THE ROYAL ARTILLERY INSTITUTION. 
81 
structed of ordinary f-incli boiler plate; this construction was adopted 
with a view of giving increased speed without increased displacement. 
It is doubtful even if the advantage gained in the increased speed obtained 
is not more than compensated by the disadvantage of having several of her 
guns so inadequately defended, that they could not be worked if fighting at 
close quarters; indeed, the thin coating of iron on bow and stern would 
greatly add to the destructive effect of the shot, as proved by some experi¬ 
ments carried on by Capt. Hewlett, C.B., H.M.S. Excellent, at Portsmouth, 
which shewed that all cast-iron shot are broken on impact with any wrought- 
iron plate fths in. thick, and pass through the plate in fragments. 
However, as the highest authorities differ on the important subject of 
sacrificing defence to speed, I will not presume to give an opinion. 
The principal disadvantages in the construction adopted in these first iron 
ships, are as follows:— 
(1) The through bolts by wounding the face of the plate render it liable 
to crack on being struck by a shot. 
(2) The IJ-in. bolt is not sufficiently strong for the purpose. 
(3) The wood backing is liable to decay, and its renewal would be 
necessary from time to time at nearly half the cost of a new ship. 
(4) The tongue and groove at the edges of the plates render it impossible 
to remove a plate if damaged, without bringing the vessel into dock, and 
even then it would be a work of great labour and expense ; they also tend 
greatly to spread the destructive effect of a shot to the surrounding plates. 
As it was considered desirable that some further experiments should be 
carried on to determine the best quality of iron for defensive purposes, a 
Committee was formed at the beginning of last year to ascertain whether 
it might not be possible by some improvement in the manufacture of 
armour plates to lessen the thickness of 4 \ -inches, and also to devise 
some mode of attachment that would obviate the necessity of bolt holes, 
and the tongue and groove. The question of employing iron for land 
defences was also submitted for their consideration, as the Defence Com¬ 
mission had some idea of employing iron very largely in constructing the 
works at Spithead, Portland, &c. This idea gave rise to the experiments 
that were carried on with the Thorneycroft bars. As greater resistance to 
shot was obtained by these bars than by any other means, and as they are 
now being employed in the defences of Antwerp, the following history of 
their origin may be interesting :— 
In the early stage of the inquiry relative to iron defences, it was found 
exceedingly difficult and expensive to obtain large forgings sufficiently sound 
to resist shot,until Mr Hartley, of the Shrubbery Iron Works, Wolverhampton, 
proposed to try the effect of rolled bars of iron tongued and grooved together; 
this proposal was agreed to, and Mr Hartley was desired to prepare a target 
with as little outlay as possible; he therefore adapted a pair of rolls he had 
in stock, and produced bars with a sectional area of 15 x 5 in., the size of 
