  Isoscalar dipole (compression) mode is studied first using schematic
harmonic-oscillator model and, then, the self-consistent Hartree-Fock (HF) and
random phase approximation (RPA) solved in coordinate space. Taking ^{208}Pb
and the SkM* interaction as a numerical example, the spurious component and the
strength in the continuum are carefully examined using the sum rules. It is
pointed out that in the continuum calculation one has to use an extremely fine
radial mesh in HF and RPA in order to separate, with good accuracy, the
spurious component from intrinsic excitations.
