ON THE MECHANICAL PROPERTIES OF IRON PROJECTILES, 181 
inflicts greatly increased punishment upon it, In this instance the amount 
of work done is in favour of the wrought iron: but this does not alter the 
condition in which the force was first delivered upon the target; on the con- 
trary, it is entirely due to the superior tenacity of wrought iron to that of 
cast iron, which yields to the blow, and is broken to pieces in consequence of 
its inferior powers of resistance. The same may be said of steel in a much 
higher degree, which delivers nearly the whole of its vis viva upon the plate. 
In the foregoing experiments it will be observed that the resistance of cast- 
iron flat-ended shot to a crushing force is about 55 tons per square inch, 
whilst in the two following we find that the round-ended specimens, of the 
same material, gaye way and were crushed with a pressure of only 263 tons— 
rather less than one-half the force required to crush the flat-ended ones, It 
is a curious but interesting fact (provided the same law governs the force of 
impact as dead pressure) that the round-ended projectile which strikes the 
target should lose, from shape alone, one-half its powers of resistance. This 
may be accounted for as under. 
Take, for example, a cylinder of cast iron, a, with a rounded end forcibly 
pressed against the steel plate A,-until it 
is crushed by a fixed law of fracture ob- 
servable in every description of crystalline 
structure; that is, the rounded end or 
part s forms itself into a cone, which, 
acting as a wedge, splits off the sides cc 
in every direction at the angle of least 
resistance, and these, sliding along the 
sides of the cone, are broken to pieces on 
the surface of the plate. 
At Shoeburyness the same results were 
observable in all the experiments with 
spherical and round-ended shot, each of 
them following precisely the same law. In every case where the shot was 
broken to pieces, the fractured parts took the same direction, forming a cone 
or central core similar to that shown at s, as exhibited in my own experi- 
ments on statical pressure with the round-ended cylindrical shot. 
The law of fracture of cast iron has been carefully investigated by the late 
Professor Hodgkinson in his paper on the strength of pillars, to which we 
haye referred. It is there clearly shown that the resistance of columns 
when broken by compression is in the ratio of 1, 2, and 3; the middle one, 
with only one end rounded, being an arithmetical mean between the other 
two. Now these important facts, according to all appearance, bear directly 
upon the forms necessary to be observed in the manufacture of projectiles, as 
we find cylindrical shot with round ends loses one-half its powers of resist- 
ance to a pressure or a blow which tends to rupture or to break it in pieces. 
My own experiments given above do not exactly agree with those of Pro- 
fessor Hodgkinson—the ratio of resistance in a column with one end rounded, 
and that of a column with both ends flat, being as 3: 1-5, instead of as 3: 2 
as in his experiments,—a discovery probably explained by considering that 
he employed cast-iron pillars from 20 to 30 diameters in length, whereas my 
own were only two diameters long. Professor Hodgkinson has, indeed, ex- 
pressed an opinion that the difference of the strengths of the three forms of 
pillars becomes less according as the number of times the length of the pillar 
exceeds the diameter decreases, which is the reverse of the results obtained in 
the foregoing experiments. But on this I may observe, that the conclusion 
