IN TIME OF WAR.

z 79

then destroy the communication with tools, and afterwardswith a chamber, which will effectually deprive the besiegedof all access.

When there are two stages of countermines, and theminers in penetrating into the upper one, find the ventilatorsbelonging to the lower stage; they should throw in suchquantities of fetid combustibles as will render it impossible forthe besieged to remain in them, taking the precaution to closethe ventilators, that they may not be incommoded by thesmell and smoke, which in these fubteraneous operations areextremely pernicious.

74. It has hitherto been suppose that the ground aroundthe place is nearly level: but when the fortress is built on atongue of land, so that the front of the attack be termi-nated on each side by a deep ravine, the miners may thendrive a (haft below the countermines, and those parts of theoutworks on which the batteries are to be erected ; andmake some chambers for blowing up the works, or at leastdestroying the countermines : or, if the place be situated onan eminence, and the slope of the glacis such that the minerscan drive a shaft below the countermines and penetrate underthe points where the second batteries are to be erected, ad-vantage should be taken of these circumstances..

It Ihould in general be understood, that whenever anysubterraneous work of great extent is carrying on, a gallerymust be made to give a free circulation of air ; but in limitedoperations, a branch which is sooner made will answer everypurpose.

74. If the besieged make no attempt to destroy the shaftsin the covered way (73), it is a sign either that they areignorant of their duty, or are seized with dismay ; where-fore, if the miners meet with any of their galleries instead ofempoisoning them, they should enter them and advancetowards the doors that lead into the ditch ; and supported•by a second detachment proceed into the large gallery on eachside, till they have passed beyond the front of the attack,and destroyed the gallery in everv part by which the besiegedcan re-enter the countermines: when there are two stages,they should endeavour to descend into the lower one, andapproach the doors that lead immediately to the body of theplace ; this gallery should also be destroyed with the greatestexpedition. Having thus taken possession of the counter-

S 4 mines,