bridges as those of Profs. Burr, Du Bois, and Johnson, and that, if he were to attempt to illustrate the principles by actual examples of designing, his book would never be finished.

As stated in Chapters XI and XIX, the second edition of the author's "General Specifications for Highway Bridges of Iron and Steel" and the first edition of his "Compromise Standard System of Live Loads for Railway Bridges and the Equivalents for Same" are now exhausted, and will not be reprinted, as this treatise will replace them.

In writing Chapters XV,XVI, XVII, and XVIII it was found necessary to copy certain portions of Chapter XIV in order to make the various specifications complete; but the amount of repetition was made as small as possible by referring, wherever no changes were introduced, whole sections of one set of specifications to the corresponding sections in a preceding set.

The subject of suspension bridges is not dealt with in this work, partly because until lately the author has not paid much attention to this class of structures, and partly because they are so different from other bridges, being suitable for very long spans only, that each suspension bridge requires special specifications of its own.

The author has the presumption to hope that there will be considerable demand for this book, for he considers that it will be useful to the following classes of readers: first, to practising bridge-engineers, because of many little suggestions that will help them to effect improvements and to avoid mistakes; second, to young engineers in offices of bridge specialists and of bridge-manufacturing companies, for perfecting them in their work; third, to professors of civil engineering, to show them the practical side of bridge-designing and building, and to aid them in giving their lectures on bridges; fourth, to students of civil engineering, as a supplementary text-book that will enable them to understand the application of what they have learned during their course in bridges; fifth, to railroad engineers, because of the bridge specifications contained, and to instil into their minds the importance of