214 ON THE WING. 



having a thickness of metal in all parts of the arch 

 equal, or 3-i6ths of an inch thick, capable of bearing 

 an internal pressure of 6,022 Ibs. to the inch of the 

 tube." 



BARREL FIGURE. 



" The generality of barrel makers spoil their metal 

 by an attempt to obtain figure ; for all extreme twist- 

 ings in the rod depreciate the metal, by separating the 

 fibres ; to .borrow a simile, they obtain only an over- 

 twisted rope. This is not only disadvantageous, but 

 useless ; for the extreme density of the metal ren- 

 ders the figure difficult to be shown distinctly, as acid 

 acts upon it but slightly, and never so well as on metal 

 fabricated from two differently constructed carbonized 

 materials. 



"Many conjectures have been advanced, and an 

 endless discussion created, to account for the watering 

 or 'jowher ' in Oriental sword-blades, and genuine 

 Damascus gun-barrels. Anything approaching the 

 truth is seldom met with ; though I think the expla- 

 nation is very simple. It must be well known that 

 there is an immense variety of different qualities in 

 both iron and steel ; no uniformity of quality is found 

 in two productions out of a hundred. The very ore, 

 the coal, the presence of oxygen, the excess of it, all 

 vary the quality of the material. An excess of carbon 

 is more detrimental than a scarcity ; for where carbon 

 has once been, it leaves an indelible mark, and though 

 extracted to as great an extent as practicable, it 

 leaves a residue that possesses an affinity to absorb 



