NEW IRON BRIDGE AT HARLEM—A GREAT PLANING MACHINE. rangement of the valves and doors of the air lock the pressure of air to keep out the water is maintained by the engine in the column while the men descend and excavate below and send up the silt through the in terior until the column has been sunk to its required depth. When this is accomplished the column is filled up inside with masonry so that when finished it is a compound of cast iron and solid masonry. The sinking of these hollow shafts has been a work of great labor and difficulty as boulders weighing from 1 to 30 tuns have to be removed to permit their de scent. On the center pier a great circular girder forming feet 9 inches deep has been laid. It is to form the roadway of the draw turn table. This girder has pose and which is the largest we have ever seen. It resembles a revolving crane with the center shaft in the middle column of the pier. The cutter travels round the girder planing as it moves. It is driven by belting from the steam engine and the cutter is made to traverse round by a pinion biting into a rack secured inside of the girder. The cutter of this planer traverses a circle of nearly 147 feet making a revo iron blocks will be laid upon the face of this girder and on this the rollers of the turn-table of the draw ter and the draw will be composed of a peculiar trip lit arched girder with its axis in the central column of the circular pier. In position it will rest on three piers ; when open it will be supported and moved on one. To allow vessels to pass the mass of the draw to be moved will weigh about 400 tuns. Each girder for the spans will be constructed of half-inch plate iron strengthened with angle iron. It will be a riveted arched box 31 feet deep 3 feet broad set in sion rod no less than 81 inches in diameter. Each span will have two girders and the flooring will be laid on rolled needle beams or floor girders one foot deep. When the spans are erected ornamental bal ustrades of cast
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