History of Electrical Engineering Andre Marie Ampere

Written By Bern Dibner The invention of the voltaic cell in 1800 gave electrical experimenters a source of a constant flow of current. Seven years later the Danish experimenter, H.C. Oersted, an¬ nounced that he would attempt to establish a relationship between an electric flow of current and a magnetic needle. Yet it required thirteen years more for this brilliant discovery to be made and announced by him in 1820. The news of Oersted's experiment reached Paris through Arago who repeated the experiment at a meeting in Paris on September 11,1820. In the audience was Ampere, then pro¬ fessor of mathematics of the Ecole Polytechnique. So deeply was Ampere impressed by the Oersted experiment that within a week he himself had repeated the experiment and elaborated it into a number of other basic relationships demonstrating the behavior of electric current flowing in straight and in formed conductors. On September 18th, Ampere presented before the Academy his observations establishing the science he designated as "electro¬ dynamics." In a paper entitled "Experiments on the New Electrodynamical Phenomena," published in 1822, Ampere stated, "I have determined to use the word electrodynamic in order to unite under a common name all these phe¬ nomena, and particularly to designate those which I have observed between two voltaic conductors." He then dis¬ tinguished electromotive action as being of two kinds, which he designated as those of electric tension and those of electric current The former exists, he said, when two bodies are separated from each other by a nonconductor, such as the tension between the poles of a voltaic cell before they are connected by a conductor. In the case of flowing current the second exists where elements form part of a circuit of conducting bodies. Thus, pointed out Ampere, two bodies similarly charged electrostatically repel each other, whereas two conductors carrying currents in the same di¬ rection attract one another. Ampere was convinced that magnetism was an electrical phenomenon and that the direction of motion of a magnetic pole, when adjacent to a current-carrying wire, was neither towards nor away from the wire "but in a line at right angles to a plane passing through the pole and the conductor." The force of this attrac¬ tion or repulsion, he proved, was directly proportional to the strength of the currents, and inversely proportional to the square of the distance between them, a relationship which prompted Clerk Maxwell to write that these achievements had "leaped full grown and fully armed from the brain of the Newton of Electricity."