Observations, around the North Sea, have been collected for twenty stations in the British Isles and for fifteen stations on the Continent during the period 6 to 10 January 1949, and used in a discussion of a large storm disturbance on 8 January. The primary object of the investigation has been to get a picture of the water movements inside the North Sea, and of the way in which these movements are produced, in the course of a storm. Maps of co-disturbance lines in the North Sea have been drawn at frequent intervals and compared with the simultaneous meteorological conditions. The disturbance around the coast, and in the Thames and Humber estuaries, has been examined in detail, and the progression around the coast has been shown to be similar to that of the diurnal tide. Estimates have been made of the changes, during the storm, in the average level of the North Sea, and it has been shown that when the level was rising there was a large inflow of water down the western half; when the level was falling the outflow was up the eastern North Sea. New light has been thrown on several problems connected with storm surges. In particular, it would appear that storm surges of external origin, which hitherto could not be explained in terms of the winds, may be a direct result of an earlier outflow of water produced during a surge when the level has been lowered; also the excessive damping normally observed in the disturbed tide at Southend, which leads to an average value of eddy viscosity in the North Sea somewhat larger than that normally accepted, may be due to a reflexion from the German bight which arrives near the time when the lowest levels are expected. Two estimates have been made of the frictional constant, on the assumption that the tractive force of the wind varies as the square of the wind velocity, and are in agreement with accepted values. Prediction of the disturbance at Southend using a previously established formula has given good results. The disturbance transmitted through the Straits of Dover has been investigated.