100 
BIRNIE. 
the curve of measured stresses and that there is no measured 
stress for the exterior surface, where, as every indication 
points, the critical strain should actually be located. It 
will be observed that the curve of deduced stress at rest in¬ 
dicates a stress of 14,676 pounds at the exterior surface. 
Taking the latter to govern the resistance, we find, from 
equation (4), P 0 = 24,167. It may be said, therefore, that 
the probable resistance, based upon an extension limit of 
60,000 pounds as taken, lies between 24,167 and 24,634 (theo¬ 
retical maximum) instead of being 24,920. 
Similar conditions are also present in the breech and 
muzzle sections before annealing, and the values given for 
them in table A and drawing should probably be reduced 
in the same proportion, or about 3 per cent. This reduction 
is made in the following table, which gives a comparison of 
the resistance of these sections and those of corresponding 
dimensions in the built-up field gun as now made. It must 
be observed, however, that in the field gun the tube is not 
hooped in the two forward'sections. 
Comparative Resistance of Initial Tension Cylinders and the 3.2-inch Built-up 
Field Gun. 
Resistance, estimated. 
Breech sec¬ 
tion. 
Breech mid¬ 
section. 
Muzzle mid¬ 
section. 
Muzzle sec¬ 
tion. 
T i (On measured) Before annealing.. 
Initial tension! Btresses> j After annealing.?......... 
Pounds 
per sq. 
inch. 
50,818 
52,015 
Pounds 
per sq. 
inch. 
59,350 
Pounds 
per sq. 
inch. 
31,316 
Pounds 
per sq. 
inch. 
15,578 
24,167 
24.634 
cylinder. ] T £ e ore& maximum.fZIZ" 
70,000 
71,652 
47,650 
3.2-inch field gun computed resistance. 
38,250 
41,030 
21,730 
13,995 
Conclusions .—The graphic representation of the curves of 
stress, &c., on the accompanying plate 6 affords the best 
means of judging the results of the treatment of the forging. 
The close accordance of the measured and deduced curves 
of stress in the forging after treatment is not accidental, 
because, as previously stated, both curves depend upon the 
