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THE SCIENTIFIC PAPERS OF 



which I wish to adduce, that is, if the material of the low elastic 

 limit happens to be chilled accidentally after manufacture, this 

 chilling does not interfere with its strength to resist blows or 

 sudden strains ; whereas with a hard material you will even come 

 to the point of contemplating with great concern the safety of the 

 structure when made, I believe it is much safer to adhere to a 

 material which stands an extreme bending test, and to assign to it 

 the same practical limit of load which you would to a harder 

 material. In dealing with wrought iron the practical limit 

 generally allowed is one quarter breaking strain, whereas in dealing 

 with cast iron we allow one-sixth breaking strain as the safe 

 working limit. What I maintain is, that in dealing with mild steel 

 the safe working limit may safely, for similar reasons, be extended 

 to one-third the breaking strain ; and if this were agreed to, a 

 ship constructed of mild steel need not be made any thicker in its 

 scantlings than one having a breaking strength of 35 tons, such as 

 I am sorry to find is now being advocated by ship-builders. Re- 

 garding the remark made by my friend Mr. Bramwell, I am ready 

 to agree with him in principle to this extent : that if a steel could 

 be produced of increased ultimate strength without in any way 

 trespassing upon the quality of extra mild steel, of maintaining 

 its ductility after tempering, and after punching or bending, that 

 material would deserve the preference ; but so long as the strength 

 has to be preserved at the expense of ductility, I must maintain 

 my objection to an advance, or rather a retrogression, in that 

 direction in ship-building. I may add one word of entire approval 

 of the opinion put forward by Mr. Denny, that all plates ought to 

 be tested at the works of the maker, in the most careful and 

 rigorous manner possible, and not at their destination, and also 

 that for riveting steel plates, steel rivets should be used. 



