120 Temperature Sections Surveyed. 



current flowing from west to east. The zones in the immediate 

 vicinity of the belt of calms are occupied by the equatorial cur- 

 rents, the surface-stratum of which, under the influence of the 

 trade-winds, moves from east to west. At the same temperature, 

 or at nearly equal temperatures, the surface-stratum of these 

 currents must be of less specific gravity than the surface-water of 

 the belt of calms, and this difference would cause the water of 

 the equatorial currents to flow over at the limits of the belt of 

 calms where the trade-winds are no longer felt. At the same 

 time, this difference of specific gravity would be greatest near the 

 eastern end of the belt of calms, where the currents arriving 

 from higher latitudes turning to westward assume for the first 

 time the character of equatorial currents ; and least towards the 

 western end, where the surface-water of these currents, after 

 flowing for some time under an equatorial sun, has already 

 increased in specific gravity. This circumstance would give the 

 water flowing over into the belt of calms a permanent tendency 

 to flow eastward, which, through accumulation of effect along the 

 whole length of the belt, would establish and maintain a per- 

 manent current flowing from west to east in the equatorial belt 

 of calms. It may be remembered that, in the absence of atmo- 

 spheric currents and of differences of temperature, the specific 

 gravity of the water is the sole arbitrator in the arrangement of 

 strata — a principle which, as we have seen, applies on a much 

 larger scale to the changes which take place in the belt of calms 

 of the parallel of lat. 30° N. and S., and in the polar areas of 

 calms. 



Actual observation has established the fact of the overflowing 

 of the water of the equatorial currents into the belt of calms, and, 

 as we might expect, chiefly along the southern limit of the belt. 

 The counter-current, arrested by the continents which stretch 

 across its course, in its turn overflows north and south, and 

 rejoins the equatorial currents on each side of it. 



