3d. Fire at the most prominent parts of the masonry left standing; beginning always at the bottom and gradually approaching the top. 4th. Fire into the broken mass with howitzers until the breach is practicable. 5. How long would it take to make a breach of 20 yards in length? Breaches of more than 20 yards in length have been opened by way of experiment, and rendered practicable in less than ten hours, by about two hundred and thirty 24-pdr. balls and forty shells in one case, and by three hundred 18-pdr. balls and forty shells in another. 6. How many discharges can an iron gun sustain? An iron gun should sustain twelve hundred discharges, at the rate of twelve an hour; but whatever may be the rate of fire, it is deemed unsafe after that number of discharges. As many as twenty an hour have been made for sixteen consecutive hours. [Sidenote: 40]] PART I. SECTION VIII. ON FIELD GUNS AND BATTERIES. 1. What proportion of artillery should be allotted to an army in the field? The proportion of artillery to other troops varies generally between the limits of one and three pieces to 1,000 men, according to the strength of the army, the character of the troops composing it, the strength and character of the enemy, the nature of the country which is to be the theatre of the war, and the character and objects of the war. 2. What regulates the selection of the kinds of artillery and the proportion of the different kinds in the train? Similar considerations to those specified in the foregoing answer. The following principles may be observed in ordinary cases: { ¼ are 12-pdrs. 3 pieces to { ⅔ guns, of which { ¾ “ 6-pdrs. 1,000 men. { { ¼ “ 24 or 32-pdrs. { ⅓ howitz., of which { ¾ “ 12-pdrs. 3. What is a field-battery? A certain number of pieces of artillery so equipped as to be available for attack or defense, and capable of accompanying cavalry or infantry in all their movements in the field. 4. How many pieces are allotted to a field-battery? Four guns and two howitzers. [Sidenote: 41]] 5. Are all field batteries alike? No; field batteries accompanying infantry are composed of the heavier, and those accompanying cavalry of the lighter pieces, the first manned by foot-artillery, and the latter by horse-artillery. 6. In what respect does a battery of horse-artillery differ from one of foot-artillery? The main difference consists in the cannoneers in a battery of horse-artillery being mounted; in rapid evolutions of foot-artillery they are conveyed on the carriages. 7. What is the composition of a field-battery on the war establishment? KIND OF BATTERY. 12-PR. 6-PR.