THREE CRUISES OF THE “ BLAKE." 
298 
quently ; while the carbonic acid, coming from the shores and 
from the disintegration of the rocks, is held in solution. Were 
it not for the constant movement of the sea, the stagnation of 
life would soon become universal. 
The specific gravity of ocean waters, free from the effects of 
local disturbing influences due to proximity of land, is found to 
vary within very narrow limits, — between 1.024 and 1.028," 
reduced to a standard temperature of 60° Fahrenheit, or 15.56° 
Centigrade. Mr. Buchanan found that the concentration of 
the waters of the Atlantic was greater than that of either the 
Pacific or the Southern Ocean, and greater in the North Atlantic 
than in the South Atlantic. Below the surface the specific grav- 
ity decreases gradually until a minimum is reached at about eight 
hundred or one thousand fathoms,’ and then increases slightly 
towards the bottom, where in the South Atlantic and Pacific 
quite a uniform specific gravity prevails.’ In the equatorial re- 
gions the specific gravity first increases to a depth of from fifty 
to one hundred fathoms, and then follows the same course as in 
other parts of the ocean. 
In the North Atlantic, the bottom specific gravity is compar- 
atively high. The principal causes for this concentration are 
apparently the tradewinds, which, as has been suggested, in- 
crease in their capacity for taking up moisture as they proceed 
on their course from colder to warmer latitudes of the trade 
regions in the Atlantic; in higher temperate latitudes the oppo- 
site effect is produced by prevailing westerly winds, which soon 
become saturated with moisture in the warmer latitudes from 
which they rise. А similar concentration is also brought about 
by the formation of ice. The accumulation of salt in the 
northern Atlantic is naturally removed by the slow flow from 
north to south which probably takes place in the North Atlantic 
below the depth of about one thousand fathoms. Similar condi- 
tions undoubtedly exist in the Pacific, but it is more difficult to 
trace them. 
1 The differences in specific gravity due sea-water is approximately compressed 
to differences of temperature are far in the ratio of 0.0009 for every hundred 
greater than those arising from the per- fathoms of depth. 
centage of salt. 8 Of 1.0257 to 1.0259. 
2 Buchanan’s observations show that 
