— Pavement base. — Location of machinery house. — Best number of ropes. — Combination of vertical lift and cantilevers. — Design for Hoogly River Bridge, Calcutta. — Comparative costs of various types of movable spans. — Records of quantities of materials in vertical-lift and bascule bridges. — Percentage weight-curves for vertical lifts and bascules. — Housatonic River Bascule Bridge. — Unit prices used in comparison of total costs. — Diagrams of vertical clearances for movable spans of equal cost. — Application of diagrams to skew layouts. — Effect of substructure conditions on comparative economics of vertical lifts and bascules. — Comparative costs of swing-span bridges with vertical lifts and bascules. — Mystic River, Brown-Balance-Beam, Bascule Bridge. — Housatonic River, Bascule Bridge. — General ratio of clear height to clear horizontal opening for vertical-lift bridges and bascules of equal cost. — Extension of investigation for economics of very short spans is unnecessary, and why. .......... 284

Data furnished by Mr. Thomas E. Brown and Major Leon L. Clarke. — Kind of

power and type of machinery depend greatly on local conditions. — Location near a city. — Steam power very objectionable. — Hydraulic pressure or compressed air. — Electric power. — Internal-combustion-engine power and its advantages. — Efficiency definition. — Probable time of operation. — Direct versus alternating current. — Accumulators. — Storage batteries. — Hydraulic power. — Conveyance of power on span. — Gear reduction. — Worm gearing. — Multi-cylinder, gasoline engines for bridge operation. — Ideal apparatus. — Division of parts of movable spans into three groups. — Carrying structure. — Supporting machinery parts. — Operating machinery. — Breakdowns. — Power required for swings, lifts, and bascules. — Amount of wind pressure for bascule designing. — Brake power for bascules. — Holding power. — Economics in using standard machinery. — Tendency to cramp machinery space. ..... 310

Various names for this type of structure. — Legitimate function of transbordeur. —

Transbordeur versus bridge. — Description of transbordeur. — Author's development of type. — Types of bridge suitable for supporting transbordeur cages. — Transbordeur design for New Orleans. — Tabulation of comparative costs of four transbordeurs, a low-level bridge, and a high-level bridge for New Orleans. — Deductions from table. — Comparative economics of long cages and short cages. — Best number of cages to adopt. — Cost of operating transbordeurs. — Character of construction and general modus operandi of transbordeur. — Details of structure. — Operation of New Orleans transbordeur. — Conditions necessitating a "corral." — Method of caring for pedestrians. — Time schedules. — Evolution of author's transbordeur type. — Comparison of capacities of transbordeur and low-level bridge. — Opportunities for building transbordeurs are scarce. — Fixed-span bridge preferable to transbordeur. — Transbordeur design for Havana Harbor. — Philadelphia-Camden transbordeur design. — Conclusion and recapitulation. ...................... 318