348 



A Description of a new Military Bridge, 



a road-way laid upon the cross-bearers, the assemblage would 

 constitute a bridge sufficiently strong for many temporary pur- 

 poses. 



Let us suppose the span to be 50 feet, then the longest piece 

 of timber required would be about 18 feet, or a little more than 

 l-3d of the opening, and the sketch shows the method of dis- 

 posing the pieces. 





For a 50 feet span, the end pieces a a, a a' ought to be about 

 9 inches deep and G inches in breadth, and 18 feet long. The 

 other pieces of the same length, but only fi inches square. 



C is a projected sketch of one of the iron straps 

 at l,h,h,h,h, in the preceding sketch. When these 

 straps are put to their proper situations, they are 

 tightened by a screw-wrench applied to the screw c. 



In fig. AB, the letters d,d,d,d,d,d, show where 

 pieces of hard wood should be let into the joints to 

 prevent any sliding of the parts when the bridge is 

 loaded. 



A bridge consisting of two frames, such as A B, 

 over a river 50 feet wide, would bear the weight of 

 infantry marching under a front of two men, files 

 close ; four flames a front of four men ; and so on. 



If Riga or Memel timber be used, the heaviest pieces will not 

 weigh more than about 140 lbs. each ; so that two men may carry 

 one of them with ease ; and from the nature of the fastenings 

 proposed, a frame may be put together or taken asunder with the 

 utmost facility, without injury to the materials. 



In cases where the proper materials have not been provided, 

 ropes might be employed instead of straps of iron ; these ropes 

 might be drawn perfectly tight by means of short staves for twist- 

 ing them ; and sjch timber might be employed as the place af- 

 forded. 



With the assistance of floats, and the force of the current in a 

 river, it would be easy to get the frames to their intended situa- 

 tion ; but Vv'ith expedients necessary for accomplishing this ob- 

 ject, military men are in general likely to be familiar : — if not, the 

 excellent work of Sir H. Douglas will supply the necessary in- 

 formation. 



