This meteorological phenomenon arises from the convergance of winds from all parts to one point on account of an extraordinary rarefaction of the air at that point. The currents acquire by their conflict at the place of meeting, and the velocity with which the rarefied air rushes upwards, a centrifugal force, which causes them to recede from the axis of rotation. When the centrifugal force thus acquired becomes equal to the pressure of the atmosphere, a space approaching almost to a vacuum surrounds the axis or centre of motion, and as the whirl, by the action of the most prevailing wind, receives a progressive motion, it is obvious that the pressure of the atmosphere will be removed from every object passed over by the base of the vacuum; consequently destruction may be expected to mark its course. Partly by the removal of the atmospheric pressure, and partly by the whirling of the air surrounding the vacuum, loose bodies, a hay-stack, for example, will be raised with irresistible impetuosity, and dissipated at a great height.