﻿ON CONSTRUCTING CANNON OF GREAT CALIBER. 15 



Now a bar of cast-iron 1 inch square weighs 3.2 pounds to the foot in length ; we 

 have then 10,000 X 3.2 = 32,000 pounds' pressure to each square inch of surface, or 

 •H"*^ = 2,133 atmospheres, on the supposition that the whole action of the powder 

 is equal to its maximum force through one third the bore of the gun. If we take the 

 whole action as equal to it maximum through two thirds of the bore, the column, 5,000 

 feet high, gives 16,000 pounds, or 1,066 atmospheres. It cannot be less than this, 

 and although it may never come up to the greater number, or 2,133 atmospheres, it 

 would not be safe to estimate it at less when providing the means to resist it. We 

 require, then, a pressure of 32,000 pounds to the inch, to obtain for a 14-inch shot 

 an initial velocity of 1,600 feet a second. We have seen that a gun formed as I 

 have proposed will be capable of resisting a pressure of 63,960 pounds to the inch, 

 or very nearly twice the pressure required to produce the velocity sought, while with 

 a gun made in the usual way, of one piece of cast-iron, the power of resistance is 

 limited to 20,000 pounds to the inch, or less than two thirds that which may be re- 

 quired to obtain the velocity. 



We have seen that a cannon constructed in the manner recommended, of what- 

 ever size, having its walls equal in thickness to the diameter of its bore, will sustain 

 a pressure of 63,960 pounds, equal to a column of fluid iron 20,000 feet high, very 

 nearly. This is half the strength required to support a cokimn capable of keeping up 

 a continued stream with a velocity of 1,600 feet a second. Suppose that we construct 

 such a cannon with a bore of 30 inches, and of such length that the ball shall receive 

 the force of the powder while it moves through a space of 10 feet, and that this force 

 be equal to a constant action of 4,266 atmospheres through 40 inches. It Avill be at 

 once perceived that it will impress the above velocity upon a cylinder -^ = 20 inches 

 long, or upon its equivalent, a sphere 30 inches in diameter. Such a sphere of 

 solid iron will weigh 3,670 pounds, and at this point the calculated power of the 

 gun meets the force required to give a velocity of 1,600 feet a second. 



Although this size may be beyond practical reach, the contemplation of it as a 

 theoretical perfection may stimulate us to attempt an approximation to it. A ball of 

 a ton weight, with a range of, say 6 miles, would, as a mere display of mechanical 

 force, be Avorthy of a great effort. 



The following columns show the stress that the several kinds of guns, as men- 

 tioned, Avill bear, by calculation, and the pressure required to give the velocity of 1,600 

 feet a second. The third column shows the proportion between the required and the 

 actual strength. 



