﻿b ON CONSTRUCTING CANNON OF GREAT CALIBER. 



The foregoing statement and comparison, however, do not present the whole case; 

 for they are made upon the supposition that the charge of powder, in each instance, 

 is as the square of the diameter of the shot, or that the cartridges of the 2 and the 

 10 inch guns are of the same length. This, if we take the charge of the small gun 

 at i of a pound, would give but 81- pounds for the large, or ts of the weight of the 

 shot. The velocity obtained from this charge would produce neither range nor practi- 

 cal effect, and to obtain these results, that is, 1,600 feet a second, we must either 

 increase the force through the whole length of the gun to 5 times that required for 

 the small gun, or, the force remaining the same, Ave must proAide for its acting 

 through 5 times the space. Neither of these conditions can be practically accom- 

 plished. However, by an increase of both the charge and the length of the bore, the 

 result may, in the limits under consideration, be attained. Thus, taking the large 

 bore, if we double its length and make the cartridge 5 times as long, increasing the 

 weight from 81 to 41| pounds, — or perhaps, having an advantage from the com- 

 parative diminution of windage and the better preservation of the heat, with a charge 

 of from 30 to 35 pounds, — we may obtain the full velocity of 1,600 feet a second. 

 But this again increases enormously the strain upon the gun. 



It does not appear obvious, at a first view, how an increase in the charge should 

 increase the tension of the fluid produced from it, if the cavity enclosing it be propor- 

 tionably enlarged. If a steam-pipe a foot long will sustain the pressure of a given 

 quantity of steam, of a given temperature, a pipe two feet long, of the same thickness 

 and diameter, will sustain the pressure produced by a double weight of steam from the 

 same boiler. Why then should the pressure upon a cannon be increased by a double 

 length of cartridge 1 The difference seems to be this ; with the steam, the pressure 

 is as in a closed canity ; with the powder, the tension depends upon the movement of 

 the shot whUe the fluid is forming. Now, whether the charge be large or small, the 

 motion of the shot commences while the pressure is the same in both cases, and 

 before the charge is fully burned, and with the same velocity in both cases; but with 

 the large charge the fluid is formed faster than with the small, Avhile the enlarge- 

 ment of the ca\ity by the movement of the shot is nearly the same in both cases. 

 This destroys the proportion between the sizes of the two cavities, and the tension 

 must increase faster, and become greater, from the larger charge. The law of this 

 increase cannot, from the complicate nature of the problem, be stated with any reliable 

 exactness, but we may, I think, conclude, from the increased velocity of the shot, and 

 many other effects, that the stress thrown upon the gun by different charges of 

 powder, within ordinary limits, will not vary essentially from the square roots of 



