MECHANICS AND USEFUL ARTS. 53 



lattice and plate in the same way. The plate corresponds to the 

 solid bar and the lattice to the wire rope, and the openings to the 

 space between the wire. Here we have undoubtedly so placed 

 the direction of the strain that it is all with the fibres, and find 

 that we have the proportion of 10 to 6 in favor of the structure 

 composed of several separate pieces. 



Now, though this is perhaps an extreme case, and the argu- 

 ment only one by analogy, yet, while perhaps the same propor- 

 tions would not exist between the degrees of resistance afforded 

 by lattice girders and solid iron plates as between the different 

 qualities of iron, from the superiority of construction obtained 

 in the former, the reasoning will apply most forcibly. It will 

 probably not be denied that the superiority of construction claimed 

 really does exist, and this one argument is, therefore, taken 

 alone, convincing. 



But, after all, the matter of the relative strength of the 

 material in different cases is really of less importance than is 

 the apparently simple problem of fastening the parts together. 

 If, after being properly arranged, the parts of the lattice can 

 be so fastened together that each piece will do its entire 

 duty without unduly straining its neighbor, there can exist 

 no doubt that the lattice will be stronger than the iron plate 

 girder, with its present form and arrangement; but, on the con- 

 trary, could the plate be placed in such a way as to be of equal 

 strength at all points, without increasing the weight of the struct- 

 ure, the iron plate would certainly rival the weak forms of lattice 

 as now constructed. Upon the ground that this perfect construc- 

 tion cannot be obtained in a solid plate, the advocates of the lat- 

 tice girders rest their claim, and it would seem that their as- 

 sertions cannot, as regards this point, be readily controverted. 

 American Builder. 



SINKING SCREW PILES. 



A machine has been lately designed by an English firm, at the 

 request of PI. Lee Smith, Esq., chief engineer for the Punjaub 

 Northern Railway, for screwing down piles to be used in con- 

 structing bridges and flood openings on that line of railway. 

 This machine consists of a wrought-iron under-carriage mounted 

 upon wheels of 5 feet 6 inches gauge, and carrying a vertical 

 boiler at one end. A strong cast-iron beam in the centre carries 

 a cylinder in which works a ram, to the top of which a strong cross- 

 beam is bolted which carries the machinery for operating on the 

 piles. This consists of a horizontal steam engine bolted to the 

 side of the cross-beam, and driving a pinion and train of spur and 

 bevel wheels which impart motion to two large horizontal wheels 

 carried in bearings at each end of the cross-beam. A friction 

 clutch is carried in the centre of each of the wheels, through the 

 boss of which the shaft of the pile to be screwed is passed. The 

 shafts are rolled with feathers or ribs on each side, which, passing 

 through corresponding recesses or key ways formed in the boss of 

 the friction clutch, form the means of imparting motion from the 

 horizontal wheels to the piles ; steam is brought from, the boiler, 



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