23:2 
MINUTES OF PROCEEDINGS OF 
which all parts of the mortar below the cup with the bed are driven backward 
and downward on discharge. If the material below the cup, the bed 
included and the platform, were perfectly rigid and unyielding, then the 
stress upon the longitudinal bolts would be a minimum; but with a 
springing and yielding platform, the mortar approximates to the same state 
of things as if it were fired suspended in mid air, when the stress on these 
bolts -would be a maximum. Platforms on land for such mortars, should 
consist of at least three layers of well fitted and united whole baulk timber, 
very solidly laid upon uniformly dense material well compacted beneath them. 
In another point, also, those mortars were placed at a great disadvantage. 
In 1855-6 the coarsest grained powder known in our service—I believe 
also then in any other—was the L.G., or large grain cannon powder. Its 
rapid combustion and brisante qualities I was not ignorant of, and saw how 
much these must be exaggerated when such then unexampled charges as 
from 40 to 80 lbs. were fired. I accordingly made application through 
Colonel Pickering, B.A., Secretary of the Ordnance Select Committee, to have 
some of what is now known as “pebble pow r der” made specially for the trial 
of these mortars; but I found that if the tedious routine of application were 
formally gone through, that then probably this coarse powder might after 
much delay be directed to be made at Waltham Abbey works; but that in 
the end, unless the mortars could be served with the ordinary cannon powder 
of the service, they probably would not be deemed satisfactory. I was there¬ 
fore reluctantly obliged to use a powder far too fast burning either to give 
fair play to the mortars or the best ranges to the shells. 
As a palliative, I proposed and was permitted, to divide the charges into 
5 or 10 lbs. flannel close bags, as stated in the memoir; but at the intensely 
high temperature of flame produced by such heavy charges, the rate of 
burning did not appear to be sensibly diminished by this mode of sub¬ 
division. 
At the present day, no artillery officer would propose to fire charges such 
as those of these mortars, unless composed of pebble or of prismatic powder. 
It is necessary I should also offer a few words of explanation as to how 
and upon what principles the superimposed integrant rings of these mortars 
were shrunk upon each other, so as to give the required initial tension. 
This was called into doubt, for his own objects, by the late Captain Blakety, 
who unauthorisedly published, in appendix E to his pamphlet “On con¬ 
structing Cannon, Ridgeway, London, 1858 (see also “Proceedings 
Boyal Irish Academy,” Yol. VII. p. 338), a private note in reply by 
Dr. Hart to a letter from Capt. R, in which Dr. Hart rather incautiously 
and quite incorrectly states that he believed I had “ utterly neglected to 
apportion the tensions of the successive rings to calculation.” 
The circumstances will be best explained by subjoining a copy of a letter 
addressed by me to Dr. Hart himself 
{Copy). 
Delyille, Co. Dublin, 
September 9, 1858. 
My dear Sir, 
I have sent you by this post (open ended) a copy of a pamphlet by Captain 
Blakely, K.A., which I recently chanced upon in London. I know not whether 
you have before seen it. 
