Edison and Upton discussed this question very thoroughly, and Edison declared he did not intend to build up a system of distribution in which the external resistance would be equal to the internal resistance. He said he was just about going to do the opposite; he wanted a large external resistance and a low internal one. He said he wanted to sell the energy outside of the station and not waste it in the dynamo and conductors, where it brought no profits.... In these later days, when these ideas of Edison are used as common property, and are applied in every modern system of distribution, it is astonishing to remember that when they were propounded they met with most vehement antagonism from the world at large." Edison, familiar with batteries in telegraphy, could not bring himself to believe that any substitute generator of electrical energy could be efficient that used up half its own possible output before doing an equal amount of outside work. Undaunted by the dicta of contemporaneous science, Mr. Edison attacked the dynamo problem with his accustomed vigor and thoroughness. He chose the drum form for his armature, and experimented with different kinds of iron. Cores were made of cast iron, others of forged iron; and still others of sheets of iron of various thicknesses separated from each other by paper or paint. These cores were then allowed to run in an excited field, and after a given time their temperature was measured and noted. By such practical methods Edison found that the thin, laminated cores of sheet iron gave the least heat, and had the least amount of wasteful eddy currents. His experiments and ideas on magnetism at that period were far in advance of the time. His work and tests regarding magnetism were repeated later on by Hopkinson and Kapp, who then elucidated the whole theory mathematically by means of formulae and constants. Before this, however, Edison had attained these results by pioneer work, founded on his original reasoning, and utilized them in the construction of his dynamo, thus revolutionizing the art of building such machines.