SHORT NOTES ON PROFESSIONAL SUBJECTS. 
15 
( 2 ) An unbacked iron plate will be penetrated by solid steel shot, of the same 
form of head but different diameters, provided their striking vis viva varies as the 
diameter nearly, that is, as the circumference of the shot. 
(3) That the resistance of unbacked wrought-iron plates, up to 5’5 inch, to 
absolute penetration by solid steel shot, of similar form, and equal diameter, varies 
as the square of their thickness, nearly.* 
(4) These experiments have proved that, although in the case of cast-iron a 
light projectile moving with a high velocity will indent iron plates to a greater 
depth than a heavier projectile with a low velocity, but equal “ work 55 or 
“ energy,” it is not as necessary that there should be a high velocity when the 
projectiles are of a hard material such as steel and chilled iron } and this result will 
be much in favour of rifled guns, by enabling them to prove effective with com¬ 
paratively moderate charges. 
Experiments shew that it takes the same amount of energy to send hemispherical 
headed steel shot and ogival headed chilled shot through 4‘5 inch and 5"5 inch 
plates fired at under similar conditions. 
When, however, the wrought-iron plates are backed by wood the ogival headed 
chilled shot has an advantage, in the proportion of about 10 to 9. 
That is to say, suppose'it required an energy of 1000 ft. tons to perforate the 
“Warrior 35 with a hemispherical headed steel shot; the same effect would be 
accomplished by 900 ft. tons in the case of an ogival headed chilled shot of the 
same diameter. 
Sufficient experiments have not yet been made to enable us to determine with 
accuracy the effect of shot with different shapes impinging obliquely on an iron 
structure. 
Allusion has been made in previous “ Occasional Notes 35 to General Mayefski’s 
work on this subject. 
Our experiments, however, do not entirely bear out General Mayefski’s con¬ 
clusions. 
Chilled projectiles almost invariably break up on impact, and the consequent 
loss of work does not appear to have been taken into account by General 
Mayefski. On the whole it has been found that practical conditions are satisfied 
by assuming that when shot strike obliquely the energy lost for purposes of 
penetration is in proportion to the sine of the angle of incidence.f 
Experiment has shewn that it requires an energy of about 60 ft. tons per inch 
of shot’s circumference to send a hemispherical headed steel shot through the 
“ Warrior, 33 the fire being direct. The same effect will be produced by 54 ft. tons 
per inch in the case of an ogival headed chilled projectile. 
If the angle of incidence be 60°, the hemispherical headed steel shot requires 
about 81 ft. tons per inch and the chilled shot 78 ft. tons per inch. 
Erom Captain W. IT. Noble’s Report it appears that the flat-headed form is one 
of the worst that could be used for the penetration of armour plated vessels either 
in direct or oblique fire. 
* This is only true when the plates are of the best quality. It is well known that it is easier to 
make a thin than a thick plate, and that the latter is liable to imperfect welding in the process of 
rolling. The manufacture of armour plates has, however, been so much improved of late, that it is 
practically allowable to assume that their resistance varies as the square of their thickness. 
f That is, the shot striking in a slanting direction may be supposed to have opposed to it a plate 
of a thickness equal to the diagonal formed by the line of direction. 
