ADAPTED HARMONIC COORDINATES

We obtain the necessary and sufficient conditions that a timelike cong ruence has to satisfy to admit three independent adapted harmonic coor dinates of space, proving in the process that if it does then these co ordinates are unique up to a linear transformation with constant coeff icients. As a particular example we prove that irrotational pure Born (i.e. not Killing) congruences never admit a system of adapted harmoni c coordinates of space.