258 



Our Surroundings 



necessary to make it possible to use effectively the new means of 

 transportation which were being invented. 



Bridges built in the form of open frameworks of wood or metal 

 are known as truss bridges. The beams and rods, or members, of 

 these frameworks are so designed and arranged as to secure great 

 strength with a comparatively small amount of material. Ordinary 

 truss bridges rest on piers, or supports, with one end fixed and the 

 other end on rollers or rockers, to allow for expansion or contrac- 

 tion with changes of temperature. 



Cantilever bridges are framed structures built out from oppo- 

 site piers, and so designed that each section is self-supporting. 



Brown Brothers. 



THE QUEBEC BRIDGE 



The cantilever trusses, built out from each pier, are self-supporting. At their channel 

 ends they support a regular truss span. 



These sections may meet at the center, or may support a regular 

 truss between their free ends. In this way, very wide spans 

 between piers are constructed. 



Travel by Wagon. As communities grew and it became 

 more and more necessary for food and supplies to be distributed 

 among the settlements, stage and freight lines were established 

 to serve the public. The early stage coaches, running with four 

 or six horses or more, changed at frequent intervals, made fairly 

 rapid time but could not carry many people. The early freight 



