200 



M. R. Thalen on the Determination of 



Table II. 

 Hard Steel. 

 A = 17*19 square dec. lin. 



Table III. 



Hard Steel. 



A = 3 7*25 square dec. lin. 



No. 



P. 



AL. 



Temp. 





No. 



P. 



AL. 



Temp. 



1 

 2 

 3 

 4 

 5 

 6 

 7 

 8 

 9 

 10 

 11 



221 



280 

 338 

 396 

 454 

 512 

 571 

 628 

 687 

 803 

 920 



ooi 



0-1 | 



o-3 y 



0-5 



0-8 J 



171 



3-5| 



63 ' 



130 f 



34-5 



62-OJ 



20l 

 205 



1 



2 



3 



4 



5 



6 



7 



8 



9 



10 



11 



12 



220 

 278 

 337 

 395 

 453 

 511 

 569 

 627 

 685 

 743 

 801 

 859 



001 

 00 1 

 0-0 f 

 0-0 J 



o-n 



0-3 

 0-8 f 

 2-4 J 

 19-1 

 3701 

 53-6 [ 

 79-4 J 



16°3 

 16-8 



175 













but 



From the preceding Tables, 



E becomes = 360 if t = 200°, 



E becomes = 520 if t 



17 c 



Hence both from Wertheim's and the above experiments, the 

 following rule can be derived : — That the limit of elasticity of a 

 metal can be lowered by heating*. 



§ 6. Explanation of the Discrepancy between Hodgkinson's 

 and Morin's results. 



With the aid of the two principles, that the limit of elasticity 

 can be raised by stretching and lowered by heating, it may be 

 explained how it is that Morin's results differ so materially from 

 those of Hodgkinson, if it is considered that the former worked 

 with wires of 2*5 to 02 millim. in diameter, and the latter with 

 bars. 



It is obvious that if the wire has gone through the screw- 

 plate, it must be considerably stretched, and the limit of elasti- 

 city lie too high. If the wire had passed several times through 

 the screw-plate, its limit of elasticity could easily be determined 

 with accuracy. To illustrate this assertion, I will in the following 

 consider the case more closely where the stretching took place 

 several times successively with the same load. 



Whether the bars used by Hodgkinson were rolled or forged 



* The truth of this follows also from the well-known fact, that the 

 metals in a warm state can be forged more easily than when cold, and are 

 also easier to work after they have once been heated. 



