66 



HOOPED CANNON. 



assented bo by am' practical engineer who may take the pains to examine 



them. Indeed, it seems to me remarkable, that, with all the attention that has been 

 given to the subject of hooped cannon in Europe, as well as in this country, for 

 several years past, the cause of the great defect, which it has been one object of 

 this paj.«r to point out and remedy, does not seem to have been discussed nor 

 Been, although the defect itself has been made known by the bursting of such 



instances as to have shaken, if it has not destroyed, the confi- 

 dence of artillerists in them, when used with heavy charges. To avoid this defect, 

 resort has been had to the use of low cast-steel, nnder the name of homogeneous 

 iron ; or to an adoption of the manufacture with wrought-iron, after the method 

 invented and practised by me more than twenty years ago, and which I after- 

 improved into the simpler and cheaper form so fully described in these 



guns in so many 



war 



Memoirs. 



I may also observe, with regard to the theory of the strength of hollow 

 cylinders, when exposed to a bursting force, that many changes to the original 

 formulas of Mr. Barlow have been proposed as expressing more exactly the phys- 

 ical conditions of these cylinders. These changes, however ingenious or learned, 

 are of very trifling practical importance in the manufacture of cannon. The 

 omission of Mr. Barlow to consider the pressure, as acting as a crushing force 

 upon the internal portion of the cylinder, and thus as aiding, to some unascertained 

 extent, its action as a distending force, in rupturing the walls of the cylinder, 

 was, I believe, first made known by me in my former Memoir. So, also, no 

 writer or engineer has yet, so far as I know, perceived or shown, that the 

 theory of the strength of hollow cylinders, as now generally adopted, is wholly 

 inapplicable to cylinders or hoops made of malleable materials, such as wrought- 

 iron or bronze; for the reason, that the inner portion of such a cylinder will, 

 as shown by my experiments herein detailed, be permanently elongated or 

 stretched circumferentially, without being ruptured or weakened until after the 

 outside has given way; a fact entirely at variance w r ith the foundation of the 

 theory. For, the assumption, on which the whole theory rests, requires that the 

 fracture shall first take place upon the inside of the cylinder; an assumption 

 that can only be true in fact, when the cylinder is formed of a material 

 which is unmalleable, that is, incapable of being elongated or stretched to any 

 considerable extent beyond the limits of its elasticity. 



