408 ELECTROKINETICS. [PT. II. CH. X. 



the current are due to the total current, and not to the conduction 

 current alone. In insulators the part d^/dt . 4?r, which alone 

 exists in insulators is called the displacement current, since 

 Maxwell calls S/^TT the electric displacement. The corresponding 

 magnetic quantity, which, since there is no magnetic conduction, 

 constitutes the magnetic current, has important physical properties, 

 which will be considered in Chapter XIII. 



