gain on descent to the level of 700 metres, to 13°C.(23'.4F.).The smount of heat lo3t by the air during its passaze across the mocntainons region by radiation, and contact with the snowy peaks, cannot be determined.I t is, of course, much greater in winter than in summer, and depencls also on the speed i ~i t l i which the current of air travels.Owing to the width of the mountain-barrier, the main result is complicated by local details ; regions of considerable precipitatiou occurring on the western slopes of each important mountain-range, with subsidiary drier regions in the lea.The last of these regions of precipitation is that of the Rocky Mountain range properly so called, in ilescel~ding f r o 3 which a further addition of heat is n ~a d e to the air, w-hich then flows down as a dry and warm current to the east.