by Isaac Asimov
THE STEAM ENGINE
The great turning point in the harnessing of energy came at the end of the seventeenth century, although there had been a dim foreshadowing in ancient times. The Greek inventor Hero of Alexandria, sometime during the first centuries A.D. (his life cannot be pinned down even to a particular century), built a number of devices that ran on steam power. He used the expanding push of steam to open temple doors, whirl spheres, and so on. The ancient world, then in decline, could not follow up this premature advance.
Then, over fifteen centuries later, a new and vigorously expanding society had a second chance. It arose out of the increasingly acute necessity of pumping water out of mines that were being driven ever deeper. The old hand pump (see chapter 5) made use of a vacuum to lift water; and as the seventeenth century proceeded, human beings came to appreciate, ever more keenly, the great power of a vacuum (or, rather, the power of air pressure called into play by the existence of a vacuum).
In 1650, for instance, the German physicist (and mayor of the city of Magdeburg) Otto von Guericke invented an air pump worked by muscle power. He proceeded to put two flanged metal hemispheres together and to pump the air out from between them through a nozzle that one hemisphere possessed. As the air pressure within dropped lower, the air pressure from without, no longer completely counterbalanced, pushed the hemispheres together more powerfully. At the end, two teams of horses straining in opposite directions could not pull the hemispheres apart; but when air was allowed to re-enter, they fell apart of themselves. This experiment was conducted before important people, including on one occasion the German emperor himself, and it made a big splash.
Now it occurred to several inventors: Why not use steam instead of muscle power to create the vacuum? Suppose one filled a cylinder (or similar vessel) with water and heated the water to a boil. Steam, as it formed, would push out the water. If the vessel was cooled (for example, by means of cold water played on the outside surface), the steam in the vessel would condense to a few drops of water and leave a virtual vacuum. The water that one wanted to raise (as out of a flooded mine) could then rise through a valve into this evacuated vessel.
A French physicist, Denis Papin, saw the power of steam as early as 1679. He developed a steam digester, then, in which water was boiled in a vessel with a tight-fitting lid. The accumulating steam created a pressure that raised the boiling point of water and, at this higher temperature, cooked food faster and better. The steam pressure within the digester must have given Papin the notion of making steam do work. He placed a little water at the bottom of a tube and, by heating it, converted it to steam. This expanded forcibly, pushing a piston ahead of it.
The first person to translate this idea into a practical working device, however, was an English military engineer named Thomas Savery. His steam engine (the word engine originally denoted any ingenious device and comes from the same Greek root as ingenious) could be used to pump water out of a mine or a well or to drive a waterwheel, so he called it the “Miner’s Friend.” But it was dangerous (because the high pressure of the steam might burst the vessels and pipes) and very inefficient (because the heat of the steam was lost each time the container was cooled). Seven years after Savery patented his engine in 1698, an English blacksmith named Thomas Newcomen built an improved engine that operated at low steam pressure; it had a piston in a cylinder and employed air pressure to push down the piston.
Newcomen’s engine, too, was not very efficient (it still cooled the chamber after each heating), and the steam engine remained a minor gadget for more than sixty years until a Scottish instrument maker named James Watt found the way to make it effective. Hired by the University of Glasgow to fix a model of a Newcomen engine that was not working properly, Watt fell to thinking about the device’s wasteful use of fuel. Why, after all, should the steam vessel have to be cooled off each time? Why not keep the steam chamber steam hot at all times and lead the steam into a separate condensing chamber that could be kept cold? Watt went on to add a number of other improvements: employing steam pressure to help push the piston, devising a set of mechanical linkages that kept the piston moving in a straight line, hitching the back-and-forth motion of the piston to a shaft that turned a wheel, and so on. By 1782, his steam engine, which got at least three times as much work out of a ton of coal as Newcomen’s, was ready to be put to work as a universal work horse (figure 9.2).
Figure 9.2. Watt’s steam engine.
In the times after Watt, steam-engine efficiency was continually increased, chiefly through the use of ever hotter steam at ever higher pressure. Carnot’s founding of thermodynamics (see chapter 7) arose mainly out of the realization that the maximum efficiency with which any heat engine can be run is proportional to the difference in temperature between the hot reservoir (steam, in the usual case) and the cold.
In the course of the 1700s, various mechanical devices were invented to spin and weave thread in more wholesale manner. (These replaced the spinning-wheel, which had come into use in the Middle Ages.) At first this machinery was powered by animal muscle or a waterwheel; but in 1790 came the crucial step: it was powered by a steam engine.
Thus, the new textile mills that were being built had neither to be situated on or near fast-moving streams nor to require animal care. They could be built anywhere. Great Britain began to undergo a revolutionary change as working people left the land and abandoned home industry to flock into the factories (where working conditions were unbelievably cruel and abominable until society learned, reluctantly, that people ought to be treated no worse than animals).
The same change took place in other countries that adopted the new system of steam-engine power and the Industrial Revolution (a term introduced in 1837 by the French economist Jerome Adolphe Blanqui).
