The author wishes to express his appreciation for the help given him by the many individuals, including railroad officials, librarians, and museum curators, who provided answers to many questions and confirmed many conjectures.

Special thanks are tendered A. B. Lawson and Lawrence W. Sagle of The Baltimore and Ohio Railroad Co., F. V. Koval of the Chicago and North Western Railway System, W. F. Kascal and Harry B. Spurrier of the New York Central System, H. T. Cover of the Pennsylvania Railroad Co., Harry E. Hammer of the Reading Co., K. C. Ingram of the Southern Pacific Co., Elizabeth O. Cullen of the Association of American Railroads, D. M. MacMaster of the Museum of Science and Industry at Chicago, H. D. Watson of the University of Maine, George M. Hart of George School in Bucks County, Pa., and Robert R. Brown of Lachine, Quebec—to name a few of those whose contributions have helped bring together the facts here presented.

It is fitting also at this time to refer to the late Charles B. Chaney, who collected over a period of almost 60 years an immense number of photographs, negatives, drawings, lithographs, and books dealing with railroading. Upon his death in 1948, he left this entire collection to the United States National Museum, of the Smithsonian Institution, confident that in the Museum it would be put to the widest possible use and would, therefore, carry forward his lifelong work of research in the history of locomotives and railroads.

His confidence was well founded. The Chaney collection of railroad material has been an invaluable source of information for the present work.

To acknowledge the contribution of Thomas Norrell of Silver Spring, Md., is likewise a pleasure. He graciously consented to read the manuscript of this work, and his authoritative comments have greatly enhanced its comprehensiveness and accuracy.