326 DR ALEXANDER BUCHAN ON 



the oceans, is found over the Bay of Bengal, and the western part of the China Sea. 

 Nowhere in inter-tropical regions does the salinity of the ocean fall to so low a point as 

 it does over this extensive region. Now, this is the most extensive region of the globe 

 characterised by an unusually heavy rainfall ; and this, eminently so, at all seasons as 

 regards the island-studded portion of the western Pacific. The rainfall of this region 

 began to be pretty exhaustively dealt with by the Dutch about seventeen years ago by 

 the planting of rain-gauges, so that now we are put in possession of good rainfall means 

 from 186 stations. At 99 of these stations the annual rainfall exceeds 100 inches, and 

 at 21 stations it exceeds 150 inches. The largest annual amount at any of the stations 

 is 181 inches, and the smallest 48 inches. During the summer monsoon the rainfall is 

 very heavy over the southern slopes of these islands ; but during the other months, when 

 the north-east trade prevails, the rainfall is very heavy over the northern slopes. Thus, 

 at all seasons, the rainfall is heavy. Hence, this abnormally low specific gravity is 

 occasioned by the low salinity of the water, as well as by its high temperature. 



Several important conclusions follow. The daily amounts are published in the Annual 

 Reports,* which show that daily falls of 5 inches occur often in many places, and on 

 rarer occasions 12 inches a day are precipitated. From the flooding of the rivers, which 

 is thus an event of very frequent occurrence, the deposits of mud must be very great, 

 far greater, indeed, and of wider extent than occurs anywhere else on the floor of the 

 ocean. 



Another consequence is the influence of this wide extended region, characterised by so 

 low a salinity of the surface, over the waters of the North Pacific. Since over this region 

 the specific gravity falls to the minimum anywhere observed in the ocean, the tendency of 

 the surface waters to descend is also at the minimum. Further, since the prevailing winds 

 for a large part of the year blow out of the northern part of this region of low salinity, 

 carrying the surface water with them to north-eastward and to east-north-eastward across 

 the Pacific towards America, water of a comparatively low salinity is spread over this 

 ocean. In all probability this is the origin of the remarkable low salinity of the North 

 Pacific* at the surface and at all depths. The map showing the specific gravity at depths 

 exceeding 1500 fathoms, Map 8, is very striking, seeing it is there evident that the largest 

 extent of the ocean characterised by specific gravities under the mean is the North Pacific 

 Ocean. To the south of this region, across the equator, specific gravities, on the other 

 hand, are above the mean ; but it is to be remarked that the surface of the sea over this 

 latter region has a high salinity. 



It is a striking circumstance that these two wide regions exhibit from the surface to 

 the bottom similar differences in their characteristic salinities, viz., salinities under the 

 mean in the North Pacific, but above the mean in the South Pacific. The specific 

 gravities in the ocean to the cast of Australia, from a depth of 300 fathoms to the 

 bottom, show excess over the North Pacific, Maps 4 to S, from which a circulation of the 

 water of the ocean from the South Pacific northwards may be inferred. 



* Regenwaarneraingen in Nedei-laiid.^eh-Indie. Batavia Landsdrukkerij. 



