by Isaac Asimov
The most common type of storage battery has plates of lead and lead oxide in alternation, with cells of fairly concentrated sulfuric acid. It was invented by the French physicist Gaston Plante in 1859 and was put into its modern form in 1881 by the American electrical engineer Charles Francis Brush. More rugged and more compact storage batteries have been invented since—for instance, a nickel-iron battery developed by Edison about 1905-but for economy, none can compete with the lead battery.
The electric voltage supplied by the storage battery is stored in the magnetic field of a transformer called an induction coil, and the collapse of this field provides the stepped-up voltage that produces the ignition spark across the gap in the familiar spark plugs.
Once an internal-combustion engine starts firing, inertia will keep it moving between power strokes. But outside energy must be supplied to start the engine. At first it was started by hand (for example, the automobile crank), and outboard motors and power lawn mowers are still started by yanking a cord. The automobile crank required a strong hand. When the engine began turning, it was not uncommon for the crank to be yanked out of the hand holding it, then to turn and break the arm. In 1912, the American inventor Charles Franklin Kettering invented a self-starter that eventually did away with the crank. The self-starter is powered by the storage battery, which supplies the energy for the first few turns of the engine.
The first practical automobiles were built, independently, in 1885 by the German engineers Gottlieb Daimler and Karl Benz. But what really made the automobile, as a common conveyance, was the invention of mass production.
The prime originator of this technique was Eli Whitney, who merits more credit for it than for his more famous invention of the cotton gin. In 1789, Whitney received a contract from the Federal Government to make guns for the army. Up to that time, guns had been manufactured individually, each from its own fitted parts. Whitney conceived the notion of making the parts uniform, so that a given part would fit any gun. This single, simple innovation—manufacturing standard, interchangeable parts for a given type of article—was perhaps as responsible as any other factor for the creation of modern mass-production industry. When power tools came in, they made it possible to stamp out standard parts in practically unlimited numbers.
It was the American engineer Henry Ford who first exploited the concept to the full. He had built his first automobile (a two-cylinder job) in 1892, then had gone to work for the Detroit Automobile Company in 1899 as chief engineer. The company wanted to produce custom-made cars, but Ford had another notion. He resigned in 1902 to produce cars on his own-in quantity.
In 1909, he began to turn out the Model T; and by 1913, he began to manufacture it on the Whitney plan—car after car, each just like the one before, and all made with the same parts.
Ford saw that he could speed up production by using human workers as one used machines, performing the same small job over and over with uninterrupted regularity. The American inventor Samuel Colt (who had invented the revolver or “Six-shooter”) had taken the first steps in this direction in 1847; and the automobile manufacturer Ransom E. Olds had applied the system to the motor car in 1900. Olds lost his financial backing, however, and it fell to Ford to carry this movement to its fruition. Ford set up the assembly line, with workers adding parts to the construction as it passed them on moving belts until the finished car rolled off at the end of the line. Two economic advances were achieved by this system: high wages for the workers, and cars that could be sold at amazingly low prices.
By 1913, Ford was manufacturing 1,000 Model T’s a day. Before the line was discontinued in 1927, 15 million had been turned out, and the price had dropped to 290 dollars. The passion for yearly change then won out, and Ford was forced to join the parade of variety and superficial novelty that has raised the price of automobiles enormously and lost Americans much of the advantage of mass production.
In 1892, the German mechanical engineer Rudolf Diesel introduced a modification of the internal-combustion engine which was simpler and more economical of fuel. He put the fuel-air mixture under high pressure, so that the heat of compression alone was enough to ignite it. The diesel engine made it possible to use higher-boiling fractions of petroleum, which do not knock. Because of the higher compression used, the engine must be more solidly constructed and is therefore considerably heavier than the gasoline engine. Once an adequate fuel-injection system was developed in the 1920s it began to gain favor for trucks, tractors, buses, ships, and locomotives and is now undisputed king of heavy transportation.
