TRANSACTIONS OF NORTHERN ILL. HORTICULTURAL SOCIETY. 269 



we may not be able to ascertain its specific gravity. As I do not propose 

 to discuss this subject here, I will merely state that I hold myself ready at 

 any other time to defend the proposition I have stated. 



I presume the best article ever written upon the law of storms, is 

 found in the Popular Science Monthly of Feb. 1873, by Prof. T. B. 

 Maury, and certainly no one has had a better opportunity for observing 

 atmospheric disturbances over nearly the whole globe. No one who reads 

 that article will ever be led into the delusion that electricity has any influ- 

 ence in the origin or progress of a storm. I should as soon think of 

 attributing the wliirlwind to the leaves which are carried up by it. 



The simplest form of a storm is a local thunder shower. On the 

 afternoon of a still, warm day, when the ground is moist, an immense 

 volume of invisible watery vapor arises from the earth, and continues to 

 ascend until it reaches a cold stratum of air. Here it is condensed and 

 we see the forming cloud, which at first is no larger than a man's hand. 

 It rapidly increases in size and density, for the condensation of vapor 

 causes a partial vacuum into whicli the surrounding air flows, and this 

 being soon condensed the drops of rain begin to fall. The electricity 

 which was carried up from the surface of the earth in the rising vapor, 

 just as we carried it up in the experiment with the electrometer, is now in 

 a region of less density and exhibits a charge that would fall to the earth 

 by gravitation, as the rain drops did, only from the fact that the air is a 

 non-conductor and resists its passage. Large quantities do no doubt ride 

 down on the drops of rain, but the great mass is stored in the cloud until 

 it finally bursts a passage through the air to the earth. 



If the rising vapor should be very dense and warm, and the stratum 

 above extremely cold, the condensation would be so rapid that the air 

 would rush in from all sides to fill the vacuum with great force, and this 

 would set the adjacent columns of air in motion towards the storm cloud, 

 until, perhaps, in a few moments the air for miles around would be in 

 motion towards a common center. For reasons which I will presently 

 give, the air from the south would curve towards the east, and that from 

 the north would curve towards the west, thus giving a vorticose or whirl- 

 ing motion to the center in a direction opposite to the hands of a watch. 

 This would be a tornado, and no other storm, which does not gyrate 

 within a few hundred feet, can properly be called a tornado. The de- 

 structive force of the tornado would naturally result from the tremendous 

 pressure of air from all sides, and to the twisting, wrenching motion which 

 every thing in its path must receive. The rushing currents which meet in 

 this terrible encounter must find some speedy means of escape. They 

 press into the earth and tear up soil, rocks, and massive roots of trees, 

 but the resistance on all sides, and below, at last forces them upwards 

 with the whirling mass of dust, trees, rocks, and every thing animate or 

 inanimate which has been swept from the narrow track of the storm. 

 This dense, rising column expands in its upward course, partly by the 

 centrifugal force of its gyration, and also on account of the decreasing 

 density of the atmosphere, so that it spreads out in tlie form of an 

 inverted cone or funnel. The quantity of electricity which must be 



