[ BOYLE] ELECTRIC CURRENT ON THE MODULUS OF ELASTICITY 169 



•00257. This gives the value of the modulus as 17-92 x 10® inch-lb. 

 units, or 1-260 x 10® cm.-kgm. units. 



Copper. 



This was a specimen, -0319" diameter, of the soft, annealed, fairly- 

 pure copper wire made by the Montreal Wire and Cable Company for 

 electrical work. 



It does not stand much tensile stress, the elastic limit corresponding 

 to a stress of 8,975 lbs. per sq.inch (=695 kgm. per sq. cm.), with 

 a strain of 000579. This gives the modulus the value 15-49 x 10« 

 cm. -kgm. units. 



"When the loading gets beyond the elastic limit there is the slow 

 pulling out of the wire shown in the other materials, so that no definite 

 extension can be said to apply to any weight. 



Aluminium. 



Specimen was of -0319" diameter. Elastic limit corresponded to 

 a stress of 12,420 lbs. per sq. in., or 874 kgm. per sq. cm. 



The calculation for the modulus gave a value 15-49 x 10® inch-lb. 

 units, or 1-090 x 10® cm.-kgm. units. 



There is not much pulling out below the load corresponding to 

 the elastic limit, though, after that, it is quite appreciable. The material 

 breaks when the load becomes a little greater than the elastic limit 

 load. 



Steel. 



This specimen was one of the strongest of pianoforte steel, dia- 

 meter, -0191". The stress for the elastic limit was as high as 246,000 

 lbs. per sq. inch, or 17,320 kgm. per sq. cm. The value of the modulus 

 was 28-96 xlO® inch-lb. units, or 2-037 x 10® cm.kgm. units. 



Conclusion. 



M. C. Xoyes, in her work on the influence of temperature and of 

 an electric current on Young's modulus, finds that for steel, although 

 temperature causes a decrease in the value of the modulus, yet, when 

 a current passes through the wire, the modulus is the same as when 

 there is no current.^ In the following 3^ear she finds that an electric 

 current in a copper wire has no eft'ect on the modulus.^ 



From the data and curves obtained here, the only^ conclusion to 

 take is that the passage of a current in a wire does not alter its 



^ Noyes — Physical Review, Vol. 2, page 277, 189.5. 

 * Noyes — Physical Review, Vol. 3, page 432, 1S9G. 



