38 



ME. J. MU1R ON THE RECOVERY OF IRON FROM OVERSTRAIN. 

 Diagram No. XII. (Mechanical vibration.) 



Extensions-diminished as explained on page IB 

 Scaie - 1 unit = j^n of An inch. 1 



Curve No. 1. Illustrates primary loading. 



1'. Is after mechanical vibration. 

 2. Immediately after No. 1'. 

 3. | hour after No. 2. 



Curve No. 4. After mechanical vibration. 



5. A 2nd loading, 16 \ hours after No. 4. 

 6. After mechanical vibration. 

 7. 4 minutes at 100 C. 



Before the experiment corresponding to Curve No. 1 was performed, a test was 

 made to ensure that such vibration aa was contemplated would have no effect on the 

 elastic properties of the primitive material. The specimen was loaded tffl a stres; 

 20 tons per square inch was attained, and the load was then removed. The extenso- 

 meter readings obtained are shown in the first column of the table given above. The 

 specimen was then taken out of the testing machine and vigorously tapped with a 

 hammer, so as to make it ring in various modes. It was then re-tested and the 

 second column of readings shown above was obtained. These readings are slightly 

 less than those obtained during the first loading, but this was to be expected on a 

 second loading, though, perhaps, to scarcely so great an extent. Large yielding 

 occurred during this test at 23 tons per square inch, which is the known yield-point 

 of the material Hence violent vibration may be said to have had no effect on the 

 primitive material, or if it had a slight effect, it was shown in the annihilation of the 

 causes of small departures from accurate obedience to the elastic law. 



Curve No. 2 of Diagram No. XII. shows the specimen to be in the ordinary semi- 



