362 



Mr. Mallet on the Physical Conditions 



Major James's, R.E., experiments on this subject, lie briefly quotes his important result, 

 also confirmatory of the views of the text, — that equal sections, cut from the interior of 

 large castings, are weaker than from portions nearer the surface (vol. i. p. 443). 



The true reason that the central parts of the mass present the largest crystals, is 

 because, having been the longest hot, these crj'stals had most time given them for large and 

 •perfect development, and the centre is the weakest part of the bar, not only because these 

 parts are rendered porous and of low specific gravity, by the drawing asunder produced 

 by the prior consolidation of the external crust, but also because the force of cohesion be- 

 tween the planes of cleavage of the largest developed crystals is the final measure of the 

 strength of this, the weakest, as they are of every other part, in proportion to their deve- 

 lopment. 



Note I.— (Sects. 43 to 50.) 



SrNCE the text has been written, a number of 13-inch sea-service mortars have been brought 

 home disabled from the Baltic, having failed on board the mortar boats, during the bom- 

 bardment of Sweaborg, after a greater or less number "of rounds, in a very remarkable 

 way, — the conditions of which do not appear as yet to be accounted for by the Depart- 

 ments at Woolwich. (March, 1856.) 



I examined these mortars (15th Dec, 1855) in the Arsenal, with much care and in- 

 terest, and advert to them here, as affording the most convincing proofs of the truth of 

 the views I had advanced as to the causes affecting the bursting of ordnance ; and I am ena- 

 bled, by the application of my views to the case, to explain completely the conditions and 

 circumstances that have produced the particular form of failure exhibited by these Baltic 

 mortars. 



Of the whole number of mortars, three have burst, or, to speak more correctly, split, — 

 the remainder still appear to hold together, — but the strong probability is, that there is not 

 a serviceable or trustworthy mortar remaining amongst them. 



List oflS-IncIi Sea Mortars, and Names of Mortar Boats, xcith Nicmber of Rounds f red, 



and result. 



I 



Each of these three mortars was split with almost perfect exactness into equal halves, by 



