Various facts of observations, climatology and topography over the Indian monsoon area during the northern summer have been considered and it is shown that there is no reason to think that the south-west summer monsoon current over the Arabian Sea is primarily of northern hemisphere origin; it is shown that the quantity of air from the west that passes over the Peninsula from the surface to about 600 mb can be accounted for satisfactorily only if one considers the same a continuation of the southerly mass of air which crosses Equator near east African coast in those levels in the longitudinal belt 30°-45°E.

The atmosphere over the Indian monsoon area can with advantage be considered as consisting of two layers, one extending from the surface to about 600 mb level and the other from about 500 mb to 200 mb, the 600 mb to 500 mb layer being considered as transitional layer, the lower and the upper layer developing independently of each other although both may develop simultaneously in some years.