IRON SHIELDS FOR FORTS. 
373 
Description 
Weight of Ram 
Fall 
Number of Blows 
Permanent Deflection 
Hollow Stringer 
1" deep, 9'' wide 
4^' Armour- 
plate, 9'^ wide 
h" Armour- 
plate, 9'' wide 
6" Armour- 
plate, 9" wide 
1 
lbs. 
} 1512 
} 1512 
} 1512 
} 1512 
Feet 
33 
33 
33 
33 
5 
5 
5 
5 
Inches 
5 
8 
2 
5 
8 
Table of Effects of each Consecutive Blow — 
Blows 
Hollow Stringer 
4-inch Plate 
5-inch Plate 
6 -inch Plate 
Inches 
Inches 
Inches 
Inches 
No. 1 
1 
8 
8 
1 
4 
1 
8 
No. 2 
1 
4 
15 
16 
bare 
1 
4 
No. 3 
3 
8 
If 
13 
16 
3 
8 
No. 4 
9 
16 
If 
ifull 
No. 5 
5 
8 
2 
1| 
5 
8 
to costly accidents, the expense of which has to be put on to 
the successful results. There is no restriction, therefore, to their 
employment in any mass of defensive work the earth will sus- 
tain — or, as we think, the water will float. All that has been 
urged against this system, with any more than the most shallow 
opposition, is an objection against its depth as interfering with a 
larger training of our heavy guns beyond an angle of 65°. How 
many of the guns now in positioD in earthworks and masonry forts 
train more than this ? Only en barbette is the range greater, 
and then the gun is totally exposed above the parapet. But 
when we come, as we do in iron structures, from fifteen feet of 
masonry and sixty feet of earthwork, to fifteen inches of solid 
armour and thirty inches of composite shield, front plate and 
compound backing both included, are we to quibble over a few 
inches of wall in our shield, or a degree or two in the training of 
our gun through a porthole of the most diminished aperture — 
an opening diminished also from dimensions in feet to dimen- 
sions in inches ? Are we, too, to overlook the necessity of time 
as an element of resistance ? One of the reasons why a solid 
15 -inch plate so rapidly breaks up under pounding may be 
because there is no backing to absorb vibration, and no suffi- 
cient time for the distribution of any considerable portion of 
