the bottom of the brickwork, a layer of water-proofing is placed over the interior area and covered with two courses of brick, upon which are built diagonal brick walls, 4 inches thick, 12 inches apart, and about 18 inches in height.  These walls are themselves perforated at intervals, and the whole is covered with hand-burned terra-cotta blocks, thus forming a cellular air space, which communicates with the exterior air and serves as an insulation against heat for the steelwork beneath.  A single layer of firebrick completes the flooring of the interior area, which is also flush with the bottom of the flue openings.

There are two flue openings, diametrically opposite, and 6 feet wide by 17 feet high to the crown of the arched top.  They are lined with fire brick, which joins the fire-brick lining of the interior of the shaft, this latter being bonded to the red-brick walls to a point 6 feet below the top of the octagon, and extended above for a height of 14 feet within the circular shaft, as an inner shell.  The usual baffle wall is provided of fire brick, 13 inches thick, extending diagonally across the chimney, and 4 feet above the tops of the flue openings.

Where the chimney passes through the roof of the boiler house, a steel plate and angle curb, which clears the chimney by 6 inches at all points, is provided in connection with the roof framing.  This is covered by a hood flashed into the brickwork, so that the roof has no connection with or bearing upon the chimney.

At a point 4 feet 6 inches below the cap of the chimney the brickwork is corbeled out for several courses, forming a ledge, around the outside of which is placed a wrought-iron railing, thus forming a walkway around the circumference of the chimney top.  The cap is of cast iron, surmounted by eight 3 x 1-inch wrought-iron ribs, bent over the outlet and with pointed ends gathered together at the center.  The lightning conductors are carried down the outside of the shaft to the roof and thence to the ground outside of the building.  Galvanized iron ladder rungs were built in the brickwork, for ladders both inside and outside the shaft.

The chimneys, except for the octagonal red-brick base, are constructed of the radial perforated bricks.  The lightning rods are tipped with pointed platinum points about 18 inches long.

[Sidenote:  North River Pier]

Exceptional facilities have been provided for the unloading of coal from vessels, or barges, which can be brought to the northerly side of the recently constructed pier at the foot of West 58th Street.  The pier was specially built by the Department of Docks and Ferries and is 700 feet long and 60 feet wide.