﻿10 ON CONSTRUCTING CANNON OF GREAT CALIBER. 



US, we caniiot fail to perceive how impossible it must be to increase the strength of 

 cast-iron cannon, in any useful degree, by an increase of their thiclmess beyond that 

 now given to them.* 



Now, to obviate the great cause of weakness arising from the conditions before 

 recited, and to obtain, as far as may be, the strength of wrought-iron instead of 

 that of cast-iron, for cannon, I propose the following mode of construction. I propose 

 to form a body for the gun, containing the caliber and breech as now formed of cast- 

 iron, but with walls of only about half the thickness of the diameter of the bore. 

 Upon this body I place rings or hoops of wrought-iron, in one, two, or more layers. 

 Every hoop is formed with a screw or thread upon its inside, to fit to a corresponding 

 screw or thread formed upon the body of the gun first, and afterwards upon each 

 layer that is embraced by another layer. These hoops are made a little, say yoVoth 

 part of their diameters, less upon their insides, than the parts that they enclose. They 

 are then expanded by heat, and being tui'ned on to their places, suffered to cool, 

 when they shrink and compress, first the body of the gun, and, afterwards, each suc- 

 cessive layer all that it encloses. This compression must be made such, that, when 

 the gun is subjected to the greatest force, the body of the gun and the several layers 

 of rings will be distended to the fracturing point at the same time, and thus all take 

 a portion of the strain up to its bearing capacity. 



There may, at the first view, seem to be a great practical difficulty in making the 

 hoops of the exact size required to produce the necessary compression. This would 

 be true if the hoops were made of cast-iron, or any body which fractures when ex- 

 tended in the least degree beyond the limit of its elasticity. But wrought-iron and 

 all malleable bodies are capable of being extended without fracture much beyond their 

 power of elasticity. They may, therefore, be greatly elongated without being weak- 

 ened. Hence we have only to form the hoops small in excess, and they will accom- 

 modate themselves under the strain without the least injury. It will be found best 

 in practice, therefore, to make the difference between the diameters of the hoops 



* I leave out of consideration another source of weakness, which comes from the unequal shrinking of 

 the iron-casting. The heat from every casting is conducted away from the outside. Hence the outside 

 sets, while the inside remains fluid. When the inside sets, the cooler solid shell that surrounds it con- 

 tains more space than is required for the solid shrinking from the liquid state. This destroys the equi- 

 librium amongst the particles, leaving them upon the stretch, or in a state exactly opposite to that in which, 

 to give the greatest strength, they ought to be in, as we shall see hereafter. But the case, as I have 

 shown it from other considerations, is so strong, or rather the gun is so weak, that I do not estimate this 

 in this place, and only mention it in this note to show that I am aware of it, as all practical men must be. 