The steam engine totally revolutionized transportation, too. In 1787, the American inventor John Fitch built a steamboat that worked, but it failed as a financial venture, and Fitch died unknown and unappreciated. Robert Fulton, a more able promoter than Fitch, launched his steamship, the Clermont, in 1807 with so much more fanfare and support that he came to be considered the inventor of the steamship, though actually he was no more the builder of the first such ship than Watt was the builder of the first steam engine.
Fulton should perhaps better be remembered for his strenuous attempts to build underwater craft, His submarines were not practical, but they anticipated a number of modern developments. He built one called the Nautilus, which probably served as inspiration for Jules Verne’s fictional submarine of the same name in Twenty Thousand Leagues under the Sea, published in 1870. That, in turn, was the inspiration for the naming of the first nuclear-powered submarine (see chapter 10).
By the 1830s, steamships were crossing the Atlantic and were being driven by the screw propeller, a considerable improvement over the side paddle wheels. And by the 1850s, the speedy and beautiful Yankee Clippers had begun to furl their sails and to be replaced by steamers in the merchant fleets and navies of the world.
Later, a British engineer, Charles Algernon Parsons (a son of the Lord Rosse who had discovered the Crab Nebula) thought of a major improvement of the steam engine in connection with ships. Instead of having the steam drive a piston that, in turn, drove a wheel, Parsons thought of eliminating the “middleman” and having a current of steam directed against blades set about the rim of a wheel. The wheel would have to withstand great heat and high speeds; but in 1884, he produced the first practical steam turbine.
In 1897, at the Diamond Jubilee of Queen Victoria, the British navy was holding a stately review of its steam-powered warships, when Parsons’s turbine—powered ship, Turbinia, moved past them, silently, at a speed of 35 knots. Nothing in the British navy could have caught it, and it was the best advertising gimmick one could have imagined. It was not long before both merchant vessels and warships were turbine-powered.
Meanwhile the steam engine had also begun to dominate land transportation. In 1814, the English inventor G
eorge Stephenson (owing a good deal to the prior work of an English engineer, Richard Trevithick) built the first practical steam locomotive. The in-and-out working of steam-driven pistons could turn metal wheels among steel rails as they could turn paddle wheels in the water. And in 1830, the American manufacturer Peter Cooper built the first steam locomotive in the Western Hemisphere. For the first time in history, land travel became as convenient as sea travel, and overland commerce could compete with seaborne trade. By 1840, the railroad had reached the Mississippi River; and by 1869, the full width of the United States was spanned by rail.
Electricity
In the nature of things, the steam engine is suitable only for large-scale, steady production of power. It cannot efficiently deliver energy in small packages or intermittently at the push of a button: a “little” steam engine, in which the fires are damped down or started up on demand, would be an absurdity. But the same generation that saw the development of steam power also saw the discovery of a means of transforming energy into precisely the form I have mentioned—a ready store of energy that could be delivered anywhere, in small amounts or large, at the push of a button. This form, of course, is electricity.
STATIC ELECTRICITY
The Greek philosopher Thales, about 600 B.C., noted that a fossil resin found on the Baltic shores, which we call amber and they called elektron, gained the ability to attract feathers, threads, or bits of fluff when it rubbed with a piece of fur. It was William Gilbert of England, the investigator of magnetism (see chapter 5), who first suggested that this attractive force be called electricity, from the Greek word elektron. Gilbert found that, in addition to amber, some other materials, such as glass, gained electric properties on being rubbed.
In 1733, the French chemist Charles Francis de Cisternay Du Fay discovered that if two amber rods, or two glass rods, were electrified by rubbing, they repelled each other. However, an electrified glass rod attracted an electrified amber rod. If the two were allowed to touch, both lost their electricity. He felt this showed there were two kinds of electricity, vitreous and resinous.
The American scholar Benjamin Franklin, who became intensely interested in electricity, suggested that it was a single fluid. When glass was rubbed, electricity flowed into it, making it “positively charged”; on the other hand, when amber was rubbed, electricity flowed out of it, and it therefore became “negatively charged.” And when a negative rod made contact with a positive one, the electric fluid would flow from the positive to the negative until a neutral balance was achieved.
This was a remarkably shrewd speculation. If we substitute the word electrons for Franklin’s fluid and reverse the direction of flow (actually electrons flow from the amber to the glass), his guess was essentially correct.
A French inventor named John Théophile Desaguliers suggested, in 1740, that substances through which the electric fluid travels freely (for example, metals) be termed conductors, and those through which it does not move freely (for example, glass and amber) be called insulators.
Experimenters found that a large electric charge could gradually be accumulated in a conductor if it was insulated from loss of electricity by glass or a layer of air. The most spectacular device of this kind was the Leyden jar. It was first devised in 1745 by the German scholar Ewald Georg von Kleist, but it was first put to real use at the University of Leyden in Holland, where it was independently constructed a few months later by the Dutch scholar Peter van Musschenbroek. The Leyden jar is an example of what is today called a condenser, or capacitor: that is, two conducting surfaces, separated by a small thickness of insulator, within which one can store a quantity of electric charge.
