=77.= =Opening Fire.=--The batteries having been completed and armed, the magazines finished and supplied, and the parks, depots and communications put in such order that the batteries can be kept fully supplied with ammunition; the fire of the batteries is commenced simultaneously, the signal being given by a gun from some selected battery. The fire once opened is continued day and night during the siege, unless stopped by the commanding officer or from inability to keep it up. It usually begins at daylight, in order to enable the ranges to be corrected by the first shots, before the defence has accurately located the batteries unmasked during the preceding night. To open fire from a few batteries before the others are ready is inexcusable, as it enables the defence to concentrate its fire upon them and destroy them in succession. The targets of each battery and gun and the rate of fire are prescribed before the fire is opened, and these are changed only by subsequent orders or from sudden emergencies. The fire is as a rule deliberate, seldom exceeding an average of 4 shots per hour for each gun by day, and 2 per hour at night. This rate may be increased or diminished by the commanding officer for special reasons and for a limited time. The fire of the batteries is directed upon all the works of the place within range, but with greater vigor upon the more important, and especially upon those near the point of attack. The fire against powder-magazines and storehouses should be uninterrupted, to prevent the removal of powder and munitions. If the artillery of a part of the work is silenced, the fire upon it may be slackened, but some fire, especially vertical, should be kept up. At night the fire is directed against the larger targets, such as communications and covers, rather than upon the guns; but the fire against the interior of the place (especially a city) is kept at about the same rate day and night. If preparations for a sortie are detected, the fire of the large pieces is directed at the points of assembly, when known, and at the openings through which the sortie is to be made. The field guns direct their fire upon the troops in accordance with the tactical use of this arm. If the batteries of the first artillery position have the proper preponderance over those of the place, they should soon clear away the advanced posts, and keep down the fire of the works so that the besieger may advance his outposts, control the exterior ground and prepare to open the first parallel and establish the second artillery position.