a 
Nov. 24, 1870] 
NATURE 
m1 

needless to say that these methods would not do for the 
construction of agun. The fiercely expanding gas of the 
exploding powder would speedily and fatally detect any | 
plane or point of weakness. Moreover, wrought-iron is not 
equally strong in all directions ; being fibrous in its texture, 
it is twice as strong with the grain as across the grain. 
As in the case of wood, which it is much more easy 
to split than to break, so it is much easier to tear the 

fibres of wrought-iron from each other than to break them 
across. It therefore follows that a gun forged in a solid 
mass, and bored out, would not put the strength of wrought- 
iron at its greatest advantage. Such a gun would be very 
strong along its longitudinal section, very strong to resist 
the strain of the gunpowder to tear out the breach ; but it 
would be only half as strong in its transverse or cross 
section to resist what may be specially termed the burst- 
























































































Fic. 
ing strain. These difficulties were entirely overcome by 
Sir William Armstrong’s system of making a gun of coils 
of wrought iron bars. By that the difficulty of forging a 
large mass is altogether put away ; and the fibre of the 
iron passing round the bore of the gun instead of along 
it, gives the greatest possible resistance to the bursting 
strain of the powder’s explosion. This was a very great 
advance, a most valuable improvement in the manufac- 



3 
ture. It took away the difficulty and expense which were 
the great obstacles to constructing ordnance of wrought- 
iron, and at the same time applied it in such a manner as 
to increase, or rather put at the utmost advantage, its 
strength in resisting the transverse or bursting strain of 
the powder’s explosion, which is the most difficult and 
important strain to overcome. It is for this last that this 
invention deserves its highest praise ; for gun-making is 




















































above all a question of strength of material. The best 
material applied in the best way is hardly strong enough 
to resist the enormous charges behind the enormous shot 
which are required to pierce the armour-plated vessels of 
modern warfare, 
The method of making the coils is as follows ; A> long 
bar of iron is heated to nearly a white heat in a long low 

furnace, and when thus rendered soft, it is hooked on to 
the side of ;what resembles a gigantic reel of iron. This 
reel or core is then turned by machinery, and the glowing 
bar is wound upon it ; being drawn from the furnace upon 
a travelling groove, which, aided by blows on the bar from 
a heavy hammer suspended above and guided sometimes 
by two men, keeps the bar in its proper position as it 1s 
