=84.= =Breaching batteries=, except those established on the crest of the counterscarp, can only breach the walls of modern forts by “curved” or “indirect” fire. To obtain the necessary angle of fall with the requisite accuracy and energy of blow, the guns must be of considerable size and placed at comparatively long range; the projectile must graze the crest of the glacis and strike the scarp wall at an angle not too oblique. Experience seems to indicate that the best effects are obtained, all things considered, when the vertical plane of fire makes an angle of from 55° to 60° with the face of the scarp wall. The distance of the battery from the wall to be breached is usually from 1000 to 1500 yards. The same considerations govern the construction and armament of batteries designed to destroy réduits, barracks, gorge walls, city gates, magazines, depots, bridges, locks, etc., etc. =85.= =Batteries of rifled mortars or of howitzers for vertical fire= should be so located, when possible, that the longest dimension of the target will be in the direction of their fire. The effect of their projectiles is greatest when they can be fired at elevations, of 60° to 70° and with large charges. These considerations, combined with those of good cover and easy supply, will govern their location. =86.= =Opening and conduct of fire from Second Artillery position.=--The batteries which are ready on the morning of the completion of the parallel open fire simultaneously upon the work, and are supported by those of the first artillery position still armed. The same rules govern the fire of the first and of the second artillery position. When the defence combines a number of batteries to silence one of the attack a heavy fire is concentrated upon these batteries by those from which the fire has been diverted. New batteries unmasked by the defence, or established in intermediate or other works, should receive prompt attention from the attack, with a view to silencing them if possible before they correct their ranges. It is of the first importance that the superiority of the artillery fire of the attack shall be established at the opening of fire from the first artillery position and be maintained throughout, and that the defence shall be prevented from repairing any batteries which have been silenced. To this end a few guns will keep up a slow fire upon these batteries so long as it may be necessary. Every gun of the defence must, if possible, be kept under a heavy fire, and the fire upon the enceinte must be opened at the earliest possible date and continued day and night, as previously described. =87.= =Musketry fire= will be opened as soon as a parallel is established at such distance as to make it effective; and this may be, for a well-regulated fire of sharpshooters, at ranges of 1200 to 1500 yards, or in some cases even greater.