following principle, which, as it does not pertain to bridge-designing, is not given in Chapter II: "In nine cases out of ten the proper way to strengthen a weak bridge is to take it out and replace it with a good one, throwing the old metal into the scrap heap."

In railway-bridge designing, for a number of years, the average ratio of weight of details to weight of main members has been gradually increasing; and the end is not yet, because the average bridge-designer has still a great deal to learn concerning the importance of good and efficient detailing. As long as contracts for bridges are awarded to bridge companies on competitive designs, and the structures are paid for by the lump sum instead of by the pound, just so long will the science of detailing be ignored, and just so long will bridges be built which will eventually wear out, simply for want of a little more metal distributed just where it is needed, viz., in the details.

The author feels that he cannot speak too forcibly concerning the importance of thoroughly scientific detailing for all kinds of metal-work; for what avails it that a structure have an excess of section in every main member, if a single important detail be lacking in strength? If the author were in a position where he had to cut down the weight of a structure even as much as thirty per cent, he would unhesitatingly take the metal almost entirely out of the sections of the main members and leave the detailing practically unchanged. A structure thus designed would long outlast one of the same type in which the weight of the details and that of the main members were reduced in the same proportion.

A few years ago the standard text-books on bridges ignored entirely the subject of detailing. Later they have taken cognizance of it by illustrating certain details in common use, both good and bad (generally the latter), but have failed to state the fundamental principles that should govern the designing of all details. These general underlying principles and complete instructions as to how to detail scientifically the author has endeavored to give in Chapters II, XIV, XV, XVI, and XVII of this work.  The bridge designer,  by studying these chapters