the Ocean at Different Depths. 13 



observations. Leaving out this latter observation, we may conclude 

 ihdiifrom the equator to 45° JV. lat. the water of the sea to the depth 

 of one thousand fathoms possesses the same degree of saltness. 



M. Lenz gives also two tables exhibiting the results of 258 ob- 

 servations made on the saltness of the sea at the surface, 105 of them 

 made in the Atlantic Ocean, between 56° 41' S., and 50° 25' N. lat., 

 and 153 in the South Sea and Indian Ocean, between 57° 27' S. and 

 56° 22' N. Lat. From these tables he deduces the following re- 

 sults : — 



1. The Atlantic Ocean is salter than the South Sea; and the In- 

 dian Ocean, being the transition from the one to the other, is salter 

 towards the Atlantic on the west than towards the South Sea on 

 the east. 



2. In each of these great oceans there exists a maximum of saltness 

 towards the north, and another towards the south, — the first is far- 

 tlier from the equator than the second. The minimum between 

 these two points is a few degrees south of the equator in the Atlan- 

 tic Ocean, and probably also in the South Sea, though Mr. Lenz's ob- 

 servations do not extend to latitudes sufficiently low in the South Sea. 



3. In the Atlantic Ocean the western portion is more salt than 

 the eastern, — in the South Sea the saltness does not appear to differ 

 with the longitude. 



4. The greatest specific gravity is found in the Atlantic at the 

 maximum point above alluded to, at 40° W. Long — 1.02856. 



In the South Sea at 1 1° 9' = 1.028084. 



This last is the only one in the South Sea giving a specific gravity 

 reaching 1.028. 



5. In going north from the northern maximum, and south from 

 the southern maximum, the specific gravity diminishes constantly as 

 the latitude increases. 



Whence then, says M. Lenz, come these maxima towards the 

 north and south, why is the maximum not rather at the equator ? To 

 answer this question, we must inquire what chiefly determines the 

 saltness of the surface. Evaporation exercises the greatest influence, 

 and by this evaporation the occurrence of these maxima may be 

 explained. In fact, evaporation is influenced both by the heat of the 

 sun, and by the more or less rapid motion of the currents of air. The 

 solar heat is greatest on the equator, but there, on the other hand, 

 the motion of the air is least. It is remarkable that in the Atlantic 

 Ocean the minimum coincides precisely with the locality of almost con- 



