Firing over friendly troops should be avoided as much as possible. Batteries that support an assault from a distance continue their fire upon the point of attack until it becomes dangerous to the assailants; they then either increase the range considerably in order to cover the ground beyond, or they direct their fire on other points of the enemy's line. Artillery does not fire at long ranges from positions in rear during a pursuit, on account of the danger to the pursuing troops; in such cases it should advance rapidly and endeavor to establish itself on the flanks of the enemy's line of retreat, where it will find the most advantageous positions. As a general rule, the fire of artillery is directed against that arm of the enemy which at the time is predominant, or which is capable of inflicting the greatest loss on the infantry or cavalry that the artillery is supporting. During the artillery duel the artillery generally avoids firing at the other arms; but if large bodies of infantry or cavalry appear in open ground within effective range a portion of the guns should be directed upon them. TARGET PRACTICE. The artillery that first finds the range will have a great advantage in the artillery duel, and in all cases its correct establishment is the first condition of accurate shooting. =Observation of Fire.=--Correct observation of the effects of fire is necessary in order to make the required corrections, and is indispensable to good shooting. It can only be acquired by much practice under the varying conditions of the wind, light, state of the atmosphere, background, foreground, and nature of the target, and is rendered more difficult in action by smoke and the liability of mistakes when more than one battery is firing at the same target. For medium as well as long ranges a good field-glass is required. As a rule, the observation is limited to ascertaining whether the shots are short or over. The observation of direct hits is unreliable except at very short ranges, or when palpable effects are produced in the enemy's ranks, limbers are blown up, or there are other manifest indications of the effect produced. When a target is on a height or behind a parapet, it is possible to distinguish hits on the slope of the hill or on the parapet, and to estimate correctly the error in range of the projectiles that fall short. There are no means of estimating the error in range of the projectiles that fall beyond the target, except when a battery is on an elevation and firing at a target on a plane below it; here shots striking beyond the target may be observed and the error estimated. When several batteries are firing at the same target, and it is difficult to distinguish the individual rounds, a fire by battery will give a group of shots that may be recognized.