HYDROGRAPHY. 



I determined to await the land-breeze, which came off at an early 

 hour in the night, when we made sail, and stood to the southward. 

 On the 9 th we had heavy showers, with lightning, but no thunder, 

 succeeded by a southeasterly wind, and a reduction of temperature, 

 which gave us great relief, as we had been suffering from the heat for 

 the last eight months. On the 11th, when we had reached the lati- 

 tude of 30° south, the air had assumed a very perceptible change in 

 respect to its hygrometric state, being now much drier, and giving a 

 feeling of more elasticity than we had experienced for some months. 

 We had fine weather, with the wind from the northward and east- 

 ward, increasing towards evening. On the 15th, we had reached the 

 latitude of 34° south and longitude 51° west, just to the northward of 

 the Rio de la Plata. The current previous to this time had been ex- 

 perienced to the southward and westward, and as we were now on 

 soundings in 80 fathoms, of ooze, the current was tried by anchoring 

 a boat, and was found to be setting north-by-west 6 fathoms. 



On the 18th January, the twelfth day from Rio, in latitude 37° 

 south, longitude 52° 40' west, we passed into the discolored water 

 of the Rio de la Plata. The line of demarcation on entering it was 

 very distinct, and its temperature 4° less than the surrounding ocean. 

 We continued in it until after passing to the southward of the latitude 

 of the La Plata, being about 80 miles in width. To the northward 

 of latitude 40° we again struck soundings, in 55 fathoms, which proved 

 to be sand. From this it is probable that the ooze deposit of the 

 river has spread over an area of great extent north and south. 



The great fall of temperature, both in the water and air, which we 

 experienced in latitude 40° south (some ten degrees), with thick fog, 

 led me strongly to believe that we were in the immediate vicinity of 

 icebergs, which have often been seen in this latitude, and longitude 

 50° west. Commodore Wadsworth, in the Vincennes, on a former 

 cruise, encountered them in latitude 39°, and longitude 54°, and had 

 great difficulty in escaping from them; on this point navigators should 

 be cautious at this season of the year (January). The best course to 

 pursue in order to avoid the ice, I am satisfied, is to keep near the 

 Patagonia coast. Ice has been seen in great quantities to the east of 

 the Falkland Islands, and although commonly in the form of field ice, 

 yet it is dangerous, requiring the greatest care on the part of the navi- 

 gator. By taking the open sea to the eastward, instead of getting out 

 of it, the probability is it would be encountered in much greater quan- 



