same length as that of the cantilever arms, viz.: 0.3125 of the main opening, instead of the more economic value of 0.2 thereof. Concerning the correctness of the last claim for economy there is some dispute in the profession; but of this matter, more anon.

In the suspension-bridge layout the backstays were not used to support side spans, but were run by approximately right lines to the anchorages. This is the most economic layout possible, because a steel-trestle approach is always cheaper than any layout of truss spans that can be made, not only because it requires less metal, but also because the unit prices thereof erected are somewhat smaller.

The main piers of all the cantilever bridges and most of those for the suspension structures were designed as two pedestals with a reinforced- concrete wall between, this wall extending a short distance below extreme- low-water mark. It was found, however, in the case of the combined four-track-railway-and-highway suspension-bridges, that it was just as economic to use a continuous pier, because of the four points of support required by the tower columns, hence that feature of construction was adopted.

The method employed for finding the quantity of concrete in the anchor pier for a cantilever bridge was to compute the maximum uplift, multiply it by two, and divide the product by the weight of one cubic foot of concrete, taking due cognizance, of course, of the buoyant effort of the water on all submerged portions thereof. If the volume thus found would work up into a properly-shaped pier, well and good; but if not, an additional amount was provided.

The method of proportioning the anchorages for suspension bridges, when the foundations were solid rock, was to make each one quite long and narrow, high in the rear and low in the front, and to let the line of pressure reach the base exactly on the edge of the middle third thereof. In case the foundation were piles, a similar shape was used, but it was necessary to keep the load on each pile of the front row down to forty tons.

When piles were employed to support the main piers, the limiting load per pile was taken also at forty tons, exclusive of the effect of wind pressure. The piles used were all assumed to be one hundred feet long.

The limiting widths of structure were as follows: In cantilever bridges one twenty-fifth of the main opening; in suspension bridges one-twentieth thereof, measuring between central planes of exterior columns over main piers; and between central planes of stiffening trusses one-thirtieth of the main opening. As a matter of economy, in some of the cantilever structures the distance between truss planes was made as small as practicable for the suspended span, and was gradually widened out to a maximum over the main pier, and then gradually reduced to a minimum over the anchor pier.

The economic lengths for the cantilever structures were taken as established twenty years or more ago by the author when preparing the MS. of