454 
PRINCIPLES OP GUNNERY. 
the diameter of the projectile, the energy per inch of circumference 
must be in a much higher proportion in order to obtain perforation. 
The 80-ton gun was fired against a target consisting of four 8-in. 
plates, with 5-in. layers of teak between each plate. This target had 
a total thickness of 32 ins. of iron. The energy per inch of pro¬ 
jectile's circumference was about 589 ft. tons, which should according 
to formula (1) perforate a solid iron plate without backing of 30*16 ins. 
The actual penetration was 27 ins., but “the point was visible through 
large cracks in the back of the target, in some places open to a width 
of 2^ ins. There was about 5*8 ins. of iron still in advance of the 
point, but this was fissured and opened in a star crack. The back 
plate was bent back nearly 14ins. ; ^ 
Types of Ships' 1 Armour , with the Energy per Inch of Circumference 
required for Perforation . 
IncRes of Inches of 
iron in wood in 
target. < target. 
Skin of 
iron. 
Energy 
per inch 
for per¬ 
foration. 
Inches of 
iron in 
target. 
Inches of 
wood in 
target. 
Skin of 
iron. 
Energy 
per inch 
for per¬ 
foration. 
4*5 
10 
ins. 
none 
ft. tons. 
34 
12 
12 
ins. 
H 
ft. tons. 
182 
5 
9 
1 
2 
42 
13 
14 
H 
204 
5‘5 
10 
1 
51 
14 
12 
if 
226 
6 
12 
X 
2 
60 
15'5 
12 
f 
237 
6 
30 
none 
70 
14 
10 
fi¬ 
259 
8 
10 
3 
<t 
84 
17 
19 
ll 
306 
8-5 
15 
none 
96 
18 
18 
if 
330 
9 
10 
1 
112 
21-5 
14 
i 
395 
10 
9 
H 
1 126 
22 
18 
H 
437 
11 
12 
l 
144 
24 
12 
if 
465 
9 
9 
H 
153 
N.B.—Tables showing the energy of projectiles are given in the “Treatise 011 
the Construction of Ordnance.” 
Vide the “Engineer,” May 11, 1877 (“The 80-ton Gun”). 
