Special cases include the axial monopole moment (=total charge) M 0 ≡ ≡ ∫ ∫ d ζ ζ λ λ ( ζ ζ ) , the axial dipole moment M 1 ≡ ≡ ∫ ∫ d ζ ζ λ λ ( ζ ζ ) ζ ζ , and the axial quadrupole moment M 2 ≡ ≡ ∫ ∫ d ζ ζ λ λ ( ζ ζ ) ζ ζ 2 . Each successive term in the expansion varies inversely with a greater power of r , e.g., the monopole potential varies as 1 r , the dipole potential varies as 1 r 2 , the quadrupole potential varies as 1 r 3 , etc. Thus, at large distances ( ζ ζ max r ≪ ≪ 1 ), the potential is well-approximated by the leading nonzero multipole term.