Nikola Tesla Books
CHAPTER I. THE ALTERNATING CURRENT AT LOW AND HIGH FREQUENCIES. While the manuscript for this book was being prepared, the author was approached by a caller who introduced himself as an enthusiastic experimenter and a reader of all manner of practical books. This gentleman explained that he was an armature winder by trade, and that he wished to take up high tension work solely as a hobby. He was possessed of but little knowledge of mathematics and had been unable to understand the many books on transformer design and construction that he had purchased. A few minutes' conversation with this caller brought to light some important points which since have prompted a radical and wholesale change in the method of treatment. Half a dozen pointed questions suggested the introduction to the general subject that is offered in the next few paragraphs. What the Alternating Current is.-An alternating current is one that periodically changes its direction of flow a certain number of times per second. It is the reverse of the direct current which is assumed to leave the battery or dynamo at the positive pole and return by way of the negative pole. With the alternating current, the terminals of the machine are alternately positive and negative. This characteristic is well shown in the diagram, Fig. 1, which may be assumed to show the course taken by a current leaving 1
