Expansive Principle applied. -- Failure of Roebuck, and partnership with Bolton. -- Patent extended to 1800. -- Counter. -- Difficulties in getting the Engines into Use. 80 CHAPTER VI. DOUBLE-ACTING STEAM ENGINE. The Single-acting Engine unfit to impel Machinery. -- Various Contrivances to adapt it to this Purpose. -- Double-Cylinder. -- Double-acting Cylinder. -- Various modes of connecting the Piston with the Beam. -- Rack and Sector. -- Double Chain. -- Parallel Motion. -- Crank. -- Sun and Planet Motion. -- Fly Wheel. -- Governor. 91 CHAPTER VII. DOUBLE-ACTING STEAM ENGINE, _continued_. On the Valves of the Double-acting Steam Engine. -- Original Valves. -- Spindle Valves. -- Sliding Valve. -- D Valve. -- Four-Way Cock. 108 CHAPTER VIII. BOILER AND ITS APPENDAGES. Level Gauges. -- Feeding apparatus. -- Steam Gauge. -- Barometer Gauge. -- Safety Valves. -- Self-regulating Damper. -- Edelcrantz's Valve. -- Furnace. -- Smoke-consuming Furnace. -- Brunton's Self-regulating Furnace. -- Oldham's Modification. 117 CHAPTER IX. DOUBLE-CYLINDER ENGINES. Hornblower's Engine. -- Woolf's Engine. -- Cartwright's Engine. 134 CHAPTER X. LOCOMOTIVE ENGINES ON RAILWAYS. High-pressure Engines. -- Leupold's Engine. -- Trevithick and Vivian. -- Effects of Improvement in Locomotion. -- Historical Account of the Locomotive Engine. -- Blenkinsop's Patent. -- Chapman's Improvement. -- Walking Engine. -- Stephenson's First Engines. -- His Improvements. -- Liverpool and Manchester Railway Company. -- Their Preliminary Proceedings. -- The Great Competition of 1829. -- The Rocket. -- The Sanspareil. -- The Novelty. -- Qualities of the Rocket. -- Successive Improvements. -- Experiments. -- Defects of the Present Engines. -- Inclined Planes. -- Methods of surmounting them. -- Circumstances of the Manchester Railway Company. -- Probable Improvements in Locomotives. -- Their capabilities with respect to speed. -- Probable Effects of the Projected Railroads. -- Steam Power compared with Horse Power. -- Railroads compared with Canals. 145 CHAPTER XI. LOCOMOTIVE ENGINES ON TURNPIKE ROADS.