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waterways, and for deep-draught ships well within the thou- 
sand yards’ range. In other words, the fort would have to 
stand its battering, if attacked under such circumstances, at 
uncomfortably close quarters. Strength and invulnerability 
ought, therefore, to be its primary qualifications. 
In respect to strength, its very massiveness and weight of 
oval wall, must require, if even the materials were simply piled 
together, a very considerable force to throw them down ; but 
materials cost money, and rolled iron in large masses a good 
deal, too, both for manufacture and carriage. Any proper 
system of iron-fort building should clearly, then, be based on 
the best mechanical plans of constructing with the use of 
the smallest amount of material employed in its cheapest 
forms. The structural cohesion of the whole fabric, and its 
power, in all its details, of clinging together, should also be 
leading features in all designs of this class, having in view 
the shattering and destructive effects of any heavy cannonade 
by modern artillery. 
It is impossible, unfortunately, to take the new iron fort at 
Plymouth as an example of remarkable engineering, or of 
first-rate constructive or scientific skill ; but it is, nevertheless, 
a topic of grave interest both in a national point of view 
and in respect to the immediate protection it is capable of 
giving to one of the most important naval arsenals of this 
country. 
In the memorable contest carried on at Shoeburyness in 
1868 an exciting interest was created between the rival targets 
constructed upon the plans of Colonel Inglis, of the Fortifica- 
tion Branch of the Boyal Engineers, and that designed by 
Mr. John Hughes, with the hollow stringer backing ; the work 
of the latter, victorious in respect to endurance and resistance, 
has already been described in this magazine (vol. vii. p. 345). 
The design for the Plymouth iron fort, which at that time 
was embodied in one of the competing targets, has since been 
carried into execution upon the same main principles which at 
that date proved so deficient of strength and cohesion in the 
representative casemate. Various parts and details . have been 
modified, as much as they could be, to bring in those improve- 
ments which the experience of the artillery attacks and the 
suggestions of criticism had dictated. We have, then, in the 
final production a formidable structure, although not a scientific 
example of the best order ; but a fort, nevertheless, of consider- 
able strength, and, for the duties it might at the present time 
be called upon to perform, sufficient probably in its essential 
qualifications. One of the main reasons constantly repeated 
for adhering to the defective principles of the fort was an 
asserted economy in the use of the narrow bars. If, however, 
