SfK WILLIAM SIEMENS, F.K.S. 



427 



point at any rate, I claim as great a strength for the mild steel as 

 the hard. Increase that strain even to 15 tons to the inch, and 

 < ioiiLMtion will still be the same. Take the load of both bars and 

 they will both come back to the original lengths. Go to 20 tons 

 and you will find a difference. The hard steel the steel that will 

 bn-ak at 50 tons to the inch will again return to its original 

 length when the load is taken off, whereas the material breaking 

 with 80 tons to the inch of the original section will show a 

 permanent elongation. This, you will say, is a sign of weakness 

 and condemns that bar ; but I would venture to maintain that 

 t li is is a sign of the strength of the latter bar. Up to the point of 

 15 tons to the inch the two materials are precisely alike, and if 

 the naval constructor takes care that no portion of his ship, 

 viewed as a girder, should receive a greater strain than 15 tons, 

 both materials are able to bear the strain, and they will both 

 deflect to precisely the same extent. But it may be said, materials 

 may be accidentally subjected to a higher strain, and in that case 

 greater strength will be needed. Taking the strain of bumping a 

 ship against a rock, or the ground, or against another ship, the 

 hard steel will no doubt stand a heavier blow, but there is just the 

 possibility that when the blow comes it will fracture, whereas the 

 soft steel we know will lead almost to any extent to sudden impact. 

 Therefore, as far as the safety of the structure against an action of 

 that description is concerned, the soft metal is decidedly the 

 stronger. Then again it has been put very forcibly by Mr. 

 Denny, that very mild steel requires no annealing ; that it is very 

 nearly as strong and as ductile annealed as unannealed ; whereas 

 if you have a harder material, a material containing more carbon, 

 annealing becomes necessary after bending ; after punching 

 certainly, and even after drilling. It becomes a necessity. But 

 by annealing, you take away some 20 per cent, of the strength, and 

 therefore I say it is much better to make at once a material that 

 requires no annealing, that does not assume a strained condition 

 when put into a definite shape, and which maintains its strength. 

 The mild material without annealing, is as strong, or at any rate 

 is as ductile practically, as after annealing ; and, I believe, at some 

 yards punching without annealing has been resorted to without 

 any practical drawback. These are powerful arguments, I think, 

 in favour of the very soft material. There is one more argument 



