STRESSES IN GUN FORGINGS. 
97 
extension in action cannot exceed the elastic limit of the 
metal. 
2d. To make the resistance to interior pressure a maxi¬ 
mum in any cylinder, the state of initial tension should be 
such that when the pressure acts from within the whole 
thickness of metal in the wall should be, as nearly as prac¬ 
ticable, uniformly strained to the elastic limit of the metal. 
3d. If p and 0 be taken equal and the compression of bore 
carried to the limit p, there is but one thickness of cylinder 
(0.65 caliber, nearly)* for which a condition of uniform 
strain in action equal to the elastic limit of the metal can 
be attained. 
4th. For cylinders of greater thickness than 0.65 caliber 
a state of uniform strain in the wall will be reached in 
action and passed before the elastic limit of the metal is 
attained, and with increasing pressure this limit will be 
fully reached only at the surface of the bore, thus determin¬ 
ing the limit of pressure. For such cylinders the best con¬ 
ditions of resistance will be obtained by utilizing the full 
limit of compression of the metal in the initial tension. 
5th. But for cylinders of less thickness than 0.65 caliber 
a state of uniform strain in action equal to the elastic limit 
of the metal can be attained with a compression of bore less 
than the limit p. The thinner the cylinder the less should 
be the initial compression imposed. It follows that the 
possible maximum resistance of such cylinders will be ob¬ 
tained by adjusting the initial compression within limits. 
If the full limit of initial compression were given, the elastic 
limit of the metal would be reached in action at the exterior 
of the cylinder sooner than at the bore. 
6th. As a consequence, also, of the preceding, the resist¬ 
ance of cylinders of less thickness than 0.65 caliber, treated 
by interior cooling, should be directly proportional to the 
thickness. This treatment gives the means of imparting the 
' greatest resistance so far known to such cylinders. 
*See Appendix B, “Gun Making” and “ Modem Gnn Construction 
and Breech Mechanism,” Congress of Engineers, 1893. 
