=67.= =Precautions against Dampness in Magazines for Siege Batteries.=--Underground magazines of the character above described are, of necessity, sometimes damp. The only ventilation usually possible is obtained by leaving the door open, the air being changed more or less by the men going in and out. The passage leading to the powder-chamber should enter it at the middle, and in the service of the guns one half of the chamber should be emptied on one day and the other half on the next. This will usually limit the time which a cartridge is exposed to the dampness of the magazine to a maximum of one or two days. CHAPTER V. SIEGE OPERATIONS. THE ATTACK. =68.= Siege operations include all the steps taken from the first approach to the work up to its final capture. These taken in regular order are as stated in Chapter II: the _investment_, the _distant artillery attack_, the _construction of approaches_ and _parallels_, _breaching by artillery or mines_, and the _final assault_. For convenience in description the siege has been divided into three periods. The _first period_ includes the preliminary operations up to the completion of the investment. The _second period_ includes all the operations between breaking ground for the batteries of the first artillery position and the first parallel, up to the completion of the most advanced parallel and the occupation of a position near the foot of the glacis from which the attack is to be made upon the breach, either by assault or sap. The _third period_ comprises the advance from the last parallel, and all subsequent operations up to the capture of the last entrenchment and the surrender of the garrison. The first and second periods are sometimes known as the “_distant_” and the third period as the “_close attack_.” FIRST PERIOD. =69.= As a preliminary to the siege of any fortified place, all possible information is obtained as to the strength and character of its fortifications, the garrison, armament, stores of provisions and ammunitions, water supply, water routes, telegraph and railroad lines, manufactures, especially those which may be converted into factories of arms and munitions, the character of the population of the place, their probable food supply and their loyalty to their state; also the topographical features and nature of the ground in the vicinity of the work, the sites of camps and parks, the prevalent diseases of the locality and the best means of preventing their attacks, etc., etc. (see Bureau of Intelligence, Art of War, par. 128). From these data the necessary materials and supplies are collected at convenient points, the railroad or water routes selected, and the cars, boats, wagons, etc., for their transportation provided; so that they may arrive promptly and in the proper order when needed.