52 ANNUAL OF SCIENTIFIC DISCOVERY. 



a thickness 1| inches, and weigh about 1 ton to the square foot in 

 height. They are manufactured in sections of 10 feet in length, 

 with inside flanges at both ends to enable them to be connected 

 together during the process of sinking, and thus form a continu- 

 ous cylinder from foundation to bridge-seat. These columns will 

 be filled with cement masonry and concrete from the bottom to 

 an elevation 10 feet above high-water line. There will be 2 piers 

 of this kind in the river, and 1 on the eastern shore. The west- 

 ern end of the bridge will rest on a stone abutment. The 3 

 spans thus formed will be each 340 feet in length, and the bot- 

 tom of the lower chord will be 50 feet above extreme high water, 

 thus leaving ample space between the piers and sufficient height 

 above the surface of water for steamboats to pass at any stage of 

 the river. The approach to the bridge at the eastern end will 

 consist of a substantial trestle work 1,500 feet long, connecting 

 with an earth embankment extending 2,500 feet further. 



LATTICE GIRDERS AND SOLID PLATES. 



The English magazines have of late been devoting much space 

 to a discussion of the relative merits of solid plates and lattice 

 girders, and though the question is certainly an important one, 

 entailing, as it does, almost a revolution in the methods of con- 

 struction, in case lattice girders possess all the advantages their 

 advocates claim, yet the topic is still discussed, and the solution 

 of this problem in mechanics seems nearly as far off as ever. 



Those who rank among the more modern class of thinkers, who 

 first theorize and then demonstrate, claim that the lattice will, for 

 the same amount of material, sustain greater strains and endure 

 shocks much better than a homogeneous plate, and the argument 

 sustaining this claim is based chiefly upon the fact that iron will 

 resist a greater force, applied in the direction of its fibres, than 

 when across them, and it is claimed that mathematical analysis 

 will render possible such an arrangement of the parts of the 

 lattice that all, or nearly all, the strain will be in the direction of 

 the grain or fibre of the iron. 



Now, if we admit, what we certainly cannot prove to be false, 

 that the engineer can, from pure theoiy and by the aid of mathe- 

 matics, so place and arrange the parts of a girder that the strains 

 will be in the direction of the fibre, and proportionate to the size 

 of the pieces, we can draw a strong comparison in favor of open 

 or lattice work. 



No scientific man will deny the fact that a wire rope is both 

 lighter and stronger than an iron rod of the same diameter, or, if 

 he claim the privilege of comparing the actual sectional area, 

 taking the sum of the sectional areas of the individual wires, we 

 can still claim greater strength for the rope upon the ground of 

 more perfect structure, as proved by experiment, the weight, of 

 course, being the same, or nearly the same, in either case. Eng- 

 lish bar iron will resist about 60,000 pounds' tensile strain to the 

 square inch, before parting, while wrought iron will resist over 

 100,000 pounds for the same actual area. Now, compare the 



