the thickness of the backing in inches.
e = the thickness of the plate in inches.

Using the above formula we can make out a table as follows:

-------+-------+-------------+-------+-------+------+---------+
Plate. |Backi'g| Gun, service| w, | a, | V. | Energy, |
Inches.|Inches.| shot. |Pounds.|Inches.| f. 8.| Impact. |
| | | | | | f. tons.|
-------+-------+-------------+-------+-------+------+---------+
6 | 36 | 6" B.L.R. | 100 | 5.96 | 1389 | 1337 |
7 | 36 | 6" " | 100 | 5.96 | 1528 | 1619 |
8 | 36 | 8" " | 250 | 7.96 | 1213 | 2550 |
9 | 36 | 8" " | 250 | 7.96 | 1308 | 2966 |
10 | 36 | 8" " | 250 | 7.96 | 1399 | 3390 |
11 | 36 | 8" " | 250 | 7.96 | 1489 | 3839 |
12 | 36 | 10" " | 500 | 9.96 | 1247 | 5386 |
13 | 36 | 10" " | 500 | 9.96 | 1315 | 5987 |
14 | 36 | 10" " | 500 | 9.96 | 1381 | 6608 |
15 | 36 | 12" " | 850 | 11.96 | 1215 | 8699 |
16 | 36 | 12" " | 850 | 11.96 | 1269 | 9710 |
17 | 36 | 12" " | 850 | 11.96 | 1332 | 10454 |
18 | 36 | 12" " | 850 | 11.96 | 1374 | 11124 |
19 | 36 | 12" " | 850 | 11.96 | 1425 | 11965 |
20 | 36 | 12" " | 850 | 11.96 | 1476 | 12837 |
-------+-------+-------------+-------+-------+------+---------+

No projectile or fragment of the plate or projectile must get wholly
through the plate and backing. The plate must not break up or give
such cracks as to expose the backing, previous to the third shot.

The penetration of projectiles of different forms into various styles
of armor has been very thoroughly studied and many attempts have been
made to bring the subject down to mathematical formulae. These formulae
are based on several suppositions, and agree very closely with results
obtained in actual experiments, but there are so many varying
conditions that it is extremely doubtful if any formulae will ever be
written that will properly express the penetration.

Many different forms have been given to the heads of projectiles, as
flat, ogival, hemispherical, conoidal, parabolic, blunt trifaced, etc.

The flat headed projectile has the shape of a right cylinder, and acts
like a punch, driving the material of the armor plate in front of it.
These proj