OF GUN-METAL.

146

upon batteries, and the shell is very unweildy; they arcprincipally used at sea in bomb-ketches, for the purpose ofbombarding maritime places from great distances.

105. Ten inch mortars are very useful in attack and de-fence, for dismounting the enemies cannon and demolishingtheir works and buildings; they are not expensive and easilyworked: the best form for their chamber is cylindric; it being<?f great importance that the firing from them should be veryexact, they should be well reinforced to enable them to resistthe shock of the shell and increase the solidity. Mortarshave been likewise constructed of 5s and 4} inches in calibre;they range but a short distance and require the greatest accu-racy and precision. It may be inferred from these remarksthat mortars cannot be made lighter without considerablydiminishing their effects.

CHAP VII.

Of Casting Artillery.

106. There must be a combination of several cir-cumstances to insure success in casting artillery : unless themetal be of good quality and properly proportioned, theguns may be defective, perhaps useless ; and though muchdepends on science and experience, yet chance has fre-quently no small share in the event. The principal motivefor examining and subjecting guns and mortars to variousproofs before they are declared sit for service, is the uncer-tainty under which the most able founders have at all timeslaboured on this head ; and among the several experimentsmade to ascertain their goodness, there are some which wouldbe highly absurd, were they not intended for the detectionof artifice or ignorance.

107. To succeed in casting guns and mortars there must be:

1. A perfect connection between the metallic par-ticles ; which depends en the degree of heat and fusionwhen the metal is run from the furnace into the moulds.

2. An exact mixture of the several metals.

3. A most accurate preparation of the moulds.

4. No vacuity in any part of the bore of the gun,lhat may render it dangerous to the men that serve it.

108. la