ON THE CONSTRUCTION OF HOOPED CANNON. 57 



Figure 4, that by a further distension of the body the re istancc of tin* hoops 

 will be very slowly increased. What will this resist a nee amount to, when th< 



cast-iron is distended to its breaking point? Although we cannot determine 

 with any great accuracy how far the cast-iron can be distended before fractun 

 we may, I think, be very certain that a fracture would be produced bv repealed 

 firing under an enlargement of T ^V<r P ar * °f lts external diameter. Bui it will 



be seen by the figure, that a strain upon the wire of 160 pound-, or 28,600 



pounds per inch section, produces an elongation of the wire of .9 of an inch, 

 or _i^ part of its length; and it must be evident, that, long before this elonga- 

 tion and distension in the hoops are reached, the castriron must give wav and 

 the gun be destroyed. But, even allowing the gun to hold together Up to 

 the strain of 23,596 pounds per square inch upon the cross section of the 

 hoop, we have the following computation of the strength of the gun, for each 

 inch in the length of the reinforce: Castriron body, 210,000 pounds per square 

 inch; wrought-iron hoops, 23,59G pounds per square inch, and, as both sides 

 give 14 inches thickness, 14X23,5003 = 330,344 pounds for each inch in length, 

 and 210,000+330,344 = 540,344 pounds for the strength through each inch in 

 the length of the reinforce of the gun of these dimensions and proportions. 



Let us next suppose a gun to be constructed, in size and material, like 

 that iust ffiven. but having this single difference in the method of preparing 



just g 



_ v~^ ~"-© 



the wrought-iron hoops : that instead of placing them upon the gun in an 

 annealed state, such as is represented by the wire from which Figure 4 was 

 formed, they shall be subjected to a process of cold hammering and stretching, 

 so as to bring them into the same condition, as near as attainable, with that 

 of the wire used in making Figures 2 and 3. 



Computing the strength of a gun covered with hoops brought into this state 

 of hardness and elasticity, we have the diameter of the body, as before, 28 

 inches. Let the hoops be .001 part of their diameter \v<< than the body, or 

 27.972 inches. 



The hoops thus made, and expanded by heat, and placed upon the 



will, when cold, compress the body to a diameter somewhere between 28 and 

 27.972 inches, — the exact degree of compression depending upon the power of 

 the body to resist compression, and that of the hoops to resist distension; hut, 



when the force of the fired gunpowder is exerted upon the caliber, and the 

 external diameter of the body is distended to its normal dimension of 28 

 inches, the power of the hoops to resist further distension will become 35,350 





