but as the materials could have been used several times, it could not have been large; while to partially offset it there is the extra cost of the adjusting apparatus and the greater cost of erection due to delays in making the central connections. Moreover, alternate simple spans could have been erected without falsework by the expedient adopted by the author for several Japanese bridges, which expedient will be described subsequently in this chapter.

There is a small cantilever bridge in Philadelphia close to the Pennsylvania Railroad where it approaches the depot, which as a cantilever has absolutely no raison d'être. It makes the observer think that, before it was built, some of the city fathers felt that Philadelphia would be behind the times if she did not have a cantilever bridge of some kind or other, and that they erected this one in consequence.

Other illustrations of unnecessary cantilevers could be quoted, but it would be a useless task to carry the illustration farther.

If a deep, narrow gorge with rocky sides has to be bridged, the cantilever construction will often prove economical for two reasons: first, the main piers, being small, are comparatively inexpensive; and, second, the cost of falsework will be almost entirely eliminated, only a small amount thereof being used for erecting the anchor arms.

Again, if a stream is to be bridged where it is impossible to put in falsework, or where there would be danger of its being washed out in case it could be put in, the cantilever will prove an economic design, although in certain cases the cantilever arch design described in Chapter VI. may be still more economical and possibly more rigid. This last feature, however, will depend somewhat upon the character of the arch adopted.

That a cantilever bridge is less rigid and deflects more vertically than a simple span bridge, no one who has examined both types of structure under load and who has measured the vertical deflections can well deny; nevertheless this comparative lack of rigidity is no great detriment or weakness, and should not be allowed to militate against the building of a