Description of a Portable Bridge. 11 



As many of each of the above described parts as are neces- 

 sary, according to the width of the river or valley intended 

 to be passed, with a sufficient quantity of planking posts, 

 chains, &c, according to the existing circumstances of the 

 case, are the whole of its component parts. 



A bridge on this principle for a river, Sec, of a consider- 

 able width is very portable ; for several of the square frames 

 may be packed upon each other in carriages or waggons of 

 the dimensions of eight feet three inches long, three feet 

 four inches wide, and as many feet high as it may be wished 

 to pack a number of frames ; two of them rising one foot. 

 The links and staples can be packed in cases, each sort se- 

 parate. 



The method to be used in passing a river with this bridge 

 shall now be described. (A valley is passed in the same man- 

 ner ; but there being no water to pass, the bridge will be 

 easier supported from the under side.) First, two sufficient 

 holes are to be dug on one side the river, at the distance 

 apart of the width of the bridge, which in this plan is nine 

 feet, and the posts I, are first to be prepared with prongs, 

 Sec, -as in the dotted figure K: next the four smaller ones 

 L, properly secured and well rammed. Then taking any 

 one of the pieces C, fix it on the posts I and L as drawn," 

 and support it en two well driven piles, if the shore will 

 permit : and hooking on the next piece with one of the 

 links F through the eyes at the bottom of the piece, and one 

 of the staples G, fixed into the holes of the upright piece or 

 parapet, it will there hang. Several more are to be hanged 

 on the same way, leaving under them, where necessary, 

 barges or other craft, moored with supporters under them 

 pro tempore. When completed to the opposite shore, the 

 same process of fixing the posts, &e., is to be repealed, and 

 when fastened to these posts, the under supports may be 

 taken away, and the whole left suspending by itself. No- 

 thing now remains but for the superintendant of the work 

 to screw the staples, by the handspike II, till the brido-e 

 rises by a small curvature by opening the interstices N at 

 the top. It is not required to rise more than a small degree 

 above level, only just enough to stiffen the whole, and cau*e 



it 



