THE EOYAL ARTILLERY INSTITUTION. 
77 
when the corner of D6 block was forced in, leaving an opening of about 
three and a half square feet. This hole was enlarged by the seventh shot to 
six square feet. 
The damage was not materially increased in external appearance by two 
more 8-in. shot, and one 9’22-in. which struck on E course afterwards. 
The aggregate value is 20,207 foot tons, the average force 2021 foot 
tons, the whole with the 600 yards charge, except the last. 
15. The Committee have now to state the general conclusions they draw 
from the practice reported. 
Both the iron shields have resisted well, and the fastenings of both may 
be said to be still effective, inasmuch as they have held them in their places 
to the last; those of the east shield are indeed hardly impaired. Those of 
the west shield have been weakened by the breaking off of three out of ten 
iron cramps, but the remainder continue to hold the plate; both shields 
continue to afford a fair amount of protection to the gun behind them, nor 
can anything be said to have got through them, although they are cracked 
through, bent, and started from the effects of the fire. 
The east or compound shield (as shown above) has been struck 13 times 
to an aggregate amount of 34,313 foot tons, or 424 foot tons to every 
square foot of its actual surface when the port hole is deducted. 
The west or simple shield has been struck nine times to an aggregate 
amount of 22,400 foot tons, or 800 foot tons to every square foot of surface 
when the port hole is deducted. 
Total, 22 blows on the iron. 
16. After deducting these 22 blows struck on the two shields, therd 
remain 65 which have struck the granite. They were distributed over a 
surface of about 514 square feet ; for the bottom course, which was not 
struck, must be deducted. The effect is such a degree of demolition as would 
have caused the abandonment of the two casemates attacked before the 
firing ceased. They were noted as beginning to be untenable after the 
33rd hit on granite, and quite so after the 54th hit. 
With them the casemates in the next tier above, and probably also any 
barbette guns in the same vertical section must have been also abandoned, 
the structure being rendered too insecure to allow of their continued use. 
The Committee must lay much stress on the irreparable character of the 
injury done to the stonework; nothing short of complete reconstruction 
would restore it, whereas a structure of iron would admit of easy repair by 
re-casing the wounded parts, which always serve as support, and might be 
actually rendered stronger than before by the accumulation of thicknesses 
of plate, and it was observed that the dust, grit, and fine splinters of granite 
sent into the work were sufficient to amount to annoyance, if not to an 
actual obstruction of the working of the gun. 
17. In making any comparison between the protective value of iron, 
such as was used in these shields, and granite, as a material for fortifications, 
it must not be forgotten that the proportion between the external surface of 
the granite and the external surface of the two shields, is that of 514 to 109 
[yol. vi.] 11 
