6 Proceedings of Boyal Society of Edinburgh. [sess. 
the most remarkable results of the inquiry that these areas of 
high surface-temperature and high salinity are found represented 
at all depths down to the bottom of the sea, with just a tendency 
to extend with increase of depth. On the other hand, on the 
eastern sides of the oceans, whence the trade-winds start on their 
course, there is an upwelling of colder water from the greater 
depths towards the surface, in a manner similar to what Dr 
Murray, in a paper read some years ago to this Society, showed to 
occur in the case of the Scottish lochs when strong winds sweep 
over their surface. These cold areas of a lower surface-temperature 
and salinity are also continued down to the bottom, with a like 
tendency to expansion of the areas with descent. It is highly 
probable that the restriction of these respective areas to the same 
parts of the ocean for all depths would not have obtained if the 
depth of the ocean in comparison to its extent had not been so 
insignificant. The presence of ice-cold water at the bottom of the 
ocean in all latitudes implies a constant supply of water of a very 
low temperature from the Southern and the Antarctic Oceans, and, 
in a less degree, from the Arctic Ocean. This slow-moving current 
of cold water athwart the bottom of all parts of the ocean is effected, 
on the one hand, by the reduction in intertropical regions of the 
surface-waters by evaporation, and by the extra-tropical winds 
blowing polewards ; and, on the other hand, by the greater specific 
gravities of the ocean in high latitudes together with the “ head ” 
of water accumulated there by the S.W. winds of the Northern 
and the N.W. winds of the Southern Hemisphere. There are 
subsidiary causes which powerfully influence oceanic circulation. 
Chief among these are abnormally heavy rainfalls — such as occur in 
the west of the Pacific ; under-currents of high temperature and 
salinity from the Mediterranean and the Red Sea ; the causes 
leading to the extensive upwelling seen in the Pacific to the south- 
east of the Sandwich Islands, and similar positions in the Atlantic 
and Indian Oceans ; and the intertropical position of the line of 
lowest mean barometric pressure, resulting in a temperature much 
higher in the North than in the South Atlantic, and much higher 
in the South than in the North Pacific Ocean. 
Mr A. J. Herbertson communicated a paper in continuation of 
his researches on Hygrometry, in which he describes the apparatus 
