In this paper we point out that the general dipole-like symmetry of the interplanetary magnetic field produces a heliospheric latitude variation in the density of modulated galactic cosmic rays. This density variation gives the observed semiannual variation in the galactic cosmic-ray flux observed at Earth, which changes phase with the sign of the solar magnetic field.

We derive an explicit expression for the symmetric cosmic-ray density gradient in the direction perpendicular to the solar equatorial plane and use it to derive a value for the cosmic-ray diffusion coefficient perpendicular to the average interplentary magnetic field.