The Italian physicist Alessandro Volta (1745-1827) invented the electric battery, or "voltaic pile," thus providing for the first time a sustained source of current electricity.
Alessandro Volta was born on Feb. 18, 1745, in Como. He resisted pressure from his family to enter the priesthood and developed instead an intense curiosity about natural phenomena, in particular, electricity. In 1769 he published his first paper on electricity. It contained no new discoveries but is of some interest as the most speculative of all Volta's papers, his subsequent ones being devoted almost exclusively to the presentation of specific experimental discoveries.
Early Investigations and Inventions
In 1774 Volta was appointed professor of physics at the gymnasium in Como, and that same year he made his first important contribution to the science of electricity, the invention of the electrophorus, a device which provided a source of electric potential utilizing the principle of electrostatic induction. Unlike earlier source of electric potential, such as the Leyden jar, the electrophorus provided a sustained, easily replenishable source of static electricity. In 1782 Volta announced the application of the electrophorus to the detection of minute electrical charges. His invention of the so-called condensing electroscope culminated his efforts to improve the sensitivity of earlier electrometers.
During these same years Volta also conducted researches of a purely chemical nature. He had for some time been experimenting with exploding various gases, such as hydrogen, in closed containers and had observed that when hydrogen and air were exploded there was a diminution in volume greater than the volume of hydrogen burned. In order to measure such changes in volume, he developed a graduated glass container, now known as a eudiometer, in which to explode the gases. Utilizing this eudiometer he studied marsh gas, or methane, and distinguished it from hydrogen by its different-colored flame, its slower rate of combustion, and the greater volume of air and larger electric spark required for detonation.
In 1779 Volta was appointed to the newly created chair of physics at the University of Pavia. In 1782 he became a corresponding member of the French Academy of Sciences. In 1791 he was elected a fellow of the Royal Society of London, and in 1794, in recognition of his contributions to electricity and chemistry, he was awarded the society's coveted Copley Medal. However, his most significant researches - those which were to lead to the discovery of current electricity - were yet to be undertaken.
Discovery of Current Electricity
Until the last decade of the 18th century electrical researchers had been primarily concerned with static electricity, with the electrification produced by friction. Then, in 1786, Luigi Galvani discovered that the muscles in a frog's amputated leg would contract whenever an electrical machine was discharged near the leg. As a result of his initial observations, Galvani undertook a long series of experiments in an effort to more thoroughly examine this startling phenomenon. In the course of these investigations he discovered that a frog's prepared leg could be made to contract if he merely attached a copper hook to the nerve ending and then pressed the hook against an iron plate on which the leg was resting so as to complete an electrical circuit, even though no electrical machines were operating in the vicinity. Galvani concluded the contraction was produced in the organism itself and referred to this new type of electricity as "animal electricity."
Galvani's experiments and interpretation were summarized in a paper published in 1791, a copy of which he sent to Volta. Although, like most others, initially convinced by Galvani's arguments, Volta gradually came to the conclusion that the two metals were not merely conductors but actually generated the electricity themselves. He began by repeating and verifying Galvani's experiments but quickly moved beyond these to experiments of his own, concentrating on the results of bringing into contact two dissimilar metals. By 1794 he had convinced himself that the metals, in his own words, "are in a real sense the exciters of electricity, while the nerves themselves are passive," and he henceforth referred to this new type of electricity as "metallic" or "contact" electricity.
The announcement of Volta's experiments and interpretation touched off one of the great controversies in the history of science. Although other factors were important as well, the physiologists and anatomists tended to support Galvani's view that the electricity was produced by the animal tissue itself whereas the physicists and chemists, like Volta, tended to see it as produced by the external bimetallic contacts. The resulting rivalry not only took on international dimensions but died out only gradually after more than a decade. Although Galvani withdrew from the arena, allowing others to carry his standard, Volta took an active role in the controversy and vigorously pursued his research.
Volta discovered that not only would two dissimilar metals in contact produce a small electrical effect, but metals in contact with certain types of fluids would also produce such effects. In fact, the best results were obtained when two dissimilar metals were held in contact and joined by a moist third body which, in modern terminology, completed the circuit between them. Such observations led directly to the construction in 1800 of the electric battery, or "pile" as Volta called it, the first source of a significant electric current.
Volta announced his discovery in a letter to Sir Joseph Banks, then president of the Royal Society of London. The letter, dated March 20, 1800, created an instant sensation. Here for the first time was an instrument capable of producing a steady, continuous flow of electricity. All previous electrical machines, including Volta's electrophorus, had produced only short bursts of static electricity. The ability to create at will a sustained electrical current opened vast new fields for investigation, and the significance of Volta's discovery was immediately recognized.
Acclaim and Retirement
Volta was summoned to Paris by Napoleon and in 1801 gave a series of lectures on his discoveries before the National Institute of France, as the Academy of Sciences was then called. A special gold medal was struck to honor the occasion, and the following year Volta was distinguished by election as one of the eight foreign associates of the institute.
Although only in his mid-50s when he announced the discovery of the "pile," Volta took no part in applying his discovery to any of the immense new fields it opened up. During the last 25 years of his life he demonstrated none of the intense creativity that had characterized his earlier researches, and he published nothing of scientific significance during these later years. He continued, at the urging of Napoleon, to teach at the University of Pavia and eventually became director of the philosophy faculty there. In 1819 he retired to his family home near Como. He died there on March 5, 1827, little realizing that current electricity would eventually transform a way of life.
Further Reading
Recommended for further details on Volta is the excellent brief treatment in Bern Dibner, Alessandro Volta and the Electric Battery (1964). A good historical account of the beginning of the age of electricity is in F. Sherwood Taylor, A Short History of Science and Scientific Thought (1949), and Bern Dibner, Galvani-Volta: A Controversy That Led to the Discovery of Useful Electricity (1952).
, then the net emf is 
. (Thus, two identical electrodes and a common electrolyte give zero net emf.) This may be called Volta's Law of the electrochemical series.
