18 PHILOSOPHY OF STORMS. 



conds. But, as the theory shows that the condensation of 

 the vapor must commence above, and descend lower and 

 lower as the column becomes lighter and lighter, whilst all 

 the time the individual particles of the visible spout are 

 moving upwards, so it is manifest that the condensation of 

 the vapor may commence lower and lower with great ra- 

 pidity, as the air down to the very surface of the sea may be 

 very rapidly relieved of part of the superincumbent weight 

 by the expansion and outward motion of the air in the up- 

 per part of the spout. 



35. The theory also accounts most satisfactorily for the 

 violent showers of hail and rain which are known to accom- 

 pany, or immediately succeed spouts both by sea and land. 



36. It also accounts for the sudden and great depression 

 of the barometer on the passage of a spout. In Orkney, 

 during a spout which threw down nine inches of hail in 

 eight minutes, the barometer fell more than one and a half 

 inches. Article 16. (See Edin. Trans. Anno 1823.) 



37. It also accounts for the great and continued rains which 

 are known to accompany the breaking out of volcanoes. 

 The mighty mass of aqueous vapor which is thrown out 

 sometimes from a volcano, in condensing, will heat up the 

 air by its latent caloric and cause it to rise and spread out 

 in all directions above. Then the air will rush in below, 

 and a violent upward motion will be established first in the 

 immediate neighborhood of the volcano ; and unless the 

 dew point is extremely low, a rain must be the consequence, 

 and as the rarefied air spreads outwards in all directions 

 above, the circumference of the rain may become wider and 

 wider, receding from the volcano in all directions, but faster 

 on that side which has the higher dew point. In the mean- 

 time, the barometer on the outside of the circle of rain at 

 some distance will rise, and within the circle of rain will 

 continue to fall ; and if within the circle, six inches of water 

 at a mean should fall, the barometer will have fallen above 



