ANDRE-MARIE AMPÈRE, the founder of the science of electrodynamics, was born at Lj'ons in January 1775. He took a passionate delight in the pursuit of knowledge from his very infancy, and is reported to have worked out lengthy arithmetical sums by means of pebbles and biscuit-crumbs before he knew the figures. His father began to teach him Latin, but left this off on discovering the boy's greater inclination and aptitude for mathematical studies. The young Ampere, however, soon resumed his Latin lessons, to enable him to master the works of Euler and Bernouilli. In later life he was accustomed to say that he knew' as much about mathematics when he was eighteen as ever he knew ; but his reading embraced nearly the whole round of knowledge,—history, travels, poetry, philosophy, and the natural sciences. At this age he had read the whole of the Encyclopédie, and with such interest and attention that he could repeat passages from it fifty years after. When Lyons was taken by the army of the Convention in 1793, the father of Ampère, who, holding the office of juge de piaix, had stood out resolutely against the previous revolutionary excesses, was at once thrown into prison, and soon after perished on the scaffold. This event produced such an impression on the susceptible mind of Ampère, that he continued for more than a year in a state little removed from idiocy. But Rousseau's letters on botany falling into his hands, the subject engrossed him, and roused him from his apathy. His passion for knowledge returned. From botany he turned to the study of the classic poets, and to the writing of verses himself. About this time (1796) an attachment sprang up, the progress of which he naively recorded in a journal (Amorum). In 1799 he was happily married to the object of his attachment. From about 1796 Ampère gave private lessons at Lyons in mathematics, chemistry, and languages; and in 1801 he removed to Bourg, as professor of physics and chemistry, leaving his ailing wife and infant son at Lyons. His wife died in 1804. After two years' absence he returned to Lyons, on his appointment as professor of mathematics at the Lyceum. His small treatise, Considerations sur la Théorie Mathématique du Jeu (Lyons, 1802), in which he successfully solved a problem that had occupied Buffon, Pascal, and others, and demonstrated that the chances of play are decidedly against the habitual gambler, attracted considerable attention. It was this work that brought him under the notice of M. Delambre, whose recommendation obtained for him the Lyons appointment, and afterwards (1805) a subordinate position in the Polytechnic School at Paris, where he was elected professor of analysis in 1809. Here he continued to prosecute his scientific researches and his multifarious studies with unabated diligence. He was admitted a member of the Institute in 1814. It is on the service that he rendered to science in establishing the relations between electricity and magnetism, and in developing the science of electromagnetism, or, as he called it, electrodynamics, that Ampere's fame mainly rests. On the 11th of September 1820 he heard of the discovery of Professor Oersted of Copenhagen, that a magnetic needle may be deflected by a voltaic current. On the 18th of the same month he presented a paper to the Academy, containing a far more complete exposition of the phenomenon, which he had in the interval investigated by experiment, and showing that magnetic defects can be produced, without magnets, by aid of electricity alone. In particular he showed that two wires connecting the opposite poles of a battery attract or repel each other according as the currents pass in the same or in opposite directions. According to the theory of magnetism which Ampere's subsequent investigations led him to adopt, every molecule of magnetic matter is acted on by a closed electric current, and magnetisation takes place in proportion as the direction of these currents approaches parallelism. The whole field thus opened up he explored with characteristic industry and care. He anticipated the invention of the electric telegraph, having suggested in 1821 an apparatus of the kind with a separate wire for each letter. Late in life he prepared a remarkable work on the classification of the sciences, which was published after his death. In addition to this and one or two works of less importance, he wrote a great number of memoirs and papers that appeared in scientific journals. He died at Marseilles in June 1836. The great amiability and childlike simplicity of Ampere's character are well brought out in his Journal et Correspondence, published by Madame Chevreux (Paris, 1872).