A SOUTH AMERICAN STORM AT SEA. An adventure, encountered by H.M.S. Pylades, on Oct. 12, during a passage from Montevideo to Rio de Janeiro, is shown in one of our Illustrations, from a sketch by Lieutenant W. H. Lewin. The ship met one of those sudden squalls or "pamperos," so frequently experienced off the River Plate. She was going about four knots per hour, under all plain sail, and, as the sea was smooth, the lower deck ports were open. During the morning watch there had been considerable lightning and thunder; but as this was passing off the anticipations of bad weather were dismissed. At six a.m. a heavy squall was seen bearing down upon the ship. It had the appearance of a dense, impervious black wall. The surface of the water in front of it was lashed up into foam; the sea was in a state of violent agitation. When this squall was first sighted it seemed to be about three miles off. It was travelling at so great a velocity that before the necessary orders for shortening sail could be carried out the ship was caught all aback, at first careening over, so that the water, entering the lower deck ports, caused some difficulty and trouble to close them. The ship being driven astern, by being so suddenly taken aback, the water-rushed in through the stern ports, and there was some danger of her being pooped ; but at this time the ship was relieved by the three topmast heads breaking, the top" gallant masts going over the side and the mainyard breaking in two pieces. The ship then righted, and her head was paid off before the wind. The whole affair occupied barely three minutes. The River Plate is well known for the terrific squalls experienced off its mouth; they are peculiar in their suddenness, as well as in the tremendous power of the wind. Blowing off the "Pampas," or prairies of South America, they are universally known as "Pamperos." These winds are different from the squalls or typhoons of other climates. They probably owe their suddenness and intensity more to some magnetic disturbance than to a difference of pressure of the atmospheric column; for though "the barometer," properly understood, is of inestimable value to the seaman, it does not appear to give such clear warning of these pamperos as it will do of storms in other parts of the world. At Montevideo, and off the mouth of the Plate, a pampero is always preceded by a peculiar swell. It has been ascertained that the squall was experienced at Montevideo in great severity on the afternoon of Oct. 11, causing several wrecks; it passed the Pylades at six a.m. next morning, and arrived at Rio de Janeiro at eleven a.m. on the same day, travelling at the rate of forty miles an hour.