Improvements in gasoline itself further enhanced the efficiency of the internal-combustion engine. Gasoline is a complex mixture of molecules made up of carbon and hydrogen atoms (hydrocarbons), some of which burn more quickly than others. Too quick a burning rate is undesirable, for then the gasoline-air mixture explodes in too many places at once, producing engine knock. A slower rate of burning produces an even expansion of vapor that pushes the piston smoothly and effectively.
The amount of knock produced by a given gasoline is measured as its octane rating, by comparing it with the knock produced by a hydrocarbon called iso-octane, which is particularly low in knock production, mixed with normal heptane, which is particularly high in knock production. One of the prime functions of gasoline refining is, among many other things, to produce a hydrocarbon mixture with a high octane rating.
Automobile engines have been designed through the years with an increasingly high compression ratio; that is, the gasoline-air mixture is compressed to greater densities before ignition. This compression milks the gasoline of more power, but also encourages knock, so that gasoline of continually higher octane rating has had to be developed.
The task has been made easier by the use of chemicals that, when added in small quantities to the gasoline, reduce knock. The most efficient of these anti-knock compounds is tetraethyl lead, a lead compound whose properties were noted by the American chemist Thomas Midgley, and which was first introduced for the purpose in 1925. Gasoline containing it is leaded gasoline or ethyl gas. If tetraethyl lead were present alone, the lead oxides formed during gasoline combustion would foul and ruin the engine. For this reason, ethylene bromide is also added. The lead atom of tetraethyl lead combines with the bromide atom of ethylene bromide to form lead bromide, which, at the temperature of the burning gasoline, is vaporized and expelled with the exhaust.
Diesel fuels are tested for ignition delay after compression (too great a delay is undesirable) by comparison with a hydrocarbon called cetane, which contains sixteen carbon atoms in its molecule as compared with eight for iso-octane. For diesel fuels, therefore, one speaks of a cetane number.
Improvements continued to be made. Low-pressure “balloon” tires arrived in 1923, and tubeless tires in the early 1950s, making blowouts less common. In the 1940s, cars became air-conditioned, and automatic drives came into use so that gear shifting began to drop out of use. Power steering and power brakes arrived in the 1950s. The automobile has become so integral a part of the American way of life that, despite the rising cost of gasoline and the rising danger of air pollution, there seems no way short of absolute catastrophe of putting an end to it.
THE AIRPLANE
Larger versions of the automobile were the bus and the truck, and oil replaced coal on the great ships, but the greatest triumph of the internal-combustion engine came in the air. By the 1890s, humans had achieved the age-old dream-older than Daedalus and Icarus—of flying on wings. Gliding had become an avid sport of the aficionados. The first man-carrying glider was built in 1853 by the English inventor George Cayley. The “man” it carried, however, was only a boy. The first important practitioner of this form of endeavor, the German engineer Otto Lilienthal, was killed in 1896 during a glider flight. Meanwhile, a violent urge to take off in powered !light had begun, although gliding as a sport remains popular.
The American physicist and astronomer Samuel Pierpont Langley tried, in 1902 and 1903, to fly a glider
powered by an internal-combustion engine, and came within an ace of succeeding. Had his money not given out, he might have got into the air on the next try. As it was, the honor was reserved for the brothers Orville and Wilbur Wright, bicycle manufacturers who had taken up gliders as a hobby.
On 17 December 1903, at Kitty Hawk, North Carolina, the Wright brothers got off the ground in a propeller-driven glider and stayed in the air for 59 seconds, flying 852 feet. It was the first airplane flight in history, and it went almost completely unnoticed by the world at large.
