1052

MODERN STEAM PRACTICE.

each post. The shoes are set in the solid rock in beds cut out fairlyto receive them at right angles to the direction of the post.

The sixteen posts all come together at the top, where they arecrowned by a heavy cast-iron cap, having sixteen cells on the innerside to receive them individually, and deep flanges on the upper sideforming channels for the reception of the saddles and rollers whichcarry the cables and stays. The timbers break joint with each other,and are firmly bolted together, and wrought-iron plates T V inchthick and central dowels are inserted in every butt joint. The postsare so firmly built and braced as to warrant them being consideredin detail as short square struts or pillars having a breadth of baseequal to one-fifth their height, and therefore not liable to bendingunder a heavy load.

The crushing force of white pine being about 5000 Ibs. to thesquare inch, or 2^ net tons, the weight required to crush down oneof the towers will be 132 x 32 x 2^ = 10,560 tons, or forty times theweight of the permanent load it has to carry. The effectivestrength of pine is estimated at one-tenth of its crushing force, and

hence the towers should be able to bear safely a load of !f2 ( ’?=io56tons.

EAST RIVER BRIDGE , NEW YORK .

The following are some details, as given by the ScientificAmerican, of the Suspension bridge now building to connect New York and Brooklyn , and which has the largest span as yet actuallycarried out.

The bridge is designed to carry three kinds of load: the outsideroadways being for waggon traffic, the middle one for a promenade,with the railway tracks on either side of it and between it and theroadways.

The total weight of metal in this bridge in round numbers is 1000tons. Of this 1,658,279 lbs. are wrought iron, 82,092 lbs. steel,27,440 lbs. Steel pins, 146,891 lbs. cast iron. The width of thebridge over all is 88 feet, length on the longest side 206 feet, lengthof longest truss 198 feet 5 inches, length of shortest truss 163 feet10 inches. The outside roadways will be 16 feet 7 inches widebetween fenders, the two railroad ways will be 12 feet each, thepromenade 17 feet 7 inches wide.

The following are the principal dimensions of the bridge:—

Size of New York Caisson, 172 x 102 feet.

Size of Brooklyn Caisson, 168 x 102 feet.