316 



ENGINEERING. 



mum running load of two tons to the foot, or 

 3,400 tons on a span. The breadth to be 

 spanned in the Forth is not much more than 

 half that of the Tay at Dundee, where the new 

 bridge, which will cost about 750,000, is 

 making rapid progress and is expected to be 

 finished in 1885. But the channels on the two 

 sides of the island of Inchgarvie are about 200 

 feet deep, and must therefore be crossed by 

 spanning the entire breadth of some 1,600 feet 

 on'each side. Three balanced cantilevers are 

 sufficient to accomplish this. Two of them 

 rest on piers erected at the edge of the channel 

 on each side of the river, and one on the 

 island. The cantilever has the shape of an 

 elongated diamond. There are four masonry 

 piers to support the four gigantic legs on which 

 are poised the balancing arms, which extend 

 675 feet on each side of the base. The uprights 

 converge upward, being 120 feet apart at the 

 base, 33 feet at the top, where the middle 

 point of the girder rests on the ends of the 

 legs. The middle cantilever is longer than the 

 other two, its base being 270 feet long, while 

 theirs are 155 feet. The four legs are steel 

 tubes, 12 inches in diameter and 320 feet 

 long. The height of the bridge above the 

 piers is 330 feet. While a lattice girder forms 

 the upper side of the cantilever, the under side 

 of the enormous truss is a hollow curve, ap- 

 proaching in form a quadrant of a circle, drawn 

 from the base of the legs, or struts, to the ends 

 of the cantilever. The ends of the beams do 

 not touch each other within 350 feet. The in- 

 termediate space is bridged by lattice-girders 

 resting on the ends of the arms. On the shore 

 sides of the outside cantilevers the weight of 

 these girders is counterpoised by an equal 

 weight of metal. The bridge will present the 

 appearance of two distended arches and a 

 half- arch at each end. The shore sections will 

 consist of girders resting on stone piers. There 

 will be eight piers within high-water mark and 

 two on land, on the south side, and six on the 

 north side, all on land. 



Garabit Viadnct A bridge, begun in 1881 

 and to be finished in 1884, which is intended 

 to carry a railroad over a river at Garabit, 



GABABIT VIADUCT. 



France, is even loftier than the lately com- 

 pleted Kinzua bridge in Pennsylvania. The 

 French viaduct has a great arch in the center. 

 The li eight from the bed of the river to the 

 rail is 413 feet, while in the Kinzua valley via- 

 duct the level of the rail is 301 feet above the 

 stream-bed. In length the French structure 

 is 1,880 feet, or 171 feet less than the other. 



American Transcontinental Railroads. The com- 

 pletion of the Northern Pacific railroad in Oc- 

 tober gives the United States three or prop- 

 erly four great transcontinental lines, while 

 two more are far advanced in construction. 

 The Atchison, Topeka, and Santa Fe, the 

 last link of which was finished two months 

 before the Northern Pacific, is the fourth to 

 reach completion. The Northern Pacific ha? 

 its eastern terminus at Duluth, where it con- 

 nects with land and water routes to the sea- 

 board. The road has recently been extended 

 eastward to Superior City, with the intention 

 of ultimately crossing the Sault Ste. Marie and 

 finding an outlet on the seaboard by one of 

 the new trunk lines. The western terminus 

 and the difficult section across the Cascade 

 range were changed from the original plan, 

 owing to the combination under the Villard 

 management with the Oregon company. In- 

 stead of terminating at Puget Sound, the Pa- 

 cific section follows Columbia river down to 

 Portland. The first of the transcontinental 

 lines that was built was the Union Pacific 

 from Omaha to Ogden, continued by the Cen- 

 tral Pacific, to San Francisco. This road was 

 chartered in 1863 and completed in 1869. The 

 Southern Pacific, in connection with the Texas 

 and Pacific, forms a third transcontinental 

 route. The eastern terminus of the Southern 

 Pacific railroad is at Galveston, and that of 

 the Texas and Pacific at New Orleans. The 

 Southern Pacific railroad has recently sup- 

 plied the link which gives it a -northern ter- 

 minus at Vicksburg in the direction of its 

 natural ocean outlet at Savannah. It ap- 

 proaches the Pacific ocean near San Diego, 

 which is its natural terminus, but it is now 

 carried up through California to San Francisco. 

 The Atlantic and Pacific, called sometimes the 

 thirty-fifth parallel road 

 (as the last mentioned is 

 called the thirty -second 

 parallel route), terminates 

 through its continuation, 

 the St.Louis and San Fran- 

 cisco road, at St. Louis. It 

 emerges on the Pacific 

 coast at the same place as 

 the Southern Pacific, and 

 uses its prolongation up 

 the coast to meet the ocean 

 commerce at San Francis- 

 co. The Atchison, Topeka, 

 and Santa Fe, which line 

 was completed in 1883, 

 forms with the Sonora 

 railroad, lately acquired 



