452 
PRINCIPLES OE GUNNERY. 
best results; but in cases where the projectile acts as a wedge and 
drives the resisting material before it— e.g., in the case of penetration 
into earth—the method of estimating the resistance per square inch of 
sectional area gives approximately the best results. The truth pro¬ 
bably lies between these methods of estimation, inclining more to the 
one or the other according as a punching or a wedging action is 
brought into play. 
Formulae The formulae which have given good results within certain limits on 
latmg per- the supposition that the thickness to be perforated may be estimated 
unbacked^ from the energy per inch of projectile's circumference,, are of the form 
wrought- 
mm plates. ener gy j n ft. tons per inch of circum. (E) — 7c x {thickness of plate in ins. ( 3 )}*; 
where 7c and x are coefficients which must be determined by experiment. 
The formula adopted in the Department of the Director of Artillery, 
given by Major W. H. Noble, R.A., is 
E = k* 9 
where 7c = 2*53 and x = 1*6; so that 
( 1 ) 
These constants are computed for ogival-headed Palliser projectiles* 
and wrought-iron plates, and within certain limits give approximately 
correct results for plates that can be perforated. Captain Andrew 
Noble, F.R.S., gives 
Colonel Maitland, It.A., has calculated a formula from experimental 
data, on the supposition that the thickness to be perforated may be 
estimated by the energy per square inch of projectile's sectional area— 
viz., 
r E _ E ^ 
“ (4'733)7iv 2 “ 14 , 87r 3 5 .^ J 
where E represents total energy in ft. tons on impact, and r the radius 
of the projectile in inches. 
As an example of calculating the thickness of plate that may be 
perforated, suppose the energy per inch of circumference of a Palliser 
shell on impact is known to be 165'6ft. tons; then by formula (1), 
,,_ 1 • e / 16 5 ■ 6 , 0 n . 
8 — /\ / —— =13-6 ms. 
"V 3-53 
* More correct results are given with steel projectiles. 
