The authors of the book are profoundly conscious of the fact that the extraordinary period of electrical development embraced in it has been prolific of great men. They have named some of them; but there has been no idea of setting forth various achievements or of ascribing distinctive merits. This treatment is devoted to one man whom his fellow-citizens have chosen to regard as in many ways representative of the American at his finest flowering in the field of invention during the nineteenth century. It is designed in these pages to bring the reader face to face with Edison; to glance at an interesting childhood and a youthful period marked by a capacity for doing things, and by an insatiable thirst for knowledge; then to accompany him into the great creative stretch of forty years, during which he has done so much. This book shows him plunged deeply into work for which he has always had an incredible capacity, reveals the exercise of his unsurpassed inventive ability, his keen reasoning powers, his tenacious memory, his fertility of resource; follows him through a series of innumerable experiments, conducted methodically, reaching out like rays of search-light into all the regions of science and nature, and finally exhibits him emerging triumphantly from countless difficulties bearing with him in new arts the fruits of victorious struggle. These volumes aim to be a biography rather than a history of electricity, but they have had to cover so much general ground in defining the relations and contributions of Edison to the electrical arts, that they serve to present a picture of the whole development effected in the last fifty years, the most fruitful that electricity has known. The effort has been made to avoid technique and abstruse phrases, but some degree of explanation has been absolutely necessary in regard to each group of inventions. The task of the authors has consisted largely in summarizing fairly the methods and processes employed by Edison; and some idea of the difficulties encountered by them in so doing may be realized from the fact that one brief chapter, for example, -that on ore milling-covers nine years of most intense application and activity on the part of the inventor. It is something like exhibiting the geological eras of the earth in an outline lantern slide, to reduce an elaborate series of strenuous experiments and a vast variety of ingenious apparatus to the space of a few hundred words. A great deal of this narrative is given in Mr. Edisons own language, from oral or written statements made in reply to questions addressed to him with the object of securing accuracy. A further large part is based upon the personal contributions of many loyal associates; and it is desired here to make grateful acknowledgment to such collaborators as Messrs. Samuel Insull, E. H. Johnson, F. R. Upton, R. N Dyer, S. B. Eaton, Francis Jehl, W. S. Andrews, W. J. Jenks, W. J. Hammer, F. J. Sprague, W. S. Mallory, and C. L. Clarke, and others, without whose aid the issuance of this book would indeed have been impossible. In particular, it is desired to acknowledge indebtedness to Mr. W. H. Meadowcroft not only for substantial aid in the literary part of the work, but for indefatigable effort to group, classify, and summarize the boundless material embodied in Edisons note-books and memorabilia of all kinds now kept at the Orange laboratory. Acknowledgment must also be made of the courtesy and assistance of Mrs. Edison, and especially of the loan of many interesting and rare photographs from her private collection