The usual method by which the guns take part in the firings while in line, is by two discharges from each piece, previous to the firing of the regiment; but this is usually regulated by the commanding officer, before the review. Though the guns when in line with a regiment in review, always remain in the intervals; in other situations of more consequence, every favorable spot which presents itself, from which the enemy can be more effectually annoyed, should be taken advantage of. In column, if advancing, the guns must be in front; if retreating, in the rear of the column. If in open column of more than one battalion, the guns in the centre must be between the divisions, and when the column is closed, these guns must move to the outward flank of that division of the column, which leads the regiment to which they are attached. In changing front, or in forming the line from column, should the guns be on that flank of the battalion on which the new line is to be formed, they will commence firing to cover the formation. In retiring by alternate wings or divisions, the guns must be always with that body nearest the enemy. That is, they will not retire with the first half, but will remain in their position till the second half retires; and will then only retire to the flanks of the first half; and when it retires again, the guns will retire likewise, but only as far as the second half, and so on. When in hollow square, the guns will be placed at the weakest angles, and the limbers in the centre of the square. In passing a bridge or defile in front, the guns will be the first to pass; unless from any particular position they can more effectually _enfilade_ the _defilé_; and thereby better open the passage for the infantry. But in retiring through a _defilé_, the guns will remain to the last, to cover the retreat. _General rule_--with very few variations, the guns should attend in all the movements of the battalion, that division of it, to which they are particularly attached; and every attention should be paid in thus adapting the movements of the guns to those of the regiment, that they be not entangled with the divisions of the line, and never so placed as to obstruct the view of the pivots, and thereby the just formation of the line; but should always seek those positions, from which the enemy can be most annoyed, and the troops to which they are attached, protected. If at any time the battalion guns of several regiments should be united and formed into brigades, their movements will then be the same as those for the artillery of the park. ARTILLERY _of the Park_--The artillery of the park is generally divided into brigades of 4, 6 or 8 pieces, and a reserve, according to the force and extent of the from of an army. The reserve must be composed of about one-sixth of the park, and must be placed behind the first line. If the front of the army be extensive, the reserve must be divided.