Entered according to Act of Congress, in the year 1873, by In the Office of the Librarian of Congress, at Washington. INTRODUCTION. It is about thirty years since the Author's attention was especially directed to the subject of BRIDGE CONSTRUCTION; and, his Original Essays published in 1847, are believed to have aided considerably toward establishing the foundation upon which a knowledge of the principles involved, and the conditions required in the proper construction of TRUSS BRIDGES, has been built up, and carried to a high state of advancement. However that may be, the flattering terms in which his former labors in the premises have often been referred to, as well as the frequent applications for copies of his former publication, since the supply became exhausted, have prompted the issue of the present volume. This work inculcates the same development of GENERAL PRINCIPLES, and treats of essentially the same General Plans, Combinations, and proportions for bridge work, as were discussed and recommended in its humble predecessor; with such additions and improvements as subsequent experience and observation have enabled the Author to introduce. The design has been to develop from Fundamental Principles, a system easy of comprehension, and such as to enable the attentive reader and student to judge understandingly for himself, as to the relative merits of different plans and combinations, and to adopt for use, such as may be most suitable for the cases he may have to deal with. It is hoped the work may prove an appropriate Text Book upon the subject treated of, for the Engineering Student, and a useful manual for the Practicing Engineer, and Bridge Builder. But as to this, the decision must be left to those into whose hands it may fall; and to that arbitrement, without further remark or explanation, it is respectfully submitted. |