The typical subway of reinforced concrete from Clinton Street to the Flatbush Avenue terminus is being constructed by the method commonly used on the Manhattan-Bronx route.  From Borough Hall to the terminus the route of the subway is directly below an elevated railway structure, which is temporarily supported by timber bracing, having its bearing on the street surface and the tunnel timbers.  The permanent support will be masonry piers built upon the roof of the subway structure.  Along this portion of the route are street surface electric roads, but they are operated by overhead trolley and the tracks are laid on ordinary ties.  It has, therefore, been much less difficult to care for them during the construction of the subway.  Work is being prosecuted on the Brooklyn Extension day and night, and in Brooklyn the excavation is made much more rapidly by employing the street surface trolley roads to remove the excavated material.  Spur tracks have been built and flat cars are used, much of the removal being done at night.

CHAPTER III

POWER HOUSE BUILDING

The power house is situated adjacent to the North River on the block bounded by West 58th Street, West 59th Street, Eleventh Avenue, and Twelfth Avenue.  The plans were adopted after a thorough study by the engineers of Interborough Rapid Transit Company of all the large power houses already completed and of the designs of the large power houses in process of construction in America and abroad.  The building is large, and when fully equipped it will be capable of producing more power than any electrical plant ever built, and the study of the designs of other power houses throughout the world was pursued with the principal object of reducing to a minimum the possibility of interruption of service in a plant producing the great power required.

The type of power house adopted provides for a single row of large engines and electric generators, contained within an operating room placed beside a boiler house, with a capacity of producing, approximately, not less than 100,000 horse power when the machinery is being operated at normal rating.

[Sidenote:  Location and General Plan of Power House]

The work of preparing the detailed plans of the power house structure was, in the main, completed early in 1902, and resulted in the present plan, which may briefly be described as follows:  The structure is divided into two main parts—­an operating room and a boiler house, with a partition wall between the two sections.  The face of the structure on Eleventh Avenue is 200 feet wide, of which width the boiler house takes 83 feet and the operating section 117 feet.  The operating room occupies the northerly side of the structure and the boiler house the southerly side.  The designers were enabled to employ a contour of roof and wall section for the northerly side that was identical with the roof and wall contour