[boylk] electric current ON THE MODULUS OF ELASTICITY 161 



This determined the elastic limit and showed the safe load to apply 

 withoTit permanently straining the material. 



The test wire was now hung from the suspension plates, and was 

 kept stretched, below the elastic limit, for two or three days in order 

 to make it free from kinks. After this the weights were removed, 

 and the wire was given at least an equal period of rest before taking 

 observations. 





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 RESISTflNCC. 



POINT CR . 



A 



C/t THE TO METER 



Fig. 1. 



The source of current through the wire was a battery of storage 

 cells giving a very steady current, which could be adjusted to any value 

 by a rheostat in the circuit. The accompanying diagram (Fig. I.) 

 shows the whole arrangement. The stress-strain curve, up to the 

 maximum safe load, determined from the preliminar)^ test, was taken 

 at first for no current in the wire. After turning on the cur- 



Sec. III., 1906. 11 



