68 PHILOSOPHY OF STORMS. 



mechanical force and by a diminution of specific gravity, 

 the air rolling out on all sides above, and pressing in on all 

 sides below, a general rain would be the consequence, and 

 this rain might spread out so far from the centre of action, 

 as to reach even the south of Europe in five days. The 

 barometer continued to fall, in Iceland, from the day before 

 the appearance of the volcano, till the twenty-sixth day 

 after it was at the lowest in different parts of Europe, and 

 two days after the prevalence of great storms in Italy and 

 France. During all this time the volcano was in active 

 operation, and even as late as the 23d of February, it 

 emitted smoke greatly resembling steam of boiling water. 

 The whole quantity of rain which fell from the 19th till the 

 24th, must have been very great ; for even as far south as 

 Genoa, the air, for several days previous to the 24th, when 

 the great tempest occurred there, " had been filled with thick 

 vapors, which vented themselves in torrents of rain, and 

 the wind blew from the south with intense violence." This 

 south wind would bring from the Mediterranean an im- 

 mense quantity of vapor, to be condensed when it entered 

 into this vast upward vortex. Let us suppose then, what 

 is certainly within bounds, that five inches on an average 

 of rain, fell over the surface of Europe, from the 19th till 

 the 24th, or the morning of the 25th ; and in Paris, where 

 the flood was not as great as in many other places, there 

 fell 6.4 inches. From the principles explained before, the 

 caloric given out by the vapor in condensing into rain, 

 would heat the whole atmosphere 11.4 for every inch of 

 rain, or in the present case 57. And as the mean tem- 

 perature of the air was certainly below 32 the expansion 

 due to this increase of temperature would be more than | 7 of 

 the whole, which would cause the air to stand at its surface 

 five and a half miles higher over the region where the rain 

 had been deposited, than in surrounding countries, provided 

 it was forty-five miles high before the deposition, and none 

 had flowed off. 



