This is another gauge in which the potentials can be expressed in a simple way in terms of the instantaneous fields A ( r , t ) = − − r × × ∫ ∫ 0 1 B ( u r , t ) u d u φ φ ( r , t ) = − − r ⋅ ⋅ ∫ ∫ 0 1 E ( u r , t ) d u .