i.e. the components of the convection current , and the electric density multiplied by .
Further I shall write
i.e., the components of and along the three axes; now if we take any two indices h, k out of the series
Then the three equations comprised in (I), and the equation (II) multiplied by i becomes
On the other hand, the three equations comprised in (III) multiplied by -i, and equation (IV) multiplied by -1, become
By means of this method of writing we at once notice the perfect symmetry of the 1st as well as the 2nd system of equations