.SYA 1 ll'lUJAM >//; .J//:. V.S", /^.S 1 . 371 



the plate, and that diminution in thickness is accounted for by these 

 forces of compression and extension set up within the metal. If 

 the metal is now subjected to a tearing strain, it has to resist besides 

 this, the abnormal states of strain into which it has been thrown by 

 the punching action, and is therefore destroyed by a force con- 

 siderably less than that, it can resist in the original condition, as 

 the paper shows. Now, if this plate after the punching has taken 

 plan- is subjected to annealing, then this strain between metal and 

 metal will be relieved and the plate will regain its full strength ; 

 or if the strained metal be rimed away, and the hole be en- 

 larged, the plate will have its full strength. But I have the 

 results of some experiments which were made by Mr. Riley at the 

 Landore Works, near Swansea, proving that punching does not 

 ii the plate, but increases the strength of it. His experi- 

 ments were not confined to one or two cases, but comprised a 

 whole series that, strange as it may appear, went to prove that the 

 punching absolutely increased the bearing strain of the punched 

 plates, without annealing, to something beyond the strength of 

 the plate per square inch before it was punched. I should first 

 say he used the precaution to make the die larger, to perhaps a 

 greater extent than is usually done, and the result was, to my 

 mind, that the mass of metal under compression of which I have 

 spoken was not formed, and that the plate was thus relieved from 

 the abnormal strains generally produced in punching. Under these 

 circumstances I can understand that a slight increase of strength 

 should take place, for the same reason that when you subject a 

 bar of metal of any form to strain, its strength will be increased. 

 It is a subject, perhaps, not sufficiently understood, but I have 

 had an opportunity of observing very extraordinary results in that 

 way. Take a bar of iron or steel and subject it to a strain exceed- 

 ing the elastic limit, and allow this strain to be active for some 

 time, in testing the same bar again you will find not only the 

 elastic limit has been raised, but that the ultimate breaking strain 

 is considerably increased. In that way whatever strain you put 

 upon a piece of metal you increase its strength, unless the strain 

 is applied in such a way as to set up contending forces within the 

 metal. Mr. Parker has alluded to two forms of construction with 

 regard to marine boilers. The one is the admirable furnace of 

 corrugated form which is represented by the drawings, and which 



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