For some twenty-five or thirty years American bridge engineers have been sadly in need of reliable information concerning certain fundamental economic functions of steel arch-bridges, and especially the relative costs of such structures in comparison with the corresponding truss bridges. The want of such information has resulted in the failure of American engineers to develop the steel arch and to use it in places where it would be both more economic and more aesthetic than the simple-truss bridge. Wherever the governing conditions of crossing are suitable for an arch structure, that type of bridge is to be preferred; for, as we now know, the arch, in all places where its use is really justified, is less expensive than the truss bridge.

For two decades or more, the author had been urging the engineering profession to make certain investigations which would settle for all time every uncertainty concerning the economics of designing steel-arch bridges, as well as the relative costs of these structures in comparison with the corresponding truss bridges. As long ago as 1897, when he wrote "De Pontibus," he appealed to the engineering profession as follows:

In concluding this chapter, the author desires to call attention to the fact that there is still a great deal to be learned about the designing of arches; and to suggest that some professor of civil engineering, who is well posted on bridge designing and who has time to spare, could spend several months to the great advantage of the engineering profession in determining the proper relations of span-lengths, rise, arch depth, width between exterior arches, etc., for the varous styles of arch, and in ascertaining the relative economies of the latter.

During the eighteen years which elapsed between the issuing of "De Pontibus" and its successor, "Bridge Engineering," the author made repeated attempts to find some bridge engineer who would be willing to undertake the task which he had suggested—but all to no avail; and in the last-mentioned treatise he made another forcible appeal to the profession to undertake the requisite investigations, speaking as follows:

"For many years the author has been endeavoring to establish some approximate relation between the weights of metal per lineal foot for trusses and laterals of arch bridges and those for the corresponding simple truss bridges; but has met with very little success. He once submitted the question to his brother bridge specialists of America, but they were unable to  throw  any  light  upon  the subject, because their opportunities to

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