This is a brief review of our present knowledge concerning one aspect of climatic control. The subject is of importance in connection with certain phases of geology such as glaciation and the Wegener hypothesis. According to this hypothesis the continents at various times have drifted apart in an east‐west direction and have also experienced large movements from south to north and from north to south again. This latter feature of Wegener's theory is supported by climatological evidence, and loses its only support if other means of securing large variations in climate are foun