PROF. H. HILDEBRAND HILDEBRANDSSON is continuing his important series of papers on the centres of action of the atmosphere, and the fourth communication, recently received, is entitled “Sur la Compensation entre les types des Saisons simultanes en diff^rentes regions de la Terre” (Kungl. Svenska Vetenskapsakademiens Handlingar, Band 45, No. 11). In his third paper he suggested that the principal cause of the different types of seasons depended very probably on the condition of the ice in the polar seas, and the evidence he brought forward was such as to show that this view had very much in its favour. In the present communication he makes a closer study of these compensations between the types of simultaneous seasons in both winter and summer seasons, and extends his researches to North America. He further directs attention to some analogous results which he finds exist in the southern hemisphere. Thus he finds both in winter and in summer that there occurs an opposition between the north and south of both Europe and of North America, and also probably between the sub-polar regions and sub-tropical regions of the southern hemisphere. There is also, in general, an opposition between the north of Europe and Siberia.