PASSAGE OF RIVERS,
47
guns and mortars; and the following different descriptions of bridges which can bemade solely of platform materials were tried in 1846, at the Royal Military Repository,Woolwich, and were approved by the Officers of the Select Committee ordered bythe Master-General and Board to report upon them:
18. First, a Trussed Lattice Bridge, as shewn in the diagram below 7 , fig. 5, havinga span of 28 feet, consisting of two separate frames, which were put together on thebank and hauled into their places by ropes,—which might perhaps be facilitated bystretching hawsers across, upon which they might slide: the baulks were lashedacross over the tops of these frames when fixed perpendicularly in their places, 8 feetapart, so as to brace them together. Baulks were also placed with their ends resting
on the lower string-pieces of each frame, to support the flooring for the roadway,which, for want of a sufficient number of baulks, was composed of pontoon chasses:the bolts were only applied along the top and bottom of each frame, as marked inthe figure, thus requiring 72 bolts and 102 baulks. An 18-pr. gun with its limber,weighing 65 cwt., was drawn over this bridge without causing any appearance ofweakness, and other experiments shew 7 ed that a similar bridge, constructed w r ith halfthe proportion of crossed baulks in the side frames, and with a span of 50 feet, wouldsuffice for the passage of 6-prs.; and that probably, if the lower edges were strength-ened with additional baulks or ropes, 12-pr. guns might cross with safety.
19. Secondly, a Suspension Bridge .—The baulks of the platform were fixed in stringsas follows, spanning 32 feet, laid down 7 feet apart, and parallel: baulks were also
Plan.
laid across the strings, so as to support the roadway : the ends of each string, havingbeen hauled tight, as explained in fig. 6, by a block tackle, were secured bypickets driven into the ground, against which the bolts connecting them rested; butthey might be attached to trees or to rocks, &c., if found more convenient. Eachset of baulks was connected with the ends of the next set by a single bolt, therefore