20 



JULITAKY COMMISSION TO KIJEOPE. 



ill summer the pi'cactical solution of simple geometrical problems by means of cords aiul stakes, 

 execution of field works, sajjs, mines, &c., with the names of their different parts. 



MILITAEY BRIDGES. 



The Birago equiiJage has been partially introduced, especially the trestles, but the Eussian 

 engineers seemed to prefer their own system of canvas pontons. 



I was informed that in the Hungarian campaign the advantage was altogether on the side of 

 the canvas pontons, and that, as a general thing, their bridge was thrown and the troops 

 crossing before the Austrian Birago wagons could fairly come into position ; it was also stated 

 that when the roads were bad the Austrian train required ten horses for each wagon. 



The canvas pontons consist of two wooden side frames, connected by movable transoms, with 

 a painted canvas cover stretched over the bottom, ends, and sides. 



The annexed figure gives the shape and dimensions of one of the side frames, which are made 

 of about 4" scantling. The bottom transoms have tenons at each end, which fit into mortices in 

 the bottom sills of the side frames ; the two top transoms are laid on the top pieces of the side 

 frames about 2' from the ends, and are lashed to them. The boat is 5' 4" wide from out to out. 



The canvass cover is painted black on both sides; it is 10' 8" wide, 30' long in the middle, 23' 

 3" long along the edges. This cover is brought over the ends of the frame and lashed to the 

 top transoms ; it is secured along the sides to the top string pieces of the side frames by small 

 nails passing through eyelet holes along the edges of the cloth. 



A plank is laid along the bottom for the pontoniers to stand on. The cables are attached to 

 the top transoms. There are four balks for each boat, each balk being 23' 4" long, 5" deep, 4" 

 Avide; the side rails are 21' long and of 3" scantling ; 4 chesses are 12' 2" long, 1.5" thick, and 

 18.6" wide, the rest being of the same length and thickness, but only 9.3" wide. The balks of 

 adjacent bays are connected by iron bolts and keys. There are special supports for the hand 

 ropes. The Birago trestle and abutments are used with this train. The wagon is very simple ; 

 it has four wheels, a flat open bottom, with a stanchion about 3' high at each angle. In loading 

 the four broad chesses are laid on edge against the stanchions, two on each side, thus forming 

 the sides of the wagon ; the narrow chesses are laid on the bottom, then the balks, side rails, 

 ponton frames, oars, &c., the anchor and cable on top of all. The canvas cover is rolled on a 

 boat hook and hung to the stanchions on the right-hand side of the wagon. 



To pass a siege train over this bridge the boats are placed 8' apart, from centre to centre, and 

 6 balks are used instead of 4. In other cases the distance between the centres of the supports 

 varies from 11' 8" to 16' Yi', according to the method of construction and the load to be crossed 

 over. 



I saw a bridge of 15 bays thrown over a lake, by cadets, in 45 minutes. In this time the 

 wagons were unloaded, the boats put together, &c. ; two of the bays were on Birago trestles, 

 and two on Birago pontons. 



The canvas ponton, with its cover, complete, weighs 720 pounds. 



Floatation of each ponton, 13,428 jjounds. 



Weight of flooring, &c., of one bay, 1,476 pounds. 



