Secondly, we must exclude transformations in which the axes are changed from a righthanded system to a lefthanded system, for then equation (1) would imply a change from positive electricity to negative electricity. Such a transformation, however, becomes relevant when equation (1) is replaced by

(1)' 
equation (2) by

(2)' 
and equation (3) by

(3)' 
These relations also imply that the transformation is a spherical wave transformation, and so a transformation which changes a righthanded system of axes into a lefthanded system is relevant, but the formulae of transformation of the components of the electric and magnetic force are not the same as before. The sign of θ will be determined later by the condition that a righthanded set of axes is transformed into a lefthanded set. If
corresponding sets of axes are both righthanded or both lefthanded. If, on the other hand,
the axes are righthanded in one system and lefthanded in the other.
It is easy to establish a relation between the two quantities
Since
