1,000 feet to 3,000 feet. The curves are for single-deck structures; but the quantities found for the double-deck structures of 1,750 feet span are shown by short dotted lines. In Fig. 29d are indicated in a similar manner the weights of metal per lineal foot of main span for alloy-steel eye-bars in bridges of that type; and in Fig. 29e are recorded correspondingly the

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quantities of nickel steel, concrete in shafts and anchorages, and mass of materials in pier bases for such structures.

In order to illustrate the manner of using these diagrams and at the same time to draw therefrom conclusions concerning the present status of the economics  of  the  two types of cable under discussion,  it will be well to