involved in the Construction of Artillery. 309 



acquired ; even some of the most initial, have still to be asked for. Thus, how 

 almost incredible it seems, that in the whole military and civil literature of the 

 world, as bearing on the subject, it cannot be found that the lUtimate crushing 

 weight for prisms of gun-metal, the coefficients of its extension and compression 

 in terms of the strain ; in fact, not one of its physical data, have as yet been accu- 

 rately determined. Yet this is the main material with which the artillerists of 

 Europe have been dealing, ever since the dawn of modern science (Note DD). 

 .319. To recapitulate in brief the subjects that have been discussed, and the 

 conclusions, so far as they have been arrived at : — 



1°. The molecular structui-e of cast and of wi'ought-iron are now for 

 the first time cleared from the confused and perplexed state in 

 which our knowledge remained, and brought under a single crys- 

 tallographic law ; which, like every truth, when once grasped, 

 not only becomes a light to clear up the darkness and confusion 

 behind, but enables us to predict the results of combinations and 

 circumstances yet to arise. 

 2°. The application of this law to cast-iron in cannon has shown the 

 nature, causes, and positions of " planes of weakness ;" their 

 resvdts in producing fracture, and the modes of their avoidance. 

 3". The application of the law to wrought-iron has shown the true rela- 

 tions of the mass, and mode of formation, to the strength, elasti- 

 city, and other properties of wrought-iron guns. 

 4°. The effects produced by mere changes of mass, all other conditions 

 being the same, have been shown both for cast and wrougl it-iron. 

 5°. The physical conditions of moulding and casting guns, in cast-iron 

 (irrespective of any questions of mere manipulation or of practical 

 detail) have been in a determinate manner discussed, their prin- 

 ciples endeavoured to be fixed, and the relations of temperature, 

 molten pressure of head, rate of cooling, &c., indicated. 

 6°. The relations as to " fitness of make" and quality of cast-iron for gun- 

 founding, of British and foreign cast-irons have been compared ; 

 mistakes as to the supposed superior and inimitable value, of the 

 latter corrected ; and the principles pointed out upon which British 

 cast-iron suited to gun-founding may be readily obtained. 

 VOL. XXUI. 2 s 



