It has been deemed desirable that the present work should deal with the fundamental principles of practical designing, but so soon as these principles have been assimilated, the reader should proceed to study carefully the many essential constructional details. A Bibliography of a considerable number of papers relating to static transformers is given at the end of Chapter I.' In conclusion, I wish to acknowledge the work of my former assistant, Mr. Evelyn Good, who carried through many of the calculations, under my direction, and prepared a good many of the curves and diagrams. My assistant, Mr. C. Martin, compiled from my data certain portions of Chapters VIII. And IX. My thanks are due to the Several manufacturing companies whose designs are described for their courtesy in providing me with the necessary information and for photographs and drawings.