CHAPTER V. 
RIO NEGRO. 
18 3 9. 
The winds proved light and variable during our passage to Kio 
Negro, and we occasionally experienced a southwesterly current, of 
little strength. On the 18th January, when seventy-eight miles 
distant from the mouth of the Rio la Plata, we passed through the 
discoloured water of that river. Its temperature was 4° less than 
that of the surrounding sea. After getting to the southward of the 
river, the direction of the current changed, and it was found to be 
setting to the northward. 
Towards evening on the 19th, we met many discoloured patches 
in the water, and found they proceeded from a species of Salpse, 
which we had not before seen. When the night closed in, the sea 
became very luminous, the vessels in passing through the water 
leaving long bright trains behind them. Vivid lightning in the 
west showed a dark bank of clouds, betokening a storm. About 10 
o'clock p. m., a haze suddenly enveloped us; the temperature of both 
air and water fell from 67° to 57°, ten degrees, giving a cold clammy 
feeling to the air. The water became quite smooth, and the breeze 
died away ; all on deck seemed awakened to a sense of danger. We 
immediately shortened . sail and sounded, but found no bottom with 
one hundred and fifty fathoms line. The vessels of the squadron 
came up in close order, sailing as it were in a sea of silver, from the 
light of which their forms became visible. The effect was beautiful, 
and increased the mysterious and alarming sensation. Shortly after 
we had a change of wind to the southwest, followed by a dense fog, 
which lasted for a day, but the temperature of both air and water 
