554 
THE DEVELOPMENT OF ARMOUR. 
of powder released by a shell already ruptured is mild compared with 
that of a shell burst asunder by its charge, nevertheless it is an evil 
that calls for absolute prevention. 
Notes on Formula proposed between 1893 and 1898. 
The unsatisfactory condition of formulae for the calculation of per¬ 
foration and fracture was noticed in 1893. Although no thoroughly 
practical investigation has been made, even on a small scale, so far as 
is known to the writer, yet some advance has been made in the way of 
arriving at working formulae which may fairly answer the purpose, 
especially considering that fracture both of shot and plate greatly in¬ 
terferes with any accuracy such as might be arrived at if the conditions 
obtained that held good with wrought iron when shot retained their 
shape while cleaving a path through unfractured armour. Captain 
Tresidder has suggested a formula which he holds to be theoretically 
correct and while this is not conceded by the highest mathematical 
authorities, it has the remarkable fact to support it that if no variation 
occurred in the sectional density of projectiles, a well known formula 
obtained entirely independently by Krupp, becomes identical with that 
of Tresidder. The latter possesses the great advantage of being 
embodied in slide rules so that perforation can be read off instantly. 
To this probably is largely due the fact that it is now used officially in 
this country, 
The following table gives a comparison of penetrations obtained by 
various formulae for high velocities :—• 
Calibre in 
W 
Weight. 
lbs. 
Velocity 
Ft.-Sec. 
Calculated perforation of Iron in Ins. on system of 
c.m. 
inches. 
De Marre 
Krupp 
Tresidder 
Fairbairn 
( Maitland 
d 3 . 
c 
2493 
30*3 
27*1 
27*8 
23*0 
23*0 
24 
9-46 
330’7 < 
2626 
33*8 
29*5 
30*1 
24*2 
24*3 
5- 0*399 
l 
2766 
35*4 
31*4 
32*3 
25*4 
26*3 
3 
( 
2493 
26*0 
25*4 
25*5 
21*0 
21*0 
-) 
21 
8-27 
242*6 < 
2628 
28*1 
27*2 
27*4 
22*1 
22*2 
t 0*429 
l 
2756 
30*2 
30*2 
29*6 
23*3 
23*4 
3 
( 
2626 
21*1 
20*0 
20*4 
16*4 
16*4 
16 
6-30 
101*4 < 
2756 
22*8 
21*5 
21*9 
17*2 
17*1 
0*406 
l 
2953 
25*3 
23*9 
24*4 
18*5 
18*7 
3 
c 
2625 
20*4 
19*5 
19*7 
15*8 
i5*a 
■) 
16 
6-91 
88*2 < 
2756 
22*0 
21*0 
21*2 
16*6 
16*7 
[■ 0*427 
l 
2953 
24*6 
23*3 
23*6 
17*8 
17*9 
3 
( 
2625 
18*7 
18*0 
18*1 
14*6 
14*8 
14 
6*51 
70*6 < 
2766 
20*1 
19*4 
19*6 
15*4 
16*6 
y 0*421 
l 
2953 
22*3 
21*6 
21*7 
16*5 
16*6 
3 
r 
2625 
18*1 
16*9 
16*9 
12*8 
12*9 
12 
4*72 
46*3 J 
2756 
2953 
17*4 
19*3 
17*1 
19*0 
17*1 
19*1 
13*6 
14*4 
13*6 
14*5 
£ 0*440 
t 
3281 
22*6 
22*3 
22*4 
16*0 
16*2 
J 
As pointed out in 1893, most formulae agree closely for 1,580 f.s. 
striking velocity. Below that, Tresidder, Krupp and De Marre give 
lower results than Maitland and Fairbairn, and it seems wrong to 
adopt the former for such low velocities seeing that the latter were 
proved to be approximately correct and almost exhaustively in past 
