across the River Dertcent at Bridgewater. 217 



crab-winches, working in toothed rails fixed on the framing 

 under the bridge. They are worked by men standing on 

 the bridge, who move along with it. 



The lateral platforms are also moved by crab-winches fixed 

 on the framing below, and working moveable toothed racks, 

 which draw the platforms apart. 



The rolling bridge is formed by large timber trusses 

 placed on either side, and further strengthened or stiffened 

 by suspension chains from a centre tower, or framing, 

 erected on the bridge for the purpose. 



A double row of fender-piles is driven (in addition to 

 those already described as belonging to the bridge) at this 

 opening, extending up and down the stream for a distance 

 of 175 feet, upon which is placed a stage, which answers 

 the purpose of a towing path for vessels while passing 

 through the opening. The present amount of traffic on 

 the river by boats passing is very trifling. A steam- 

 boat once a day, and two or three small craft which 

 occasionally pass, are all the vessels which require the 

 bridge to be opened. No inconvenience or hindrance is 

 felt by the steam-boat in going through, her passage being 

 quite uninterrupted. 



It may not be out of place to mention that some piles, which 

 were driven 18 or 20 years ago for the jetty of the ferry on 

 the north shore, showed no symptoms of the ravages of the 

 worm {Teredo navalis), which is generally so destructive 

 to timber works constructed in salt water ; there is, 

 therefore, every reason to hope that the bridge may escape 

 injury from such a cause. 



The extreme length of the causeway across the mud flats 

 on the southern shores of the river is 2350 feet, and it 

 averages in breadth 70 feet. 



The length of the bridge from the end of the causeway 

 to the northern shore is 960 feet, with a breadth of roadway 

 of 24 feet. 



