﻿12 ON CONSTRUCTING CANNON OF GREAT CALIBER. 



diameter being three inches, is nine inches. Deduct from this the area of the caliber, 

 and we have eight circular inches. That is, the section of the iron is eight times 

 greater than that of the fluid ; whereas in the fonner case, of longitudinal section, the 

 iron gave but twice as much surface as the fluid ; and if we take, as before, the iron 

 at 65,000 pounds per inch cohesive foixe, it \\411 not be broken unless the force of the 

 fluid exceed 520,000 pounds. It will be fomid, upon a further examination, that 

 the relations of these sections to each other may be varied, as we take the diameter of 

 the caliber to be greater or less, as compared with the thickness of the sides, but their 

 difference can never be made less than as two to one. Here then is a principle, or 

 rather a fact, of the utmost importance in forming cannon of any material, the strength 

 of which is different in different directions ; for as a cannon made in the proportions 

 above specified, if the materials be in all directions of equal strength, will possess four 

 times as much power to resist a cross fracture as it does to resist a longitudinal fracture, 

 it follows, that a fibrous material which possesses four times the strength in one direc- 

 tion that it does in another, will form a cannon of equal strength, if the fibres be 

 directed round the axis of the caliber. It is this fact which gives the great superiority 

 to the various kinds of twist gun-bai-rels. For in these, although the fibres do not 

 enclose the caliber iu circles, yet they pass around it in spu-als, thus gi^ing their re- 

 sisting force a diagonal du-ection, which is vastly superior to the longitudinal direc- 

 tion in which the fibres are arranged in a common musket-barrel." 



The foregoing example supposes the cavity immovably closed at its ends, and gives to 

 the powder more force than it actually exerts, in gun-practice, to produce cross frac- 

 ture, compared with its force to produce lengthwise fracture, even at the part nearest 

 to the breech of the gun ; and as the recoil is resisted by the whole gun, the stress 

 upon any part will diminish as the inertia, or weight, diminishes from the breech to 

 the muzzle. 



"With these facts, principles, and laws, thus stated, I proceed to give some calcu- 

 lations to show the sti'ength of a cannon constructed in the way that I have pointed 

 out, as compared with one made in the usual manner. Take a cannon of 14 inches' 

 caliber, which wUl carry a spherical solid ball of 374 pounds, with sides 14 inches 

 thick, made up of 7 inches of cast-iron, and two hoops or rings, 3^ inches each, of 

 wrought-iron. The external layer of cast-iron wUl, from its position, as before ex- 

 plained, possess but one fourth of the strength of the inner layer, or whole strength 

 of the iron, and the mean strength of the whole wUl be reduced one half Take 

 cast-iron at 30,000 pounds to the inch area, and we have 30,000 X ^ ^ 15,000 poimds 

 to the inch. The thickness, of both sides, is 14 inches, and 15,000 X 14=: 210,000 



