374 
POPULAR SCIENCE REVIEW. 
the force of the blow laterally over the plate in the form of 
tension. Tension needs time as a most essential element ; time 
as an element is correlative with depth of structure. In the 
notion of extreme of thinness of iron wall we seem to be chasinof 
a shadow in a wrong direction. It is friction which arrests the 
shot ; friction is the work done. A shot passing through the 
air flies a long way because the friction is small. What it takes 
thousands of yards to do in the atmosphere, is done in a few 
hundred at most in the water — would be done in a few feet by 
lead — is done in a few ioches by iron. What seems, therefore, 
requisite for an armour-plate is a moderately yielding iron that 
will squash out as the shot enters with the greatest amount of 
molecular friction.- This ideal iron has been actually produced 
in the shield and casemate manufactured at the Millwall works. 
The shots squash holes in the face-plates, and do not star or 
split them. From the ten shots flred against the front plate of 
the Gribraltar shield, in which Cammells, of Sheffield, put first- 
rate iron, of the kind hitherto in general favour, there were no 
fewer than thirteen severe fissures, besides large detached pieces ; 
from ten shots in the Plymouth fort there were thirty-two bad 
cracks, besides pieces similarly broken off, in excellent plates of 
hard quality made to order by Sir John Browm. In the face of 
the Millwall shield there was not, after the ten rounds, a single 
fissure of any account, and except for the pittings the shield was 
all but as good for the defence as before the first shot was fired 
against it. The inner skin of the shield was absolutely perfect ; 
a few rivets were jarred off, but with far too little force to 
inflict a wound even at close quarters, some simply dropping 
down on ledges beneath ; a few bolt nuts were loosened through 
the squashing of the india-rubber packing. The only scars 
visible at the rear of the defence were the jagged edge of the 
front lintel of the porthole, where the 450-pounder Eodman 
struck it, at the fourteenth round, as it were right in the eye, 
and the scoops made by the langridge of that shot as it glanced 
downward upon the inside edge of the port-cill. We have given 
the faces of the rival shields after the actions ; we now present 
the state of their backs, leaving judgment of the efficacy of the 
rival systems to all beholders. 
Since these pages were in type, the most powerful gun in the 
world — our rifled 600-pounder — has been brought against Mr. 
Hughes’ admirable shield, which has most successfully resisted 
it at the very close quarters of only 70 yards range, and fired 
with 74-^ lbs. charge of powder. 
One paragraph only in conclusion. We have spoken of the 
attacks against the shields solely as made by British projectiles. 
No other country possesses shot or guns of the like tremendous 
penetrative power. The heaviest guns that could at present be 
