AMERICAN INSTITUTE. 617 



present purpose of relieving the economy of the wire rope, espe- 

 cially in the point of service 



The ditierence iu price in this country, however, between the 

 wire ropes and hempen ropes, is not so large; the great disparity 

 iu England being, I suppose, partially attributable to the late war 

 witli liussia. Again: wire rope, unlike hemp rope, is not affected 

 by the sudden changes of temperature ; as in a northern climate, 

 when tarred rigging gets hard, unyielding and brittle, or under a 

 tropical sun, where the tarred rigging becomes soft and flows — 

 giving thereby great annoyance. 



Neither is it liable to those sudden changes in lengths, to which 

 hemp is subject, and which, as every sailor knows, gives rise to 

 inconvenience, and great labor in setting up the rigging, and to 

 serious accidents, when, as often happens, the change takes place 

 in a single night, in circumstances that render it impossible to 

 set up the rigging before trouble has ensued. 



I have endeavored, at some length, to call your attention to 

 this field for the application of wire rope, not only because the 

 great bulk of ropes manufactured are for this purpose, nor alone 

 from the fact that its advantages are so numerous and well sus- 

 tained abroad; but because its manufacture in this country is of 

 modern date, and its introduction for vessel's standing rigging 

 not yet made, or so limited only as not to be known. 



However, when it shall have tecome developed by our own 

 experience in the naval and mercantile service of this country, 

 as I am convinced it soon must, I feel assured that its advantages 

 will be as generally appreciated here, as they now are with our 

 friends across the Atlantic, and its application become common — 

 as general. 



Bridges — With regard to the application of wire rope to bridges, 

 I need only to mention the " Niagara suspension railway bridge," 

 the complete success of which stands as a noble monument to the 

 skill and persevering energy of its projector and builder, Mr. 

 John W. Roebling, whose success is the more gratifying from the 

 general distrust that was felt at its commencement. 



The cables of this bridge are four in number, each being ten 

 inches in diameter, and containing seven strands, each strand 

 having 520 wires of size No. 9, wire gauge, or 3,640 wires for a 

 cable. Sixty of these wires form one square inch of solid section, 

 making the solid section of each cable, 60.4 square inches, wrap- 

 ping not included. Tlie aggregate strength of the whole four 

 cables being about 23,878,400 lbs. 



