PRINCIPLES OP GUNNERY. 
453 
It is found that this formula gives good results when the plate can 
be perforated; but for a very thick plate which cannot be perforated 
it does not follow that the penetration of the shell will be 13*6 ins.but 
the result may be approximated to in many cases by allowing a deduc¬ 
tion of about 10 per cent.— i.e., the actual penetration of the above 
shell into a wrought-iron armour-plate of considerable thickness may 
be approximated to at about 12'3 ins. 
Table showing Approximate Energy in foot tons per inch of Shot’s Circumference 
required for the Perforation of Unbacked Iron Plates by Steel Shell. 
Thickness of 
Energy per 
inch of cir- 
Difference. 
Thickness of 
plates. 
Energy per 
inch of cir¬ 
Difference. 
plates. 
cuxnference. 
cumference. 
ins. 
ft. tons. 
ins. 
ft. tons. 
13 
13 
14 
14 
14 
14 
14 
14 
14 
15 
15 
15 
15 
15 
15 
16 
16 
16 
16 
16 
16 
17 
17 
17 
17 
17 
17 
18 
18 
18 
18 
4 i 
25 
4 
5 
22-5 
368 
4’5 
29 
23 
381 
5 
34 
23-5 
395 
5’5 
39 
A 
24 
409 
6 
45 
O 
r* 
24-5 
423 
6-5 
51 
O 
6 
6 
H 
25 
437 
7 
57 
25-5 
451 
7-5 
63 
26 
465 
8 
70 
/ 
fj 
26-5 
479 
8-5 
77 
4 
f 7 
27 
494 
9 
84 
8 
8 
8 
9 
o 
27-5 
509 
9-5 
92 
28 
524 
10 
100 
28-5 
539 
10-5 
108 
29 
554 
11 
117 
29-5 
569 
11-5 
126 
Q 
30 
685 
12 
135 
Q 
30*5 
601 
12-5 
144 
V 
Q 
31 
617 
13 
153 
y 
9 
10 
10 
11 
11 
11 
11 
11 
11 
11 
11 
■J o 
31-5 
633 
13-5 
162 
32 
649 
14 
172 
32-5 
665 
14-5 
182 
33 
682 
15 
193 
33-5 
699 
15 # 5 
204 
34 
716 
16 
215 
34-5 
733 
16‘5 
226 
35 
750 
17 
237 
35*5 
767 
17-5 
248 
36 
785 
18 
259 
36’5 
803 
18-5 
270 
37 
821 
19 
282 
12 
12 
12 
1 o 
37*5 
839 
18 
18 
18 
18 
18 
19-5 
294 
38 
857 
20 
306 
38-5 
875 
20-5 
318 
39 
893 
21 
330 
S.6 
12 
13 
39-5 
911 
21-5 
342 
40 
929 
22 
355 
Calculated from the equation E = 2-53s 1- 6 (Major Noble’s formula), E being the energy in foot tons per 
inch of the shot’s circumference required to perforate a plate of s ins. in thickness. 
It has been ascertained by experiment that projectiles of similar 
forms of head and different calibres require approximately the same 
amount of energy per inch of circumference to perforate the same 
armour when the plate is not much thicker than the diameter of the 
projectile; but when the plate is more than one-fourth thicker than 
