Cyclones or hurricanes of this class, do not occur in our northern States; tornadoes, however, do in rare instances. These extend in width not more than a few hundred yards, or even feet, and come and go within the space of one or two minutes. In power and violence, however, they are as destructive as the cyclones. In tornadoes the storm-cloud, in nearly all instances, has a rotary motion; the wind also sweeping forward progressively at the rate of from five to twenty miles an hour. Science has shown that in the latitude where these rare visitors come, they nearly always proceed from south-west to north-east. In the great Illinois hurricane in May, 1855, that passed over Cook county, it is said that a family of nine persons was carried up in the air in a frame house, four of the nine being killed outright and the remainder severely injured. The house went to pieces amid the fury of the storm. Generally these great storms are accompanied by peculiar electrical phenomena, though not in all instances. Rain and hail often go with them. The storm-cloud of a tornado is nearly always funnel-shaped, the small end of the funnel extending downward. It looks like an immense balloon, and revolves on its axis with fearful rapidity. The air beyond the limits of this cloud is also in rapid motion, but merely partakes of the character of a very high wind and is not particularly destructive. The death-dealing and destructive power of the storm is confined to the limit of the conical cloud. All movements for personal safety must extend entirely beyond the circumference established by the rotary motion. The primary cause of these tornadoes is probably due to a low barometric condition of the atmosphere accompanied by a high temperature, and spreading over an area of very irregular shape. An area of high barometer, accompanied by a low temperature, encroaches upon the former, and then comes the mighty effort to equalize these two different conditions of the atmosphere and restore the equilibrium, which is the constant effort of nature. The more diverse these two conditions are, the greater will be the struggle of the giants in the contest. Of course the electrical condition of the atmosphere existing at the time may form a very important factor in the tornado which may follow. What was the character and condition of the atmosphere on the memorable first of July last, when the storm-cloud which spread desolation over a narrow belt of not more than two hundred yards at most, swept across the western half of Chester county, Penn'a? The middle part of the day was hot and oppressive; the thermometer stood at about 92 and the barometer about 29.6. The atmosphere seemed very close, and the inhaling of air in the lungs was attended with rather more difficulty than usual. I remarked to a friend that there was a peculiar condition of the atmosphere, and yet who could have foretold the terrible results of that afternoon? The oldest inhabitant had never heard of a