Relative cost of water-proofing to that of total cost of structure. — Interest on investment may be ignored. — Probable life of water-proofing. — Qualities of materials for water-proofing. — Deterioration of water-proofing and causes therefor. — Damage due to lack of water-proofing. — Water-proofing in steel bridges. — Brine drip. — Water-proofing of concrete viaducts. — Water-proofing of flat slabs. — Water-proofing of concrete roads. — Disintegrating effects of water-penetration on concrete. — Leaching of alkalies. — Erosive action of water percolating concrete. — Effect of freezing on reinforced concrete. — Cracks in floor slabs. — Electrolysis. — Softening of concrete and expansion thus induced. — Appearance deteriorated by water percolation. — Excrescence of magnesia and other salts. — AEsthetics and economics. — Water-proofing is a form of insurance. — Effect of this dissertation on author's future policy in the designing and construction of bridges. — Mr. Rhett's conclusions re water-proofing. ......... 449

Fundamental Economics of Military Engineering. — Time factor substituted for

cost factor. — Principle of "Bare Necessities Only." — Safety and permanence. — Waste not justifiable. — Classes of Military Bridges. — Types of Military Bridges. — The typical military bridge. — Framed trestles. — Economic span for military trestle bridges. — Spar bridges. — Pile trestles. — Trusses. — Sectional trusses and girders. — Cribs. — Suspension bridges. — Ponton or floating bridges. — New type of ponton equipage. — Railroad bridges. — Foot-bridges. — Deck or flooring of military bridges. — Width of roadway. — Side-rails and hand-rails. — Materials employed in Military Bridging. — Timber. — Piling. — Steel. — Concrete. — Stone. — Paint. — Joints and fastenings. — Sizes of individual members. — Plant and tools. — Class of labor available. — Improvisation and standardization. — Utilization of existing bridges. — Utilization of local resources. — Loading of military bridges. — Transportation of materials. — Selection of site. — Protection against flood and drift. — Inspection of military bridges. .................... 459

Explanation of innovation in technical literature. — Reasons why this is to be

author's last technical treatise. — Great expense involved in technical-book writing. — Great amount of valuable time involved. — Subject of bridges about exhausted by author's various writings. — Probable economic investigation on "Molybdenum Steel for Bridges." — This treatise is mainly author's own personal work. — Suggested method of utilizing "Bridge Engineering" and "Economics of Bridgework" by young engineers desirous of becoming "Bridge Experts." ........486

Chronologically arranged list of author's various investigations and writings on the

subject of "Bridge Economics." ........................................... 489