Instructions on Modern American Bridge Building — A Reader’s Guide

A Methodical Structure for Instruction

Tower divides his book into two clear parts: first, the strains on beams and the calculation of a simple truss; second, the members of a bridge truss with worked examples. He promises subsequent volumes on other wooden bridges, masonry, and iron bridges—none of which appear in this edition. The organization reflects a classroom sequence, moving from general principles to specific truss types. Each section builds on the previous one, with frequent cross-references to the four plates and thirty figures that illustrate the text.

Howe and Pratt Trusses in Parallel

The core of the manual presents two competing truss designs: the Howe, with wooden diagonals in compression and iron rods in tension, and the Pratt, which reverses the arrangement. Tower provides dimension tables from both Vose and Trautwine for each type, spanning 25 to 200 feet. He notes that a bridge built to either table would be “amply strong,” but he does not declare a preference. Instead, he walks through the strain calculations step by step, showing how to size chords, braces, posts, and rods. The Pratt section includes a detail on bevel blocks fitted to avoid crushing action—a practical touch.

The Language of Load and Dimension

Tower’s prose is direct and numerical. He writes of “strains,” “tension,” and “compression” with precision, using proportions like “Height : diagonal :: W : W'” to derive rod diameters. The tables are dense with figures: spans in feet, rise in feet, panel lengths, and piece sizes in inches. He specifies that his tables assume a single railroad track but notes they “would answer equally well for a double Highway Bridge.” This economical phrasing reveals his audience—practitioners who need adaptable data, not theoretical discussion.

Acknowledged Borrowings and Practical Limits

Tower is unusually candid about his sources. He credits Vose’s Hand-book of Railroad Construction as authority in cases of disagreement among authors, and he admits that some parts are “quoted entirely.” He also cites Trautwine, another engineer of note. This transparency is rare in technical manuals of the period. Yet Tower does not claim completeness: he explicitly limits the book to “three or four of the more prominent styles of Truss,” leaving other forms for later. The reader is left with a focused, honest introduction, not a false promise of exhaustive coverage.

Tower’s manual is best read as a classroom supplement, not a standalone reference. The tables and examples reward careful study, but the book assumes familiarity with basic engineering concepts. Readers should compare the Vose and Trautwine tables to see how different authorities approached the same problem. The absence of later promised volumes means the Howe and Pratt trusses dominate; those seeking other wooden or iron bridges must look elsewhere.

There is a particular patience in Tower’s old manual, the way it trusts a young mind with load tables and strain diagrams. I find that same quiet faith in its wireless companion, Wireless Telegraph Construction For Amateurs — Themes and Context, where a spark in the dark becomes a careful lesson, not a spectacle. Both speak to hands that want to build.