OF PROJECTILES. 2ZI

vice : the bombardiers having been already trained at theschool os practice (233) will be enabled to execute withprecision and efficacy the order they receive.

243- In bombarding military edifices, the shells may fallon solid works of masonry, built upon arches, or on softsubstances, as earth, &c. with which arches are frequentlycovered, to secure them from shells. When they fall onsolid works of masonry, they tend by their shocks to pene-trate and split the casemates, and by their explosion to over-turn the counterforts, and shatter the walls.

Arches constructed on the principles laid down in thefirst ami second books of Military Architecture, are capableof resisting the most violent shocks from 13 inch shells: theirresistance increases when they are constructed of the bestmaterials, in a climate favourable to their acquiring greattenacity ; and when they are contiguous to solid and im-moveable bodies.

In buildings totally detached from others, or built oneminences, the counterforts should be so proportioned, asnot only to resist the pressure of the vaulted roofs, but everyshock to which they may be exposed from shells.

244 All the effect of a shell falling upon a solid work ofmasonry built on arches, is reduced, if the arch be wellturned and made of choice materials, to a small excavationin the place where it falls: it even often happens that theshell breaks before it bursts, particularly when cast of brittleiron. But if the arch be not firmly supported, the counter-forts not sufficiently solid ; or in insulated buildings not well'proportioned to resist the (hock, and the unnecessary thicknesswhich masons generally give to the arches, under the ideaof rendering them impenetrable; the substances in too smalla mass, as in detached powder magazines ; or the stone ofof so elastic a nature, as considerably to increase the shock ;(Treatise on Moving Bodies] in all these cases the shellswill produce the desired effects. A shell on - penetrat-ing a brick arch, makes a hole nearly circular, if thebricks be of a good quality : but if horn the negligence orignorance of the workmen, the materials be bad or badlyworked up; or if o wing to the climate, they have notacquired a sufficient degree of tenacity, the shell, beside ma-king a hole, will split and shatter the building.

245. Shells falling on arches covered with earth or other softmaterials (243) bury themselves without doing any mate-P 4 rial