Jefimenko's equations can be found from the retarded potentials φ and A : φ φ ( r , t ) = 1 4 π π ε ε 0 ∫ ∫ ρ ρ ( r ′ , t r ) | r − − r ′ | d V ′ , A ( r , t ) = μ μ 0 4 π π ∫ ∫ J ( r ′ , t r ) | r − − r ′ | d V ′ , which are the solutions to Maxwell's equations in the potential formulation, then substituting in the definitions of the electromagnetic potentials themselves: E = − − ∇ ∇ φ φ − − ∂ ∂ A ∂ ∂ t , B = ∇ ∇ × × A and using the relation c 2 = 1 ε ε 0 μ μ 0 replaces the potentials φ and A by the fields E and B.