The attack is first opened by a cannonade; light troops are sent forward to annoy the enemy, and, if possible, to pick off his artillerists. The main body then advances in two lines: the first displays itself in line as it arrives nearly within the range of grape-shot; the second line remains in columns of attack formed of battalions by division, at a distance from the first sufficient to be beyond the reach of the enemy's musketry, but near enough to support the first line, or to cover it, if driven back. The artillery, in the mean time, concentrates its fire on some weak point to open a way for the reserve, which rushes into the opening and takes the enemy in flank and rear. The cavalry charges at the opportune moment on the flank of the enemy's columns or penetrates an opening in his line, and cutting to pieces his staggered troops, forces them into retreat, and completes the victory. During this time the whole line of the enemy should be kept occupied, so as to prevent fresh troops from being concentrated on the threatened point. The following maxims on battles may be studied with advantage:--1st. _General battles_ are not to be fought but under the occurrence of one of the following circumstances: when you are, from any cause, decidedly superior to the enemy; when he is on the point of receiving reinforcements, which will materially effect your relative strength; when, if not beaten or checked, he will deprive you of supplies or reinforcements, necessary to the continuance or success of your operations; and, generally, when the advantage of winning the battle will be greater than the disadvantage of losing it. 2d. Whatever may be your reason for risking a general battle, you ought to regard as indispensable preliminaries,--a thorough knowledge of the ground on which you are to act; an ample supply of ammunition; the most perfect order in your fire-arms; hospital depots regularly established, with surgeons, nurses, dressings, &c., sufficient for the accommodation of the wounded; points of rendezvous established and known to the commanders of corps; and an entire possession of the passes in your own rear. 3d. The battle being fought and _won_, the victory must be followed up with as much alacrity and vigor, as though nothing had been gained,--a maxim very difficult of observance, (from the momentary disobedience which pervades all troops flushed with conquest,) but with which an able general will never dispense. No one knew better the use of this maxim than Napoleon, and no one was a more strict and habitual observer of it.