240 
PEOFESSOE FOECHIIAMMEE ON THE COMPOSITION 
5° N. lat. and 5° S. lat. with those between 5° and 20° to the North and of 5° to 30° to 
the South, we find the interesting fact that the water flowing in the vicinity of the 
Equator contains less salt than that which flows both to the north and to the south of 
it. For the equatorial region (5° S. to 5° N.) the mean of six observations is 35*575 
per 1000 ; or if we leave out a sample from Sir James Ross, from 150 fathoms’ depth 
(that from the surface is wanting), it is 35 ‘520. From 5° to 20° N. the mean of eight 
analyses is 36 ’2 79, and from 5° to 30° S. the mean of six analyses is 36*631 per 1000. 
This difference is still more striking on comparing the salinity of the equatorial region 
with that of the northern Atlantic region (second region), whose mean is 35*932 per 
1000 salt. It deserves further attention, that the maximum of the equatorial region is 
below the mean of its neighbours both to the south and to the north. It appears to me 
that this curious fact can be explained only by the vast quantity of fresh water which 
the Niger, the Ogaway, and a number of other West African rivers carry in this region 
into the sea, which all gets into the equatorial current, and moves to the westward. It 
is evident that this warm water must increase its relative quantity of salt by evaporation 
during its motion across the Atlantic, and a comparison of the analyses of the single 
samples of the water from the equatorial current shows that this effect really takes 
place. The easternmost sample contains the minimum, with 34*238 per 1000, and the 
two westernmost samples contain the greatest quantity of salt, with 36*084. Thus the 
equatorial current appears as a continuation of the large West African rivers of the 
equatorial zone, which dilute the sea-water of the equatorial region with about 8 per 
cent, of fresh water, and thus counteract the great evaporation. While the equatorial 
current continues its course along the north-east coast of South America, it receives and 
carries with it the waters of the Paranahyba, the Araguai, the Amazon river, the Esse- 
quibo, the Orinoco, and numerous smaller rivers of the north coast of South America ; 
but though I have no observations from this part of the current*, the fact is shown by 
three observations from the sea in the neighbourhood of the Danish islands of St. Croix 
* [When my remarks on the equatorial current between Cape Eoque and the West Indian islands were 
written, I was not aware of the very interesting observations which General Sabine made in 1822, on the 
influence of the water of the Amazon river on that of the Equatorial current. I shall now insert them here, 
their hearing being in the same way as my deficient observations. 
In 5° 8' N. lat. and 50° 28' W. long, a distinct line of separation was observed between the pure blue water 
of the ocean and the discoloured water mixed with that from the Amazon river, the mouth of which was about 
300 miles distant. The blue water had a specific gravity of 1-0262, which according to my calculation (p. 37) 
is =33-672 per 1000 salt, while the water on the other side of the line of separation was 1-0204=26-345 per 
1000 salt; further on, under the influence of the river, it was 1-0185=23-800 per 1000 salt. But the river 
water kept on the surface and in a depth of 126 feet, the specific gravity was l-0262(= 33-672 per 1000 salt).. 
In 7° 1' N. lat. and 52° 38'-5 W. long, the specific gravity was 1-0248=31-905 per 1000 salt, and in 120 feet 
depth again 1-0262 specific gravity. 
In 7° 5' N. lat. and 53° 30' W. long, it was 1-0253=32-549 per 1000 salt. 
In the Gulf of Paria, off the mouth of the Orinoco, the specific gravity was 1-0204=26-345 per 1000 salt, and 
in crossing one of the branches of the- river itself the specific gravity was found to be only 1-0064=8-234 per 
1000 salt. See ‘An Account of Experiments to determine the Figure of the Earth, by Edwakd Sabine. London, 
1825.’— G, F., April, 1865.] 
