In July, 1820, a discovery of a vastly different character was made by Oersted in Copenhagen; the discovery that if a current of electricity be passed over or under a magnetic needle, the needle will be deflected in a direction and to a degree depending on the strength and direction of the current and the position of the conducting wire relatively to the needle. Now Laennec invented a simple and little instrument that began virtually perfect, and that exists today substantially as it started. Oersted did something equally important, that ultimately initiated intricate inventions of many kinds, and yet he did not really invent anything whatever. The importance of his discovery was recognized at once; so quickly, in fact, and by so many experimenters and inventors, that Oersted soon found himself in the extraordinary position of being left behind, in an art to which himself had almost unknowingly given birth! That some relation existed between magnetism and electricity had long been evident to physicists; but what that relation was they did not know until Oersted told them. They seized on his information with avidity, with results that the whole world knows now. The first man heard from was Ampère, who communicated the results of his experiments in the new art to the Institute of France as early as September 18th. Almost immediately afterward, Arago discovered that, if a conducting wire were wrapped around iron wires, those iron wires became magnets and remained magnets as long as the electric current continued to pass. Thereupon, Arago made and announced his epoch-making invention, the electro-magnet. The influence of this invention on the subsequent history of the machine of civilization, it is hardly needful to point out.