from the gap. Fifty men being put to each tackle, the frames were lowered down to cross each other at H. Gang boards were then shoved out, and men sent to put in key-bolts, previously prepared a ridge-piece was then fixed in the fork H, the beams laid,

We might add to these descriptions an account of the operations

of the staff corps, in repairing two arches in the bridge at St.Jean-de-Luz, which the enemy, after their defeat on the Nivelle, had broken down ; but we should only repeat in substance what is here given in sufficient detail. We go on, therefore, to notice other exigencies for which every leader of an advanced corps ought to be prepared-such as his arrival at the bank of a narrow but deep river, where there is neither a bridge nor any ostensible means of forming one-where boats are not to be had - and

only a few trees grow, all of them too short to be stretched from one bank to another. If, indeed, there be one tree within reach long enough to stretch across, he is safe enough. He has only to fell it into the water, confining the trunk to its own bank, and letting the current force the head round to the opposite side. The branches will be sure to get jammed there with great force, which will assist the natural buoyancy of the tree in carrying weight. But we assume that, though there are trees, none happen to be of sufficient length to effect this object. What is the officer to do?

'If the river be too wide to be spanned by one tree, and that two or three men can, in any manner, get across, let a large tree be felled into the water on each side, and placed close to the banks, opposite to each other, with their heads upwards. Fasten a rope to the head of each tree confine the trunks - shove the heads off to receive the action of the current, and ease off the ropes, so that the branches may meet in the middle of the river, in an angle pointing upwards: the branches of the trees will be jammed together by the force of the current, and so be sufficiently united to form a tolerable communication, when a few of the upper branches are cleared away. If insufficient, towards the middle of the river, to bear the weight of men crossing, a few stakes, with forks left near their heads, may be thrust down, through the branches, to the bottom of the river, and hitched to the main branches of the trees; or the force of the current may be made to yield vertical support to the communication, by applying a few planks, forming a plane, inclined to the surface of the current in an angle of about 50°: by this means, that power which, in the flying bridge, acts horizontally, may be obtained vertically, in a manner that will greatly add to the stability of the rough structure.'

Another ingenious method of constructing a bridge in a hurry is this. An officer has at his disposal a pair of wheels, —a gun carriage will do,-connected by the axle-tree, a few beams, and a sufficiency of rope. He fastens the ends of two beams, A B and C D, to the axle on one side, and to the beams A D, on

Η

the other he regulates the opening A G D according to the known breadth and depth of the impediment to be surmounted, and prepares his floor of a few light planks. It is laid, and at a convenient season the whole machine is run up from the rear, and

pushed forward into the river or ditch, till the extremity CC mainly rests upon the near edge. The wheel is thus in the middle. of the water, and by letting go the line which keeps G A C in an elevated position, that section of the bridge falls, and a communication between the opposite sides is established. The merit of this invention belongs to the late Lieut.-Gen. Sir William Congreve, of the Royal Artillery. He meant his bridge to attend columns of attack in the assault of field works, on which occasions we doubt not that it would prove very serviceable.

Suspension bridges are important chiefly as establishing the communication of an army with its rear, and enabling it to pass rivers which the enemy have long abandoned and of which we are therefore in full possession. The principles on which they are constructed demand no elucidation at our hands. They do not vary, whether the bridges themselves be designed to facilitate warlike operations or peaceful traffic. One great difference, however, is found in them-that whereas the civil engineer has iron rods and ties at his disposal, the military artificer is obliged to depend upon ropes and timber. One of the most beautiful specimens ever executed of bridge architecture of this sort was presented to the admiring gaze of the British army in 1812. Sir Howard has made it the frontispiece to his treatise. We cannot do better than leave to him the pleasant task of describing it.

'One of the principal arches of Trajan's bridge across the Tagus, at Alcantara, having been destroyed by the French, Lord Wellington found it necessary to direct that a communication over that bridge should be re-established, for the purpose of bringing up artillery and stores from Badajos for the attack of the forts at Salamanca. Timber of sufficient dimensions to effect this could not easily be procured; and, indeed, any application of that material to make good such a fracture would have been extremely difficult, and required much labour to be performed on the spot in fashioning, framing, and setting-up the work; and which, consequently, would have given warning to the enemy before the campaign opened of some important movement in that quarter being intended.

To obviate these difficulties and objections the officer sent in April, 1812, to make preparations for this operations- a man of fertile genius and great practical knowledge-happily devised an application of cordage, which might be prepared secretly and even in privacy at any distance from the place at which it was to be used; it might also be easily transported thither entire, and speedily stretched across whenever it might be required. The formidable impediment was very nearly 100 feet wide. The materials of which this extraordinary work was constructed were as follow:

1. 4 beams of poplar, each 30 feet long, 12 by 8 inches.
2. 8 ditto, each 20 feet long, 6 inches square.

quaintance with the principles on which a system of beams is combined for the purpose of forming the roof of an ordinary building, an officer will experience little difficulty, provided there be adequate means at his disposal, in connecting the piers of a ruined bridge upon a river of which both banks are in his possession. But, in following up an enemy, this can seldom be the case, and then it is that the skill and ingenuity of the engineer are taxed. Listen to Sir Howard, and examine at the same time his diagram, of which we subjoin a copy.

'In restoring, by carpentry, communications across broken arches, and (as in following up a retreating army) when only one side of the impediment can be got at, the great difficulty is to get the first beam across the gap. The method of effecting this was frequently resorted to in the Peninsula. For this a pair of wheels and an axle-tree are sufficient; and the process is so incapable of

injuring them, that gun or waggon wheels, or limbers, may with great propriety be used, taking care, if a limber, with its shafts (the ammunition boxes being removed), is employed, to lash two beams (one of which, A B, only appears in the figure) to the shafts, so as to project beyond the wheels. Then, the beam C, to be laid over, be placed on skids sufficiently high, the carriage, with the beams A fixed as described, is backed till the axle-tree is a little within one end of the beam C: the beams A are then elevated, at the ends where the men are, in the figure, till their opposite points are so much depressed as to admit of the cross-beam B being placed underneath the beam C, which is to be laid across the impediment. The lever A is then worked downwards, and as soon as the beam is lifted, the whole is easily moved forward to the edge of the gap, where a high sill should be laid, to prevent the wheels from approaching too near.'

Again:

'The stone bridge across the Coa at Almeida, having been destroyed by the French in their retreat, and a passage across the river there being necessary for the operations of the allied army, a communication was established in the following manner :-Notches A, B were made in the masonry, and two frames, A F, BE, eased down, vertically, from the edges of the gap, in the upright positions A F, B E, resting upon the notches A, B. Two tackles, applied to each frame, led to ring-bolts set in the masonry at about 30 feet

from the gap. Fifty men being put to each tackle, the frames were lowered down to cross each other at H. Gang boards were then shoved out, and men sent to put in key-bolts, previously prepared: a ridge-piece was then fixed in the fork H, the beams laid,

braces 1, 2, 3 put in, and the communication served without shake or failure.'

We might add to these descriptions an account of the operations

of the staff corps, in repairing two arches in the bridge at St.Jean-de-Luz, which the enemy, after their defeat on the Nivelle, had broken down; but we should only repeat in substance what is here given in sufficient detail. We go on, therefore, to notice. other exigencies for which every leader of an advanced corps ought to be prepared-such as his arrival at the bank of a narrow but deep river, where there is neither a bridge nor any ostensible means of forming one-where boats are not to be had- and