88 How Bridges are Built. 



CHAPTER X. 



BRIDGES. 



i. Here is a suspension bridge. It is made by 

 building two tall piers or towers, and stretching 

 large, strong ropes or cables, usually made of 

 wire, across the tops of these. The cables neces- 

 sarily sag by their own weight, so as to make a 

 curve. Pieces of rope or iron rods are fastened 

 to the cables, and, as they hang straight down, 

 are fastened to the ends of beams, on which 

 the floor of the bridge is laid. On this floor 

 people walk, or wagons pass, or even locomo- 

 tives with trains can cross when the bridges 

 are made strong enough. 



Blackboard Drawing 1 . Mark the piers one foot apart ; then the 

 cables "over the tops of the piers ; next, the rods and floors, or 

 roadway. 



2. The oldest of these is said to have been 

 made in China in the year 65. It was made 

 of chain cables with a floor of wood. 



3. The Indians in South America make 

 them of bark ropes, and sometimes, instead of a 

 floor for the traveler to walk on, there is a bas r 



