The barometer always falls pretty steadily for from two to four days before the pampero, and always rises for some days after the squall. Temperature is always very high before the squall, and then the sudden change of wind sends the thermometer rapidly down, sometimes as much as 33° in six hours. Thunder accompanies about three out of four pamperos; but more or less rain always falls, except in the rarest cases. The wind before this class of pampero almost invariably blows moderately or gently for some days from easterly points, and then with a sudden burst the southwest wind comes down with its full strength, and, after blowing thus from ten to thirty minutes, either ceases entirely or continues with diminished force for a certain number of hours. In all cases but one the upper wind-currents have been seen to come from the northwest before, during and after the pampero. The general appearance of a pampero will be best understood by a description of an actual squall. “In the early morning of a day in November, the wind blew rather strongly from the northeast. The sky was cloudy, but not overcast, save in the southwest horizon. The clouds were moving very slowly from the west, or a little south of it, throwing out long streamers eastward. About 8 A. M. the threatening masses in the southwest had advanced near enough to show that at their head marched two dense and perfectly regular battalions of cloud, one behind the other, in close contact, yet not intermingling, and completely distinguished by their striking difference of color, the first being of a uniform leaden gray, while the second was as black as the smoke of a steamer. On arriving overhead, it was seen that the front, although slightly sinuous, was perfectly straight in its general direction, and that the bands were of uniform breadth. As they rushed at a great speed under the other clouds without uniting with them, preserving their own formation unbroken, their force seemed irresistible, as if they were formed of some solid material rather than vapor. The length of these wonderful clouds could not be conjectured, as they disappeared beneath the horizon at both ends, but probably at least fifty miles of them must have been visible, as the ‘Cerro’ commands a view of twenty miles of country. Their breadth was not great, as they only took a few minutes to pass overhead, and appeared to diminish from the effects of perspective to mere lines on the horizon. At the instant when the first band arrived, the wind--which was still blowing, and something more than gently, from the northeast--went round by north to southwest; at the same time a strong, cold blast fell from the leaden cloud, and continued to blow till both bands had passed.” A whirlwind may be described as a mass of air whose height is enormously greater than its width, rotating rapidly round a more or less vertical axis.