BATTERY

Battery, also electric cell, device that converts chemical energy into electricity. Strictly speaking, a battery consists of two or more cells connected in series or parallel, but the term is also used for single cells. All cells consist of a liquid, paste, or solid electrolyte and a positive electrode, and a negative electrode. The electrolyte is an ionic conductor; one of the electrodes will react, producing electrons, while the other will accept electrons. When the electrodes are connected to a device to be powered, called a load, an electrical current flows.

Batteries in which the chemicals cannot be reconstituted into their original form once the energy has been converted (that is, batteries that have been discharged) are called primary cells or voltaic cells. Batteries in which the chemicals can be reconstituted by passing an electric current through them in the direction opposite that of normal cell operation are called secondary cells, rechargeable cells, storage cells, or accumulators.

PRIMARY CELLS

The most common form of primary cell is the Leclanché cell, invented by the French chemist Georges Leclanché in the 1860s. It is popularly called a dry cell or flashlight battery. The Leclanché cell in use today is very similar to the original invention. The electrolyte consists of a mixture of ammonium chloride and zinc chloride made into a paste. The negative electrode is made of zinc, as is the outside shell of the cell, and the positive electrode is a carbon rod surrounded by a mixture of carbon and manganese dioxide. The Leclanché cell produces about 1.5 V.
Another widely used primary cell is the zinc-mercuric-oxide cell, more commonly called a mercury battery. It can be made in the shape of a small flat disk and is used in this form in hearing aids, photoelectric cells, and electric wristwatches. The negative electrode consists of zinc, the positive electrode is of mercuric oxide, and the electrolyte is a solution of potassium hydroxide. The mercury battery produces about 1.34 V.
The fuel cell is another type of primary cell. It is unique in that the chemicals are not contained within the cell but are supplied from outside.

SECONDARY CELLS
The storage battery, or secondary cell, which can be recharged by reversing the chemical reaction, was invented in 1859 by the French physicist Gaston Planté. Planté's cell was a lead-acid battery, the type widely used today. The lead-acid battery, which consists of three or six cells connected in series, is used in automobiles, trucks, aircraft, and other vehicles. Its chief advantage is that it can deliver a strong current of electricity for starting an engine; however, it runs down quickly. The electrolyte is a dilute solution of sulfuric acid, the negative electrode consists of lead, and the positive electrode of lead dioxide. In operation, the negative lead electrode dissociates into free electrons and positive lead ions. The electrons travel through the external electric circuit, and the positive lead ions combine with the sulfate ions in the electrolyte to form lead sulfate. When the electrons reenter the cell at the positive lead-dioxide electrode, another chemical reaction occurs. The lead dioxide combines with the hydrogen ions in the electrolyte and with the returning electrons to form water, releasing lead ions in the electrolyte to form additional lead sulfate.
A lead-acid storage cell runs down as the sulfuric acid gradually is converted into water and the electrodes are converted into lead sulfate. When the cell is being recharged, the chemical reactions described above are reversed until the chemicals have been restored to their original condition. A lead-acid battery has a useful life of about four years. It produces about 2 V per cell. Recently, lead batteries with useful lives of 50 to 70 years have been developed for special applications.

Another widely used secondary cell is the alkaline cell, or nickel-iron battery, developed by the American inventor Thomas Edison in the 1900s. The principle of operation is the same as in the lead-acid cell except that the negative electrode consists of iron, the positive electrode is of nickel oxide, and the electrolyte is a solution of potassium hydroxide. The nickel-iron cell has the disadvantage of giving off hydrogen gas during charging. This battery is used principally in heavy industry applications. The Edison battery has a useful life of approximately ten years and produces about 1.15 V.
Another alkaline cell similar to the Edison battery is the nickel-cadmium cell, or cadmium battery, in which the iron electrode is replaced by one consisting of cadmium. It also produces about 1.15 V, and its useful lifetime is about 25 years.
A number of new types of batteries have been designed for use in electric vehicles. Improved versions of conventional storage batteries have been developed for electric cars, but they still suffer the drawbacks of either short range, high expense, bulkiness, or environmental problems. Advanced batteries that show promise for use in electric vehicles include lithium-iron sulfide, zinc-chlorine, nickel metal hydride, and sodium-sulfur. The U.S. Advanced Battery Consortium (USABC), a consortium that includes the U.S. Department of Energy and the three major American automakers, was set up in 1991 to speed development of advanced storage batteries. Such batteries are also being developed by electric utilities to be used for “load leveling,” to compensate for momentary system load fluctuations. Such battery modules could be installed close to sites of variable demand. They cause few environmental problems and occupy little space.

