021v - - - - - [continued]
Others place two well—staked poles into the earth in such a way that the one is as far from the edge of the cannon’s mouth as the other. And underneath they place the above—mentioned ruler. Then when want to fire the cannon at night, they push their cannon straight towards the above—mentioned ruler and make it so that the edge of the mouth rests on the end of the aforesaid ruler. Next, they measure with a ruler, or a similar tool with measured intervals, from one pole to the side of the cannon and if it is too close or too far, they adjust the canon and make it the same distance as from the other pole.
Unspiking your cannon
Some people say that one should remove the cannonball if the cannon is loaded and introduce fire into the mouth of the cannon. But it is probable that the fire will leave again through the mouth rather than seek its exit through the touch hole which is spiked and restricted. The most reliable way is that the cannoneer, who is often a founder, drive in a nail and turn back the point of the nail that the enemies placed therein, and with a trephine, make another touch hole at the side of the spiked one, which can be done in an hour. And if with time the violence of the powder loosens the nail that the cannon was spiked with, you will make a nut in the second touchhole and place a screw in it, so perfectly that it will never come undone.
Defense of a town
There is nothing more efficient for defending a breach than mortars placed at the front line, as soon as the initial assault. They carry a lot of ammunition and are filled with cart nails, big steel dice, bits of chains and similar items. And when one senses that the enemy is close, one lights everything on fire. Grenades, well—constructed and thrown at the right moment, also cause much damage. And to make them worse, one can add some roughly crushed glass, either in the mold or in the crucible, when one casts them. This worsens the wounds. The grenades must not be too brittle, but it is good that they be somewhat alloyed with the material of the grenade so that instead of breaking up, they resist shock better and inflict more violence.