André Marie Amp'e

views updated

André Marie Amp'e

The French physicist André Marie Amp'e (1775-1836), with his original and penetrating analysis of the magnetic effects of current-carrying wires, was the founder of electrodynamics.

Born on Jan. 20, 1775, in Lyons, André Marie Amp'e was the second child of Jean Jacques Amp'e, a prosperous businessman, and Jeanne Antoinette Desuti'es-Sarcey Amp'e. Once the boy had mastered the art of reading under his father's guidance, he showed a voracious appetite for everything in printed form. His principal love was mathematics and geometry. In these subjects his father's library soon failed to provide suitable material, so his father took him to the Lyons library, only to find that some of the best works in mathematics, such as most treatises by Leonhard Euler and Daniel Bernoulli, were in Latin. Young Amp'e mastered Latin in a few weeks, as he had not only an uncommon talent for languages but also a consuming interest in the possibility of a universal language.

Intellectual Journey

Amp'e married Julie Carron in 1799, and the responsibilities of married life helped him to start systematic work in mathematical physics. The years of his first public teaching position at the Coll'e de Bourg saw the publication of his essay on probability calculus. As a result, he was called to Paris to take the position of instructor at the Polytechnique. There he developed an absorbing interest in psychology and metaphysics, to the point that he wrote in 1805, "I delve more than ever into metaphysics … how admirable is the science of psychology … the only thing that still has interest for me."

The phrase is equally indicative of the impulsiveness of Amp'e's intellectual journey. Shortly afterward, his brilliant but restless mind turned avidly toward the study of chemistry with the hope of elucidating the fundamental constitution of matter, as shown in his memoirs on molecular and atomic theories. But he kept returning to questions of physics and mathematics. During the first 15 years following his appointment at the Polytechnique, Amp'e published memoirs on problems relating to geometry, calculus, mechanics, theory of gases, and optics. At the same time he was also at work on a book which he wanted to publish under the title "Introduction à la philosophie."

Amp'e's admission in 1814 to the Academy of Sciences followed a steady rise in the academic world. In 1808 he became inspector general of the University of Paris, in 1809 professor of analytical mathematics and mechanics at the Polytechnique. As inspector general he had to travel frequently, and it became his custom to name some of his scientific findings after the places where they occurred to him. Thus, he had his Theory of Avignon, his Demonstration of Grenoble, his Theorem of Montpellier, and his Proposition of Marseilles.

Achievements in Electrodynamics

In 1820, at the regular weekly meeting of the Academy of Sciences, Amp'e heard a startling report: Hans Oersted, a few months earlier in Copenhagen, had discovered that a current-carrying wire had an influence on a magnetic needle. Two weeks later Amp'e began his series of six weekly reports to the academy, much of which was published in the Annales de chimie et de physique (1820) and is now known as his first memoir on electrodynamics. In it he disclosed his historic discovery that in Oersted's experiment the magnet can be replaced by another current-carrying wire. Amp'e also established that two parallel wires attract one another when the direction of current is the same in both and repel one another when the directions are opposite.

To this crucial experimental discovery Amp'e added a wealth of experimental and theoretical details, many of which proved of lasting value. To provide for measurements independent of the earth's magnetic field, he devised a new instrument which he aptly called the "astatic magnetic needle." He showed that current-carrying wire wound as a helix acts in every respect as a bar magnet. He theorized that terrestrial magnetism in part is due to the circulation from east to west of electrically charged material inside the earth. He also anticipated the findings of 20th-century physics as he described ordinary magnets as an assemblage of closed electric circuits. Last but not least, he made the first suggestion about the use of his discovery as a telegraph.

Amp'e read his second memoir before the academy in 1822. In it he gave his now-famous formula for the force acting between two current-carrying wires: the force is proportional to the product of the currents in the two wires and to the length of the wires, and inversely proportional to the square of the distance between the two. The memoir was also a classic example of the clarification of a physical problem through the thorough analysis of the geometrical situations involved.

Enormous as was Amp'e's achievement in electrodynamics, it was clearly not to be the "last word" in the field of physics. His search for a definitive comprehension of all available information led him to the ambitious project of drawing up a final coordination of all sciences. The first part of his Essai sur la philosophie des sciences, or analytical exposition of the natural classification of all human knowledge, was published in 1834. The second part was published posthumously in 1843 by Amp'e's son, Jean Jacques, who earned a reputation as a literary critic and author.

Amp'e lived his last years in a state of mental exhaustion. Apart from his preoccupation with the classification of sciences, he had no taste or energy for anything. Many of his books remained unopened and uncut. He did not even care to provide the publisher with title and preface for his widely used text on differential and integral calculus. But to the end, he attended faithfully to his official duties. As he left Paris in May, 1836, on one of his tours of inspection, he fell sick and arrived in Marseilles in grave physical condition. There a sudden seizure of fever proved fatal on June 10, 1836.