trated determine what process of sinking to adopt; and as the cost of the substructure depends upon the said process, so also will the layout.

Navigation Influences

The influences of navigation that are likely to prevail during the time of the contractor's operations may be of such moment as to affect more or less the design and the layout of the structure; although this is not very likely. Again, the possibility in the future of greatly augmented river-traffic may influence the type of movable span adopted.

Construction Facilities

The availability or otherwise at the bridge site of sand, gravel, concrete- stone, a machine shop for repairs, and a reliable source of supplies for the work and workmen, the accessibility or the contrary of the site from the nearest railroad depot or siding, the length and difficulty of wagon-haul or other means of transportation of materials and supplies, the facilities for securing and retaining labor, and the availability of supplies of timber and piling all affect greatly the cost of the substructure and to possibly a somewhat less degree that of the superstructure-hence also the layout of spans and piers.

Erection Considerations

The difficulties that may be anticipated for erection, and the method thereof finally adopted, whether by falsework, cantilevering, semi-cantilevering, or flotation, are important factors affecting the layout of the structure, as are also the questions of the maintenance of traffic and the replacement of an existing bridge.

Aesthetics

Too often the question of aesthetics is totally ignored; but when it is given proper consideration, it may cause modifications in span lengths, truss dimensions, and shapes of piers. How much extra money it is legitimate for a bridge engineer to spend for the purpose of beautifying a structure is a mooted point. It depends greatly upon the designer's appreciation of the beautiful in nature and in art, as well as upon the elasticity of the client's purse and the extent of the influence upon him exerted by his consulting engineer, also upon the location and surroundings. Generally speaking, the best layout for all the other ruling causes is the best also for aesthetic reasons; but there are cases when a little extra expenditure of money, time, and brains will secure great improvement in appearance; and in such cases the beautifying of the construction should, if possible, be accomplished.