UNIFICATION OF METHODS IN TESTING MATERIALS, XLI, 
whole subject, and the various decisions arrived at. Although 
no formal action of a similar character had yet been taken in this 
matter in England, still a very large amount of attention had 
been given to it both scientifically and commercially, and he failed 
to discover in the recommendations anything that was not well 
known and in many cases the practice there for the last ten years 
or more, he could not see how Professor Warren’s paper had in 
any way improved matters other than from an educational point 
of view. The author had stated in the paper that it was essential 
to accurately determine three factors in each tensile test, one of 
which was the “yield” or “ breaking-down” point, but nothing 
had been said as regards the determination of an apparent limit 
of elasticity, though several purely physical points had been 
touched on. Mr. Selman, however, contended that the “yield 
point” was a very unsatisfactory criterion of the elastic properties 
of materials. If was true that it was generally a well defined 
point on the diagram, and by no means difficult of fairly exact 
determination ; but as the range of its exact position, as regards 
its distance from the limit of elasticity was so very variable, it 
was no safe indication of the exact value or position of the latter. 
Notwithstanding that a number of most elaborate instruments 
had been designed, having for their object the determination of 
the elastic limit, yet the writer believed that it was still an inde- 
terminate quantity, and that the only practical solution of the 
difficulty would be to adopt some definite and convenient point 
lying between the true elastic limit and the yield point. 
Quite recently in America, Professor Johnson, an authority on 
this matter, had proposed an “ apparent limit of elasticity ” based 
on the determination of a tangent point on the diagram at which 
the rate of elongation was 50% greater than what it was at the 
origin. No doubt this was a practical step in the right direction, 
but the writer had found the method difficult of application from 
the uncertainty of being able to locate the exact position of the 
tangent point on account of the personal error and the smallness 
of curvature at the tangent point. Mr. Selman proposed as a 
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