SOLAR BATTERY
Solar batteries produce electricity by a photoelectric conversion process. The source of electricity is a photosensitive semiconducting substance such as a silicon crystal to which impurities have been added. When the crystal is struck by light, electrons are dislodged from the surface of the crystal and migrate toward the opposite surface. There they are collected as a current of electricity. Solar batteries have very long lifetimes and are used chiefly in spacecraft as a source of electricity to operate the equipment aboard..

DEMOCRACY

Democracy (Greek demos,”the people”; kratein, “to rule”), political system in which the people of a country rule through any form of government they choose to establish. In modern democracies, supreme authority is exercised for the most part by representatives elected by popular suffrage. The representatives may be supplanted by the electorate according to the legal procedures of recall and referendum, and they are, at least in principle, responsible to the electorate. In many democracies, such as the United States, both the executive head of government and the legislature are elected. In typical constitutional monarchies such as the United Kingdom and Norway, only the legislators are elected, and from their ranks a cabinet and a prime minister are chosen.

Although often used interchangeably, the terms democracy and republic are not synonymous. Both systems delegate the power to govern to their elected representatives. In a republic, however, these officials are expected to act on their own best judgment of the needs and interests of the country. The officials in a democracy more generally and directly reflect the known or ascertained views of their constituents, sometimes subordinating their own judgment.

DEMOCRACY IN ANCIENT GREECE AND ROME
Rule by the people played an important part in the democracies of the pre-Christian era. The democracies of the city-states of classical Greece and of Rome during the early years of the Republic were unlike the democracies of today. They were direct democracies, in which all citizens could speak and vote in assemblies that resembled New England town meetings. Representative government was unknown and unnecessary because of the small size of the city-states (almost never more than 10,000 citizens). Ancient democracy did not presuppose equality of all individuals; the majority of the populace, notably slaves and women, had no political rights. Athens, the greatest of the city democracies, limited the franchise to native-born citizens. Roman democracy resembled that of the Greeks, although Rome sometimes granted citizenship to men of non-Roman descent. The Roman Stoic philosophy, which defined the human race as part of a divine principle, and the Jewish and Christian religions, which emphasized the rights of the underprivileged and the equality of all before God, contributed to the development of modern democratic theory.
The Roman Republic ended in the despotism of the empire. The free cities of Italy, Germany, and Flanders carried on the democratic tradition and applied some principles of democracy during the Middle Ages. Slaves ceased to constitute a major portion of national populations. As feudalism ended, a rich commercial middle class arose, possessing the money and leisure necessary to participate in governmental affairs. One result was the rebirth of a spirit of freedom based on ancient Greek and Roman principles. Concepts of equal political and social rights were further defined during the Renaissance, when the development of humanism was fostered, and later during the Reformation, in the struggle for religious freedom.

WESTERN EUROPE AND THE U.S.

Beginning with the first popular rebellion against monarchy in England (1642), which was brought to a climax by the execution of King Charles I, political and revolutionary action against autocratic European governments resulted in the establishment of democratic governments. Such action was inspired and guided largely by political philosophers, notably the French philosophers Montesquieu and Jean Jacques Rousseau, and the American statesmen Thomas Jefferson and James Madison. Before the end of the 19th century, every important Western European monarchy had adopted a constitution limiting the power of the Crown and giving a considerable share of political power to the people. In many of these countries, a representative legislature modeled on the British Parliament was instituted. British politics was then possibly the greatest single influence on the organization of world democracies, although the French Revolution also exerted a powerful influence. Later, the success of democratic institutions in the United States served as a model for many peoples.

The major features of modern democracy include individual freedom, which entitles citizens to the liberty and responsibility of shaping their own careers and conducting their own affairs; equality before the law; and universal suffrage and education. Such features have been proclaimed in great historic documents, for example, the U.S. Declaration of Independence, which asserted the right to life, liberty, and the pursuit of happiness; the French Declaration of the Rights of Man and of the Citizen, which affirmed the principles of civil liberty and of equality before the law; and the Atlantic Charter, which formulated the four basic freedoms.

By the middle of the 20th century, every independent country in the world, with only a few exceptions, had a government that, in form if not in practice, embodied some of the principles of democracy. Although the ideals of democracy have been widely professed, the practice and fulfillment have been different in many countries.

VAMPIRE

Vampire, in folklore, a corpse that rises from the grave during the night, often in the form of a bat, and, for nourishment, sucks the blood of sleeping humans. Various talismans and herbs supposedly avert vampires, but, according to tradition, they can be destroyed only by cremation or by stakes driven through their hearts. Belief in vampires originated in ancient times and was especially widespread among the Slavs. The novel Dracula (1897) by the British writer Bram Stoker tells the story of the Transylvanian vampire Count Dracula, who became one of the most popular subjects of horror films.