There is no feature of a bridge so pleasing to the eyes of all observers, cultivated and ignorant alike, as perfect symmetry in the layout of spans; consequently it should be attained whenever practicable, even if some extra expense be involved thereby.

Unfortunately the conditions are not always favorable to perfect symmetry of design, for the bed-rock will often dip rapidly, and thus necessitate the use of spans of different lengths, and the channel of the river often refuses to keep at midstream, persisting in hugging one shore. In such cases it becomes necessary to do the best one can with the unfavorable conditions, and to make the structure sightly, if not symmetrical. If there be a draw-span on one side of the river, it is best generally to make all of the fixed spans alike. Should each span—because of the gradual shelving off of the bedrock, and for the sake of economy—be made longer as the bedrock deepens, the result will be unsightly, even if the increment of span length be regular, for the reason that to an observer there is no apparent motive for thus diversifying the spans.

Any divergence from symmetry and regularity for which there is a self-evident reason produces no unfavorable impression upon the beholder, although it may be sufficient cause for failure to excite his admiration for the structure. If one can see at a glance the raison d'être of all the principal parts and peculiar features of a bridge, his sense of fitness will be satisfied, and his general impression will be favorable; but the nearer the approach to perfect symmetry and the more artistic the outlines, the more thorough will be his appreciation of the general effect of the structure.

In making a study of the aesthetics of a bridge design, after determining what spans are applicable, it is well to make one or more layouts on a large scale on the brown paper used in engineers' offices for pencil-drawings, indicating the circumscribing lines of all main mem-bers to scale, and tinting or filling between said lines with pencil-shading; then tack the paper on a wall, and stand off at various distances to judge the effect.   By doing  this  one  can  form a very correct opinion