THE EOYAL ARTILLERY INSTITUTION. 
233 
In a letter bearing your name (Appendix E, p. 50), some injustice is done me. 
If the letter be yours, unintentionally I am quite sure. 
The statements therein which I have marked are to the effect that my 3 6-inch 
mortars are not constructed at all upon the principle of graduated compression of 
the inner and tension of the outer rings, the theory of which you investigated for 
me, but the general principles of which had been known to me a long time—before 
even the first day that Professor Downing, C.E., and I called upon you on the 
subject. Let me assure you that you are quite mistaken in supposing that I have 
utterly neglected the principle of graduated strain, &c. in those mortars. The 
graduation, however, was not effected by difference of temperature in the successive 
rings, as you proposed, and which I soon saw would be quite impracticable to 
carry out, but by the requisite nice adjustment of the diameters, when cold, of the 
successive rings, so that when all heated to about the same temperature they 
should grip differently, as required. 
That the effect has been practically pretty much what was intended, the last 
day’s practice showed, when a charge of 80 lbs. of powder, which threw a shell 
about a mile and three quarters, produced no effect upon chase or chamber. 
I may have myself led you into this error (which, however, I am sorry to find 
published), for I recollect telling you that I had shrunk on all the rings at one 
temperature. May I ask if you gave Captain Blakely permission to publish your 
letter? He don’t say so. 
Believe me, dear Sir, 
Very truly yours, 
Dr. H. S. Hart, F.T.C.D., EGBERT MALLET. 
Trinity College, Dublin. 
It is impossible within the limits of a note already too long, to enter 
fully upon the complicated question of the relations that take place between 
all the parts in a system of rings superimposed with initial tension, keeping 
in view all the conditions which in nature are operative. 
The mathematical investigations which have been made all neglect some 
of the most important of these conditions, and the laws of successive tensions 
and compressions as thus fixed are, in fact, impossible to be realised rigidly 
in practice. 
For a statement of some of the reasons of this, I may refer to my work 
“ On the Physical Conditions, &c., of Artillery,” p. 152-156, and to note W, 
p. 266 ; but there are many other circumstances besides those there referred 
to, which render uncertain the mutual strains brought into play between 
such superimposed rings, some of which Mr. Longridge (“ Const. Artill.” 
Proc. Ins. C.E,, Yol. XIX., p. 301), has well pointed out. 
If two equal rings only, each of some considerable thickness, have the 
internal diameter of the outer so adjusted to the exterior of the inner—both 
being cold—that after heating and superposition of the external one a very 
moderate tension, say not exceeding one ton per square inch, shall result, it 
will be found that not only is the actual compression of the interior ring 
less than corresponds to the assigned tension of the outer, but the circum¬ 
ferential tension of the latter is less than would be assigned by the differences 
of diameters of the gripping surfaces. The rings, in fact, cling together 
at their opposed surfaces. As the absolute strain is augmented, the trails- 
