286 SERVICE OF ARTILLERY

against the enterprises of the enemy; and then in the sidesof the canal excavate one or two chambers large enough tomake a breach in the wall. In every cafe, the miner shouldbe secured against the attacks of the garrison, by posting somegrenadiers at proper places, and it necessary/ by raising anepaulment across the ditch to the foot of the wall; whichmay be easily effected under cover of a fire of musquetry,by the means of wool-packs or mattraffes.

90. When the gates of a town through the negligence or •ignorance of the garrison are insufficiently guarded, or badlyconstructed, they are sometimes forced open by petards tit is the business of the artillery-men to fix them : they aresupported by the detachment of infantry intended to rushinto the town the moment the gates are burst open.

The party destined for this service approach secretlyduring the night, and screw an iron hook into the gate*on which they hang the petard with its bottom fiat againstthe gate, and propped behind by a strong iron fork: thefuse is then set fire to, and as soon as the petard takes effect,the column of infantry rushes in. As the opening madeby the explosion of the petard may not be large enough toadmit the men, some carpenters should be in readiness withtheir axes to cut away any obstruction.

yi. Blockades are so termed when the besieger havinginvested a place, and carried on regular approaches, suspendshis operations either through choice or necessity ; confininghimself to keeping up a sire from his artillery. This me-thod of attack is practised in the following cases :

1. When a town is unprovided with casemates andmagazines : whence the besieger may have reason tohope that by keeping up a continual fire, the inhabitantsmay be so harrasied as to rife against the garrison; orat least, that a part of the ammunition and provisionsmay be destroyed.

2. When a town full of inhabitants, strongly fortified,and well'provided with troops, artillery, and ammu-nition, is destitute of sufficient supplies of provisionsto sustain a siege ; from which circumstance, the gover-nor may in a short time be induced to surrender, pro-vided that by the investiture his conduct is apparentlyjustified.

3. When from morasses, inundations, rocks, ravines,or precipices, it is found impracticable to carry on thy

approaches