The wonders of modern mechanismA résumé of recent progress in mechanical, physical, and engineering science . PIVOT-CENTRE FOR SWING-BRIDGE. truss, consisting of X-shaped braces between beams orgirders. The triangular or V-shaped truss is also com-mon. The parabolic truss is a comparatively new andhandsome form, and is shown in Figure 6. The latticeform of girder is also a favorite style of construction. EXTRAORDINARY BRIDGES. 35 It has an upper and a lower beam connected by a lattice-work of crossed bars. The plate bridge or plate-girderbridge is made of very wide steel beams, usually in cros
The wonders of modern mechanismA résumé of recent progress in mechanical, physical, and engineering science . PIVOT-CENTRE FOR SWING-BRIDGE. truss, consisting of X-shaped braces between beams orgirders. The triangular or V-shaped truss is also com-mon. The parabolic truss is a comparatively new andhandsome form, and is shown in Figure 6. The latticeform of girder is also a favorite style of construction. EXTRAORDINARY BRIDGES. 35 It has an upper and a lower beam connected by a lattice-work of crossed bars. The plate bridge or plate-girderbridge is made of very wide steel beams, usually in crosssection resembling an I. Such bridges are called deckbridges when the roadway is on a level with the top of thetrusses, through bridges when the roadway passes betweenthe trusses on a line with the lower beams, and half deckwhen the roadway is midway of the trusses. Fig. HIGHWAY BRIDGE AT BINGHAMTON, NEW YORK. Bridge-building is undoubtedly on the increase, andwith the decreased price of steel, together with the in-creased strains which it is made to bear, we may reason-ably expect to see many more such mammoth structuresas that contemplated over the Hudson. Indeed, greaterones are possible with present materials, and the cost isthe only thing that prevents the building of spans a milein length. As materials cheapen, and the worlds ideasof necessity and convenience advance, probably the one-mile span will spring into being. 36 WONDERS OF MODERN MECHANISM. SOME GREAT TUNNELS. Methods of blasting through Mountains, driving Shields underRivers, and forcing Needles under City Streets. Next to the aspiration for fame that leads men to erectsky-kissing towers, there comes the desire to dig far downinto the bowels of the earth, to scorn the opposing moun-tain that will not be crossed, and make a straight roadthrough its vitals to daylight. No engineerhig fea
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