Spectroscopic measures of the rotation of the Sun are given for 190 photospheric positions in the latitude range 45–75° (section 1). After a correction for limb effect, made from the measures themselves (section 2), these velocities show meridional currents directed towards the equator and a difference of rotation in the northern and southern hemispheres (section 3.1). Interpreting these velocities as the result of a balanced motion between a postulated meridional pressure gradient and an inertial Coriolis force, the polar retardation of the Sun's rotation appears to be due to zonal currents moving towards the apparent east in an otherwise uniformly rotating photosphere (section 3.2). A re-discussion of unconfirmed measures of limb darkening in 1959–60 shows differences of polar and equatorial temperature which may be the origin of the meridional pressure gradient and which quantitatively describe the observed velocities (section 3.3). Moreover from an analysis of the meridional components of velocity some evidence is found of Rossby waves, a phenomenon characteristic of well-established zonal winds in the Earth's atmosphere (section 4). From these zonal currents which tend to brake the rotation of the photosphere and from the suspected polar heating, it is speculatively inferred that beneath the hydrogen convection zone the Sun may complete a rotation in some 12.5 hours (section 5).