330 
of us first invented the method of construction now universally em- 
ployed for large rifled cannon. If I rightly understand Mr. Mallet, he 
considers himself to have been the original inventor, and he is under 
the impression that he only asked Dr. Hart to calculate exactly the 
degree of strain necessary for each consecutive layer of tubes. He also 
believes that Dr. Hart gave him this calculation in 1854. 
Dr. Hart, on the contrary, told us most distinctly that Mr. Mallet 
came to him for advice about a plan for making mortars of thick lon- 
gitudinal voussoirs surrounded by hoops, and that he, Dr. Hart, had 
proposed the use of the present system of concentric tubes, as giving 
much greater strength with less weight. 
I expressed astonishment at the date of 1854 being assigned as that 
of Dr. Hart’s investigation, because, when the matter was more fresh in 
our memories, both Mr. Mallet and Dr. Hart had mentioned July, 1855, 
as the date. As my first cannon was made in the spring of 1855, I 
had, therefore, always considered myself the first discoverer. 
Nothing, Sir, could be more unsatisfactory than to leave the ques- 
tion in such an undecided state ; as, although I should never have tres- 
passed on your valuable time to raise such a question, yet, as it has 
been raised by Mr. Mallet, Iventure to hope you will allow me to 
throw some further light on it. First, I will say that I have found two 
published letters from Mr. Mallet, corroborating my view of the dates. 
One is to ‘‘ The Press’ (Noy. 14, 1857), and in it he states that Dr. 
Hart first communicated with him on this subject on the 6th July, 
1855. In the other letter to ‘‘The Mechanics’ Magazine” (Dec. 12, 1857, 
page 563), he says—‘‘ My first communications from Dr. Hart were 
received very early in July, 1855.” 
Now, Sir, I hope to be able to show where the mistake has arisen, 
viz., in some confusion as to the exact date of Mr. Mallet’s valuable 
and interesting paper on the construction of artillery. That was read 
to this Academy, June 25, 1855, but not published till the year after, 
and I think the theory in question was communicated by Dr. Hart in the 
interim, and inserted in the paper. I found, on examination, that some 
parts of the paper, as published, must have been written in September, 
1855, at the earliest, for at page 232 Mr. Mallet alludes to a proposal to 
shrink hoops on a 13-inch mortar, and this proposal was, I know, made 
by Colonel Eardley Wilmot, on September 25, 1855, and based on the 
success of a gun made by me in the spring of that year. 
I must, in consequence of the discovery of this error in the date 
ascribed to Mr. Mallet’s publication, retract my former admission, that 
he was the first to publish the theory. Not only was I before him, 
but also Mr. James Longridge and Sir Charles Fox. The late Mr. 
Brunel, too, early in 1855, proposed to Sir William Armstrong to make 
cannon on the same principle. 
In looking for Mr. Mallet’s published letter in ‘‘ The Mechanics’ 
Magazine,” I found one from Dr. Hart (page 176, Feb. 21, 1857),~ 
defending the theory against severe criticism, and calling it his own— 
“‘ My proposal, on which Mr. Mallet has acted,” are the words used. 
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