MECHANICS AND USEFUL AKTS. Ill 



long shot not only strains our guns excessively, but loses us much 

 of the useful effect of our powder. 



The initial pressure of the powder gas is less in the American 

 gun than in the English, from the less load per square inch of 

 area of bore which the ball imposes. The bursting or damaging 

 action is therefore less, while the dynamic value is greater, 

 precisely the effects which we wish to produce, as our object is 

 not to burst the gun, but to propel the shot. 



It has already been explained in these pages how we may, tiy 

 the aid of piston shot and other devices, best expend the energy 

 of a projectile in producing penetration of armor or other intend- 

 ed effects. Heretofore the difficulty has been how to impart the 

 requisite amount of energy to the shot, and two systems for doing 

 this have been propounded, the English high-pressuro system, 

 "with which it is almost impossible to avoid the bursting of the 

 gun, even when of wrought iron, and the American low-pressure 

 system, in which the want of pressure is compensated by increased 

 area of bore, and by which cast-iron guns may be used with com- 

 parative safety. Of course, there is nothing to prevent the Ameri- 

 can principle from being produced in wrought iron as well as in 

 cast ; and no one would contend that the wrought iron would not 

 be better. But whereas we have adopted a system which has 

 already brought us up to the limit of our best materials, the Amer- 

 icans have adopted a system which, while realizing greater 

 dynamic power, has not yet brought them to the limit of their 

 worst. It is almost an insult to our intelligence to ask us which 

 system is to be preferred. Engineering. 



We will briefly observe that the big monitor smooth bore, the 

 identical gun installed in our turrets over five years ago, at the 

 commencement of the rebellion, has shown that it can put its 

 shot through any iron-clad in the British nav\ T . 



Even if in future trials the Shoeburyness artillerists succeed in 

 bursting the American gun, it will not materially help their case, 

 as the important fact of the great power of large round shot 

 against armor plates has been fairly established. 



One of Captain Ericsson's communications to the government 

 of his native country on naval improvements has been made pub- 

 lic in Europe, and is highly instructive as to the merits of different 

 systems of heavy-gun making. The trial of the 20-inch guns at 

 Fort Hamilton, in March last, furnishes him with data for compar- 

 ing the performance of these guns with the best English wrought- 

 iron rifled cannon. By the trials at Shoeburyness, the initial 

 velocity of the 511 pounds rifled shot from the 13^-inch Armstrong 

 gun being 1,250 feet in a second, its actual force is computed 

 equal to 12^ millions of foot pounds ; since a body moving at a 

 velocity of 1,250 feet per second has the force acquired by a body 

 falling in vacua 24,414 feet, or 24,414 times enough to raise its 

 own weight 1 foot. On the other hand, the force of the 20-inch, 

 1,080 pounds shot, with the proved initial velocity of 1,400 feet, is 

 computed by the same rule at 82h millions of pounds. The area 

 of the English elongated shot exposed to direct atmospheric resist- 

 ance is 14o square inches, and that of the American spherical shot 



