42 PHILOSOPHY OF STORMS. 



many hundred yards, must have been quite adequate to 

 produce this effect, if it could be brought to act instantaneous- 

 ly, or even very suddenly, which, in the present case, the 

 whole description of the phenomena induces me to believe 

 was the fact. Now, the diminution of the weight of the 

 column of air under a cloud of great perpendicular diame- 

 ter, when the dew point is very high, may be shown to be 

 so great that the barometer under that cloud would fall as 

 much as it is known to do in the midst of great storms, and 

 if it falls only one inch in a water-spout or tornado, the 

 air would spout up with a velocity of two hundred and 

 forty feet a second, and, on coming over a house suddenly, 

 the pressure on the outside would be diminished half a 

 pound to the square inch, and the air within would thus be 

 able to explode any ordinary wall. 



Windows, also, have been known to have been burst open 

 outwards in this country, by a violent and narrow storm, 

 attended with hail, even when the houses were not thrown 

 down; but as this might sometimes occur when an open 

 door might be directed to a horizontal current, it is not ad- 

 duced here as proof positive that this effect was produced 

 by an upward vortex. Nevertheless, as the same spout 

 which burst out windows, also lifted up, and carried to 

 a great distance, heavy materials, these facts may well be 

 adduced as favorable to the theory. In one case, however, 

 which may be considered very strong in favor of the theory, 

 the roof was taken off from a barn, and the grain in the in- 

 side carried out at the top, without the walls being thrown 

 down. 



In the eighty-eighth volume of the Journal de Physique, 

 page 274, is an account of a great many spouts, both by 

 sea and land. One of these, in the south of France, un- 

 roofed eighty houses, dispersed through the country the 

 sheaves of corn which it carried out of a barn, broke the 

 doors and windows of a chateau, and tore up the pavement 



