256 SERVICE OF ARTILLERY

feet long; a second layer of planks ii inch thick, and rOfeet long is laid transversely. The pairs of boats thusfastened together are placed at 8 feet distant from each other,joined by baulks 6 or 8 inches square and 10 feet long, naileddown to the gunnels, and covered with chesses as before.To every two boats there is an anchor, and a cable from eachto hold them against the stream ; and when from its greatrapidity this is found insufficient, a fheer-line from eachboat is made fast to the banks of the river. Rails 4. feethigh are placed along each side of the bridge for the safety ofpassengers.

If the river be navigable an opening is occasionally madein the bridge, by placing the center pair of boats almost con-tiguous to those on each side, and joining them by baulksthat are not nailed down ; thus, they may be easily removedto give a passage to an/ boats or vessels passing up or down.

To render the bridge more secure against lwells, largestakes are driven into the bed of the river, at the places wherethe anchors lay, and the boats are fastened to them withstrong cables. And when there is any reason to apprehendthat the enemy have a design of sending down with the cur-rent, boats filled with combustibles to set fire to the bridge,a strong iron chain should be stretched across the river, andsupported by stakes at aoout if foot above the surface ofthe water.

38. When the bridges are made, and the roads repaired,the train of artillery, &c. sets off, divided into several con-voys : for if the whole moved at once, the line of marchwould be nearly 17 miles ; since each pair of oxen takesup at least 10 feet, and each carriage about the fame. Thedistribution should be made into four parts ; this will enablethe officers to pay more attention, wiil render the matchless troublesome and tedious, and they will be more amplysupplied with provisions and forage on the road.

In the first convoy should be sent the intrenching toolsof all forts, that the troops may proceed to throw up linesand open the trenches, together with every article belongingto the laboratory, and a certain proportion of shells andpowder ; that the laboratory may be instantly established,and the necessary preparations made for the ensuing siege.

The second convoy should be composed of the gunsintended for the royal battery, the mortars for the second

' parallel,