth century, however, a process of color photography was developed by the Luxembourg-born French physicist Gabriel Lippmann, and won him the Nobel Prize for physics in 1908. That proved a false start, however, and practical color photography was not develcped until 1936. This second, and successful, try was based Onthe observation, in 1855, by Maxwell and von Helmholtz that any color in the spectrum can be produced by combining red, green, and blue light. On this principle, the color film is composed of emulsions in three layers-one sensitive to the red, one to the green, and one to the blue components of the image. Three separate but superimposed pictures are formed, each reproducing the intensity of light in its part of the spectrum as a pattern of black-and-white shading. The film is then developed in three successive stages, using red, blue, and green dyes to deposit the appropriate colors on the negative. Each spot in the picture is a specific combination of red, green, and blue, and the brain interprets these combinations to reconstitute the full range of color.
In 1959, Land presented a new theory of color vision. The brain, he maintained, does not require a combination of three colors to create the impression of full color. All it needs is two different wavelengths, or sets of wavelengths, one longer than the other by a certain minimum amount. For instance, one of the sets of wavelengths may be an entire spectrum, or white light. Because the average wavelength of white light is in the yellow-green region, it can serve as the “short” wavelength. Now a picture reproduced through a combination of white light and red light (serving as the long wavelength) comes out in full color. Land has also made pictures in full color with filtered green light and red light and with other appropriate dual combinations.
The invention of motion pictures came from an observation first made by the English physician Peter Mark Roget in 1824.He noted that the eye forms a persistent image, which lasts for an appreciable fraction of a second. After the inauguration of photography, many experimenters, particularly in France, made use of this fact to create the illusion of motion by showing a series of pictures in rapid succession. Everyone is familiar with the parlor gadget consisting of a series of picture cards which, when riffled rapidly, make a figure seem to move and perform acrobatics. If a series of pictures, each slightly different from the one before, is flashed on a screen at intervals of about 1/16 second, the persistence of the successive images in the eye will cause them to blend together and so give the impression of continuous motion.
It was Edison who produced the first movie. He photographed a series of pictures on a strip of film and then ran the film through a projector, which showed each in succession with a burst of light. The first motion picture was put on display for public amusement in 1894; and, in 1914, theaters showed the full-length motion picture, The Birth of a Nation.
To the silent movies, a sound track was added in 1927. The sound track also takes the form of light: the wave pattern of music and the actor’s speech is converted, by a microphone, into a varying current of electricity; and this current lights a lamp that is photographed along with the action of the motion picture. When the film, with this track of light at one side, is projected on the screen, the brightening and dimming of the lamp in the pattern of the sound waves is converted back to an electric current by means of a phototube, using the photoelectric effect, and the current in turn is reconverted to sound.
Within two years after the first talking picture, The Jazz Singer, silent movies were a thing of the past, and so, almost, was vaudeville. By the late 1930s, the talkies had added color. In addition, the 1950s saw the development of wide-screen techniques and even a short-lived fad for three-dimensional (3D) effects, involving two pictures thrown on the same screen. By wearing polarized spectacles, an observer saw a separate picture with each eye, thus producing a stereoscopic effect.
Internal-Combustion Engines
While kerosene, a petroleum fraction, gave way to electricity in the field of artificial illumination, a lighter petroleum fraction, gasoline, became indispensable for another technical development that revolutionized modern life as deeply, in its way, as did the introduction of electrical gadgetry. This development was the internal-combustion engine, so called because in such an engine, fuel is burned within the cylinder so that the gases formed push the piston directly. Ordinary steam engines are external-combustion engines, the fuel being burned outside and the steam being then led, ready-formed, into the cylinder.
THE AUTOMOBILE
This compact device, with small explosions set off within the cylinder, made it possible to apply motive power to small vehicles in ways for which the bulky steam engine was not well suited. To be sure, steam-driven “horseless carriages” were devised as long ago as 1786, when William Murdock, who later introduced gas lighting, built one. A century later, the American inventor Francis Edgar Stanley invented the famous Stanley Steamer, which for a while competed with the early cars equipped with internal combustion machines. The future, however, lay with the latter.
Actually, some internal-combustion engines were built at the beginning of the nineteenth century, before petroleum came into common use. They burned turpentine vapors or hydrogen as fuel. But it was only with gasoline, the one vapor-producing liquid that is both combustible and obtainable in large quantities, that such an engine could become more than a curiosity.
The first practical internal-combustion engine was built in 1860 by a French inventor Etienne Lenoir, who hitched it to a small conveyance which became the first “horseless carriage” with such an
engine. In 1876, the German technician Nikolaus August Otto, having heard of the Lenoir engine, built a four-cycle engine (figure 9.9). First a piston fitting tightly in a cylinder is pushed outward, so that a mixture of gasoline and air is sucked into the vacated cylinder. Then the piston is pushed in again to compress the vapor. At the point of maximum compression the vapor is ignited and explodes. The explosion drives the piston outward, and it is this powered motion that drives the engine. It turns a wheel which pushes the piston in again to expel the burned residue or exhaust—the fourth and final step in the cycle. Now the wheel moves the piston outward to start the cycle over again.
Figure 9.9. Nikolaus Otto’s four-cycle engine, built in 1876.
A Scottish engineer named Dugald Clerk almost immediately added an improvement. He hooked up a second cylinder, so that its piston was being driven while the other was in the recovery stage: this device made the power output steadier. Later, the addition of more cylinders (eight is now a common number) increased the smoothness and power of this reciprocating engine.
Such an engine was essential if automobiles were to be made practical, but auxiliary inventions were also necessary. The ignition of the gasoline-air mixture at just the right moment presented a problem. All sorts of ingenious devices were used; but by 1923, it became common to depend on electricity. The supply comes from a storage battery, which, like any other battery, delivers electricity as the result of a chemical reaction. But it can be recharged by sending an electric current through it in the direction opposite to the discharge; this current reverses the chemical reaction and allows the chemicals to produce more electricity. The reverse current is provided by a small generator driven by the engine.