igo of projectiles.

this work, is a slight tremulous motion in the point of im-pact, incapable of producing the least separation os the parts :so much does its mass exceed the mass of the Ihot. Thereis in this cafe no method of making a breach but bymining, however tedious or difficult the operation may be.

181. There are three Ways in which works that yield tocannon balls (180) may be destroyed :

i. By separating the constituent parts, when the shotcannot penetrate.

2- By penetrating without splitting or shivering them.

3. Or by producing both these effects at the fametime.

In the first case, the upper parts being by repetition of theshocks deprived of their base fall down ; as in walls builtvery solidly of haid stones, cemented with mortar: themore speedily to effect this, shot of the largest calibre shouldbe projected with the greatest initial velocity, and the gunsplaced very near to the object, and fired in salvos ; that theseveral shocks being made at the fame instant, may be themore efficacious. The 641b. shot formerly in use, werewell adapted to this purpose ; as they demolished the wallin a very little time, even with an initial velocity less by i~than that of a zrlb. shot; since from ihe greater quantity-of movement, they sooner separate and open works of ma-sonry (Treatise on Moving Bodies, 370, 371,372). Theseobservations on wails conllructed of hard stone and lime, arein some degree applicable to works cut out in soft or friablestone; with this difference that the upper part of the rockbeing by its nature firmly fixed in the ground, is less shakenthan a wall supported by earth, which though an adjunct,is little affected by the shock; whereas, the rock being onebody, the shock is communicated to its whole mass ; and isso generally diffused, as to be almost insensible. Supposingthe two works to be of equal tenacity, that cut out of therock will suffer less from the shot.

182. Works are destroyed in the second manner (i8l.No. 2) when the shot penetrating to different depths, disu-nite the contiguous parts; as in turf, earth, &c. The for-mula /S "Or? (246), serves to determine precisely thepenetrations of shots of different diameters, into works ofthis kind: she penetration of a 32IK shot, which with an initialvelocity os 1517 feet, impinges on a work of this fort, is tothat of a 4>b. Ihot, with the velocity of ioxo feet, as 5. 760

x J517 2 :