Burst the projectiles 50 yards short and about 6 yards (at medium ranges) above, the object aimed at. A rough rule for height of burst is height of burst in _feet_=the number of hundred yards in range. In firing at troops behind cover, such as banks, rising ground, or earthworks, burst the projectiles about 25 yards, or less, in front of, and from 7 to 10 feet above, the cover. =Shrapnel with Percussion-fuze= is generally used against moving targets, for rapid firing, and for firing over friendly troops; against enemy's troops in a village or woods; metal shields; and in cavalry combats as soon as the ground which was masked by one's own troops becomes cleared. Shrapnel gives the best results when the fire is distributed, a part of the target being apportioned to each gun. When the time-fuze is used, it will often be advisable to vary the elevation and length of fuze in each battery so as to cover about 200 yards in depth, and thus bring the enemy's supports and reserves, as well as his front line, under fire. =Canister= is used against living targets at close ranges. Its effect is largely diminished when the ground in front of the guns is rough or soft, and particularly when covered with brush or standing crops. It would be used against cavalry at 500 yards, and against infantry at 300 yards. =Order of Fire.=--The order of fire is habitually by piece in each battery, and usually commences on the leeward flank. It is the most effective, as the errors in the service of any one gun can generally be observed, and therefore corrected. Salvos, or the fire by battery, may be used to find the range under circumstances that render it difficult to observe a single shot, to avoid the inconvenience of smoke, and occasionally, instead of rapid fire by piece, to take advantage of quickly passing opportunities. The fire at will is only used in the defence of the guns at very short ranges. The fire by piece from one flank of a battalion to the other may be used to avoid smoke, or to enable the field-officer commanding the battalion to take personal charge of the firing in order to find the range under difficult circumstances, or to regulate the fire in exceptional cases. The fire by platoon is only used to facilitate the observation of fire under exceptional circumstances that permit two shots to be observed more easily than one, and also to increase the interval of time between successive discharges, to allow the smoke to drift away, without diminishing the amount of fire. In most cases the fire by piece or by battery is preferable to it. =Rapidity of Fire.=--The rapidity of fire is dependent on the range, the circumstances of the action, the facilities for the observation of the fire, and the amount of unexpended ammunition.