In comparing the equivalent loads for spans of one hundred feet, given on Pl. III, with those given on Pl. IV, an apparent discrepancy will be noticed. This is due to the fact that Pl. III is for plate-girder spans, for which the equivalent loads were obtained from the bending moment at mid-span; while Pl. IV is for truss-spans, for which the equivalent loads are the average of those at all of the panel points.

In computing the equivalent loads for Pls. III and IV, it was assumed that cars may precede as well as follow the locomotives.

Since De Pontibus was published, it has become necessary to add Classes Q, R, and S to the "Compromise Standard System" in order to be not only abreast of the times, but also slightly in the lead thereof; for there has appeared lately a tendency to specify exceedingly heavy live loads for railway bridges, because, probably, several excessively heavy locomotives have been manufactured recently.

Pls. I, II, III and IV of this book show the new classes of loading, their end shears and their equivalent uniform loads.