involved in the Construction of Artillery. 283 



previous mode of manufacturing wrought-iron artillery. The molecular condi. 

 tion of the iron and its coefficients of strength would not become impaired, until 

 after a thickness of from 2 to 3 inches of metal had been reached. 



The problem, therefore, seems within easy reach, as respects small calibers, 

 and these would be the materials from which to form a wrought-iron field artil- 

 lery. (Note V. ) But the question remains, how are all the larger and heavier, and, 

 perhaps, much more important calibers, to be safely produced in wrought-iron ? 

 Here, production in single masses seems nearly impracticable, even if our 

 machinery of production were increased to the magnitude and power, requisite 

 to enable rolled masses of the necessary size to be attained ; for the length of 

 time alone indispensable, to both the heating and the cooling of those huge 

 pieces, inevitably results in changes of molecular structure of an injurious 

 character (chap. 23) to the metal. 



272. We are, therefore, limited to the use of such forms and such dimen- 

 sions of iron as can be rolled with determinate direction of fibre, and of such 

 dimensions, as shall be heated and cooled with the required rapidity. 



The larger calibers of wrought-iron ordnance must, therefore, be built up 

 in separate pieces, and in such a manner, that the tangential, and the longitu- 

 dinal stretching strains, shall be resisted, each by masses, whose directions of 

 fibre (or crystals), and therefore whose maximum elastic extension shall coin- 

 cide with these directions respectively. 



We are now to analyze these forces, and 

 consider how this combination may be effected, 

 and whether the necessity of combining a num- 

 ber of separate pieces to form the whole body 

 of the gun is attended with advantage or disad- 

 vantage to its materials, in resisting the forces 

 produced by the explosion of the charge. 



273. Let the shaded portion a,/, d, be the 

 transverse section, and a unit in length, of a 

 gun formed in one mass. The pressure of the 

 elastic fluids of the explosion, acting upon ^'s- '■ 



the interior of the cylinder, is resolved in at least three distinct directions of 

 forces acting upon or within the metal of the gun, and tending to produce as 

 many distinct distortions. 



