322 
DR. HART’S REMARKS, MADE AFTER THE READING OF CAPTAIN BLAKELY’S 
PAPER.* 
Dr. Harr having been called on by Professor Haughton for an account 
of his investigations, said that his attention had been directed to the 
subject by Mr. Mallet, who, about the year 1854,+ asked his opinion on a 
mechanical question, which he represented as an application of the prin- 
ciple of the lever to a cylinder by surrounding it with a series of blocks 
of a considerable thickness, and fastening on a hoop outside these blocks. 
Having expressed his dissent from this idea of converting such blocks 
into levers, he was reminded of the well-known fact, that, when a cylin- 
der is submitted to a strong internal pressure the inner surface is more 
strained than the outer, and consequently yields, and is split before the 
outer surface has borne any considerable portion of the strain. Now, it 
is obvious that this inequality of strain depends on the ratio of the in- 
ner and outer diameters of the cylinder, and, therefore, that Mr. Mallet’s 
outer hoop, being considered as a cylinder whose thickness bore a small 
ration to its diameter, would be more uniformly strained, and, therefore, 
stronger than it would have been if applied directly without the inter- 
vention of blocks. 
As it appeared, however, that this construction would add so enor- 
mously to the weight of a gun as to render it quite unsuitable for the 
purpose of the Russian war, Dr. Hart endeavoured to find some other 
mode of equalizing the strain without introducing these large blocks, 
which merely transmitted the force, without bearing any part of it them- 
selves. 
The obvious suggestion of using concentric cylinders of materials 
which differed in elastic qualities having been rejected by Mr. Mallet, 
the next idea that occurred was that of fitttmg on successive cylinders of 
iron with different degrees of initial tension, so calculated that when the 
internal strain approached the bursting point, all portions of the cylin- 
der should be equally strained. 
Mr. Mallet having at once admitted the validity of this principle, 
Dr. Hart gave him a calculation of the requisite amounts of initial 
strain, deduced from a formula which was afterwards published by Mr. 
Mallet in the Transactions of the Academy ; and it was believed to be 
in conformity with this suggestion that Mr. Mallet’s monster mortar was 
constructed. 
It is said, however, that there are many practical difficulties in the 
way of applying this principle of construction with the requisite accu- 
racy, and that it is liable to lose its initial tensions by time, and by re- 
peated shocks; and it, therefore, seems highly important that Mr. 
Mallet’s original suggestion should not be neglected. The objection of 
weight, although conclusive againstits application to field artillery, would 
probably be of no importance in the case of a fixed battery. The prin- 
ciple of this construction is sufficiently explained by one of Captain : 
* [These remarks, as also those at p. 324, are printed from a memorandum furnished 
by Dr. Hart.—Eb. ] 
+ [We are requested by Dr. Hart to say, that he did not correctly state the date of this 
communication. It was made to him, not in 1854, but in the spring of 1855.—Ep. ] 
