Dielectric Polarization Potential and the Law of Superposition for Hard Rubber

If a constant potential $E_1$ is applied to an imperfect dielectric like hard rubber, there is evidence that an electrical potential ${\mathrm{E}}_p$ is built up in the dielectric. If, after a long-time charge at $E_1$, the applied potential is suddenly reduced to a lower value $E_2$, current will flow in a negative direction if $E_p$ is greater than $E_2$. Therefore, a sample of hard rubber was subjected to several exactly similar conditions of charge at $E_1=884\mathrm{}$ volts per centimeter, but different conditions of discharge in the $E_2$ was varied from 829 to 882 volts per centimeter. The results indicate that for hard rubber the polarization potential built up during a long-time charge is approximately equal and opposite to the charging potential. Under the assumption that Curie's law of superposition held true for the existing conditions, the curve of current against time was predicted from data obtained for the same test piece over two years ago. The time when this current changed direction (measured from the instant the lower voltage was applied) was also predicted. The close correspondence between the predicted and actual curves bore out the truth of the law of superposition for the gradients used.