OF GUN-METAL. *45

101. Mortars are moreover liable to an accident thatdefeats every good purpose expected from the use of them ;viz. the bursting of the shell in the mortar, or immediatelyon quitting it. This may proceed from a defect in the fuse,the negligence of the bombardiers in loading the mortar, ornot priming it before the fuse is set fire to, or from a hole inthe shell through which the fire from the explosion com-municates with the powder. When from either of thesecauses it bursts in the mortar, it generally renders it unfit forfurther service. Increasing the thickness of metal in mortars,whatever be the motive, will be always advantageous ; pro-vided they are not too unweildy: since in all fire-arms soli-dity adds to the justness of execution.

102.. The trunnions if equal in diameter to the femi-dia-meter of the mortar will be sufficiently strong : they shouldbe let into the bed throughout the whole length, or at leastthe points of support should be near the breech of the mortar;for when they are supported only by the extremities, theyare liable to bend and break, as has frequently happened.

103. Mortars are made of different diameters according tothe uses for which they are designed ; those from 15 to 20inches, are for throwing stones to retard the progress ofthe besiegers, and are never fired to a greater distance than35° yards, as in longer ranges, the stones are too muchscattered to do execution j their chambers therefore are in

*form of a truncated cone, with the greatest base towards themuzzle and contain but little powder. This mortar havingno great effort to sustain,' may be less reinforced: thethicknesses allotted for stone mortars will answer for everypurpose in which it is used, as in throwing lire balls, car-casses, &c.

104. Thirteen inch mortars, with chambers spherical,elliptical, or in form of a pear, are designed for throwingshells to destroy magazines and other military edifices. Ifit be wished by increasing the range to add to the effects ofthe shell by the height of the fall, the spherical chamber isthe best; but then it is necessary to increase the thicknesses ofmetal, to insure proper resistance and solidity. In the lastcentury, 20 inch mortars were made with curvilinear cham-bers to fire from very great distances, that the shells mightfall with irresistible force on magazines and other buildings:but their excessive weight has caused them to be disused inland service: even 15 inch mortars are very difficult to work

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