1YO ANNUAL OF SCIENTIFIC DISCOVEKY. 



the fluid ; whereas, hi the former 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 force, it will not be broken unless the force of 

 the fluid exceed 520,000 pounds. It will be found, upon a further examina- 

 tion, that the relations of these sections to each other may be varied, as we 

 take the diameter of the calibre 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 iu 

 forming cannon of any material, the strength of which is different in different 

 directions ; for as a cannon made hi 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 fol- 

 lows, that a fibrous material which possesses four times the strength in one 

 direction that it does in another, w T Ul form a cannon of equal strength, if the 

 fibres be directed round the axis of the calibre. It is this fact which gives the 

 great superiority to the various kinds of twist gun-barrels. For hi these, although 

 the fibres do not inclose the calibre in circles, yet they pass around it in 

 spirals, thus giving their resisting force a diagonal direction, which is vastly 

 superior to the longitudinal direction 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 pro- 

 duce cross fracture, 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 iner- 

 tia, or weight, diminishes from the breech to the muzzle. 



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

 calculations to show the strength 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 calibre, which will 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, 31 inches each, of wrought iron. The external layer of cast iron 

 will, from its position, as before explained, possess but one fourth of the 

 strength of the inner layer, or whole strength of the iron, and the mean 

 strength of the whole will be reduced one half. Take cast iron at 30,000 

 pounds to the inch area, and we have 30,000 x % = 15.000 pounds to the inch. 

 The thickness of both sides is 14 inches, and 15,000 x 14 = 210,000 pounds 

 for the strength of the casting, to each inch of its length. The first hoop has its 

 strength reduced from 1 to a mean of .8. Take the strength of wrought iron at 

 60,000 pounds to the inch, and we have 60,000 x .8 = 48,000 pounds to the 

 inch. The thickness of both sides is 7 inches, and 48,000x7 = 336,000 

 pounds. The outside ring must be reduced in strength by the same rule, for 

 its mean from 1 to .832, which gives it 49,920 pounds per inch, and for the 7 

 niches 349,440 pounds. We have then, for each inch in length, 



Cast iron body of the gun 210,000 pounds. 



Inner wrought iron hoop 336,000 



Outer wrought iron hoop 349,440 " 