There was considerably more public excitement after the Wrights had achieved flights of 25 miles and more, and when, in 1909, the French engineer Louis Bleriot crossed the English Channel in an airplane. The air battles and exploits of the First World War further stimulated the imagination; and the biplanes of that day, with their two wings held precariously together by struts and wires, were familiar to a generation of postwar moviegoers. The German engineer Hugo Junkers designed a successful monoplane just after the war; and the thick single wing, without struts, took over completely. (In 1939, the Russian-American engineer Igor Ivan Sikorsky built a multiengined plane and designed the first helicopter, a plane with upper vanes that made vertical takeoffs and landings and even hovering practical.)
But, through the early 1920s, the airplane remained more or less a curiosity—merely a new and more horrible instrument of war and a plaything of stunt flyers and thrill seekers. Aviation did not come into its own until, in 1927, Charles Augustus Lindbergh flew nonstop from New York to Paris. The world went wild over the feat, and the development of bigger and safer airplanes began.
Two major innovations have been effected in the airplane engine since it was established as a means of transportation. The first was the adoption of the gas-turbine engine (figure 9.10). In this engine, the hot, expanding gases of the fuel drive a wheel by their pressure against its blades, instead of driving pistons in cylinders. The engine is simple, cheaper to run, and less vulnerable to trouble, and it needed only the development of alloys that could withstand the high temperatures of the gases to become practicable. Such alloys were devised by 1939. Thereafter, turboprop planes, using a turbine engine to drive the propellers, became increasingly popular.
Figure 9.10. A turbojet engine. Air is drawn in, compressed, and mixed with fuel, which is ignited in the combustion chamber. The expanding gases power a turbine and produce thrust.
But they were quickly superseded, at least for long flights, by the second major development—the jet plane. In principle the driving force here is the same as the one that makes a toy balloon dart forward when its mouth is opened and the air escapes. This is action and reaction: the motion of the expanding, escaping air in one direction results in equal motion, or thrust, in the opposite direction—just as the forward movement of the bullet in a gun barrel makes the gun kick backward in recoil. In the jet engine, the burning of the fuel produces hot, high-pressure gases that drive the plane forward with great force as they stream backward through the exhaust. A rocket is driven by exactly the same means, except that it carries its own supply of oxygen to burn the fuel (figure 9.11).
Figure 9.11. A simple liquid-fueled rocket.
Patents for jet propulsion were taken out by a French engineer, René Lorin, as early as 1913; but at the time, it was a completely impractical scheme for airplanes. Jet propulsion is economical only at speeds of more than 400 miles an hour. In 1939, an Englishman, Frank Whittle, flew a reasonably practical jet plane; and, in January 1944, jet planes were put into war use by Great Britain and the United States against the buzz-bombs, Germany’s V-1 weapon, a pilotless robot plane carrying explosives in its nose.
After the Second World War, military jets were developed that approached the speed of sound. The speed of sound depends on the natural elasticity of air molecules, their ability to snap back and forth. When the plane approaches that speed, the air molecules cannot get out of the way, so to speak, and are compressed ahead of the plane, which then undergoes a variety of stresses and strains. There was talk of the sound barrier as though it were something physical that could not be approached without destruction. However, tests in wind tunnels led the way to more efficient streamlining; and on 14 October 1947, an American X-1 rocket plane, piloted by Charles Elwood Yeager, “broke the sound barrier.” For the first time in history, a human being surpassed the speed of sound. The air battles of the Korean War in the early 1950s were fought by jet planes moving at such velocities that comparatively few planes were shot down.
The ratio of the velocity of an object to the velocity of sound (which is 740 miles per hour at O° C) in the medium through which the object is moving is the Mach number, after the Austrian physicist Ernst Mach, who first investigated, theoretically, the consequences of motion at such velocities in the mid-nineteenth century. By the 1960s, airplane velocities surpassed Mach 5—an achievement of the experimental rocket plane X-15, whose rockets pushed it high enough, for short periods of time, to allow its pilots to qualify as astronauts. Military planes travel at lower velocities, and commercial planes at lower velocities still.
