480 THE POPULAR SCIENCE MONTHLY. 



are built in this country or in Europe ; and in this way, as in 

 many others, the Japanese show that two or three hundred years 

 ago they had advanced to a wonderful degree in the study of 

 applied mechanics and the " strength and resistance of material." 

 The only trouble is, that they stopped advancing for two or three 

 hundred years, and up to ten or twenty years ago were not as far 

 ahead as two hundred years earlier. 



In closing, I wish to call your attention for a few moments to 

 some of the differences that exist between the American and 

 English practice of bridge-building, and the causes that have led 

 to these differences. The characteristic difference is in the meth- 

 ods used in joining together the different parts of the bridge. 

 American bridges, as a class, are pin-connected that is, the 

 different members, when possible, are joined by means of a steel 

 pin passing through holes in the ends of the pieces. These joints 

 are perfectly flexible, and each member is designed to do its own 

 particular work. English bridges, as a class, have " riveted con- 

 nections" that is, the members are fastened rigidly together, 

 and each member is designed to act simply as a part of a rigid, 

 inflexible whole. 



The causes that have led to this difference are as follow : In 

 the construction of bridges the English engineer started with 

 the flanged girder of cast or rolled iron, or some other form of a 

 stiff beam, and as the bridges increased in size so as to necessitate 

 the framing of a truss, his whole effort was directed toward mak- 

 ing that truss as nearly similar to the original flanged or box gird- 

 er as possible. This led to perfect rigidity at the joints. 



The American engineer, on the other hand, had very little or 

 no iron and steel to work with, and of necessity used wood. As 

 the necessary bridges were of considerable span, the only possible 

 solution of the problem was the pinning together of small pieces 

 of wood so as to form a connected series of triangles. The joints 

 in wood could not easily have been made rigid, and it was not de- 

 sirable that they should be, as the strength of wood is very slight 

 when the strain is applied in any direction other than in the 

 direction of the fibers of the piece, and the use of the pin joint, 

 theoretically at least, insures this line of action. There has been 

 much ingenuity displayed by our engineers, in the years gone by, 

 in the combinations of triangles used in bridge-designing, and in 

 many cases this has led to absurdities. The whole tendency, how- 

 ever, at present in American practice is to extend the use of riv- 

 eted joints, and in English practice to extend the use of the " pin 

 connections." Both are working in opposite directions, but from 

 opposite sides, and therefore toward the same point. 



One great drawback to the more general use of pin connec- 

 tions by English engineers is the immense first cost of the plant 



