Special cases include the interior axial monopole moment ( ≠ ≠ the total charge) M 0 ≡ ≡ ∫ ∫ d ζ ζ λ λ ( ζ ζ ) ζ ζ , the interior axial dipole moment M 1 ≡ ≡ ∫ ∫ d ζ ζ λ λ ( ζ ζ ) ζ ζ 2 , etc. Each successive term in the expansion varies with a greater power of r , e.g., the interior monopole potential varies as r , the dipole potential varies as r 2 , etc. At short distances ( r ζ ζ min ≪ ≪ 1 ), the potential is well-approximated by the leading nonzero interior multipole term.