A plane traveling at a supersonic velocity (over Mach 1) carries its sound waves ahead of it since it travels more quickly than the sound waves alone would. If close enough to the ground to begin with, the cone of compressed sound waves may intersect the ground with a loud sonic boom. (The crack of a bullwhip is a miniature sonic boom, since, properly manipulated, the tip of such a whip can be made to travel at supersonic velocities.)
Supersonic commercial Right was initiated in 1970 by the British-French Concorde, which could, and did, cross the Atlantic in three hours, traveling at twice the speed of sound. An American version of such SST (supersonic transport) flight was aborted in 1971, because of worry over excessive noise at airports and of possible environmental damage. Some people pointed out that this was the first time a feasible technological advance had been stopped for being inadvisable, the first time human beings had said, “We can, but we had better not.”
On the whole, it may be just as well, for the gains do not seem to justify the expense. The Concorde has been an economic failure, and the Soviet SST program was ruined by the crash of one of their planes in a 1973 exhibition at Paris.
Electronics
THE RADIO
In 1888, Heinrich Hertz conducted the famous experiments that detected radio waves, predicted twenty years earlier by James Clerk Maxwell (see chapter 8). What he did was to set up a high-voltage alternating current that surged into first one, then another of two metal balls separated by a small air gap. Each time the potential reached a peak in one direction or the other, it sent a spark across the gap. Under these circumstances, Maxwell’s equations predicted, electromagnetic radiation should be generated. Hertz used a receiver consisting of a simple loop of wire with a small air gap at one point to detect that energy. Just as the current gave rise to radiation in the first coil, so the radiation ought to give rise to a current in the second coil. Sure enough, Hertz was able to detect small sparks jumping across the gap to his detector coil, placed across the room from the radiating coil. Energy was being transmitted across space.
By moving his detector coil to various points in the room, Hertz was able to tell the shape of the waves. Where sparks came through brightly, the waves were at peak or trough. Where sparks did not come through at all, they were midway. Thus he could calculate the wavelength of the radiation. He found that the waves were tremendously longer than those of light.
In the decade following, it occurred to a number of people that the Hertzian waves might be used to transmit messages from one place to another, for the waves were long enough to go around obstacles. In 1890, the French physicist Édouard Branly made an improved receiver by replacing the wire loop with a glass tube filled with metal filings to which wires and a battery were attached. The filings would not carry the battery’s current unless a high-voltage alternating current was induced in the filings, as Hertzian waves would do. Wi
th this receiver he was able to detect Hertzian waves at a distance of 150 yards. Then the English physicist Oliver Joseph Lodge (who later gained a dubious kind of fame as a champion of spiritualism) modified this device and succeeded in detecting signals at a distance of half a mile and in sending messages in Morse code.
The Italian inventor Guglielmo Marconi discovered that he could improve matters by connecting one side of the generator and receiver to the ground and the other to a wire, later called an antenna (because it resembled, I suppose, an insect’s feeler). By using powerful generators, Marconi was able to send signals over a distance of 9 miles in 1896, across the English Channel in 1898, and across the Atlantic in 1901. Thus was born what the British still call wireless telegraphy and the Americans named radiotelegraphy, or radio for short.
Marconi worked out a system for excluding static from other sources and tuning in only on the wavelength generated by the transmitter. For his inventions, Marconi shared the Nobel Prize in physics in 1909. with the German physicist Karl Ferdinand Braun, who also contributed to the development of radio by showing that certain crystals can act to allow current to pass in only one direction. Thus ordinary alternating current could be converted into direct current such as radios needed. The crystals tended to be erratic; but in the 1910s, people were bending over their crystal sets to receive signals.
The American physicist Reginald Aubrey Fessenden developed a special generator of high-frequency alternating currents (doing away with the spark-gap device) and devised a system of modulating the radio wave so that it carried a pattern mimicking sound waves. What was modulated was the amplitude (or height) of the waves; consequently this was called amplitude modulation, now known as AM radio. On Christmas Eve 1906, music and speech came out of a radio receiver for the first time.