AND PROOF OF GUNS. l6i

that the elasticity of the fluid in the charging cylinder isgreater in the strongest powder, though the pressure bywhich the shot is first put in motion be equal in bothcharges.

3. The resistance to the explosion of the powdertoward the mouth of the piece, is compounded of theweight and friction of the shot and wads : the resistancefrom friction ceases as soon as the shot and wads are in

• motion; but the resistance from the weight of the shotexists during the whole length of the piece, and isgreater as the elevation at which the gun is laid ishigher; this resistance may be calculated in the ratio ofthe right fines of the angles of elevation.

4. The fluid generated at the bottom of the bore onstriking the shot is reflected laterally against the sides ofthe gun with so much the more force, as the chargeoccupies a greater space, or as all the powder is moreinstantaneously inflamed: whence proceed orbicular cavi-ties, whenever the hardness of metal is not sufficient toresist the impulsion.

136. From the preceding remarks we may infer that;

1. The proof charge should never occupy less spacein the bore than the largest service charge.

2. The gun should be laid at a higher elevation thanwhen mounted on its carriage.

3. The powder should be stronger than what is gene-rally used, its quantity combined with the greatest re-sistance of the shot and wads, and proportioned to the

. largest service charge, in the ratio of the metal whencold, to the metal heated so as to fire powder (35).

4. If a shot made of a soft metal as lead, tin, &c.fcy any irregular movement proceeding from the strengthof the charge strike against the sides of the gun, it shouldbe unable to make the least impression.

1 37‘ The defects of a gun loaded in this manner will beas fully discovered in a few rounds as with a great numberfired in the common mode ; nor will there be the least rea-son to be apprehensive of bursting the gun, if it has beencast in the manner, and with the proportions already pre-scribed. When the guns have been thus fired, they shouldbe again subjected to the water proof and re-examined : andif any flaw that may prove detrimental to the service can bediscovered (133) they ought to be rejected.

138. There