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André-Marie Ampère

[am' pEr] the first scientist to "measure electricity"

Andre-Marie Ampere

André-Marie Ampère was born in the village of Polémieux (near Lyon), France, on January 22, 1775, the son of a prosperous businessman. Although he never attended school, he received an excellent education. At the age of 13, Ampère submitted his first paper to the Académie at Lyon, in which he attempted to solve the problem of constructing a line of the same length as an arc of a circle. The paper was not found worthy of publication, however, and Ampére realized that he needed to learn more mathematics.

When Ampère was eighteen years old, his father, a dedicated monarchist, was involved in the city of Lyon's rebellion against the Republican government of France. Convicted of treason, he was publicly executed. Ampère was so shaken by the event that he gave up his study of mathematics for eighteen months.

It took a young woman by the name of Julie to revive Ampère's spirit. The couple was engaged to be married in 1797, and soon after Ampère began tutoring mathematics in Lyon. He married Julie in 1799, and the couple's son Jean-Jacques was born in 1800. Ampère continued tutoring mathematics until 1802, when he was appointed Professor of Physics and Chemistry at Bourg Ecole Centrale. Unfortunately, he had to leave his young wife behind because she had been stricken by an unidentified illness.

Continuing his research in mathematics at Bourg, Ampère composed a treatise on probability, The Mathematical Theory of Games, which was published by the Paris Academy in 1803. This work was followed by one on the calculus of variations in 1803.

After a year in Bourg, Ampére was appointed to a mathematics position at the Lycée in Lyon, allowing him to be closer to his now seriously ill wife. Although he continued to produce good work, his life was shattered when Julie died in July 1803. The blow was too almost too much for Ampère and for some years he lived alone, seeing no one and fighting against a depression that threatened to destroy his sanity. A failed second marriage that began in 1806 and ended in 1807 caused him even more grief. Slowly, however, his interest in science and mathematics reasserted themselves and, as he returned to his academic work, his mental state improved. In 1809, his intellectual powers fully restored, he secured the post of Professor of Mathematics at the Ecole Polytechnique in Paris, where he remained until 1828.

Although a mathematics professor by profession, Ampère's interest included metaphysics, physics and chemistry.

Mathematics Working on partial differential equations, he produced a classification which he presented to the National Institute of Sciences in 1814.

Chemistry In 1811, he suggested that an anhydrous acid prepared two years earlier was a compound of hydrogen with an unknown element, for which he suggested the name fluorine. In 1816 he produced a classification of elements.

Physics In 1815 he published a paper on the refraction of light, and by 1816 he was a strong advocate of a wave theory of light. About 1820 he began conducting experiments on electricity and magnetism, and it is for this work that he is best remembered today.

In 1820 the scientific world was excited by a momentous discovery. A little known Danish physicist named Hans Christian Øersted had noticed that a compass needle was deflected when brought close to a wire carrying an electric current. It was the first suggestion of a link between magnetism and electricity, the two most mystifying phenomena of the time. Ampére immediately repeated Øersted's experiment under carefully controlled conditions; within a week of Øersted's original announcement, Ampère had worked out a rule relating the direction in which the compass needle was deflected to the direction in which the electric current flowed along the wire. The "swimmer's rule," as Ampère called it, states that if an observer were to swim along the current-carrying wire in the direction of the current and facing the compass needle, the north pole of the needle would be deflected toward the swimmer's left hand.

Ampère is also credited with another version of the rule, called the "right-hand grip" rule. In this rule the observer's right hand is imagined gripping the wire through which the current flows, with the thumb pointing along the wire in the direction of the current. The fingers, curling around the wire, indicate the direction in which the compass needle will be deflected. This concept anticipated the theory of electromagnetic force, formulated several years later, which showed that a magnetic field encircles an electrified wire just as do the fingers of the hand in Ampère's right-hand rule.

Continuing his investigations, Ampère found that wires could be made to behave like magnets by passing currents through them, and that the polarity of their magnetism depended upon the direction of the current. In his best-known experiment, Ampère arranged two parallel wires, one fixed, the other moveable. When he placed the wires end to end and passed a current in the same direction through them both, the moveable wire was attracted toward the fixed one. When current was passed through the wires in opposite directions, the wires repelled each other. Their behavior was the same as two ordinary bar magnets in which like poles repel each other and opposite poles attract. The experiment established that the phenomena of magnetism and electricity were inextricably bound up together.

The first person to develop measuring techniques for electricity, Ampère built an instrument utilizing a free-moving needle to measure the flow of electricity -- what we now know as a galvanometer. A simple galvanometer, like the one shown here, is a compass with a wire wrapped around it, with each end connected to a power source (in this case a battery). If the needle is deflected then a current has been created. The stronger the current, the greater the needle will be deflected.
simple galvanometer

Having explored the way in which electricity and magnetism were linked, Ampère was convinced that electric current was somehow the actual origin of the phenomenon of magnetism. In 1826 he published Mathematical Theory of Electrodynamic Phenomena, a remarkable mathematical theory showing that the properties of a magnet could be explained by assuming that innumerable tiny currents were circling within it. But Ampére was way ahead of his time and his contemporaries received this theory with open skepticism.

Windings for a linear induction motor. The movement of a magnet due to the flow of an electric current was in fact the first electric motor, the predecessor of one of man's most important sources of power. Electric motors vary greatly in size and can be classified into different categories. Their uses are numerous. Linear induction motors, for example, are found in high-speed ground transportation, textile looms, and aircraft and missile launchers.
windings for a linear induction motor

In 1826 Ampère was given a position at the Collègen de France, where he was allowed to teach courses of his own design. He died at Marseille, France, on June 10, 1836.

Ampère's contribution to the understanding of electromagnetism has been recognized in one way by naming the unit of electric current after him. An ampere of electricity is formally defined as the amount of current in a wire that will exert a certain force on another nearby current-carrying wire.


Anthony Feldman and Peter Ford Scientists and Inventors, The People Who Made Technology from Earliest Times to Present Day New York: Facts on File, 1979

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This page was last updated on 01/22/2019.