2 
Mr. Seppings on the great strength given to 
the materials entering into the construction of a ship, has at 
different times, for more than a century past, been suggested 
by English ship-builders ; and partial alterations have, in 
consequence, been introduced; but no one, that I am aware 
of, has at any time proposed the system of a diagonal trussed 
frame. If I have received any assistance in the progress of 
this new system, now universally adopted in the British 
navy, it was from the plans and drawings of the celebrated 
bridge of Schaff hausen, and from no other source. 
The extensive application of this principle to no less than 
thirty-eight sail of the line, and thirty frigates, might per- 
haps be conclusive as to the advantages expected to be 
derived from the new system ; but as the Royal Society did 
me the honour to introduce my account of that system into 
their Transactions, at an early period of its adoption, I am 
led to hope that the result of a practical experiment, made 
with a view of proving the correctness of the principle, may 
not be deemed an improper or an uninteresting corollary to 
my former paper. 
In the early part of this year (1817) the Justitia, an old 
Danish seventy-four gun ship, was ordered to be broken up 
on account of her defective state ; and having observed her 
to be considerably arched, or hogged, as it is usually termed, 
I determined, notwithstanding her age and defective state, 
to apply the trussing principle to a certain extent, with a 
view to observe what effect it would produce on a fabric 
reduced to so weak and shaken a condition. 
The officers of the yard were directed to place sights on 
the lower and upper gun-decks, prior to her being taken into 
the dock ; and to ascertain, when she grounded on the 
