A very large amount of valuable work has been done in measuring the forces on models of aeroplane surfaces placed in a wind channel, and the results obtained are of the greatest value to the designer. Doubt has however been thrown on the applicability of the results obtained to calculations referring to the full–size aeroplane in flight, and it is of great importance to obtain definite information regarding the corrections, if any, which should be applied to the wind channel results. The experiments described below were made with the object of comparing the pressure-distribution on an aeroplane wing in flight with the distribution measured on a model of the same wing in a wind channel. The measurements were carried out on an aeroplane constructed by the writer, which for the purpose: of the experiments was flown over the sands at Llanddona, on the east coast of Anglesey. The beach at this place is an ideal one for experiments of this nature, there being a stretch of hard level sand obtainable fully three miles long and over a mile broad.