In the case of the Leyden jar, the charge is built up on tinfoil coating a glass jar, via a brass chain stuck into the jar through a stopper. When you touch the charged jar, you get a startling electric shock. The Leyden jar can also produce a spark. Naturally, the greater the charge on a body, the greater its tendency to escape. The force driving the electrons away from the region of highest excess (the negative pole) toward the region of greatest deficiency (the positive pole) is the electromotive force (EMF), or electric potential. If the electric potential becomes high enough, the electrons will even jump an insulating gap between the negative and the positive poles. Thus they will leap across an air gap, producing a bright spark and a crackling noise. The light of the spark is caused by the radiation resulting from the collisions of innumerable electrons with air molecules, and the noise arises from the expansion of the quickly heated air, followed by the clap of cooler air rushing into the partial vacuum momentarily produced.
Naturally one wondered whether lightning and thunder were the same phenomenon, on a vast scale, as the little trick performed by a Leyden jar. A British scholar, William Wall, had made just this suggestion in 1708. This thought was sufficient to prompt Benjamin Franklin’s famous experiment in 1752. The kite he flew in a thunderstorm had a pointed wire, to which he attached a silk thread which could conduct electricity down from the thunderclouds. When Franklin put his hand near a metal key tied to the silk thread, the key sparked (figure 9.3). Franklin charged it again from the clouds, then used it to charge a Leyden jar, obtaining the same kind of charged Leyden jar in this fashion as in any other. Thus, Franklin demonstrated that the thunderclouds were charged with electricity, and that thunder and lightning are indeed the effect of a Leyden-jar-in-the-sky in which the clouds form one pole and the earth another.
Figure 9.3. Franklin’s experiment.
The luckiest thing about the experiment, from Franklin’s personal standpoint, was that he survived. Some others who tried it were killed, because the induced charge on the kite’s pointed wire accumulated to the point of producing a fatally intense discharge to the body of the man holding the kite.
Franklin at once followed up this advance in theory with a practical application. He devised the lightning rod, which was simply an iron rod attached to the highest point of a structure and connected to wires leading to the ground. The sharp point bled off electric charges from the clouds above, as Franklin showed by experiment; and, if lightning did strike, the charge was carried safely to the ground.
Lightning damage diminished drastically as the rods rose over structures all over Europe and the American colonies—no small accomplishment. Yet even today, 2 billion lightning flashes strike each year, killing (it is estimated) twenty people a day and hurting eighty more.
Franklin’s experiment had two electrifying (please pardon the pun) effects. In the first place, the world at large suddenly became interested in electricity. Second, it put the American colonies on the map, culturally speaking. For the first time an American had actually displayed sufficient ability as a scientist to impress the cultivated Europeans of the Age of Reason. When, a quarter-century later, Franklin represented the infant United States at Versailles and sought assistance, he won respect, not only as the simple envoy of a new republic, but also as a mental giant who had tamed the lightning and brought it humbly to earth. That flying kite contributed more than a little to the cause of American independence.
Following Franklin’s work, electrical research advanced by leaps. Quantitative measurements of electrical attraction and repulsion were carried out in 1785 by the French physicist Charles Augustin de Coulomb. He showed that this attraction (or repulsion) between given charges varied inversely as the square of the distance. In this, electrical attraction resembles gravitational attraction. In honor of this finding, the coulomb has been adopted as a name for a common unit of quantity of electricity.
DYNAMIC ELECTRICITY
Shortly thereafter, the study of electricity took a new, startling, and fruitful turning. So far I have been discussing static electricity, which refers to an electric charge that is placed on an object and then stays there. The discovery of an electric charge that moves, of electric currents or dynamic electricity, began with the Italian anatomist Luigi Galvani. In 1791, he accidentally discovered that thigh muscles from dissected fro
gs would contract if simultaneously touched by two different metals (thus adding the verb galvanize to the English language).
The muscles behaved as though they had been stimulated by an electric spark from a Leyden jar, and so Galvani assumed that muscles contain something he called animal electricity. Others, however, suspected that the origin of the electric charge might lie in the junction of the two metals rather than in muscle. In 1800, the Italian physicist Alessandro Volta studied combinations of dissimilar metals, connected not by muscle tissue but by simple solutions.
He began by using chains of dissimilar metals connected by bowls half-full of salt water. To avoid too much liquid too easily spilled, he prepared small disks of copper and of zinc, piling them alternately. He also made use of cardboard disks moistened with salt water so that his voltaic pile consisted of silver, cardboard, zinc, silver, cardboard, zinc, silver, and so on. From such a setup, electric current could be drawn off continuously.
Any series of similar items indefinitely repeated may be called a battery. Volta’s instrument was the first electric battery (figure 9.4). It may also be called an electric cell. It was to take a century before scientists would understand how chemical reactions involve electron transfers and how to interpret electric currents in terms of shifts and flows of electrons. Meanwhile, however, they made use of the current without understanding all its details.
Figure 9.4. Volta’s battery. The two different metals in contact give rise to a flow of electrons, which are conducted from one cell to the next by the salt-soaked cloth. The familiar dry battery, or flashlight battery, of today, involving carbon and zinc, was first devised by Bunsen (of spectroscopy fame) in 1841.
