IKON SHIELDS FOR FORTS. 
365 
of impact the passage of the missiles, hut are not capable of 
yielding any greatly increased destructive effects after complete 
penetration is effected. We can therefore, for simplicity sake, 
here regard them as only a slightly more penetrative kind of 
shot. 
We have, in the second place, to consider equally what we 
have to provide for in designing a shield. It is evident, if ever 
the shield does any duty, that it must meet with injuries, and 
repairs therefore will be needed. It is also evident that, whether 
single solid plates, or several plates, or many planks or bars of 
iron were employed, that they could not be merely stuck in the 
ground or heaped upon one another ; therefore a framework 
is required to fasten the armour upon and to hold it together, 
as also to permit of repairs being made after action, or in con- 
sequence of decay. Incidentally, also, there is the prospect of 
strengthening being required to meet the possible advance in 
the power of ordnance. 
Bearing in mind these primary conditions, we have, in the 
third place, to consider how we can best meet these require- 
ments; and, in doing so, we must further understand the effects 
of vibration of one plate upon another, the action produced by 
the shot upon the armour, the strains upon the bolts, the 
means of dispersion of the striking force, t'le resistive strength 
of the metal, and the manner in which it acts and is acted 
upon, as also the qualities of material best suited to arrest the 
shot in the shortest possible time with the least possible injury 
to the shield. 
The frame is, then, the first element in the design of these 
defensive works. For ourselves we shall in this article have 
been saved much trouble and space by the results of the recent 
Grovernment trials at Shoebury, which have clearly and deci- 
sively shown the mechanical and resistive superiority of the 
Mill wall shield, as well as the superiority of its metal, over all 
competitors past or present. Of Mr. Hughes it ought to be 
fairly and proudly said, that he has both taught the world how 
to make armour plates and how to use them. Moreover, the 
frames used for all the systems of armour so far tested have been 
modifications of the plan first proposed many years ago by this 
gentleman — a self-made man, by nature and experience a 
consummate iron worker, and a thorough mechanician. We 
shall therefore take this best example for our type, and we 
present our readers with its portrait, just as it stood up to be 
shot at. The reader, however, must bear in mind that this 
shield was designed to carry cut three experiments, and that 
therefore a shield of this class erected in a fortification would 
have a perfectly fair smooth face, and not the irregular one in this 
case, caused by the three different thicknesses of armour-plating 
