9th. Navigable locks. Canal lock; its management; form of the chamber; profile of the cheeks. Trace of the pier on which the gates work. Means of filling and emptying the chambers. Means of raising the paddle-valves. Wood-work of the gates sheathed in timber. Planes. Details of the pivots, collars and rollers. Arrangements for the management of the sheathed gates. 10th. Gates sheathed in wood; curves. Ties of cast-iron, and lining in wood or sheet-iron. Cast-iron gates. _River Navigation._--Advantages and disadvantages of water transit. Conditions of a navigable river. Works for the improvement of the navigation on a river. _Artificial Navigation._--Classification of canals. Conditions which determine the best position for a summit level. Search after a minimum of elevation. Expenditure of water at the summit level. 11th. Principal processes employed to economise the water in passing through a lock. Profile of a navigable canal. Deep cuttings; their profile. Great landslips and means of remedying them. Tunnels; their profile. Piercing of a tunnel. 12th. Bridges in masonry. Position; breadth of the roadway; outlet to be left for the water; size and form of the arches; trace of the surbased arches on more than five centers. Expansion of the bridge-heads. Profile of the arch. Thickness of the piles and abutments. Apparatus for the arches and bridge-heads. Parts above the arches. Leveling with the banks. Fixed and movable centerings. Removal of the centerings of arches. 13th. _Wooden Bridges_ composed of straight pieces. Arrangement of the stakes and starlings. Different construction of the openings according to their span. Arrangement of the platform. _American Bridges._--Arrangement of the earliest form of bridge on Town’s system. Height of the trusses constructed in the form of trellis-work. Modifications introduced to increase the resistance of the bridge. Calculation of the resistance of the trusses. Arched frame-work of bridges. Composition of the arches. Junction of the straight beams with the arches. _Cast-iron Bridges._--Different systems. General principles of their construction. _Aqueducts_ in masonry; in cast-iron. 14th. _Suspension Bridges._--Equation of the curve of the chains and construction of this curve. Tension supported by the suspension cables, their thickness. Influence of the length of the flèche upon the tension of the cables. Inconveniences resulting from a long flèche. Vibrations and means of diminishing them. Limits of length of the flèche. Length of the curve of suspension. Causes operating to vary this length; means of obviating the effects produced by them. Length of the suspension rods. Number of supports to be adopted. Thickness of the piles. Points at which the fixing cables are to be attached. Advantages and disadvantages of chains composed of bars and of cables of iron wire. Some details of construction. 15th. _Drawbridges._--Conditions which they must satisfy. General principle of their balance.