2d. The second system of formation, that is, a line of columns of attack on the central division for infantry, is by battalion, but for cavalry, by regiment. If the regiment is composed of eight squadrons, the column will contain four lines, two squadrons forming a division; but if composed of only six squadrons, the column will contain only three lines, and consequently will be six files in depth. In either case the distance between the lines should be that of a demi-squadron, when the troops are drawn up in battle array; but when charging, the divisions may close to a less distance. 3d. In forming a grand division of two brigades, by the third or mixed system, two regiments may be deployed in the first line, and three formed in columns of attack in rear of the flanks and centre, as is shown in Fig. 33, the sixth being held in reserve. This formation is deemed a good one. 4th. The fourth system, of deep columns of cavalry, is entirely unsuited for the charge, and this formation can only be employed for troops drawn up in reserve. The flanks of lines or columns of cavalry are always much exposed, and squadrons should therefore be formed in echelon on the right and left, and a little in rear of the main body, in order to protect the flanks from the attacks of the enemy's horse. Irregular cavalry is usually employed for this purpose. In the formation of a grand division in line of battle, care should be taken not to give too great an extent to the command of the generals of brigade. If the formation be in two lines, neither brigade should form an entire line, but each should form a wing of the division, two regiments of the same brigade being placed in rear of each other. This rule is an important one, and should never be neglected. It may also be laid down as a maxim, in the formation of cavalry on the battle-field, that the first line after the charge, even if most successful, may require reforming in rear of the second line, and that this last should be prepared to act in the front line after the first onset. The success of the battle frequently depends upon the charge of the final reserve of cavalry on the flanks of lines already engaged. It is on account of this frequent manoeuvring of the cavalry on the battle-field, its reforming for repeated charges, that great bodies deployed in full lines are principally objected to. They cannot be handled with the facility and rapidity of columns of regiments by divisions. The attack of Nansouty's cavalry, formed in this way, on the Prussian cavalry, deployed in advance of Chateau-Thierry, in 1814, is a good proof of this.