60 ON THE CONSTRUCTION OF HOOPED CANNON 



The preceding computations, therefore, place it beyond doubt, that, even allow- 

 ing that the lateral pressure of the fired powder upon the cast-iron body of the 

 gun may impair the tensile strength of the body in resisting cross-fracture, yet, 

 under this condition, and thus admitting as a truth that of which we have no 



o 



evidence, we see that we may rely with perfect confidence upon the strength 

 of the hoops alone, when secured to the gun by the screw-thread, as described 

 in the former Memoir, to preserve the gun from cross-fracture. 



In the Specification and Memoir before mentioned, I propose to form the 

 screw "of about eight threads, each thread taking about one-eighth of an inch 

 space, so that one turn advances each thread one inch," and "to make the 

 threads of the female screws sensibly finer than those of the male, to draw 

 by the shrink, the inner rings together endwise." The advantage of this form 



•o" v "o 



of construction will appear in this: that by the rapid advance of the hoop 



to its place the shrinkage from cooling during its passage over the body will 

 be avoided; while the dividing of the inch space of the spiral into several 

 parts, enables us to give a great bearing surface to very shallow threads. 

 I give, in Figure 5, a drawing of the threads as I would form them for 



Fig, 5. 



•threaded 



screw. They have an .18 inch pitch, and a depth of .04 in., being 

 .11 in. thick at the root or bottom, and .07 in. breadth upon the face. Threads 

 of this shape may be more easily and exactly made than any other, as a large 

 part of the surfaces left by the boring and turning tools reauires no chan 



from the screw-tool, but remains and forms the flat faces of both the male and 

 female screws. By tnis means the gauged sizes and requisite diameters of both 

 the body and the hoops are more easily ascertained and preserved, when the 

 screw-threads are formed. 



The depth of the threads given in this figure must be ample ; for, as 

 shrink? V Vhei \ 0nCe illterl <*ked and in place, are kept in contact by the 



pon 



outer ,1 °f ^ h0 ° PS Snd the diste ™°n of the gunpowder, the idea of 



a LI It PPmg ^ riding °™ the «-" ones/like - loo* nut ' 

 a screw bolt, „ slmply p reposterous 



«r r m h r p iCal T iVal6nt fW the screw -«>read S may be found in small cir- 

 pronnnences formed upon one 8 „ r f aC e, to fit into corresponding grooves 



cular 



