Edison, His Life and Inventions [114]
not only a practicable lamp, but also a SYSTEM of commercial electric lighting. Such a scheme involved the creation of an entirely new art, for there was nothing on the face of the earth from which to draw assistance or precedent, unless we except the elementary forms of dynamos then in existence. It is true, there were several types of machines in use for the then very limited field of arc lighting, but they were regarded as valueless as a part of a great comprehensive scheme which could supply everybody with light. Such machines were confessedly inefficient, although representing the farthest reach of a young art. A commission appointed at that time by the Franklin Institute, and including Prof. Elihu Thomson, investigated the merits of existing dynamos and reported as to the best of them: "The Gramme machine is the most economical as a means of converting motive force into electricity; it utilizes in the arc from 38 to 41 per cent. of the motive work produced, after deduction is made for friction and the resistance of the air." They reported also that the Brush arc lighting machine "produces in the luminous arc useful work equivalent to 31 per cent. of the motive power employed, or to 38 1/2 per cent. after the friction has been deducted." Commercial possibilities could not exist in the face of such low economy as this, and Mr. Edison realized that he would have to improve the dynamo himself if he wanted a better machine. The scientific world at that time was engaged in a controversy regarding the external and internal resistance of a circuit in which a generator was situated. Discussing the subject Mr. Jehl, in his biographical notes, says: "While this controversy raged in the scientific papers, and criticism and confusion seemed at its height, 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.
After thorough investigation of the magnetic qualities of different kinds of iron, Edison began to make a study of winding the cores, first determining the electromotive force generated per turn of wire at various speeds
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.
After thorough investigation of the magnetic qualities of different kinds of iron, Edison began to make a study of winding the cores, first determining the electromotive force generated per turn of wire at various speeds