88 
BIRNIE. 
forging, annealing, oil-tempering and annealing. In the 
final annealing, while still in the annealing furnace and 
uniformly heated to redness, water was passed into and 
through the bore of the forging until it was cool enough to 
handle. 
The several circular sections shown in the drawings, each 
about 0.5 of an inch thick, were then cut from different parts 
of the forging to ascertain the strains in concentric element¬ 
ary cylinders of which the section may be conceived to be 
composed. Each section was marked to be divided into a 
number of circular rings about 0.15 of an inch in radial 
thickness. Before cutting out these rings datum points w r ere 
marked on the face of each to measure two diameters at 
right angles. The rings were removed consecutively and 
measurements of the diameters made at each stage of the 
operation. The change in diameter of a ring on being re¬ 
leased from the section is taken as a measure of the circum¬ 
ferential strain or stress to which it was subjected in the 
forging. A ring which expands on being released was evi¬ 
dently under circumferential compression in the forging, and 
one which contracts was under tension. The datum points 
for the curves of initial tension shown in the figures are de¬ 
rived from the difference in the original diameters of the 
rings and their diameters after release. As seen in these 
curves, the compression is greatest at or near the surface of 
the bore, whence it gradually decreases to zero at the neutral 
point. At this point the strains of tension begin and in¬ 
crease gradually toward the exterior of the cylinder. The 
strains of compression and extension are in equilibrium. 
Duplicate sections from the breech and muzzle ends of the 
forging are illustrated, the originals being taken directly 
after the treatment by interior cooling and the duplicates 
when the parts of the forging to which they belonged had 
been subjected to partial annealing. The object of this 
treatment was to show how the strains originally produced 
could be controlled and ameliorated, if necessary, by anneal¬ 
ing a forging after interior cooling. 
