BRIDGES. 
7*i3 
Bridges OF Boats. 
These are either made of copper or wooden boats, made fast with 
stakes or anchors, and laid over with planks. One of the most notable 
exploits of Julkis Csesar was his expeditiously making a bridge of boats 
over the Rhine. Modern armies carry copper or tin boats, named 
pontoons, to be in readiness for making bridges ; several of these 
being joined side by side until they reach across the river, and planks 
laid over them, make a plain for the men to march on. There are five 
bridges of boats at Beaucaire and Rouen, which rise and fall with 
the water; and that of Seville is said to exceed them both. The 
bridge of boats in Rouen, built instead of the state stone-bridge 
erected there by the Romans, is represented by a modern writer as 
the wonder of the present age. It always floats, and rises and falls 
with the tide, or as the land waters fill the river. It is near three 
hundred yards long, and is paved with stone like the streets ; caiiiages 
with the greatest burdens go over it with ease, and men and horses 
with safety, though there are no rails on either hand. The boats 
are very firm, and w'ell moored with strong chains, and the whole 
well looked after, and constantly repaired, though now very old. 
Peistdent Bridges. 
These bridges are not supported either by posts or pillars, but 
hung at large in the air, only supported at the two ends or hutments. 
Instances of such bridges are given by Palladia and others. Dr. 
Wallace gives the design of a timber bridge seventy feet long, with- 
out any pillars, which may be useful in some places w here pillars 
cannot be conveniently erected. Dr, Plot assures us, that there was 
formerly a large bridge over the castle-ditch at Tilbury in Stafford- 
shire, made of pieces of timber, none much above a yard long, and 
yet not supported underneath either with pillars or arch work, or any 
sort of prop whatever. 
Rushen and other Bridges. 
Rushen bridges are made of large sheaves of rushes, growing in 
marshy grounds, which they cover with boards or planks : they 
serve for crossing ground that is boggy, miry, or rotten. The Ro- 
mans had also a sort of subitaneous bridges, made by the soJdiers, 
of boats, or sometimes of casks, leathern bottles, or bags, or even 
of bullocks’ bladders blown up and fastened together, called Ascogafic. 
Mr. Couplet gives the figure of a portable bridge, tw'o hundred feet 
long, easily taken asunder and put together again, and which forty 
men may carry. Frazier speaks of a W'onderful kind of bridge at 
Apurima in Lima, made Df ropes formed of the bark of a tree. 
The Great Canal of Scotland. 
This is a navigable canal between the Forth and Clyde, dividing 
the kingdom into tw'o parts; it was first thought of by Charles II. for 
