The centre to limb increase in wave-length, which is observed for medium strength solar lines, occurs almost wholly over the last 10 per cent of the way across the disk. So far, measurements have not been made in this region with nearly high enough disk resolution. The Oxford 35 m telescope, which gives a solar image of radius 165 mm, is used to make detailed observations of limb effect for 261 disk points in latitudes near to the solar equator. The observed points all lie close to the limb, at radial distances from the centre between 85 and 100 per cent of the disk radius. The individual observations show considerable fluctuations about a mean curve, which are attributed to the local velocity fields which are known to exist on the Sun. The systematic differences which appear in the measures from the east limb and the west limb, for radial distances greater than 98 per cent of the disk radius, are shown to be the result of light scattering. In the observational determination of the limb-effect curve it is most important that distortions, due to velocity fields and scattered light, should be taken into account. The new limb-effect curve is in fair agreement with the old determinations, over the range in common. At the extreme limb there is a shift with respect to the centre wave-lengths which, expressed as a Doppler velocity, amounts to 0.53 km sec −1 . This indicates at the extreme limb a red shift of 0.84 km sec −1 compared with the Einstein shift of 0.636 km sec −1 .