July 4, 1902.] 



SCIENCE. 



19 



The channel span of the cantilever bridge 

 over the Mississippi River at Memphis, 

 Tenn., is the longest one of any bridge of 

 this class in America. It measures 790^ 

 feet between centers of supports. This 

 bridge was finished in 1890, the same year 

 that marked the close of the seven-year 

 period of construction and erection of the 

 mammoth cantilever bridge over the Firth 

 of Forth in Scotland. A number of canti- 

 lever bridges have been built since then, 

 but most of them have comparatively short 

 spans. There is one now under construc- 

 tion over the Monongahela River in Pitts- 

 burgh, and which is expected to be finished 

 this year, whose span is to be a little longer 

 than that of the Memphis bridge. It is on 

 the new extension of the Wabash Railroad 

 system, and the distance between pier cen- 

 ters is 812 feet. 



But there is another one being built 

 which will not only have a longer span 

 than any other cantilever bridge in this 

 country, but longer than that of any other 

 bridge whatsoever. It is located near Que- 

 bec, Canada, and its channel span over 

 the Saint Lawrence River is to have the 

 unprecedented length of 1,800 feet or 

 nearly a hundred feet longer than that of 

 the Forth cantilever bridge and two hun- 

 dred feet longer than the Brooklyn suspen- 

 sion bridge. The towers will have a height 

 of 360 feet above high tide. It will ac- 

 commodate a double-track railroad, besides 

 two electric railway tracks and highways. 

 In the piers the courses of masonry are 

 four feet high and individual stones weigh 

 about fifteen tons each. The character of 

 its design and the simplicity of its details 

 will permit its construction with unusual 

 rapidity and economy for a bridge of this 

 magnitude. Several other cantilever struc- 

 tures whose largest spans range from 600 

 to 671 feet are either now or soon will be 

 under construction. 



The Brooklyn bridge, completed in 



1883, is still the largest suspension bridge 

 in the world, its span being 1,595^ feet. 

 More people cross this bridge than any 

 other in any country. The New East River 

 bridge, which is now being built, has a 

 span of 1,600 feet, and its capacity will be 

 very much greater than that of the Brook- 

 lyn bridge. Each of its four cables has a 

 safe strength of over 10,000,000 pounds in 

 tension. 



One of the most interesting develop- 

 ments relating to the subject under consid- 

 eration is the construction of a considerable 

 number of metallic arch bridges in recent 

 years and the promise of their still greater 

 use in the future. On account of their 

 form they constitute one of the handsomest 

 classes of bridges. 



The first important steel bridge in the 

 world was completed in 1874. It is the 

 arch bridge which in three spans crosses 

 the Mississippi River at St. Louis. Its 

 arches . are without hinges and their ends 

 are firmly fixed to the piers. This is one 

 of the most famous bridges in existence. 

 For a long time after its construction no 

 metallic arches were erected in this coun- 

 try, although many were built in Europe. 

 In 1888, however, the highway bridge 

 across the Mississippi River at Minneapo- 

 lis was erected, consisting of two spans of 

 456 feet each and which still remains the 

 longest span of any three-hinged arch. 

 The following year the Washington bridge 

 over the Harlem River in New York city 

 was completed. It consists of two spans of 

 510 feet in the clear and has the largest 

 two-hinged arch ribs ^vith solid web plates. 



These were followed by a n^^mber of 

 arches of various types, the most noted of 

 which are the two arch bridges over the 

 Niagara River. The first one is a spandrel- 

 braced, two-hinged arch with a span of 

 550 feet and replaced the Roebling sus- 

 pension bridge in 1897. It accommodates 

 the two tracks of the Grand Trunk Rail- 



