-g ON THE CONSTRUCTION OF HOOPED CANNON 



pounds (or every inch area of their cross-section (this being equal to 240 pounds' 



train upon the wire). 



From this point the distending force of the gunpowder will be resisted, both by 



the hoops and by the body; and, if we suppose the cast-iron body, in this as 

 in the last case, to be fractured only after a distension of T oVo tu P art °f lts 

 normal external diameter, we shall find that that point will not be reached until 

 a strain of more than 70,700 pounds per square inch (shown by 480 pounds upon 

 the wire) has been exerted upon the hoops. Then, taking the body, as before, 

 to resist with a force of 210,000 pounds per inch in length, we have, as the 

 whole strength of the gun: Body 210,000, and hoops 14 X Vn,700 = 989,800, 

 making together 1,199,800 pounds for each inch of its length, — decidedly more 

 than twice the strength shown in the former case, where the hoops were an- 

 nealed before being put in 



In this statement, 1 have taken the comparative diameters of the body and 

 the hoops at 28 and 27.972 inches. Now this difference is so small, that it 



cannot bo produced in practice with geometrical precision ; nor is this neces- 

 sity; all that is required being, that the difference shall not be less than that 



here given, though a deviation by which the difference of diameters shall b 



twice, or even thrice, as great as this, will not affect injuriously the construction 



Th» suppose the hoops, instead of being 27.972 inches, be made 27.916 



niches, in diameter. A heat of 800°, to which the hoops may be heated with- 

 out affecting their elasticity, will expand them to 28.004 inches, thus giving a 

 mMgin of .064 or about ^th of an inch, for play, and imperfect workman- 

 hip, when the hoops are run on to their places. In this case, although the 

 first eompres-ion of the body would be greater than if the hoops were made of 



gned, yet the first discharge of the powder would, by a little 



permanent elongation of the hoops, bring them to the true diameter, without 



»l<"'gmg them beyond their elastic limit 



the 



« «» preceding computations of strength, I have confined myself to that 



■■••-n, esUUon of lt which preserves the gun from longitudinal fracture. But a 



ahbou "l .' f Urcd transverse 'y. or diagonally, as well as longitudinally 



; J; v. e, ' et0fWC fU ' ly P roved > ** * ™* of a material which h* 

 » d .,„„ gt . w eacll dil , ction; the or bas a v;istly 



tp, ,, T ' r S ' ing Cr ° SS ' than taBSWhi fracture This is likewi* 



• jr* r t ; r al , f " ac,ure - But as these *- °- *«» ■*•*■* : n 



' l ° thc ' r bcn W formed, i» part at leasti of fibrou8 wrought- 



