PHILOSOPIIV Ol' STORMS. 277 



this to the laws of spouthig fluids, and take the square root of tliis num- 

 ber, which would be 30, and multiply it by 8, we will have the velocity 

 upwards in the centre of the storm of 240 feet per second, and so in 

 proportion to the fall of the barometer, A column of mercury one inch 

 square and 30 inches high, the average height of the mercury in the bar- 

 ometer at the level of the sea, being equal in weight to 15 lbs., one inch 

 of mercury will be equal to k lb. weight, aud the barometer being one 

 inch lower under the cloud, the upward pressure of the air must be equal 

 to half a pound upon every square inch of surface. 



With this immense velocity and this great upward pressure it will 

 be readily understood why, in the progress of such a storm, bottles ex- 

 plode their corks, and cellar-floors, roofs of houses, trees, &c., are thrown 

 up as the tornado passes over them, taking oft' the pressure of the air 

 above, while the rapid expansion of the air below and within explodes 

 them. 



The diameter of these storms at the surface of the earth does not 

 generally exceed two or three hundred yards; and as the annulus all 

 around the tornado extends about as far beyond the borders of the storm 

 as the borders are distant from its centre, there will be a calm, not only 

 in the centre, but also all around the meteor, only two or three hundred 

 yards from its borders. And beyond this annulus, in consequence of its 

 greater pressure, the wind will blow gently outwards. 



As the tornado-cloud rises very high at its top, its upper part will be 

 in the upper current of the air, and as this gives direction to the storm, 

 the course of the latter will be governed by the motion of this current. 

 It is known that this current observes the same direction in the same lat- 

 itude, but varying with the latitude, the course of these storms must ne- 

 cessarily vary with their geographical position. 



The variation in the direction of this upper current depends upon 

 several circumstances, viz : — 1 . When the air at the equator rises ten 

 miles from the surface of the earth, as Mr. Esi)y remarks, it will, on the 

 principle of the conservation of areas, be 1-400 further from the centre, 

 and of course it will [\ill back towards the west by more than 1-400 of 

 the equatorial velocity of the earth, eastwardly by its diurnal motion, or 

 about 25 miles per hour, besides the motion, which it may have had to- 

 wards the west at the earth's surface. The upper current, therefore, near 

 the equator, will be found to move from the east to the west. — 2. The 

 meantemperature of the air in the torrid zone is about SO degrees greater 

 than in the frigid zones, and as the mean temperature of the air in the 

 frigid zones is about zero, the air, according to Mr. Espy, is, in conse- 

 quence of expansion by heat, 80-118 of its whole height higher at the 



