ON THE MECHANICAL PROPERTIES OF IRON PROJECTILES. 179 
ance of plates of different thicknesses to missiles of various weights and velo- 
cities. 
These investigations led to inquiries into the state of the manufacture of 
plates calculated to resist heavy and powerful projectiles directed against the 
sides of an iron-plated ship, and, moreover, to determine the exact thickness 
of plates that a vessel was able to carry. Again, they had reference to the 
quality of the plates and their powers of resistance to impact. There were 
three conditions necessary to be observed in the manufacture: 1st, that the 
material should be soft and ductile; 2nd, that it should be of great tenacity ; 
and, lastly, that it should be fibrous and tough. All these conditions apply 
to the manufacture of plates, and they also apply, with equal force, to the 
projectiles in their resistance to pressure and impact. 
In the experiments at Shoeburyness, it was found that the ordinary cast- 
iron service shot were not adapted for penetration, as they invariably broke 
into fragments when discharged against a sufficiently thick armour-plate. In 
most cases when delivered at high velocities, they had the power of damaging 
and breaking the plates ; but owing to their crystalline character and defective 
tenacity, a considerable portion of the power was expended in their own 
destruction. To some extent the same law was applicable to wrought-iron 
shot, as part of the force, from its greater ductility, was employed in distorting 
its form, and depriving it of its powers to penetrate the plate. Cast and 
wrought iron are therefore inferior as a material for projectiles intended to 
be employed against iron-plated ships and forts. With steel hardened at the 
end the case is widely different, as its tenacity is not only much greater than 
that of cast and wrought iron, but the process of hardening the head prevents 
compression and its breaking up by the blow when the whole of its force is 
delivered upon the plate. Steel, although much superior to cast or wrought 
iron in its power of resistance in the shape of shot, is, nevertheless, suscep- 
tible of distortion and compression, and in every instance when employed 
against powerful resisting targets the compression, and consequently the dis- 
tortion, was distinctly visible. 
There is another consideration besides the material which enters largely 
into the question of the resisting powers of shot, and that is form. It will 
‘be recollected that, some years since, the late Professor Hodgkinson instituted 
a series of experiments to determine the strength of iron pillars, and the 
results obtained were in the following ratios ;— 
Ibs. 
Ist. That pillars of about 20 to 30 diameters in length, with 3000 
two flat ends, broke with)... 06 5. 0000 S00. e 0. 
2nd. Pillars with one end rounded and one flat broke with © 2000 
And 3rd. Pillars with both ends rounded broke with...... 1000 
being in the ratio of 1, 2,3. Now in order to ascertain the effects of form 
on cylindrical shot, a series of experiments were instituted to determine the 
force of impact and statical pressure produced upon shot of different shapes, 
and from these experiments the following results were obtained. 
The description of shot experimented upon was cast-iron of the cylindrical 
form, with flat and round ends; and it is interesting to observe that the re- 
sults correspond with those where both ends are rounded and one end only 
rounded, as obtained by Mr. Hodgkinson on long columns; but in the short 
Specimens with both ends rounded the results are widely different, as may 
be seen by the following Table. 
n2 
