94 W. H. WARREN. 
day, was unknown 25 years ago. The displacement of 
wrought iron by steel is the most important feature in 
bridge building during the last twenty-five years, which, 
coupled with the gradual improvement in the quality of 
the material due to the more perfect methods adopted by 
the steel manufacturers, as well as the equipment of the 
workshops with special tools and appliances for manufac- 
turing the various members of bridges, has rendered pos- 
sible the attainment of such structures as the great Forth 
Bridge with its two spans of 1,710 feet, as well as many 
large bridges constructed in America, such as the 550 feet 
spans across the Ohio at Cincinatti and Louisville, the Red 
Rock and Memphis cantilevers, also more recently the 
great cantilever constructions at Pittsburg, and the 1,800 
feet span now being constructed across the St. Lawrence 
River, near Quebec. The wonderful progress in the art of 
bridge building made during the last few years may be 
realized by considering the various designs prepared by 
American engineers for crossing the Hudson River at New 
York, which include a suspension bridge of 3,100 feet span 
carrying six lines of railway. 
Various designs have been submitted by British, American 
and German engineers for the Sydney Harbour Bridge,which 
if constructed, would be ranked among the most important 
bridges of the world. 
The modern treatment in the design of the stiffened 
suspension bridges which is illustrated by the Hast River 
Bridge at New York City, 1,600 feet span, and by one of 
the proposed designs for the Sydney Harbour Bridge. 
The tensile strength of the steel wire used in the Hast 
River Bridge was found to be 223,000 ths. per square inch. 
The cables are thoroughly saturated with waterproof compo- 
sition wrapped with a triple layer of canvas and an outer 
covering of steel plate, and the whole will be carefully 
