André Marie Ampère

French physicist and mathematician. Born in Lyon, he was educated in the Emile style by his father, a merchant who was an admirer of Rousseau, and was strongly influenced by Buffon's Natural History and the Encyclopedia. In 1793, during the French Revolution, his father, a magistrate, was arrested and executed. He himself married in 1799, but his wife died of illness four years later. He remarried but was divorced soon after. His two children were also unable to find a stable life, which caused him trouble. His family life was full of misfortune. In 1802, he became a professor of physics and chemistry at the Ecole Centrale in Bourg-en-Bresse, and after working as a teacher at a high school in Lyon, he became an inspector under the new university system in 1808, and in 1819 he became head of philosophy at the University of Paris. In 1820, he was appointed assistant professor of astronomy at the same university, and in 1824, he was appointed professor of experimental physics at the Collège de France. In his later years, financial worries and poor health led to his death in Marseilles in solitude.

His most important scientific achievement was the establishment of electrodynamics, but his research covered many areas. Early on he was known as a mathematician, and before 1820 he also became interested in chemistry, discovering the elemental nature of chlorine and iodine before Davy, and attempting to construct an entire chemical system based on the similarities between Lavoisier's element classification system and Linnaeus's plant classification. In the field of gas molecular physics, he discovered "Avogadro's law," which is known in France as "Avogadro-Ampere's law."

In 1820, when Oersted of Denmark discovered that electric current exerts a force on a magnetic needle, Ampere immediately began experiments on the magnetism of electric current, discovered that a force acts between current-carrying conductors, analyzed this mathematically, and proposed Ampere's law on electric current and magnetism. He also hypothesized molecular electric currents based on the equivalence of electric currents flowing through helical conductors and Fresnel's hints, and proposed the hypothesis of electrodynamic molecules. He considered this mechanical model to be a new theory of matter that explains not only electrical phenomena but also magnetic phenomena, chemical bonds, electric affinity, and more, and he combined it with his unique philosophy, which was one of the reasons why his electrodynamic theory was not immediately accepted by the world. However, his hypothesis later became the basis of Weber's electromagnetic theory. These mathematical studies on electrodynamics from 1821 to 1825 were published in 1827 as " Mémoire sur la théorie mathématique des phénomènes electrodynamics uniquement déduite de l'expérience" (Memoire of the mathematical theory of electrodynamic phenomena ), and his theory of the classification of sciences and philosophy of science, influenced by Kant, were compiled in 1834 as " Essai sur la philosophie des sciences" (Essai sur la philosophie des sciences) . He also invented the astationary magnetic needle. The unit of electric current, the "ampere", is named after him.

[Tadaaki Kimoto June 19, 2018]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

フランスの物理学者、数学者。リヨンに生まれ、ルソーに傾倒する商人の父から『エミール』Emile式に教育され、ビュフォンの『博物誌』や、『百科全書』に強い影響を受けた。1793年、フランス革命の際、治安判事をしていた父が逮捕、処刑され、彼自身も1799年に結婚したが、4年後に妻が病没、再婚したがまもなく離婚し、また二人の子も安定した生活が得られず悩みの種になるなど、家庭的には不幸続きであった。1802年、ブール・カン・ブレスのエコール・セントラルの物理学および化学教授となり、その後リヨンの高等学校教師を経て、1808年新大学制度下での監察官、1819年パリ大学の哲学担当となり、翌1820年同大学天文学助教授、1824年コレージュ・ド・フランスの実験物理学教授に選任された。晩年には金銭上の心配も加わり、健康を害し、孤独のうちにマルセイユで没した。

　科学的業績としては電気力学の建設がもっとも重要であるが、研究は多方面にわたる。初期には数学者として知られ、1820年以前には化学にも傾倒、デービーに先んじて塩素やヨードの単体性に気づいたほか、ラボアジエの元素分類法とリンネの植物分類の類似性から、全化学体系の構築を試みた。気体分子物理面では「アボガドロの法則」を発見し、この法則はフランスでは「アボガドロ‐アンペールの法則」とよばれている。

　1820年、デンマークのエールステッドが、電流が磁針に力を及ぼすことを発見すると、アンペールもただちに電流の磁気に関する実験を開始し、電流の流れる導線間に力が作用することを発見、これを数学的に解析し、電流と磁気に関する「アンペールの法則」を提出した。さらに螺旋(らせん)形導線を流れる電流と磁石の同等性およびフレネルのヒントから分子電流を想定、電気力学的分子の仮説を提唱した。彼がこの力学モデルを電気現象のみならず、磁気現象や化学結合、電気親和力などすべてを説明する物質の新理論とみなしたことや、彼の特異な哲学とも結び付けたことが、彼の電気力学理論がただちに世に受け入れられない一因ともなった。しかし彼の仮説はのちにウェーバーの電磁理論の基礎となった。これらの1821～1825年の電気力学に関する数学的研究は1827年に『電気力学的諸現象の数学的理論集』Mémoire sur la théorie mathématique des phénomènes électrodynamiques uniquement déduite de l'expérienceとして公刊され、また、カントに影響を受けた科学分類論、科学哲学は1834年の『科学哲学試論』Essai sur la philosophie des sciencesにまとめられた。無定位磁針の発明もある。電流の単位「アンペア」は彼の名に由来する。

［木本忠昭　2018年6月19日］

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