STANDARD works on oceanography usually show water temperatures for February and August, on the normally valid assumption that these months represent the seasonal extremes. Various aspects of water circulation and climatic rhythm in the Western Australian region are quite anomalous1,2 and cannot be explained in terms of atmospheric or terrestrial factors alone. In the course of this investigation, it seemed advisable to determine the time of mean highest and lowest temperatures at the surface of the ocean. The US Naval Oceanographic Office's charts3 were used because they embodied the most numerous data.