THEORY CONFIRMED BY PHENOMENA. 67 



92. It has been thought, also, that the centrifugal force of 

 the wind blowing over the curvature of the earth's surface, 

 might cause these great depressions of the barometer. But 

 if we suppose the whole of the air in motion with a velocity 

 of one hundred miles an hour, and calculate its centrifugal 

 force according to the principles laid down before, its grav- 

 ity would be diminished, when the wind was west, only 

 about one hundred thousandth of its whole weight, which 

 would cause the barometer to fall .0003 of an inch ; and if 

 the wind is east, it will readily be perceived that its gravity 

 will be increased to the same amount. The theory will also 

 account for the great depression of the barometer, which 

 is known sometimes to accompany the action of volcanoes. 



93. On the 19th of December, 1821, a violent eruption 

 commenced from the old volcano Eyaf jeld Jokkul, in Ice- 

 land, which had been quiet since the year 1612. On the 

 very day of the commencement of the eruption the waters 

 of the rivers which descended from the surrounding moun- 

 tains, were considerably increased. All over Europe dread- 

 ful storms of wind, hail and rain succeeded the commence- 

 ment of this eruption. On the 24th, particularly, extraor- 

 dinary devastations were experienced in very distant parts 

 of Europe, and generally, wherever the hurricane appeared, 

 deluges of rain accompanied it. At Genoa, and many other 

 parts of Italy, the storm is described as particularly severe, 

 (wind S. and S. E.,) many parts of the country and the 

 roads being entirely submerged; and the next day, the 

 25th, the barometer fell unusually low all over Europe, 

 including Great Britain. Now it is highly probable, that 

 the eruption of the volcano threw out immense quantities 

 of vapor, and if so, the condensation of this vapor would 

 heat up the atmosphere by the evolution of its latent caloric, 

 as was explained before, and this heated air would rise and 

 spread out in all directions ; and a vortex being thus estab- 

 lished and kept up by the action of the volcano, both by 



