EFFECT OF TENSION ON CERTAIN ARNORMAL METALS. 



57 



cated, but there seems to be nothing essentially unusual about it. 

 The permanent effect is an increase of resistance. There are also slow 

 changes with time, both on applying and removing the load, as is 

 normal. 



Discussion of Results, excepting Nickel. 



The results obtained above are collected into Table I, in which is 

 given the tension coefficient of observed resistance, the pressure coeffi- 

 cient of observed resistance, the cubic compressibility, the reciprocal 

 of Young's modulus, that is, the extension under unit load, Poisson's 



TABLE I. 



ratio, and the tension coefficient of specific resistance. The unit of 

 stress, whether of tension or pressure, for which the various coefficients 

 is given is the kg/cm-. By the coefficient o^ "observed resistance" is 

 meant the change of resistance, per kg. per cm-, of the wire as actually 

 measured in the experiments, with fixed electrodes. Such a wire 

 increases in length and decreases in cross section under tension, and 

 decreases both in length and section under pressure. The coefficient 

 of " observed resistance," when corrected for the changes of dimensions, 

 gives the coefficient of specific resistance, that is the change of resist- 

 ance of a unit cube. The tension coefficient of specific resistance is 

 obtained by subtracting (1 + 2a)/ E from the coefficient of observed 

 resistance. 



Since the mechanism of conduction is an affair of atoms and elec- 

 trons, and since the number of atoms and electrons in a unit cube both 

 change when the material is subject to tension or pressure, it does not 



